ORCID Profile
0000-0002-1457-8028
Current Organisations
The Univesity of Melbourne
,
University of Melbourne
,
Florey Institute of Neuroscience and Mental Health
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Research Topics
In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Top 5 Research Topics
ANZSRC Field of Research (FoR)
Neurosciences | Animal Physiology—Cell | Central Nervous System | Cellular Nervous System | Protein Targeting And Signal Transduction | Physiology | Neurology and Neuromuscular Diseases | Medical Biotechnology not elsewhere classified | Neurogenetics |
ANZSRC Socio-Economic Objective (SEO)
Nervous System and Disorders | Nervous system and disorders | Inherited Diseases (incl. Gene Therapy) | Expanding Knowledge in the Biological Sciences | Biological sciences | Expanding Knowledge in the Medical and Health Sciences
Related Links
Publications
Mechanisms of human inherited epilepsies
Publisher: Elsevier BV
Date: 2009
DOI: 10.1016/J.PNEUROBIO.2008.09.016
Abstract: It is just over a decade since the discovery of the first human epilepsy associated ion channel gene mutation. Since then mutations in at least 25 different genes have been described, although the strength of the evidence for these genes having a pathogenic role in epilepsy varies. These discoveries are allowing us to gradually begin to unravel the molecular basis of this complex disease. In the epilepsies, virtually all the established genes code for ion channel subunits. This has led to the concept that the idiopathic epilepsies are a family of channelopathies. This review first introduces the epilepsy syndromes linked to mutations in the various genes. Next it collates the genetic and functional analysis of these genes. This part of the review is ided into voltage-gated channels (Na+, K+, Ca2+, Cl(-) and HCN), ligand-gated channels (nicotinic acetylcholine and GABA(A) receptors) and miscellaneous proteins. In some cases significant advances have been made in our understanding of the molecular and cellular deficits caused by mutations. However, the link between molecular deficit and clinical phenotype is still unknown. Piecing together this puzzle should allow us to understand the underlying pathology of epilepsy ultimately providing novel therapeutic strategies to complete the clinic-bench-clinic cycle.
Fundamental Neurochemistry Review: GABAA receptor neurotransmission and epilepsy: Principles, disease mechanisms and pharmacotherapy
Publisher: Wiley
Date: 18-02-2023
DOI: 10.1111/JNC.15769
Abstract: Epilepsy is a common neurological disorder associated with alterations of excitation‐inhibition balance within brain neuronal networks. GABA A receptor neurotransmission is the most prevalent form of inhibitory neurotransmission and is strongly implicated in both the pathophysiology and treatment of epilepsy, serving as a primary target for antiseizure medications for over a century. It is now established that GABA exerts a multifaceted influence through an array of GABA A receptor subtypes that extends far beyond simply negating excitatory activity. As the role of GABA A neurotransmission within inhibitory circuits is elaborated, this will enable the development of precision therapies that correct the network dysfunction underlying epileptic pathology. image
The P2X7 receptor drives microglial activation and proliferation: A trophic role for P2X7R pore
Publisher: Society for Neuroscience
Date: 25-03-2009
DOI: 10.1523/JNEUROSCI.5512-08.2009
Abstract: Microglial activation is an integral part of neuroinflammation associated with many neurodegenerative conditions. Interestingly, a number of neurodegenerative conditions exhibit enhanced P2X 7 receptor (P2X 7 R) expression in the neuroinflammatory foci where activated microglia are a coexisting feature. Whether P2X 7 R overexpression is driving microglial activation or, conversely, P2X 7 R overexpression is a consequence of microglial activation is not known. We report that overexpression alone of a purinergic P2X 7 R, in the absence of pathological insults, is sufficient to drive the activation and proliferation of microglia in rat primary hippoc al cultures. The trophic responses observed in microglia were found to be P2X 7 R specific as the P2X 7 R antagonist, oxidized ATP (oxATP), was effective in markedly attenuating microgliosis. oxATP treatment of primary hippoc al cultures expressing exogenous P2X 7 Rs resulted in a significant decrease in the number of activated microglia. P2X 7 R is unusual in exhibiting two conductance states, a cation channel and a plasma membrane pore, and there are no pharmacological agents capable of cleanly discriminating between these two states. We used a point mutant of P2X 7 R (P2X7R G345Y ) with intact channel function but ablated pore-forming capacity to establish that the trophic effects of increased P2X 7 R expression are exclusively mediated by the pore conductance. Collectively, and contrary to previous reports describing P2X 7 R as a “death receptor,” we provide evidence for a novel trophic role for P2X 7 R pore in microglia.
HCN1 epilepsy: From genetics and mechanisms to precision therapies
Publisher: Wiley
Date: 11-08-2023
DOI: 10.1111/JNC.15928
Abstract: Pathogenic variation in HCN1 is now an established cause of epilepsy and intellectual disability. Variation in HCN1 causes a spectrum of disease with a genotype–phenotype relationship emerging. De novo pathogenic variants that occur in the transmembrane domains of the channel typically cause a cation ‘leak’ that associates with severe developmental and epileptic encephalopathy (DEE). Genotype–phenotype associations for variants that fall outside of the transmembrane domains are less well established but do include milder forms of epilepsy that can be either de novo or inherited. HCN1 DEE mouse models have been generated which recapitulate the seizures and learning difficulties seen in human patients. These mice have also acted as powerful preclinical models which share pharmacoresponsiveness with human HCN1 DEE patients. Data from these mouse models support the conclusion that anti‐seizure medications with sodium channel block as their primary mechanism of action should be used with caution in HCN1 DEE. Other comorbidities of HCN1 DEE including retinal dysfunction have also been modelled in HCN1 DEE mice, suggesting HCN1 variants can cause a dramatically reduced sensitivity to light with limited ability to process temporal information. Our understanding of the genetics and pathophysiological mechanisms underlying HCN1 epilepsy has progressed significantly and is already influencing therapy. However, more research effort is needed to fully understand the natural histories of HCN1 epilepsies and to develop precision therapeutic approaches. image
Myoclonus epilepsy and ataxia due to KCNC1 mutation: Analysis of 20 cases and K+channel properties
Publisher: Wiley
Date: 05-2017
DOI: 10.1002/ANA.24929
Abstract: To comprehensively describe the new syndrome of myoclonus epilepsy and ataxia due to potassium channel mutation (MEAK), including cellular electrophysiological characterization of observed clinical improvement with fever. We analyzed clinical, electroclinical, and neuroimaging data for 20 patients with MEAK due to recurrent KCNC1 p.R320H mutation. In vitro electrophysiological studies were conducted using whole cell patch-cl to explore biophysical properties of wild-type and mutant K Symptoms began at between 3 and 15 years of age (median = 9.5), with progressively severe myoclonus and rare tonic-clonic seizures. Ataxia was present early, but quickly became overshadowed by myoclonus 10 patients were wheelchair-bound by their late teenage years. Mild cognitive decline occurred in half. Early death was not observed. Electroencephalogram (EEG) showed generalized spike and polyspike wave discharges, with documented photosensitivity in most. Polygraphic EEG-electromyographic studies demonstrated a cortical origin for myoclonus and striking coactivation of agonist and antagonist muscles. Magnetic resonance imaging revealed symmetrical cerebellar atrophy, which appeared progressive, and a prominent corpus callosum. Unexpectedly, transient clinical improvement with fever was noted in 6 patients. To explore this, we performed high-temperature in vitro recordings. At elevated temperatures, there was a robust leftward shift in activation of wild-type K MEAK has a relatively homogeneous presentation, resembling Unverricht-Lundborg disease, despite the genetic and biological basis being quite different. A remarkable improvement with fever may be explained by the temperature-dependent leftward shift in activation of wild-type K
Stargazin and AMPA receptor membrane expression is increased in the somatosensory cortex of Genetic Absence Epilepsy Rats from Strasbourg
Publisher: Elsevier BV
Date: 04-2011
DOI: 10.1016/J.NBD.2011.01.003
Abstract: Absence-like seizures in the Genetic Absence Epilepsy Rats from Strasbourg (GAERS) model are believed to arise in hyperexcitable somatosensory cortical neurons, however the cellular basis of this increased excitability remains unknown. We have previously shown that expression of the Transmembrane AMPA receptor Regulatory Protein (TARP), stargazin, is elevated in the somatosensory cortex of GAERS. TARPs are critical regulators of the trafficking and function of AMPA receptors. Here we examine the developmental expression of stargazin and the impact this may have on AMPA receptor trafficking in the GAERS model. We show that elevated stargazin in GAERS is associated with an increase in AMPA receptor proteins, GluA1 and GluA2 in the somatosensory cortex plasma membrane of adult epileptic GAERS. Elevated stargazin expression is not seen in the epileptic WAG/Rij rat, which is a genetically distinct but phenotypically similar rat model also manifesting absence seizures, indicating that the changes seen in GAERS are unlikely to be a secondary consequence of the seizures. In juvenile (6 week old) GAERS, at the age when seizures are just starting to be expressed, there is elevated stargazin mRNA, but not protein expression for stargazin or the AMPA receptor subunits. In neonatal (7 day old) pre-epileptic GAERS there was no alteration in stargazin mRNA expression in any brain region examined. These data demonstrate that stargazin and AMPA receptor membrane targeting is altered in GAERS, potentially contributing to hyperexcitability in somatosensory cortex, with a developmental time course that would suggest a pathophysiological role in the epilepsy phenotype.
Generation of Local CA1 γ Oscillations by Tetanic Stimulation
Publisher: MyJove Corporation
Date: 14-08-2015
DOI: 10.3791/52877
GABAA receptor mutations in epilepsy (Commentary on Lachance‐Touchette et al.)
Publisher: Wiley
Date: 07-2011
'Neonatal' Na(v)1.2 reduces neuronal excitability and affects seizure susceptibility and behaviour
Publisher: Oxford University Press (OUP)
Date: 06-11-2015
DOI: 10.1093/HMG/DDU562
Abstract: Developmentally regulated alternative splicing produces 'neonatal' and 'adult' isoforms of four Na(+) channels in human brain, NaV1.1, NaV1.2, NaV1.3 and NaV1.6. Heterologously expressed 'neonatal' NaV1.2 channels are less excitable than 'adult' channels however, functional importance of this difference is unknown. We hypothesized that the 'neonatal' NaV1.2 may reduce neuronal excitability and have a seizure-protective role during early brain development. To test this hypothesis, we generated NaV1.2(adult) mice expressing only the 'adult' NaV1.2, and compared the firing properties of pyramidal cortical neurons, as well as seizure susceptibility, between the NaV1.2(adult) and wild-type (WT) mice at postnatal day 3 (P3), when the 'neonatal' isoform represents 65% of the WT NaV1.2. We show significant increases in action potential firing in NaV1.2(adult) neurons and in seizure susceptibility of NaV1.2(adult) mice, supporting our hypothesis. At postnatal day 15 (P15), when 17% of the WT NaV1.2 is 'neonatal', the firing properties of NaV1.2(adult) and WT neurons converged. However, inhibitory postsynaptic currents in NaV1.2(adult) neurons were larger and the expression level of Scn2a mRNA was 24% lower compared with the WT. The enhanced seizure susceptibility of the NaV1.2(adult) mice persisted into adult age. The adult NaV1.2(adult) mice also exhibited greater risk-taking behaviour. Overall, our data reveal a significant impact of 'neonatal' NaV1.2 on neuronal excitability, seizure susceptibility and behaviour and may contribute to our understanding of NaV1.2 roles in health and diseases such as epilepsy and autism.
Mapping somatosensory connectivity in adult mice using diffusion MRI tractography and super-resolution track density imaging
Publisher: Elsevier BV
Date: 11-2014
DOI: 10.1016/J.NEUROIMAGE.2014.07.048
Abstract: In this study we combined ultra-high field diffusion MRI fiber tracking and super-resolution track density imaging (TDI) to map the relay locations and connectivity of the somatosensory pathway in paraformaldehyde fixed, C57Bl/6J mouse brains. Super-resolution TDI was used to achieve 20 μm isotropic resolution to inform the 3D topography of the relay locations including thalamic barreloids and brainstem barrelettes, not described previously using MRI methodology. TDI-guided mapping results for thalamo-cortical connectivity were consistent with thalamo-cortical projections labeled using virus mediated fluorescent protein expression. Trigemino-thalamic TDI connectivity maps were concordant with results obtained using anterograde dye tracing from brainstem to thalamus. Importantly, TDI mapping overcame the constraint of tissue distortion observed in mechanically sectioned tissue, enabling 3D reconstruction and long-range connectivity data. In conclusion, our results showed that diffusion micro-imaging at ultra-high field MRI revealed the stereotypical pattern of somatosensory connectivity and is a valuable tool to complement histologic methods, achieving 3D spatial preservation of whole brain networks for characterization in mouse models of human disease.
Genetic and pharmacological modulation of giant depolarizing potentials in the neonatal hippocampus associates with increased seizure susceptibility.
Publisher: Wiley
Date: 05-11-2013
A targeted resequencing gene panel for focal epilepsy
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 30-03-2016
Distinctive in vitro phenotypes in iPSC-derived neurons from patients with gain- and loss-of-function SCN2A developmental and epileptic encephalopathy
Publisher: Cold Spring Harbor Laboratory
Date: 15-02-2023
DOI: 10.1101/2023.02.14.528217
Abstract: SCN2A encodes Na V 1.2, an excitatory neuron voltage-gated sodium channel and major monogenic cause of neurodevelopmental disorders, including developmental and epileptic encephalopathies (DEE) and autism. Clinical presentation and pharmocosensitivity vary with nature of SCN2A variant dysfunction with gain-of-function (GoF) cases presenting with pre- or peri-natal seizures and loss-of-function (LoF) patients typically having infantile spasms after 6 months of age. Here, we established and assessed patient induced pluripotent stem cell (iPSC) - derived neuronal models for two recurrent SCN2A DEE variants with GoF R1882Q and LoF R853Q associated with early- and late-onset DEE, respectively. Patient-derived iPSC lines were differentiated using a Neurogenin-2 overexpression yielding populations of cortical-like glutamatergic neurons. Electrophysiological and transcriptomic profiles were assessed after 2-4 weeks in culture. Increased neuronal activity at both cellular and network level was observed for R1882Q iPSC-derived neurons at three weeks of differentiation. In contrast, R853Q neurons showed only subtle changes in excitability after four weeks in vitro . In alignment with the reported efficacy in some GoF SCN2A patients, phenytoin (sodium channel blocker) reduced excitability of neurons to the control levels in R1882Q neuronal cultures. Transcriptomic alterations in neurons were detected for each variant and convergent pathways pointed at the shared mechanisms underlying SCN2A DEE.
A companion to the preclinical common data elements for proteomics, lipidomics, and metabolomics data in rodent epilepsy models. A report of the TASK3‐WG4 omics working group of the ILAE/AES joint tra
Publisher: Wiley
Date: 13-11-2022
DOI: 10.1002/EPI4.12662
Abstract: The International League Against Epilepsy/American Epilepsy Society (ILAE/AES) Joint Translational Task Force established the TASK3 working groups to create common data elements (CDEs) for various preclinical epilepsy research disciplines. This is the second in a two‐part series of omics papers, with the other including genomics, transcriptomics, and epigenomics. The aim of the CDEs was to improve the standardization of experimental designs across a range of epilepsy research‐related methods. We have generated CDE tables with key parameters and case report forms (CRFs) containing the essential contents of the study protocols for proteomics, lipidomics, and metabolomics of s les from rodent models and people with epilepsy. We discuss the important elements that need to be considered for the proteomics, lipidomics, and metabolomics methodologies, providing a rationale for the parameters that should be documented.
Gabapentin Modulates HCN4 Channel Voltage-Dependence.
Publisher: Frontiers Media SA
Date: 21-08-2017
Mossy fiber sprouting interacts with sodium channel mutations to increase dentate gyrus excitability
Publisher: Wiley
Date: 21-12-2009
DOI: 10.1111/J.1528-1167.2009.02202.X
Abstract: Idiopathic epilepsy is caused by the complex interaction of genetic and environmental factors. The purpose of this study was to use computational approaches to explore the interaction between changes in sodium channel availability caused by mutations and mossy fiber sprouting. We used a previously published biophysically realistic computer model of dentate gyrus neurons and networks. A sensitivity analysis probed the effects of typical mutation-like changes in either single- or multiple-gating parameters. Isolated neuron models were stimulated with current injections, and networks were stimulated with perforant path synaptic input. The gene-environment interaction was studied by including mossy fiber sprouting into these networks. Single neuron responses to current injections were complex, with increased sodium channel availability paradoxically reducing firing rates. In the absence of mossy fiber sprouting, control networks showed strong accommodation supporting the role of the dentate gyrus as a gate. Availability changes alone were not able to drive the networks into ictal states, even though they reduced the effectiveness of the dentate gyrus gate. Interestingly, the presence of electrophysiologic changes substantially increased the ability of mossy fiber sprouting to induce ictal activity. (1) Increased sodium channel availability does not necessarily lead to increased firing rates, (2) network excitability is most sensitive to changes in steady state activation of sodium channels, (3) mutation-induced changes in availability reduce the effectiveness of the dentate gyrus gate, and (4) mutations interact strongly with structural network changes to allow ictal-like activity in the dentate gyrus.
Reduced cortical inhibition in a mouse model of familial childhood absence epilepsy
Publisher: Proceedings of the National Academy of Sciences
Date: 30-10-2007
Abstract: Mutations in the GABA A receptor γ2 subunit are associated with childhood absence epilepsy and febrile seizures. To understand better the molecular basis of absence epilepsy in man, we developed a mouse model harboring a γ2 subunit point mutation (R43Q) found in a large Australian family. Mice heterozygous for the mutation demonstrated behavioral arrest associated with 6-to 7-Hz spike-and-wave discharges, which are blocked by ethosuximide, a first-line treatment for absence epilepsy in man. Seizures in the mouse showed an abrupt onset at around age 20 days corresponding to the childhood nature of this disease. Reduced cell surface expression of γ2(R43Q) was seen in heterozygous mice in the absence of any change in α1 subunit surface expression, ruling out a dominant-negative effect. GABA A -mediated synaptic currents recorded from cortical pyramidal neurons revealed a small but significant reduction that was not seen in the reticular or ventrobasal thalamic nuclei. We hypothesize that a subtle reduction in cortical inhibition underlies childhood absence epilepsy seen in humans harboring the R43Q mutation.
Biophysical analysis of an HCN1 epilepsy variant suggests a critical role for S5 helix Met-305 in voltage sensor to pore domain coupling [Prog. Biophys. Mol. Biol. 166 (2021) 156-172]
Publisher: Elsevier BV
Date: 08-2022
Optical Quantal Analysis Indicates That Long-Term Potentiation at Single Hippocampal Mossy Fiber Synapses Is Expressed through Increased Release Probability, Recruitment of New Release Sites, and Acti
Publisher: Society for Neuroscience
Date: 07-04-2004
DOI: 10.1523/JNEUROSCI.3567-03.2004
Abstract: It is generally believed that long-term potentiation (LTP) at hippoc al mossy fiber synapses between dentate granule and CA3 pyramidal cells is expressed through presynaptic mechanisms leading to an increase in quantal content. The source of this increase has remained undefined but could include enhanced probability of transmitter release at existing functional release sites or increases in the number of active release sites. We performed optical quantal analyses of transmission at in idual mossy fiber synapses in cultured hippoc al slices, using confocal microscopy and intracellular fluorescent Ca 2+ indicators. Our results indicate that LTP is expressed at functional synapses by both increased probability of transmitter release and recruitment of new release sites, including the activation of previously silent synapses here visualized for the first time.
Learning about kainate receptors
Publisher: Elsevier BV
Date: 05-2000
Loss-of-function variants in the cardiac Kv11.1 channel as a genetic biomarker for SUDEP
Publisher: Cold Spring Harbor Laboratory
Date: 19-03-2021
DOI: 10.1101/2021.03.19.436102
Abstract: To compare the frequency and impact on channel function of KCNH2 variants in SUDEP patients with epilepsy controls comprising patients older than 50 years, a group with low SUDEP risk, and establish loss-of-function KCNH2 variants as predictive biomarkers of SUDEP risk. We searched for KCNH2 variants with a minor allele frequency of 5%. Functional analysis in Xenopus laevis oocytes was performed for all KCNH2 variants identified. KCNH2 variants were found in 11.1% (10/90) of SUDEP in iduals compared to 6.0% (20/332) of epilepsy controls ( p = 0.11). Loss-of-function KCNH2 variants, defined as causing 20% reduction in maximal litude, were observed in 8.9% (8/90) SUDEP patients compared to 3.3% (11/332) epilepsy controls suggesting about three-fold enrichment (nominal p = 0.04). KCNH2 variants that did not change channel function occurred at a similar frequency in SUDEP (2.2% 2/90) and epilepsy control (2.7% 9/332) cohorts ( p 0.99). Rare KCNH2 variants ( 1% allele frequency) associated with greater loss of function and an ∼11-fold enrichment in the SUDEP cohort (nominal p = 0.03). In silico tools were unable to predict the impact of a variant on function highlighting the need for electrophysiological analysis. These data show that loss-of-function KCNH2 variants are enriched in SUDEP patients and suggest that cardiac mechanisms contribute to SUDEP risk. We propose that genetic screening in combination with functional analysis can identify loss-of-function KCNH2 variants that could act as biomarkers of an in idual’s SUDEP risk.
Rare coding variants in genes encoding GABAA receptors in genetic generalised epilepsies: an exome-based case-control study
Publisher: Elsevier BV
Date: 08-2018
Testing broad-spectrum and isoform-preferring HCN channel blockers for anticonvulsant properties in mice
Publisher: Elsevier BV
Date: 12-2020
Optogenetic Demonstration of Functional Innervation of Mouse Colon by Neurons Derived From Transplanted Neural Cells
Publisher: Elsevier BV
Date: 05-2017
DOI: 10.1053/J.GASTRO.2017.01.005
Abstract: Cell therapy offers the potential to treat gastrointestinal motility disorders caused by diseased or absent enteric neurons. We examined whether neurons generated from transplanted enteric neural cells provide a functional innervation of bowel smooth muscle in mice. Enteric neural cells expressing the light-sensitive ion channel, channelrhodopsin, were isolated from the fetal or postnatal mouse bowel and transplanted into the distal colon of 3- to 4-week-old wild-type recipient mice. Intracellular electrophysiological recordings of responses to light stimulation of the transplanted cells were made from colonic smooth muscle cells in recipient mice. Electrical stimulation of endogenous enteric neurons was used as a control. The axons of graft-derived neurons formed a plexus in the circular muscle layer. Selective stimulation of graft-derived cells by light resulted in excitatory and inhibitory junction potentials, the electrical events underlying contraction and relaxation, respectively, in colonic muscle cells. Graft-derived excitatory and inhibitory motor neurons released the same neurotransmitters as endogenous motor neurons-acetylcholine and a combination of adenosine triphosphate and nitric oxide, respectively. Graft-derived neurons also included interneurons that provided synaptic inputs to motor neurons, but the pharmacologic properties of interneurons varied with the age of the donors from which enteric neural cells were obtained. Enteric neural cells transplanted into the bowel give rise to multiple functional types of neurons that integrate and provide a functional innervation of the smooth muscle of the bowel wall. Circuits composed of both motor neurons and interneurons were established, but the age at which cells are isolated influences the neurotransmitter phenotype of interneurons that are generated.
Oxcarbazepine and its active metabolite, (S)-licarbazepine, exacerbate seizures in a mouse model of genetic generalized epilepsy
Publisher: Wiley
Date: 08-12-2015
DOI: 10.1111/EPI.12866
Abstract: Oxcarbazepine (OXC), widely used to treat focal epilepsy, is reported to exacerbate seizures in patients with generalized epilepsy. OXC is metabolized to monohydroxy derivatives in two enantiomeric forms: (R)-licarbazepine and (S)-licarbazepine. Eslicarbazepine acetate is a recently approved antiepileptic drug that is rapidly metabolized to (S)-licarbazepine. It is not known whether (S)-licarbazepine exacerbates seizures. Here, we test whether OXC or either of its enantiomers exacerbates the number of spike-and-wave discharges (SWDs) in mice harboring the human γ-aminobutyric acid A receptor (GABAA)γ2(R43Q) mutation. OXC (20 mg/kg), (S)-licarbazepine (20 mg/kg), and (R)-licarbazepine (20 mg/kg) all significantly increased the number of SWDs, while their duration was unaffected. The potential for (S)-licarbazepine to exacerbate SWDs suggests that eslicarbazepine acetate should be used with caution in generalized epilepsy. Furthermore, generalized seizure exacerbation for first-, second-, and third-generation carbamazepine-based compounds is likely to occur through a common mechanism.
Nonuniform distribution of Ca2+ channel subtypes on presynaptic terminals of excitatory synapses in hippocampal cultures
Publisher: Society for Neuroscience
Date: 15-04-1997
DOI: 10.1523/JNEUROSCI.17-08-02738.1997
Abstract: Several subtypes of Ca 2+ channel support the release of glutamate at excitatory synapses. We investigated the pattern of colocalization of these subtypes on presynaptic terminals in hippoc al cultures. N-type (conotoxin GVIA-sensitive) or P/Q-type (agatoxin IVA-sensitive) Ca 2+ channels were blocked selectively, and the reduction in transmitter release probability ( P r ) was measured with MK-801. The antagonists completely blocked release at some terminals, reduced P r at others, and failed to affect the remainder. In contrast, nonselective reduction of presynaptic Ca 2+ influx by adding Cd 2+ or lowering external Ca 2+ reduced P r uniformly at all terminals. We conclude from these results that the mixture of N-type and P/Q-type channels varies markedly between terminals on the same afferent. The distribution of Ca 2+ channel subtypes was the same for high and low P r terminals. Given that Ca 2+ channel subtypes are affected differentially by neuromodulators, these findings lead to the possibility of terminal-specific modulation of synaptic function.
Neurons derived from human embryonic stem cells extend long-distance axonal projections through growth along host white matter tracts after intra-cerebral transplantation
Publisher: Frontiers Media SA
Date: 2012
Synaptic Zn2+and febrile seizure susceptibility
Publisher: Wiley
Date: 28-11-2017
DOI: 10.1111/BPH.13658
Multiple molecular mechanisms for a single GABAA mutation in epilepsy.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 13-02-2013
Optical Quantal Analysis reveals a presynaptic component of LTP at hippocampal schaffer-associated synapses
Publisher: Elsevier BV
Date: 06-2003
DOI: 10.1016/S0896-6273(03)00325-8
Abstract: The mechanisms by which long-term potentiation (LTP) is expressed are controversial, with evidence for both presynaptic and postsynaptic involvement. We have used confocal microscopy and Ca(2+)-sensitive dyes to study LTP at in idual visualized synapses. Synaptically evoked Ca(2+) transients were imaged in distal dendritic spines of pyramidal cells in cultured hippoc al slices, before and after the induction of LTP. At most synapses, from as early as 10 min to at least 60 min after induction, LTP was associated with an increase in the probability of a single stimulus evoking a postsynaptic Ca(2+) response. These observations provide compelling evidence of a presynaptic component to the expression of early LTP at Schaffer-associational synapses. In most cases, the store-dependent evoked Ca(2+) transient in the spine was also increased after induction, a novel postsynaptic aspect of LTP.
Discovering the pharmacodynamics of conolidine and cannabidiol using a cultured neuronal network based workflow.
Publisher: Springer Science and Business Media LLC
Date: 15-01-2019
DOI: 10.1038/S41598-018-37138-W
Abstract: Determining the mechanism of action (MOA) of novel or naturally occurring compounds mostly relies on assays tailored for in idual target proteins. Here we explore an alternative approach based on pattern matching response profiles obtained using cultured neuronal networks. Conolidine and cannabidiol are plant-derivatives with known antinociceptive activity but unknown MOA. Application of conolidine/cannabidiol to cultured neuronal networks altered network firing in a highly reproducible manner and created similar impact on network properties suggesting engagement with a common biological target. We used principal component analysis (PCA) and multi-dimensional scaling (MDS) to compare network activity profiles of conolidine/cannabidiol to a series of well-studied compounds with known MOA. Network activity profiles evoked by conolidine and cannabidiol closely matched that of ω-conotoxin CVIE, a potent and selective Cav2.2 calcium channel blocker with proposed antinociceptive action suggesting that they too would block this channel. To verify this, Cav2.2 channels were heterologously expressed, recorded with whole-cell patch cl and conolidine/cannabidiol was applied. Remarkably, conolidine and cannabidiol both inhibited Cav2.2, providing a glimpse into the MOA that could underlie their antinociceptive action. These data highlight the utility of cultured neuronal network-based workflows to efficiently identify MOA of drugs in a highly scalable assay.
Posttraumatic Epilepsy: Basic and Clinical Aspects
Publisher: Wiley
Date: 21-04-2023
DOI: 10.1111/JNC.15826
Abstract: Post‐traumatic epilepsy (PTE) is a common form of epilepsy affecting a significant proportion of people who sustain a brain injury. The complex pathophysiological mechanisms that drive the process of epileptogenesis after a traumatic brain injury (TBI) are incompletely understood. A new book entitled ‘Posttraumatic Epilepsy: Basic and Clinical Aspects’ by Jonak and colleagues provides an introduction into to the topic of PTE, starting from a historical perspective and extending through to our current understanding of the pathophysiological mechanisms, and evaluation of the most promising therapeutic candidates. Here, we review the book highlighting strengths and suggesting a few areas of potential improvements. We conclude that the book provides an excellent read for scientists and clinicians entering the PTE field.
Epilepsy, energy deficiency and new therapeutic approaches including diet
Publisher: Elsevier BV
Date: 11-2014
DOI: 10.1016/J.PHARMTHERA.2014.06.001
Abstract: Metabolic dysfunction leading to epilepsy is well recognised. Dietary therapy, in particular the ketogenic diet, is now considered an effective option. Recent genetic studies have highlighted the central role that metabolism can play in setting seizure susceptibility. Here we discuss various metabolic disorders implicated in epilepsy focusing on energy deficiency due to genetic and environmental causes. We argue that low, uncompensated brain glucose levels can precipitate seizures. We will also explore mechanisms of disease and therapy in an attempt to identify common metabolic pathways involved in modulating seizure susceptibility. Finally, newer therapeutic approaches based on diet manipulation in the context of energy deficiency are discussed.
Seizure-like thalamocortical rhythms initiate in the deep layers of the cortex in a co-culture model
Publisher: Elsevier BV
Date: 2011
DOI: 10.1016/J.EXPNEUROL.2010.11.001
Abstract: The oscillatory rhythms underlying many physiological and pathological states, including absence seizures, require both the thalamus and cortices for full expression. A co-culture preparation combining cortical and thalamic explants provides a unique model for investigating how such oscillations initiate and spread. Here we investigated the dynamics of synchronized thalamocortical activity by simultaneous measurement of field-potential recordings and rapid imaging of Ca(2+) transients by fluorescence methods. Spontaneous sustained hypersynchronized "seizure-like" oscillations required reciprocal cortico-thalamocortical connections. Isolated cortical explants can independently develop brief discharges, while thalamic explants alone were unable to do so. Rapid imaging of Ca(2+) transients demonstrated deep-layer cortical initiation of oscillatory network activity in both connected and isolated explants. Further, cortical explants derived from a rat model of genetic absence epilepsy showed increased bursting duration consistent with an excitable cortex. We propose that thalamocortical oscillatory network activity initiates in deep layers of the cortex with reciprocal thalamic interconnections enabling sustained hyper-synchronization.
GABA-mediated tonic inhibition differentially modulates gain in functional subtypes of cortical interneurons
Publisher: Proceedings of the National Academy of Sciences
Date: 23-01-2020
Abstract: GABA (γ-aminobutyric acid) is the brain’s predominant inhibitory neurotransmitter and exerts a strong inhibitory influence through extrasynaptic GABA A receptors. This form of neurotransmission is known as tonic inhibition. Tonic inhibition is usually thought to reduce the excitability of all neurons, but here we show that it can selectively modulate the excitability of different types of neurons. Surprisingly, tonic inhibition can increase excitability in a common subtype of interneuron, and modeling results suggest this is achieved through the neuron’s electrophysiological, or functional, properties. These results provide insight into the impact of tonic inhibition upon neural activity and suggest a mechanism through which GABA may modulate the excitability of neurons in a selective manner.
Brain basis of communicative actions in language
Publisher: Elsevier BV
Date: 2016
Developmental Impact of a Famial GABAA Receptor Epilepsy Mutation
Publisher: Wiley
Date: 28-09-2008
DOI: 10.1002/ANA.21440
Increased thalamic inhibition in the absence seizure prone DBA/2J mouse.
Publisher: Wiley
Date: 20-02-2008
Efficacy of antiseizure medication in a mouse model of HCN1 developmental and epileptic encephalopathy
Publisher: Wiley
Date: 12-11-2023
DOI: 10.1111/EPI.17447
Abstract: Acquisition of drug‐sensitivity profiles is challenging in rare epilepsies. Anecdotal evidence suggests that antiseizure medications that block sodium channels as their primary mechanism of action exacerbate seizures in HCN1 developmental and epileptic encephalopathies (DEEs), whereas sodium valproate is effective for some patients. The Hcn1 M294L heterozygous knock‐in (Hcn1 M294L ) mouse carries the homologue of the recurrent gain‐of‐function HCN1 M305L pathogenic variant and recapitulates the seizure and some behavioral phenotypes observed in patients. We used this mouse model to study drug efficacy in HCN1 DEE. Hcn1 M294L mice display epileptiform spiking on electrocorticography (ECoG), which we used as a quantifiable measure of drug effect. Phenytoin, lamotrigine, and retigabine significantly increased ECoG spike frequency, with lamotrigine and retigabine triggering seizures in a subset of the mice tested. In addition, there was a strong trend for carbamazepine to increase spiking. In contrast, levetiracetam, diazepam, sodium valproate, and ethosuximide all significantly reduced ECoG spike frequency. Drugs that reduced spiking did not cause any consistent ECoG spectral changes, whereas drugs that increased spiking all increased power in the slower delta and/or theta bands. These data provide a framework on which to build our understanding of gain‐of‐function HCN1 DEE pharmacosensitivity in the clinical setting.
A companion to the preclinical common data elements for rodent genetic epilepsy models. A report of the TASK3‐WG1B : Paediatric and genetic models working group of the ILAE /A
Publisher: Wiley
Date: 28-09-2022
DOI: 10.1002/EPI4.12642
Abstract: Rodent models of epilepsy remain the cornerstone of research into the mechanisms underlying genetic epilepsy. Reproducibility of experiments using these rodent models, occurring across a ersity of laboratories and commercial vendors, remains an issue impacting the cost‐effectiveness and scientific rigor of the studies performed. Here, we present two case report forms (CRFs) describing common data elements (CDE) for genetic rodent models, developed by the TASK3‐WG1B Working Group of the International League Against Epilepsy (ILAE)/American Epilepsy Society (AES) Joint Translational Task Force. The first CRF relates to genetic rodent models that have been engineered based on variants described in epilepsy patients. The second CRF encompasses both spontaneous and inbred rodent models. This companion piece describes the elements and discusses the important factors to consider before documenting each required element. These CRFs provide tools that allow investigators to more uniformly describe core experimental data on different genetic models across laboratories, with the aim of improving experimental reproducibility and thus translational impact of such studies.
Altered EEG power spectrum, but not sleep-wake architecture, in HCN1 knockout mice
Publisher: Elsevier BV
Date: 02-2023
DOI: 10.1016/J.BBR.2022.114105
Abstract: Sleep is a complex biological state characterized by large populations of neurons firing in a rhythmic or synchronized manner. HCN channels play a critical role in generating and sustaining synchronized neuronal firing and are involved in the actions of anaesthetics. However, the role of these channels in sleep-wakefulness per se has yet to be studied. We conducted polysomnographic recordings of Hcn1 constitutive knockout (Hcn1 KO) and wild-type (WT) mice in order to investigate the potential role of HCN1 channels in sleep/wake regulation. EEG and EMG data were analysed using the Somnivore™ machine learning algorithm. Time spent in each vigilance state, bout number and duration, and EEG power spectral activity were compared between genotypes. There were no significant differences in the time spent in wake, rapid eye movement (REM) or non-REM (NREM) sleep between Hcn1 KO and WT mice. Wake bout duration during the inactive phase was significantly shorter in Hcn1 KO mice whilst no other bout parameters were affected by genotype. Hcn1 KO mice showed a reduction in overall EEG power which was particularly prominent in the theta (5-9 Hz) and alpha (9-15 Hz) frequency bands and most evident during NREM sleep. Together these data suggest that HCN1 channels do not play a major role in sleep architecture or modulation of vigilance states. However, loss of these channels significantly alters underlying neuronal activity within these states which may have functional consequences.
A companion to the preclinical common data elements for genomics, transcriptomics, and epigenomics data in rodent epilepsy models. A report of the TASK3‐WG4 omics working group of the
Publisher: Wiley
Date: 09-09-2022
DOI: 10.1002/EPI4.12640
Abstract: The International League Against Epilepsy/American Epilepsy Society (ILAE/AES) Joint Translational Task Force established the TASK3 working groups to create common data elements (CDEs) for various preclinical epilepsy research disciplines. The aim of the CDEs is to improve the standardization of experimental designs across a range of epilepsy research‐related methods. Here, we have generated CDE tables with key parameters and case report forms (CRFs) containing the essential contents of the study protocols for genomics, transcriptomics, and epigenomics in rodent models of epilepsy, with a specific focus on adult rats and mice. We discuss the important elements that need to be considered for genomics, transcriptomics, and epigenomics methodologies, providing a rationale for the parameters that should be collected. This is the first in a two‐part series of omics papers with the second installment to cover proteomics, lipidomics, and metabolomics in adult rodents.
Low blood glucose precipitates spike-and-wave activity in genetically predisposed animals
Publisher: Wiley
Date: 22-12-2011
DOI: 10.1111/J.1528-1167.2010.02911.X
Abstract: Absence epilepsies are common, with a major genetic contribution to etiology. Certain environmental factors can influence absence occurrence but a complete understanding of absence precipitation is lacking. Herein we investigate if lowering blood glucose increases spike-wave activity in mouse models with varying seizure susceptibility. Three mouse models were used: an absence seizure model based on the knockin of a human GABA(A) γ2(R43Q) mutation (DBA(R43Q)), the spike-wave discharge (SWD)-prone DBA/2J strain, and the seizure resistant C57Bl/6 strain. Electrocorticography (ECoG) studies were recorded to determine SWDs during hypoglycemia induced by insulin or overnight fasting. An insulin-mediated reduction in blood glucose levels to 4 mm (c.a. 40% reduction) was sufficient to double SWD occurrence in the DBA(R43Q) model and in the SWD-prone DBA/2J mouse strain. Larger reductions in blood glucose further increased SWDs in both these models. However, even with large reductions in blood glucose, no discharges were observed in the seizure-resistant C57Bl/6 mouse strain. Injection of glucose reversed the impact of insulin on SWDs in the DBA(R43Q) model, supporting a reduction in blood glucose as the modulating influence. Overnight fasting reduced blood glucose levels to 4.5 mm (c.a. 35% reduction) and, like insulin, caused a doubling in occurrence of SWDs. Low blood glucose can precipitate SWDs in genetically predisposed animal models and should be considered as a potential environmental risk factor in patients with absence epilepsy.
A companion to the preclinical common data elements for rodent models of pediatric acquired epilepsy: A report of the TASK3‐WG1B , Pediatric and Genetic Models Working Group of the ILAE
Publisher: Wiley
Date: 05-10-2022
DOI: 10.1002/EPI4.12641
Abstract: Epilepsy syndromes during the early years of life may be attributed to an acquired insult, such as hypoxic–ischemic injury, infection, status epilepticus, or brain trauma. These conditions are frequently modeled in experimental rodents to delineate mechanisms of epileptogenesis and investigate novel therapeutic strategies. However, heterogeneity and subsequent lack of reproducibility of such models across laboratories is an ongoing challenge to maintain scientific rigor and knowledge advancement. To address this, as part of the TASK3‐WG1B Working Group of the International League Against Epilepsy/American Epilepsy Society Joint Translational Task Force, we have developed a series of case report forms (CRFs) to describe common data elements for pediatric acquired epilepsy models in rodents. The “Rodent Models of Pediatric Acquired Epilepsy” Core CRF was designed to capture cohort‐general information while two Specific CRFs encompass physical induction models and chemical induction models, respectively. This companion manuscript describes the key elements of these models and why they are important to be considered and reported consistently. Together, these CRFs provide investigators with the tools to systematically record critical information regarding their chosen model of acquired epilepsy during early life, for improved standardization and transparency across laboratories. These outcomes will support the ultimate goal of such research that is, to understand the childhood onset‐specific biology of epileptogenesis after acquired insults, and translate this knowledge into therapeutics to improve pediatric patient outcomes and minimize the lifetime burden of epilepsy.
Development of a rapid functional assay that predicts GLUT1 disease severity
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 12-2018
DOI: 10.1212/NXG.0000000000000297
Abstract: To examine the genotype to phenotype connection in glucose transporter type 1 (GLUT1) deficiency and whether a simple functional assay can predict disease outcome from genetic sequence alone. GLUT1 deficiency, due to mutations in SLC2A1 , causes a wide range of epilepsies. One possible mechanism for this is variable impact of mutations on GLUT1 function. To test this, we measured glucose transport by GLUT1 variants identified in population controls and patients with mild to severe epilepsies. Controls were reference sequence from the NCBI and 4 population missense variants chosen from public reference control databases. Nine variants associated with epilepsies or movement disorders, with normal intellect in all in iduals, formed the mild group. The severe group included 5 missense variants associated with classical GLUT1 encephalopathy. GLUT1 variants were expressed in Xenopus laevis oocytes, and glucose uptake was measured to determine kinetics (V max ) and affinity (K m ). Disease severity inversely correlated with rate of glucose transport between control (V max = 28 ± 5), mild (V max = 16 ± 3), and severe (V max = 3 ± 1) groups, respectively. Affinities of glucose binding in control (K m = 55 ± 18) and mild (K m = 43 ± 10) groups were not significantly different, whereas affinity was indeterminate in the severe group because of low transport rates. Simplified analysis of glucose transport at high concentration (100 mM) was equally effective at separating the groups. Disease severity can be partly explained by the extent of GLUT1 dysfunction. This simple Xenopus oocyte assay complements genetic and clinical assessments. In prenatal diagnosis, this simple oocyte glucose uptake assay could be useful because standard clinical assessments are not available.
Interleukin-1β has trophic effects in microglia and its release is mediated by P2X7R pore
Publisher: Springer Science and Business Media LLC
Date: 30-06-2016
Presynaptic Ca2+ channels: A functional patchwork
Publisher: Elsevier BV
Date: 12-2003
DOI: 10.1016/J.TINS.2003.10.003
Abstract: A key step in the release of neurotransmitter is the entry of Ca(2+) into the presynaptic terminal via voltage-activated Ca(2+) channels. N-type and P/Q-type Ca(2+) channels play a predominant role but, surprisingly, their distribution across presynaptic terminals lacks any apparent order. They form a patchwork: at some terminals only N-type channels contribute to transmitter release and in others only P/Q-type channels contribute, but in many terminals both sub-types are active. The physiological implications of this non-uniform distribution are starting to emerge. Recent studies reveal that G-protein-mediated depression of N-type channels is stronger than that of P/Q-type channels, whereas voltage-dependent relief of inhibition is more pronounced for P/Q-type channels. The patchwork distribution of Ca(2+) channel subtypes might therefore enable terminal-specific modulation of transmitter release, enhancing the power of synaptic processing.
HCN channelopathies: pathophysiology in genetic epilepsy and therapeutic implications.
Publisher: Wiley
Date: 06-12-2012
Are Variants Causing Cardiac Arrhythmia Risk Factors in Sudden Unexpected Death in Epilepsy?
Publisher: Frontiers Media SA
Date: 08-09-2020
N- and P/Q-type Ca2+ channels mediate transmitter release with a similar cooperativity at rat hippocampal autapses
Publisher: Society for Neuroscience
Date: 15-04-1998
DOI: 10.1523/JNEUROSCI.18-08-02849.1998
Abstract: The relationship between extracellular Ca 2+ concentration and EPSC litude was investigated at excitatory autapses on cultured hippoc al neurons. This relationship was steeply nonlinear, implicating the cooperative involvement of several Ca 2+ ions in the release of each vesicle of transmitter. The cooperativity was estimated to be 3.1 using a power function fit and 3.3 using a Hill equation fit. However, simulations suggest that these values underestimate the true cooperativity. The role of different Ca 2+ channel subtypes in shaping the Ca 2+ dose–response relationship was studied using the selective Ca 2+ channel blockers ω-agatoxin GIVA (ω-Aga), which blocks P/Q-type channels, and ω-conotoxin GVIA (ω-CTx), which blocks N-type channels. Both blockers broadened the dose–response relationship, and the Hill coefficient was reduced to 2.5 by ω-Aga and to 2.6 by ω-CTx. This broadening is consistent with a nonuniform distribution of Ca 2+ channel subtypes across presynaptic terminals. The similar Hill coefficients in ω-Aga or ω-CTx suggest that there was no difference in the degree of cooperativity for transmitter release mediated via N- or P/Q-type Ca 2+ channels. A model of the role of calcium in transmitter release is developed. It is based on a modified Dodge–Rahamimoff equation that includes a nonlinear relationship between extracellular and intracellular Ca 2+ concentration, has a cooperativity of 4, and incorporates a nonuniform distribution of Ca 2+ channel subtypes across presynaptic terminals. The model predictions are consistent with all of the results reported in this study.
P2X7 receptors are a potential novel target for anti-glioma therapies
Publisher: Springer Science and Business Media LLC
Date: 28-08-2014
Can mutation-mediated effects occurring early in development cause long-term seizure susceptibility in genetic generalized epilepsies?
Publisher: Wiley
Date: 16-04-2018
DOI: 10.1111/EPI.14077
Abstract: Epilepsy has a strong genetic component, with an ever-increasing number of disease-causing genes being discovered. Most epilepsy-causing mutations are germ line and thus present from conception. These mutations are therefore well positioned to have a deleterious impact during early development. Here we review studies that investigate the role of genetic lesions within the early developmental window, specifically focusing on genetic generalized epilepsy (GGE). Literature on the potential pathogenic role of sub-mesoscopic structural changes in GGE is also reviewed. Evidence from rodent models of genetic epilepsy support the idea that functional and structural changes can occur in early development, leading to altered seizure susceptibility into adulthood. Both animal and human studies suggest that sub-mesoscopic structural changes occur in GGE. The existence of sub-mesoscopic structural changes prior to seizure onset may act as biomarkers of excitability in genetic epilepsies. We also propose that presymptomatic treatment may be essential for limiting the long-term consequences of disease-causing mutations in genetic epilepsies.
Protective effects of medium chain triglyceride diet in a mouse model of Dravet syndrome.
Publisher: Wiley
Date: 28-10-2021
DOI: 10.1111/EPI.17101
Abstract: Dravet syndrome (DS) is a severe developmental and epileptic encephalopathy with early childhood onset. Patients with DS do not respond well to antiepileptic drugs and have only a few treatment options available. Here, we evaluated the effect of medium chain triglyceride (MCT) diet therapy in a mouse model of DS. Scn1a R1407X/+ DS mice were given diets supplemented with MCTs with varying ratios of decanoic (C10) and octanoic (C8) acid or a control diet for 4 weeks. Video monitoring was performed to evaluate spontaneous convulsive seizure frequency. Susceptibility to hyperthermia‐induced seizures was also examined. Medium chain fatty acids, and mitochondrial and antioxidant markers were assessed in brain homogenate. Dietary intervention with MCTs significantly prolonged survival and reduced convulsive seizure frequency during the critical period of highest seizure occurrence in the Scn1a R1407X/+ DS mice. Moreover, MCT diet therapy showed protective effects against hyperthermia‐induced seizures. We demonstrated that coadministration of C10/C8 was effective at reducing both seizures and mortality, whereas C10 alone only reduced mortality, suggesting that the ratio of C10 to C8 in the MCT is an important factor for efficacy. When C10 and C8 are supplemented at an 80:20 ratio in the diet, C10 accumulates in the brain in high enough concentrations to enhance brain energy metabolism by both stimulating mitochondrial enrichment and increasing its antioxidant status. The results from this study indicate that MCT diet therapy may provide therapeutic benefits in DS. Future clinical studies would elucidate whether these positive effects are mirrored in human patients.
Antisense oligonucleotide therapy for KCNT1 encephalopathy
Publisher: Cold Spring Harbor Laboratory
Date: 14-11-2020
DOI: 10.1101/2020.11.12.379164
Abstract: Developmental and epileptic encephalopathies (DEE) are characterized by pharmacoresistant seizures with concomitant intellectual disability. Epilepsy of infancy with migrating focal seizures (EIMFS) is one of the most severe of these syndromes. De novo mutations in ion channels, including gain-of-function variants in KCNT1 , have been found to play a major role in the etiology of EIMFS. Here, we test a potential precision therapeutic approach in KCNT1 -associated DEE using a gene silencing antisense oligonucleotide (ASO) approach. The homozygous p.P924L (L/L) mouse model recapitulates the frequent, debilitating seizures and developmental compromise that are seen in patients. After a single intracerebroventricular bolus injection of a Kcnt1 gapmer ASO in symptomatic mice at postnatal day 40, seizure frequency was significantly reduced, behavioral abnormalities improved, and overall survival was extended compared to mice treated with a control ASO (non-hybridizing sequence). ASO administration at neonatal age was also well-tolerated and effective in controlling seizures and extending the lifespan of treated animals. The data presented here provides a proof of concept for ASO-based gene silencing as a promising therapeutic approach in KCNT1 -associated epilepsies.
Postsynaptic calcium transients evoked by activation of individual hippocampal mossy fiber synapses
Publisher: Society for Neuroscience
Date: 04-2001
Channelrhodopsins shed light on a new pathway in absence epilepsy
Publisher: Future Medicine Ltd
Date: 2012
DOI: 10.2217/FNL.11.66
Abstract: Evaluation of: Paz JT, Bryant AS, Peng K et al. A new mode of corticothalamic transmission revealed in the Gria4 -/- model of absence epilepsy. Nat. Neurosci. 14(9), 1167–1173 (2011). Absence seizures are a common form of epilepsy characterized by sudden behavioral arrest in conjunction with a stereotypical spike-and-wave discharge on electroencephalography. A reciprocally connected network of thalamocortical neurons that normally controls sleep and other functions, misfires to cause absence epilepsy and is perhaps one of the most studied seizure networks. In a recent paper, Paz and colleagues further dissect this network to understand the basis of seizure initiation in a new animal model of absence epilepsy. Exploiting state-of-the-art ‘optogenetic’ methodology they systematically isolate monosynaptic connections in thalamocortical nuclei to reveal the key pathological mechanism underlying absence seizures in the Gria4 -/- mouse. The main finding is a reduction in the strength of synapses made by excitatory cortical projection neurons onto the reticular thalamic nucleus. The consequent fall in reticular thalamic nucleus inhibitory neuron output results in less feed-forward inhibition of thalamocortical neurons and an increase in thalamic excitability that is, presumably, sufficient to initiate oscillations and absence seizures. The manuscript adds significantly to our understanding of how absence seizures can initiate by implicating, in this case, a thalamic rather than cortical basis. Further, the demonstration of this mode of circuit activity may have significant implications for how the thalamocortical network behaves physiologically.
Hippocampal volume and cell density changes in a mouse model of human genetic epilepsy
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 06-03-2013
Enhanced in vitro CA 1 network activity in a sodium channel β1(C 121W ) subunit model of genetic epilepsy
Publisher: Wiley
Date: 07-03-2014
DOI: 10.1111/EPI.12568
Abstract: A NaV β1(C121W) mouse model of human genetic epilepsy has enhanced neuronal excitability and temperature sensitivity attributed to a decreased threshold for action potential firing in the axon initial segment. To investigate the network consequences of this neuronal dysfunction and to establish a genetic disease state model we developed an in vitro assay to investigate CA1 network properties and antiepileptic drug sensitivity. CA1 network oscillations were induced by tetanic stimulation and average number of spikes, interspike interval (ISI), duration, and latency were measured in slices from control and NaV β1(C121W) heterozygous mice in the presence and absence of retigabine or carbamazepine. Retigabine was also tested in a thermogenic seizure model. Oscillations were reliably induced by tetanic stimulation and were maintained after severing connections between CA3 and CA1, suggesting a local recurrent circuit. Blocking α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), γ-aminobutyric acid receptor A (GABAA ), Ih , and T-type Ca(2+) channels/receptors reduced the number of spikes. Slices from NaV β1(C121W) heterozygous mice displayed several hallmarks of increased network excitability including increases in duration of the oscillation, the number and frequency of spikes and a decrease in their onset latency. The effect of genotype on network excitability was temperature sensitive, as it was seen only at elevated temperatures. Carbamazepine and retigabine were more effective in reducing network excitability in slices from NaV β1(C121W) heterozygous mice. Retigabine appeared to be more effective in suppressing time to thermogenic seizures in NaV β1(C121W) heterozygous mice compared to wild-type (WT) controls. Hippoc al networks of the NaV β1(C121W) heterozygous mouse model of genetic epilepsy show enhanced excitability consistent with earlier single neuron studies bridging important scales of brain complexity relevant to seizure genesis. Altered pharmacosensitivity further suggests that genetic epilepsy models may be useful in the development of novel antiepileptic drugs that target disease state pathology. A PowerPoint slide summarizing this article is available for download in the Supporting Information section here.
HCN channelopathy and cardiac electrophysiologic dysfunction in genetic and acquired rat epilepsy models
Publisher: Wiley
Date: 04-03-2014
DOI: 10.1111/EPI.12563
Abstract: Evidence from animal and human studies indicates that epilepsy can affect cardiac function, although the molecular basis of this remains poorly understood. Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels generate pacemaker activity and modulate cellular excitability in the brain and heart, with altered expression and function associated with epilepsy and cardiomyopathies. Whether HCN expression is altered in the heart in association with epilepsy has not been investigated previously. We studied cardiac electrophysiologic properties and HCN channel subunit expression in rat models of genetic generalized epilepsy (Genetic Absence Epilepsy Rats from Strasbourg, GAERS) and acquired temporal lobe epilepsy (post-status epilepticus SE). We hypothesized that the development of epilepsy is associated with altered cardiac electrophysiologic function and altered cardiac HCN channel expression. Electrocardiography studies were recorded in vivo in rats and in vitro in isolated hearts. Cardiac HCN channel messenger RNA (mRNA) and protein expression were measured using quantitative PCR and Western blotting respectively. Cardiac electrophysiology was significantly altered in adult GAERS, with slower heart rate, shorter QRS duration, longer QTc interval, and greater standard deviation of RR intervals compared to control rats. In the post-SE model, we observed similar interictal changes in several of these parameters, and we also observed consistent and striking bradycardia associated with the onset of ictal activity. Molecular analysis demonstrated significant reductions in cardiac HCN2 mRNA and protein expression in both models, providing a molecular correlate of these electrophysiologic abnormalities. These results demonstrate that ion channelopathies and cardiac dysfunction can develop as a secondary consequence of chronic epilepsy, which may have relevance for the pathophysiology of cardiac dysfunction in patients with epilepsy.
In Vitro Differentiated Human Stem Cell-Derived Neurons Reproduce Synaptic Synchronicity Arising during Neurodevelopment
Publisher: Elsevier BV
Date: 07-2020
Oxcarbazepine, not its active metabolite, potentiates GABA(A) activation and aggravates absence seizures
Publisher: Wiley
Date: 2009
DOI: 10.1111/J.1528-1167.2008.01759.X
Abstract: Studies in genetic absence epileptic rats from Strasbourg (GAERS) indicate that enhancement of gamma aminobutyric acid (GABA(A)) receptor activity is a critical mechanism in the aggravation of seizures by carbamazepine (CBZ). We examined whether structural analogs of CBZ, oxcarbazepine (OXC), and its active metabolite, monohydroxy derivative (MHD), also potentiate GABA(A) receptor current and aggravate seizures. In vitro studies in Xenopus oocytes compared the three drugs' effect on GABA(A) receptor currents. In vivo studies compared seizure activity in GAERS after intraperitoneal drug administration. OXC potentiated GABA(A) receptor current and aggravated seizures in GAERS, similarly to the effect of CBZ. Conversely, MHD showed only a minor potentiation of GABA(A) receptor current and did not aggravate seizures. A hydroxyl group at the C-10 position on the CBZ tricyclic structure in MHD reduces GABA(A) receptor potentiation and seizure aggravation. Reports of the aggravation of absence seizures in patients taking OXC may result from circulating unmetabolized OXC rather than MHD.
Selective Na V 1.1 activation rescues Dravet syndrome mice from seizures and premature death
Publisher: Proceedings of the National Academy of Sciences
Date: 03-08-2018
Abstract: Spider venom is a rich source of peptides, many targeting ion channels. We assessed a venom peptide, Hm1a, as a potential targeted therapy for Dravet syndrome, the genetic epilepsy linked to a mutation in the gene encoding the sodium channel alpha subunit Na V 1.1. Cell-based assays showed Hm1a was selective for hNa V 1.1 over other sodium and potassium channels. Utilizing a mouse model of Dravet syndrome, Hm1a restored inhibitory neuron function and significantly reduced seizures and mortality in heterozygote mice. Evidence from the structure of Hm1a and modeling suggest Hm1a interacts with Na V 1.1 inactivation domains, providing a structural correlate of the functional mechanisms. This proof-of-concept study provides a promising strategy for future drug development in genetic epilepsy and other neurogenetic disorders.
GABA-mediated tonic inhibition differentially modulates gain in functional subtypes of cortical interneurons
Publisher: Cold Spring Harbor Laboratory
Date: 18-04-2019
DOI: 10.1101/613075
Abstract: The binding of GABA to extra-synaptic GABA A receptors generates tonic inhibition that acts as a powerful modulator of cortical network activity. Despite GABA being present at low levels throughout the extracellular space of the brain, previous work has shown that GABA may differentially modulate the excitability of neuron subtypes through variation in chloride gradient. Here, we introduce a distinct mechanism through which extracellular GABA can differentially modulate the excitability of neuron subtypes through variation in neuronal electrophysiological properties. Using biophysically-detailed computational models, we found that tonic inhibition enhanced the responsiveness (or gain) of models with electrophysiological features typically observed in somatostatin (Sst) interneurons and reduced gain in models with features typical for parvalbumin (Pv) interneurons. These predictions were experimentally verified using patch-cl recordings. Further analysis revealed that differential gain modulation is also dependent upon the extent of outward rectification of the GABA A receptor-mediated tonic current. Our detailed neuron models demonstrate two subcellular consequences of tonic inhibition. First, tonic inhibition enhances somatic action potential repolarisation by increasing current flow into the dendritic compartment. This enhanced repolarisation then reduces voltage-dependent potassium currents at the soma during the afterhyperpolarisation. Finally, we show that reductions of potassium current selectively increase gain within neurons exhibiting action potential dynamics typical for Sst interneurons. Potassium currents in Pv-type interneurons are not sensitive to this mechanism as they deactivate rapidly and are unavailable for further modulation. These findings introduce a neuromodulatory paradigm in which GABA can induce a state of differential interneuron excitability through differences in intrinsic electrophysiological properties.
Carbogen-Induced Respiratory Acidosis Blocks Experimental Seizures by a Direct and Specific Inhibition of NaV1.2 Channels in the Axon Initial Segment of Pyramidal Neurons.
Publisher: Society for Neuroscience
Date: 02-02-2023
DOI: 10.1523/JNEUROSCI.1387-22.2022
Abstract: Brain pH is a critical factor for determining neuronal activity, with alkalosis increasing and acidosis reducing excitability. Acid shifts in brain pH through the breathing of carbogen (5% CO 2 /95% O 2 ) reduces seizure susceptibility in animal models and patients. The molecular mechanisms underlying this seizure protection remain to be fully elucidated. Here, we demonstrate that male and female mice exposed to carbogen are fully protected from thermogenic-triggered seizures. Whole-cell patch-cl recordings revealed that acid shifts in extracellular pH (pHo) significantly reduce action potential firing in CA1 pyramidal neurons but did not alter firing in hippoc al inhibitory interneurons. In real-time dynamic cl experiments, acidification reduced simulated action potential firing generated in hybrid model neurons expressing the excitatory neuron predominant Na V 1.2 channel. Conversely, acidification had no effect on action potential firing in hybrid model neurons expressing the interneuron predominant Na V 1.1 channel. Furthermore, knockdown of Scn2a mRNA in vivo using antisense oligonucleotides reduced the protective effects of carbogen on seizure susceptibility. Both carbogen-mediated seizure protection and the reduction in CA1 pyramidal neuron action potential firing by low pHo were maintained in an Asic1a knock-out mouse ruling out this acid-sensing channel as the underlying molecular target. These data indicate that the acid-mediated reduction in excitatory neuron firing is mediated, at least in part, through the inhibition of Na V 1.2 channels, whereas inhibitory neuron firing is unaffected. This reduction in pyramidal neuron excitability is the likely basis of seizure suppression caused by carbogen-mediated acidification. SIGNIFICANCE STATEMENT Brain pH has long been known to modulate neuronal excitability. Here, we confirm that brain acidification reduces seizure susceptibility in a mouse model of thermogenic seizures. Extracellular acidification reduced excitatory pyramidal neuron firing while having no effect on interneuron firing. Acidification also reduced dynamic cl firing in cells expressing the Na V 1.2 channel but not in cells expressing Na V 1.1 channels. In vivo knockdown of Scn2a mRNA reduced seizure protection of acidification. In contrast, acid-mediated seizure protection was maintained in the Asic1a knock-out mouse. These data suggest Na V 1.2 channel as an important target for acid-mediated seizure protection. Our results have implications on how natural variations in pH can modulate neuronal excitability and highlight potential antiseizure drug development strategies based on the Na V 1.2 channel.
The Potential Antidepressant Compound Org 34167 Modulates HCN Channels Via a Novel Mode of Action.
Publisher: American Society for Pharmacology & Experimental Therapeutics (ASPET)
Date: 06-06-2023
Method of derivation and differentiation of mouse embryonic stem cells generating synchronous neuronal networks
Publisher: Elsevier BV
Date: 2018
DOI: 10.1016/J.JNEUMETH.2017.08.018
Abstract: Stem cells-derived neuronal cultures hold great promise for in vitro disease modelling and drug screening. However, currently stem cells-derived neuronal cultures do not recapitulate the functional properties of primary neurons, such as network properties. Cultured primary murine neurons develop networks which are synchronised over large fractions of the culture, whereas neurons derived from mouse embryonic stem cells (ESCs) display only partly synchronised network activity and human pluripotent stem cells-derived neurons have mostly asynchronous network properties. Therefore, strategies to improve correspondence of derived neuronal cultures with primary neurons need to be developed to validate the use of stem cell-derived neuronal cultures as in vitro models. By combining serum-free derivation of ESCs from mouse blastocysts with neuronal differentiation of ESCs in morphogen-free adherent culture we generated neuronal networks with properties recapitulating those of mature primary cortical cultures. After 35days of differentiation ESC-derived neurons developed network activity very similar to that of mature primary cortical neurons. Importantly, ESC plating density was critical for network development. Compared to the previously published methods this protocol generated more synchronous neuronal networks, with high similarity to the networks formed in mature primary cortical culture. We have demonstrated that ESC-derived neuronal networks recapitulating key properties of mature primary cortical networks can be generated by optimising both stem cell derivation and differentiation. This validates the approach of using ESC-derived neuronal cultures for disease modelling and in vitro drug screening.
Chapter 4 Ion channels and febrile seizures: It’s not just SCN1A
Publisher: Elsevier
Date: 2023
Sodium channel expression and transcript variation in the developing brain of human, Rhesus monkey, and mouse
Publisher: Elsevier BV
Date: 03-2022
DOI: 10.1016/J.NBD.2022.105622
Abstract: Genetic variation in voltage-gated sodium (Na
Axon initial segment dysfunction in a mouse model of genetic epilepsy with febrile seizures plus
Publisher: American Society for Clinical Investigation
Date: 02-08-2010
DOI: 10.1172/JCI42219
Axon initial segment dysfunction in epilepsy
Publisher: Wiley
Date: 28-05-2010
Functional variants in HCN4 and CACNA1H may contribute to genetic generalized epilepsy.
Publisher: Wiley
Date: 05-08-2017
DOI: 10.1002/EPI4.12068
Differential expression of exon 5 splice variants of sodium channel α subunit mRNAs in the developing mouse brain
Publisher: Elsevier BV
Date: 03-2010
DOI: 10.1016/J.NEUROSCIENCE.2009.12.011
Abstract: Sodium channel alpha subunit genes expressed in the human brain, SCN1A, SCN2A, SCN3A and SCN8A, are subject to alternative splicing of coding exons 5N and 5A. In this study we examined expression of alpha subunit mRNA and exon 5 splicing in the developing mouse brain. Expression levels of Scn1a, Scn2a and Scn8a mRNAs increase postnatally, whereas Scn3a mRNA expression levels decrease. Scn1a mRNA contains only exon 5A, due to the absence of exon 5N in the mouse Scn1a gene. At birth, Scn2a is the only sodium channel alpha subunit mRNA that contains higher or equal amounts of the 5N isoform compared to the 5A isoform in most brain regions. In contrast, the predominant isoform of Scn3a and Scn8a mRNAs in the newborn mouse brain is 5A. 5N/5A ratios for each of the three mRNAs vary across brain regions, with cortex >or= hippoc us>thalamus>cerebellum. In all brain regions and for all three alpha subunits, 5N/5A ratios gradually decrease with age, levelling at a value between 0.1 and 0.2. These findings suggest potential involvement of common factors in the alternative splicing of exon 5 for all three transcripts, and that expression of these factors varies between brain regions and changes during development. Differences in the strength of exon 5N and/or exon 5A splice sites in Scn2a pre-mRNA as compared to Scn1a and Scn8a may underlie the observed differences in 5N/5A ratios in the three alpha subunit mRNAs.
Perturbations in cortical development and neuronal network excitability arising from prenatal exposure to benzodiazepines in mice
Publisher: Wiley
Date: 04-03-2013
DOI: 10.1111/EJN.12167
Abstract: During brain development, many factors influence the assembly and final positioning of cortical neurons, and this process is essential for proper circuit formation and normal brain function. Among many important extrinsic factors that guide the maturation of embryonic cortical neurons, the secreted neurotransmitter GABA has been proposed to influence both their migratory behaviour and their terminal differentiation. The full extent of the short-term and long-term changes in brain patterning and function caused by modulators of the GABA system is not known. In this study, we specifically investigated whether diazepam, a commonly used benzodiazepine that modulates the GABAA receptor, alters neuronal positioning in vivo, and whether this can lead to lasting effects on brain function. We found that fetal exposure to diazepam did not change cell positioning within the embryonic day (E)14.5 mouse cerebral cortex, but significantly altered neuron positioning within the E18.5 cortex. In adult mice, diazepam treatment affected the distribution of cortical interneurons that express parvalbumin or calretinin, and also led to a decrease in the numbers of calretinin-expressing interneurons. In addition, we observed that neonatal exposure to diazepam altered the sensitivity of mice to a proconvulsant challenge. Therefore, exposure of the fetal brain to benzodiazepines has consequences for the positioning of neurons and cortical network excitability.
Augmented currents of an HCN2 variant in patients with febrile seizure syndromes
Publisher: Wiley
Date: 04-2010
DOI: 10.1002/ANA.21909
Acute effect of carbamazepine on corticothalamic 5-9-Hz and thalamocortical spindle (10-16-Hz) oscillations in the rat
Publisher: Wiley
Date: 06-12-2013
DOI: 10.1111/EJN.12441
Abstract: A major side effect of carbamazepine (CBZ), a drug used to treat neurological and neuropsychiatric disorders, is drowsiness, a state characterized by increased slow-wave oscillations with the emergence of sleep spindles in the electroencephalogram (EEG). We conducted cortical EEG and thalamic cellular recordings in freely moving or lightly anesthetized rats to explore the impact of CBZ within the intact corticothalamic (CT)-thalamocortical (TC) network, more specifically on CT 5-9-Hz and TC spindle (10-16-Hz) oscillations. Two to three successive 5-9-Hz waves were followed by a spindle in the cortical EEG. A single systemic injection of CBZ (20 mg/kg) induced a significant increase in the power of EEG 5-9-Hz oscillations and spindles. Intracellular recordings of glutamatergic TC neurons revealed 5-9-Hz depolarizing wave-hyperpolarizing wave sequences prolonged by robust, rhythmic spindle-frequency hyperpolarizing waves. This hybrid sequence occurred during a slow hyperpolarizing trough, and was at least 10 times more frequent under the CBZ condition than under the control condition. The hyperpolarizing waves reversed at approximately -70 mV, and became depolarizing when recorded with KCl-filled intracellular micropipettes, indicating that they were GABAA receptor-mediated potentials. In neurons of the GABAergic thalamic reticular nucleus, the principal source of TC GABAergic inputs, CBZ augmented both the number and the duration of sequences of rhythmic spindle-frequency bursts of action potentials. This indicates that these GABAergic neurons are responsible for the generation of at least the spindle-frequency hyperpolarizing waves in TC neurons. In conclusion, CBZ potentiates GABAA receptor-mediated TC spindle oscillations. Furthermore, we propose that CT 5-9-Hz waves can trigger TC spindles.
Prediction by Modeling That Epilepsy May Be Caused by Very Small Functional Changes in Ion Channels
Publisher: American Medical Association (AMA)
Date: 10-2009
DOI: 10.1001/ARCHNEUROL.2009.219
Abstract: To use computer simulation to perform a "genetic sensitivity" analysis to predict which genes are best positioned to increase risk as well as to predict functionally how variants in these genes might increase network excitability. A previously published, biophysically realistic model of the dentate gyrus that included mossy fiber sprouting between granule cells was used to model putative environmental changes associated with temporal lobe epilepsy. Properties of voltage-gated ion channels, either 1 at a time or in combinations, were varied systematically to determine their effect on network excitability. We found that the network is most sensitive to changes in steady-state voltage dependence of activation and relatively insensitive to changes in inactivation. Changes in sodium channels had the greatest effect on excitability, followed by changes in fast-delayed rectifier potassium channels and then N-type calcium channels. We also investigated the effects of simultaneous small changes in several ion channels, modeling a complex genetic background expected for common epilepsies. A combination of 2 or 3 simultaneous voltage shifts in steady-state activation as small as 2 mV could produce large changes in network excitability. Statistical power calculations indicate that changes this small are effectively undetectable with current experimental practices, thus posing new challenges for the functional analysis and validation of epilepsy genes.
Decreases in HCN mRNA expression in the hippocampus after kindling and status epilepticus in adult rats
Publisher: Wiley
Date: 10-2008
DOI: 10.1111/J.1528-1167.2008.01593.X
Abstract: Studies in animal models and patients have implicated changes in hyperpolarization-activated cyclic nucleotide-gated cation channel (HCN) expression in the pathogenesis of temporal lobe epilepsy (TLE). However, the nature of HCN changes during the epileptogenic process and their commonality across different TLE models is unknown. Here HCN1 and HCN2 mRNA expression was quantitatively measured at different time points during epileptogenesis in two distinct animal models of TLE the kainic acid (KA)-induced status epilepticus (SE) and amygdala kindling models. Hippoc al subregions (CA1, CA3, and dentate gyrus [DG]) and entorhinal cortex were dissected at different time-points. For KA-induced SE animals this was 24 h, 7 days (preepileptic), and 6 weeks (epileptic) post status. For amygdala kindling animals this was 2 weeks after reaching either "partially kindled" (one class II/III seizure) or "fully kindled" (five class V seizures) states. Quantification of regional hippoc al neuronal loss in the KA-treated animals was done using NeuN immunofluorescence and confocal microscopy. HCN mRNA levels decreased in an isoform and region specific manner at all time points after KA-induced SE. The decrease in neuronal number could not account for all reductions in HCN mRNA levels post-KA insult, implicating transcriptional changes. A reduction in HCN2 mRNA levels was also observed in fully kindled animals in the CA3 region. A reduction in HCN mRNA levels is present in two different models of TLE. This supports the case that a reduction in HCN channel expression is an accompaniment of epileptogenesis in different adult models of TLE.
Spike-and-wave discharge mediated reduction in hippocampal HCN1 channel function associates with learning deficits in a genetic mouse model of epilepsy
Publisher: Elsevier BV
Date: 04-2014
DOI: 10.1016/J.NBD.2013.12.007
Abstract: The GABAAγ2(R43Q) mouse is an established model of absence epilepsy displaying spontaneous spike-and-wave discharges (SWD) and associated behavioral arrest. Absence epilepsy typically results from cortico-thalamic networks. Nevertheless, there is increasing evidence for changes in hippoc al metabolism and electrical behavior, consistent with a link between absence seizures and hippoc us-related co-morbidities. Hyperpolarization-activated-cyclic-nucleotide-gated (HCN) channels are known to be transcriptionally regulated in a number of seizure models. Here we investigate the expression and function of these channels in the hippoc us of the genetic epilepsy model. A reduction in HCN1, but not HCN2 transcript, was observed in GABAAγ2(R43Q) mice relative to their littermate controls. In contrast, no change in HCN1 transcript was noted at an age prior to seizure expression or in a SWD-free model in which the R43Q mutation has been crossed into a seizure-resistant genetic background. Whole-cell recordings from CA1 pyramidal neurons confirm a reduction in Ih in the GABAAγ2(R43Q) mouse. Further, a left-shift in half-activation of the Ih conductance-voltage relationship is consistent with a reduction in HCN1 with no change in HCN2 channel expression. Behavioral analysis using the Morris water maze indicates that GABAAγ2(R43Q) mice are unable to learn as effectively as their wildtype littermates suggesting a deficit in hippoc al-based learning. SWD-free mice harboring the R43Q mutation had no learning deficit. We conclude that SWDs reduce hippoc al HCN1 expression and function, and that the reduction associates with a spatial learning deficit.
The mechanism of carbamazepine aggravation of absence seizures
Publisher: American Society for Pharmacology & Experimental Therapeutics (ASPET)
Date: 08-08-2006
Abstract: Carbamazepine (CBZ) aggravates many generalized seizures types, particularly absence seizures, but the mechanisms underlying this are poorly understood. GABA signaling within the reticular nucleus (Rt) and the ventrobasal complex (VB) of the thalamus is critical to the neurophysiology of absence seizures. The hypothesis that CBZ aggravates absence seizures by acting at the VB thalamus via a GABA(A) receptor-mediated mechanism was investigated in a genetic rat model, generalized absence epilepsy rats from Strasbourg (GAERS). Seizure activity was quantified by a 90-min electroencephalogram recording postdrug injection. Intracerebroventricular injections of CBZ (15 microg in 4 microl) resulted in seizure aggravation versus vehicle treatment, with a mean increase in seizure time of 40%. This indicates that CBZ acts directly, rather than via a metabolite, on the brain to aggravate seizures. Seizure aggravation also occurred following bilateral microinjection of CBZ (0.75 microg in 0.2 microl) into the VB (53%) but not following injection into the Rt (-9%). However, seizure aggravation was blocked when the GABA(A) receptor antagonist, bicuculline (BIC, 0.04 microg in 0.2 microl), was coinjected with CBZ into the VB. Injection of BIC alone (versus vehicle) into the VB also blocked seizure aggravation following systemic administration of CBZ (15 mg/kg i.p.). In vitro studies in Xenopus oocytes expressing recombinant GABA(A) receptors demonstrated that CBZ produced a dose-dependent potentiation of the GABA current at a physiological relevant concentration range (1-100 microM). These data demonstrate that CBZ acts at the VB thalamus to aggravate absence seizures in GAERS and that activation of GABA(A) receptors is critical to this effect.
Low glycaemic index diet reduces seizure susceptibility in a syndrome-specific mouse model of generalized epilepsy
Publisher: Elsevier BV
Date: 2013
DOI: 10.1016/J.EPLEPSYRES.2013.10.014
Abstract: Clinical evidence suggests that low glycaemic index diets are effective at reducing seizure frequency potentially through the stabilization of blood glucose levels. Here we investigate if diets containing carbohydrates with varying glycaemic index (GI) can modulate seizure susceptibility in a mouse model of generalized epilepsy. Electrocortical recordings were made from mice harboring the GABAAγ2 (R43Q) epilepsy mutation after three weeks on a low-or high-GI diet. Standard rodent diet was used as a control. Occurrence and durations of spike-wave-discharges (SWDs) were measured. An insulin injection was used to reduce blood glucose to levels known to precipitate SWDs in the GABAAγ2 (R43Q) mouse on the low and high-GI diets. SWD occurrence was reduced by approximately 35% in mice on the low-GI compared to high-GI diet. SWD occurrence was not different between high-GI diet and a standard diet suggesting that low-GI diet is protective. Weight gain of mice for all diet groups was identical suggesting that they were equally well tolerated. Under low blood glucose conditions SWD occurrence increased in the low and high-GI diets. Importantly, under low glucose conditions the low-GI diet no longer conferred protection against SWDs. SWDs were reduced in mice on a low GI-diet suggesting it may be an effective and well tolerated therapy for generalized epilepsy. The lack of effect of low-GI diet when glucose levels are reduced suggests that seizure protection in the GABAAγ2 (R43Q) mouse model may be due to the diets ability to stabilize blood glucose levels.
Gain-of-function HCN2 variants in genetic epilepsy.
Publisher: Hindawi Limited
Date: 13-11-2017
DOI: 10.1002/HUMU.23357
Abstract: Genetic generalized epilepsy (GGE) is a common epilepsy syndrome that encompasses seizure disorders characterized by spike-and-wave discharges (SWDs). Pacemaker hyperpolarization-activated cyclic nucleotide-gated channels (HCN) are considered integral to SWD genesis, making them an ideal gene candidate for GGE. We identified HCN2 missense variants from a large cohort of 585 GGE patients, recruited by the Epilepsy Phenome-Genome Project (EPGP), and performed functional analysis using two-electrode voltage cl recordings from Xenopus oocytes. The p.S632W variant was identified in a patient with idiopathic photosensitive occipital epilepsy and segregated in the family. This variant was also independently identified in an unrelated patient with childhood absence seizures from a European cohort of 238 familial GGE cases. The p.V246M variant was identified in a patient with photo-sensitive GGE and his father diagnosed with juvenile myoclonic epilepsy. Functional studies revealed that both p.S632W and p.V246M had an identical functional impact including a depolarizing shift in the voltage dependence of activation that is consistent with a gain-of-function. In contrast, no biophysical changes resulted from the introduction of common population variants, p.E280K and p.A705T, and the p.R756C variant from EPGP that did not segregate with disease. Our data suggest that HCN2 variants can confer susceptibility to GGE via a gain-of-function mechanism.
PRIMA1 mutation: A new cause of nocturnal frontal lobe epilepsy
Publisher: Wiley
Date: 03-07-2015
DOI: 10.1002/ACN3.224
Antisense oligonucleotide therapy reduces seizures and extends life span in an SCN2A gain-of-function epilepsy model.
Publisher: American Society for Clinical Investigation
Date: 12-2021
DOI: 10.1172/JCI152079
Impaired Color Recognition in HCN1 Epilepsy: A Single Case Report
Publisher: Frontiers Media SA
Date: 10-03-2022
DOI: 10.3389/FNEUR.2022.834252
Abstract: Variants in HCN1 are associated with a range of epilepsy syndromes including developmental and epileptic encephalopathies. Here we describe a child harboring a novel de novo HCN1 variant, E246A, in a child with epilepsy and mild developmental delay. By parental report, the child had difficulty in discriminating between colors implicating a visual deficit. This interesting observation may relate to the high expression of HCN1 channels in rod and cone photoreceptors where they play an integral role in shaping the light response. Functional analysis of the HCN1 E246A variant revealed a right shift in the voltage dependence of activation and slowing of the rates of activation and deactivation. The changes in the biophysical properties are consistent with a gain-of-function supporting the role of HCN1 E246A in disease causation. This case suggests that visual function, including color discrimination, should be carefully monitored in patients with diseases due to HCN1 pathogenic variants.
Antisense oligonucleotide therapy for KCNT1 encephalopathy.
Publisher: American Society for Clinical Investigation
Date: 08-12-2022
DOI: 10.1172/JCI.INSIGHT.146090
Abstract: Developmental and epileptic encephalopathies (DEE) are characterized by pharmacoresistant seizures with concomitant intellectual disability. Epilepsy of infancy with migrating focal seizures (EIMFS) is one of the most severe of these syndromes. De novo variants in ion channels, including gain-of-function variants in KCNT1, have been found to play a major role in the etiology of EIMFS. Here, we test a potential precision therapeutic approach in KCNT1-associated DEE using a gene silencing antisense oligonucleotide (ASO) approach. We generated a mouse model carrying the KCNT1 p.P924L pathogenic variant only the homozygous animals presented with the frequent, debilitating seizures and developmental compromise that are seen in patients. After a single intracerebroventricular bolus injection of a Kcnt1 gapmer ASO in symptomatic mice at postnatal day 40, seizure frequency was significantly reduced, behavioral abnormalities improved, and overall survival was extended compared to mice treated with a control ASO (non-hybridizing sequence). ASO administration at neonatal age was also well-tolerated and effective in controlling seizures and extending the lifespan of treated animals. The data presented here provide proof of concept for ASO-based gene silencing as a promising therapeutic approach in KCNT1-associated epilepsies.
Using a Multiplex Nucleic Acid in situ Hybridization Technique to Determine HCN4 mRNA Expression in the Adult Rodent Brain
Publisher: Frontiers Media SA
Date: 28-08-2019
Use of Local Field Potentials of Dissociated Cultures Grown on Multi-Electrode Arrays for Pharmacological Assays
Publisher: IEEE
Date: 08-2016
Enhanced spatial memory and hippocampal long-term potentiation in p75 neurotrophin receptor knockout mice
Publisher: Wiley
Date: 2010
DOI: 10.1002/HIPO.20598
Abstract: Previous reports have described increases in the size and number of cholinergic neurons in the basal forebrain in p75 neurotrophin receptor (p75(NTR)) knockout mice. In an earlier study, we also found improved spatial memory in these mice, raising the possibility that p75(NTR) regulates hippoc al function by its effects on the cholinergic basal forebrain. We therefore investigated hippoc al long-term potentiation in p75(NTR) knockout mice that shared the same genetic background as control 129/Sv mice. We also investigated heterozygous mice, carrying just one functional p75(NTR) allele. The p75(NTR) knockout mice had enhanced long-term potentiation in the Schafer collateral fiber synapses of the hippoc us. Heterozygous mice had an intermediate level, greater than controls but less than knockout mice. Hippoc al choline acetyltransferase activity was also markedly elevated in p75(NTR) knockout mice, with a smaller increase in heterozygous mice. In the Barnes maze, p75(NTR) knockout mice displayed markedly superior learning to controls, and this was evident over the three age brackets tested. At each age, the performance of heterozygous mice was intermediate to the other groups. In the open field test, p75(NTR) knockout mice exhibited greater stress-related behavioral responses, including freezing, than did control animals. There were no differences between the three groups in a test of olfactory function. The dose-dependent effects of p75(NTR) gene copy number on hippoc al plasticity and spatial memory indicate that p75(NTR) has profound effects on hippoc al function. Bearing in mind that p75(NTR) is very sparsely expressed in the adult hippoc us and has a potent effect on hippoc al choline acetyltransferase activity, the effects of p75(NTR) on hippoc al function are likely to be mediated indirectly, by its actions on basal forebrain cholinergic neurons.
Triheptanoin reduces seizure susceptibility in a syndrome-specific mouse model of generalized epilepsy
Publisher: Elsevier BV
Date: 2013
DOI: 10.1016/J.EPLEPSYRES.2012.09.016
Abstract: Triheptanoin is a triglyceride containing heptanoate, an odd-chained medium fatty acid that is metabolized to produce propionyl-CoA and subsequently C4 intermediates of the citric acid cycle and therefore capable of anaplerosis. These metabolic products are believed to underlie triheptanoin's anticonvulsant effects in rodent seizure models. Here we investigate the anticonvulsive effects of oral triheptanoin in a syndrome-specific genetic mouse model of generalized epilepsy based on the GABA(A)γ2(R43Q) mutation. Mice were fed a diet supplemented with triheptanoin from weaning for three weeks prior to electrocortical recordings. Occurrence and durations of spike and wave discharges (SWDs) were measured. Triheptanoin did not alter body weight or basal blood glucose levels suggesting that it was well tolerated. Triheptanoin supplementation halved the time spent in seizures due to a reduction in both SWD occurrence and duration. An injection of insulin was used to reduce blood glucose, a metabolic stress known to precipitate seizures in the GABA(A)γ2(R43Q) mouse. The reduction in seizure count was also evident following insulin induced hypoglycemia with the triheptanoin treated group having significantly less SWDs than control animals under similar low blood glucose conditions. In summary, triheptanoin may be an effective and well tolerated dietary therapy for generalized epilepsy.
Gap Junctions Link Regular-Spiking and Fast-Spiking Interneurons in Layer 5 Somatosensory Cortex
Publisher: Frontiers Media SA
Date: 17-07-2017
Development of low-affinity, membrane-targeted Ca2+ sensors suitable for measuring presynaptic Ca2+
Publisher: Wiley
Date: 12-2004
DOI: 10.1111/J.1440-1681.2004.04098.X
Abstract: 1. Our aim is to measure near-membrane Ca(2+) flux within the presynaptic terminals of central neurons by modifying new genetically encoded Ca(2+) sensors to develop tools capable of measuring localized Ca(2+) signals. 2. We used standard recombinant DNA technologies to generate the DNA coding for a fusion construct of a modified fluorescent 'pericam' Ca(2+) biosensor with a presynaptic P2X7 receptor (P2X7R). The Ca(2+) sensitivity of the biosensor was modified by rational site-directed mutagenesis of the calmodulin portion of the pericam. 3. Biosensor-receptor fusions were transfected into expression systems for evaluation. Expression studies in HEK-293 cells showed that biosensor-receptor fusion construct-delivered protein was localized exclusively to the plasma membrane, confirming that fusion did not affect the ability of the receptor to undergo normal protein synthesis and trafficking. 4. The Ca(2+)-dependent fluorescence of the pericam portion of the fusion protein was also retained. Site-direct mutagenesis within the calmodulin moiety of the pericam significantly reduced the Ca(2+) affinity of the complex. The dynamic range of the sensor following this modification is better matched to the higher Ca(2+) levels expected within presynaptic Ca(2+) microdomains.
Models for discovery of targeted therapy in genetic epileptic encephalopathies
Publisher: Wiley
Date: 05-09-2017
DOI: 10.1111/JNC.14134
Abstract: Epileptic encephalopathies are severe disorders emerging in the first days to years of life that commonly include refractory seizures, various types of movement disorders, and different levels of developmental delay. In recent years, many de novo occurring variants have been identified in in iduals with these devastating disorders. To unravel disease mechanisms, the functional impact of detected variants associated with epileptic encephalopathies is investigated in a range of cellular and animal models. This review addresses efforts to advance and use such models to identify specific molecular and cellular targets for the development of novel therapies. We focus on ion channels as the best-studied group of epilepsy genes. Given the clinical and genetic heterogeneity of epileptic encephalopathy disorders, experimental models that can reflect this complexity are critical for the development of disease mechanisms-based targeted therapy. The convergence of technological advances in gene sequencing, stem cell biology, genome editing, and high throughput functional screening together with massive unmet clinical needs provides unprecedented opportunities and imperatives for precision medicine in epileptic encephalopathies.
Excitotoxic-mediated transcriptional decreases in HCN2 channel function increase network excitability in CA1
Publisher: Elsevier BV
Date: 09-2009
Spectrum of GABAA receptor variants in epilepsy.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 04-2019
Retinal Dysfunction in a Mouse Model of HCN1 Genetic Epilepsy
Publisher: Society for Neuroscience
Date: 22-02-2023
DOI: 10.1523/JNEUROSCI.1615-22.2022
Abstract: Pathogenic variants in HCN1 are associated with a range of epilepsy syndromes including a developmental and epileptic encephalopathy. The recurrent de novo HCN1 pathogenic variant (M305L) results in a cation leak, allowing the flux of excitatory ions at potentials where the wild-type channels are closed. The Hcn1 M294L mouse recapitulates patient seizure and behavioral phenotypes. As HCN1 channels are highly expressed in rod and cone photoreceptor inner segments, where they shape the light response, mutated channels are likely to impact visual function. Electroretinogram (ERG) recordings from male and female mice Hcn1 M294L mice revealed a significant decrease in the photoreceptor sensitivity to light, as well as attenuated bipolar cell (P2) and retinal ganglion cell responses. Hcn1 M294L mice also showed attenuated ERG responses to flickering lights. ERG abnormalities are consistent with the response recorded from a single female human subject. There was no impact of the variant on the structure or expression of the Hcn1 protein in the retina. In silico modeling of photoreceptors revealed that the mutated HCN1 channel dramatically reduced light-induced hyperpolarization, resulting in more Ca 2+ flux during the response when compared with the wild-type situation. We propose that the light-induced change in glutamate release from photoreceptors during a stimulus will be diminished, significantly blunting the dynamic range of this response. Our data highlight the importance of HCN1 channels to retinal function and suggest that patients with HCN1 pathogenic variants are likely to have a dramatically reduced sensitivity to light and a limited ability to process temporal information. SIGNIFICANCE STATEMENT Pathogenic variants in HCN1 are emerging as an important cause of catastrophic epilepsy. HCN1 channels are ubiquitously expressed throughout the body, including the retina. Electroretinogram recordings from a mouse model of HCN1 genetic epilepsy showed a marked decrease in the photoreceptor sensitivity to light and a reduced ability to respond to high rates of light flicker. No morphologic deficits were noted. Simulation data suggest that the mutated HCN1 channel blunts light-induced hyperpolarization and consequently limits the dynamic range of this response. Our results provide insights into the role HCN1 channels play in retinal function as well as highlighting the need to consider retinal dysfunction in disease caused by HCN1 variants. The characteristic changes in the electroretinogram open the possibility of using this tool as a biomarker for this HCN1 epilepsy variant and to facilitate development of treatments.
Rare sudden unexpected death in epilepsy SCN5A variants cause changes in channel function implicating cardiac arrhythmia as a cause of death
Publisher: Wiley
Date: 22-04-2022
DOI: 10.1111/EPI.17254
Abstract: Sudden unexpected death in epilepsy (SUDEP) is a leading cause of premature death in epilepsy. The underlying pathological mechanisms are likely to be multifactorial. Cardiac arrhythmia has been suggested as a cause of death in some patients with SUDEP. SCN5A encodes the cardiac Na v 1.5 sodium channel. SCN5A variants that result in either loss or gain of channel function cause cardiac arrhythmias. Rare SCN5A variants have been reported in SUDEP cases, but the impact of these variants on channel function is unknown. Here, we use whole‐cell voltage cl recordings to perform functional analyses of rare SCN5A SUDEP variants, p.V223G, p.I397V, and p.R523C. Expression and biophysical properties, including activation, inactivation, and recovery from inactivation, were probed. Each SCN5A variant significantly impacted human Na V 1.5 channel function, indicating that they could cause cardiac arrhythmias. The patient carrying the p.R523C variant was on lamotrigine, an antiseizure medication implicated in SUDEP. Therapeutic concentration of lamotrigine caused a slowing of the rate of recovery from inactivation and a hyperpolarizing shift in the voltage of inactivation of human Na V 1.5 wild‐type, but not p.R523C channels, implicating a gene‐by‐drug interaction. These data suggest that SCN5A arrhythmogenic variants may confer increased risk of sudden death in in iduals with epilepsy.
A Cav3.2 T-type calcium channel point mutation has splice-variant-specific effects on function and segregates with seizure expression in a polygenic rat model of absence epilepsy
Publisher: Society for Neuroscience
Date: 14-01-2009
DOI: 10.1523/JNEUROSCI.5295-08.2009
Abstract: Low-voltage-activated, or T-type, calcium (Ca 2+ ) channels are believed to play an essential role in the generation of absence seizures in the idiopathic generalized epilepsies (IGEs). We describe a homozygous, missense, single nucleotide (G to C) mutation in the Ca v 3.2 T-type Ca 2+ channel gene ( Cacna1h ) in the genetic absence epilepsy rats from Strasbourg (GAERS) model of IGE. The GAERS Ca v 3.2 mutation ( gcm ) produces an arginine to proline (R1584P) substitution in exon 24 of Cacna1h , encoding a portion of the III–IV linker region in Ca v 3.2. gcm segregates codominantly with the number of seizures and time in seizure activity in progeny of an F1 intercross. We have further identified two major thalamic Cacna1h splice variants, either with or without exon 25. gcm introduced into the splice variants acts “epistatically,” requiring the presence of exon 25 to produce significantly faster recovery from channel inactivation and greater charge transference during high-frequency bursts. This gain-of-function mutation, the first reported in the GAERS polygenic animal model, has a novel mechanism of action, being dependent on exonic splicing for its functional consequences to be expressed.
Genetic absence epilepsy rats from Strasbourg have increased corticothalamic expression of stargazin
Publisher: Elsevier BV
Date: 08-2008
DOI: 10.1016/J.NBD.2008.04.012
Abstract: Stargazin is membrane bound protein involved in trafficking, synapse anchoring and biophysical modulation of AMPA receptors. A quantitative trait locus in chromosome 7 containing the stargazin gene has been identified as controlling the frequency and duration of absence seizures in the Genetic Absence Epilepsy Rats from Strasbourg (GAERS). Furthermore, mutations in this gene result in the Stargazer mouse that displays an absence epilepsy phenotype. GAERS stargazin mRNA expression is increased 1.8 fold in the somatosensory cortex and by 1.3 fold in the thalamus. The changes were present before and after the onset of absence seizures indicating that increases are not a secondary consequence of the seizures. Stargazin protein expression was also significantly increased in the somatosensory cortex after the onset of spontaneous seizures. The results are of significant importance beyond the GAERS model, as they are the first to show that an increase in stargazin expression may be pro-epileptic.
Two lines of transgenic mice expressing cre-recombinase exhibit increased seizure susceptibility
Publisher: Elsevier BV
Date: 03-2013
DOI: 10.1016/J.EPLEPSYRES.2012.10.005
Abstract: Conditional mouse models based on the Cre-recombinase (Cre)-loxP method are a powerful tool for determining the spatial and temporal function of genes in neuroscience research. The Emx1-Cre conditional model is designed to drive Cre expression in a predominantly excitatory neuron specific manner and the Dlx5/6-Cre mouse expresses Cre predominantly in cortical inhibitory neurons. The mouse models expressing the Cre transgene are healthy, active and have no overt behavioural or brain histological phenotypes. Subcutaneous pentylenetetrazol (scPTZ) is a proconvulsant frequently used to probe neuronal network excitability. In both the Emx1-Cre and Dlx5/6-Cre conditional mouse models the latency to scPTZ-induced seizures was significantly shorter than for their wild-type littermates. This shows that mouse models carrying the Cre transgene alone can have significant behavioural phenotypes. This may act as a confound to the interpretation of data obtained from crosses with loxP-flanked targets especially in the context of epilepsy phenotypes. These data highlight that appropriate control experiments that compare wild-type mice to those that carry the cre-transgene but not the loxP-flanked target are essential when using this method.
Cation leak: a common functional defect causing HCN1 developmental and epileptic encephalopathy
Publisher: Oxford University Press (OUP)
Date: 2023
DOI: 10.1093/BRAINCOMMS/FCAD156
Abstract: Pathogenic variants in HCN1 are an established cause of developmental and epileptic encephalopathy (DEE). To date, the stratification of patients with HCN1-DEE based on the biophysical consequence on channel function of a given variant has not been possible. Here, we analysed data from eleven patients carrying seven different de novo HCN1 pathogenic variants located in the transmembrane domains of the protein. All patients were diagnosed with severe disease including epilepsy and intellectual disability. The functional properties of the seven HCN1 pathogenic variants were assessed using two-electrode voltage-cl recordings in Xenopus oocytes. All seven variants showed a significantly larger instantaneous current consistent with cation leak. The impact of each variant on other biophysical properties was variable, including changes in the half activation voltage and activation and deactivation kinetics. These data suggest that cation leak is an important pathogenic mechanism in HCN1-DEE. Furthermore, published mouse model and clinical case reports suggest that seizures are exacerbated by sodium channel blockers in patients with HCN1 variants that cause cation leak. Stratification of patients based on their ‘cation leak’ biophysical phenotype may therefore provide key information to guide clinical management of in iduals with HCN1-DEE.
Loss-of-function variants in Kv11.1 cardiac channels as a biomarker for SUDEP
Publisher: Wiley
Date: 18-05-2021
DOI: 10.1002/ACN3.51381
Abstract: To compare the frequency and impact on the channel function of KCNH2 variants in SUDEP patients with epilepsy controls comprising patients older than 50 years, a group with low SUDEP risk, and establish loss‐of‐function KCNH2 variants as predictive biomarkers of SUDEP risk. We searched for KCNH2 variants with a minor allele frequency of %. Functional analysis in Xenopus laevis oocytes was performed for all KCNH2 variants identified. KCNH2 variants were found in 11.1% (10/90) of SUDEP in iduals compared to 6.0% (20/332) of epilepsy controls ( p = 0.11). Loss‐of‐function KCNH2 variants, defined as causing % reduction in maximal litude, were observed in 8.9% (8/90) SUDEP patients compared to 3.3% (11/332) epilepsy controls suggesting about threefold enrichment (nominal p = 0.04). KCNH2 variants that did not change channel function occurred at a similar frequency in SUDEP (2.2% 2/90) and epilepsy control (2.7% 9/332) cohorts ( p 0.99). Rare KCNH2 variants ( % allele frequency) associated with greater loss of function and an ~11‐fold enrichment in the SUDEP cohort (nominal p = 0.03). In silico tools were unable to predict the impact of a variant on function highlighting the need for electrophysiological analysis. These data show that loss‐of‐function KCNH2 variants are enriched in SUDEP patients when compared to an epilepsy population older than 50 years, suggesting that cardiac mechanisms contribute to SUDEP risk. We propose that genetic screening in combination with functional analysis can identify loss‐of‐function KCNH2 variants that could act as biomarkers of an in idual’s SUDEP risk.
Postsynaptic expression of long-term potentiation in the rat dentate gyrus demonstrated by variance-mean analysis
Publisher: Wiley
Date: 07-1999
DOI: 10.1111/J.1469-7793.1999.0121R.X
Abstract: 1. Long-term potentiation (LTP) of synaptic transmission is the putative mechanism underlying learning and memory. Despite intensive study, it remains controversial whether LTP is expressed at a pre- or postsynaptic locus. A new approach was used to investigate this question at excitatory synapses from the medial perforant path (MPP) onto granule cells in the hippoc al dentate gyrus. The variance of the evoked synaptic litude was plotted against mean synaptic litude at several different Cd2+ concentrations. The slope of the variance-mean plot estimates the average litude of the response following the release of a single vesicle of transmitter (Qav). A presynaptic modulation should not affect Qav, but a postsynaptic modulation should alter it. 2. The variance-mean technique was tested by applying the analysis before and after three different synaptic modulations: (i) a reduction in Qav by the addition of the competitive antagonist CNQX (ii) a reduction in the average probability of transmitter release (Pav) by the addition of baclofen and (iii) an increase in the number of active synaptic terminals (N) by increasing the stimulus strength. CNQX reduced the average synaptic litude and Qav to the same extent, consistent with a postsynaptic action. In contrast, neither a change in N nor Pav altered Qav. This confirms that the variance-mean technique can distinguish between a pre- and a postsynaptic site of modulation. 3. Induction of LTP increased EPSC litude by 50 +/- 0.4 % (n = 5) and, in the same cells, increased Qav by 47 +/- 0.6 %. There was no significant difference between the increase in EPSC litude and the increase in Qav. Thus, LTP of the MPP input to dentate granule cells can be explained by an increase in the postsynaptic response to transmitter.
New therapeutic opportunities in epilepsy: A genetic perspective
Publisher: Elsevier BV
Date: 11-2010
DOI: 10.1016/J.PHARMTHERA.2010.07.003
Abstract: Epilepsy is a common and serious neurological disorder. Despite recent advances in drug therapy, treatment for epilepsy is still largely empirical and rational prescribing based on the mechanism of action in an in idual patient is generally not possible. Genetic studies have identified an increasing collection of disease-causing genes providing a fundamental molecular foundation on which to build this understanding, at least for some forms of epilepsy. The impact of these genetic discoveries is likely to be wide reaching-from the discovery and validation of new drug targets to the potential to enable rational prescribing based on genetic makeup and even further through animal experimentation to tease out molecular and cellular mechanisms that lead to hyperexcitable neuronal networks causing epilepsy. Here we discuss how we can use knowledge of genetic mechanisms to improve treatment strategies now and into the future.
Calcium stores in hippocampal synaptic boutons mediate short-term plasticity, store-operated Ca2+ entry, and spontaneous transmitter release
Publisher: Elsevier BV
Date: 2001
DOI: 10.1016/S0896-6273(01)00190-8
Abstract: Evoked transmitter release depends upon calcium influx into synaptic boutons, but mechanisms regulating bouton calcium levels and spontaneous transmitter release are obscure. To understand these processes better, we monitored calcium transients in axons and presynaptic terminals of pyramidal neurons in hippoc al slice cultures. Action potentials reliably evoke calcium transients in axons and boutons. Calcium-induced calcium release (CICR) from internal stores contributes to the transients in boutons and to paired-pulse facilitation of EPSPs. Store depletion activates store-operated calcium channels, influencing the frequency of spontaneous transmitter release. Boutons display spontaneous Ca2+ transients blocking CICR reduces the frequency of these transients and of spontaneous miniature synaptic events. Thus, spontaneous transmitter release is largely calcium mediated, driven by Ca2+ release from internal stores. Bouton store release is important for short-term synaptic plasticity and may also contribute to long-term plasticity.
Cocaine-mediated synaptic potentiation is absent in VTA neurons from mGlu5-deficient mice
Publisher: Oxford University Press (OUP)
Date: 23-06-2010
The hyperpolarization‐activated cyclic nucleotide‐gated 4 channel as a potential anti‐seizure drug target
Publisher: Wiley
Date: 17-06-2020
DOI: 10.1111/BPH.15088
Epigenetic genes and epilepsy — emerging mechanisms and clinical applications
Publisher: Springer Science and Business Media LLC
Date: 20-07-2022
DOI: 10.1038/S41582-022-00693-Y
Abstract: An increasing number of epilepsies are being attributed to variants in genes with epigenetic functions. The products of these genes include factors that regulate the structure and function of chromatin and the placing, reading and removal of epigenetic marks, as well as other epigenetic processes. In this Review, we provide an overview of the various epigenetic processes, structuring our discussion around five function-based categories: DNA methylation, histone modifications, histone-DNA crosstalk, non-coding RNAs and chromatin remodelling. We provide background information on each category, describing the general mechanism by which each process leads to altered gene expression. We also highlight key clinical and mechanistic aspects, providing ex les of genes that strongly associate with epilepsy within each class. We consider the practical applications of these findings, including tissue-based and biofluid-based diagnostics and precision medicine-based treatments. We conclude that variants in epigenetic genes are increasingly found to be causally involved in the epilepsies, with implications for disease mechanisms, treatments and diagnostics.
Glutamate is associated with a higher risk of seizures in patients with gliomas
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 25-07-2012
Antisense oligonucleotide therapy for SCN2A gain-of-function epilepsy
Publisher: Cold Spring Harbor Laboratory
Date: 11-09-2020
DOI: 10.1101/2020.09.09.289900
Abstract: The clinical spectrum associated with SCN2A de novo mutations (DNMs) continues to expand and includes autism spectrum disorder with or without seizures, in addition to early and late seizure onset developmental and epileptic encephalopathies (DEEs). Recent biophysical studies on SCN2A variants suggest that the majority of early seizure onset DEE DNMs cause gain of function. Gain of function in SCN2A, the principal sodium channel of excitatory pyramidal neurons, would result in heightened neuronal activity and is likely to underlie the pathology seen in early seizure onset DEE patients. Supratherapeutic dosing of the non-selective sodium channel blocker phenytoin, is effective in controlling seizures in these patients but does not impact neurodevelopment, raising the idea that more profound and specific reduction in SCN2A function could significantly improve clinical outcome. To test the potential therapeutic benefit of reducing SCN2A in early seizure onset DEE we centrally administered an antisense oligonucleotide (ASO) targeting mouse Scn2a (Scn2a ASO) to a mouse model of human SCN2A early seizure onset DEE. Mice were genetically engineered to harbour the human equivalent SCN2A p.R1882Q mutation (Q/+), one of the most recurrent mutations in early seizure onset DEE. Q/+ mice presented with spontaneous seizures at postnatal day (P) 1 and did not survive beyond P30. Intracerebroventricular Scn2a ASO administration into Q/+ mice between P1-2 (that reduced Scn2a mRNA levels by 50%) significantly extended lifespan and markedly reduced spontaneous seizures occurrence. Across a range of cognitive and motor behavioural tests, Scn2a ASO treated Q/+ mice were largely indistinguishable from wildtype (+/+) mice. Further improvements in survival and behaviour were seen by adjustment of dosing regimens during development. Scn2a ASO efficacy was also evident at the cellular level. Whole cell patch cl recording showed that Scn2a ASO administration reversed changes in neuronal excitability in layer 2/3 pyramidal neurons of Q/+ mice to levels seen in +/+ mice. Safety was assessed in +/+ mice and showed a developmental stage dependent tolerability and a favourable therapeutic index. This study suggests that a human SCN2A gapmer ASO could profoundly and safely impact early seizure onset DEE patients and heralds a new era of precision therapy in neurodevelopmental disorders.
Temperature elevation increases GABAA-mediated cortical inhibition in a mouse model of genetic epilepsy
Publisher: Wiley
Date: 22-12-2011
Null mutation of the α4 nicotinic receptor subunit increases the propensity of muscarinic-mediated neuronal bursting in mouse hippocampal slices
Publisher: Elsevier BV
Date: 09-2006
DOI: 10.1016/J.NEUROPHARM.2006.05.001
Abstract: Alpha4 subunit nicotinic cholinergic receptor (nAChR) knock out mice (KO) have a greater susceptibility to proconvulsant-induced seizures than do wild type (WT). The underlying mechanisms remain obscure. We tested whether such seizure-like activity was reflected in bursting activity of hippoc al neurons by recording with intracellular microelectrodes from CA1 pyramidal neurons in slices from WT and KO mice. Intriguingly, while carbachol-induced bursting activity occurred in only 21% of WT slices, qualitatively identical patterns of bursting occurred in 72% of KO slices. Extracellular recordings from CA1 and CA3 regions suggest that carbachol-mediated population activity was regionalized in our preparations. The relative weighting of excitatory to inhibitory synaptic potentials was similar between WT and alpha4 KO mice. However, burst-firing cells had a smaller input time constant than non-bursters. Low-concentration DHbetaE (selective alpha4beta2 nAChR antagonist) did not increase the propensity of WT slices to burst-fire, indicating that absence of alpha4 subunits per se, cannot explain the differences in activity between slices from WT and KO mice. These observations suggest that alpha4 nAChRs are unlikely to be involved in modulating the pattern of bursting neural activity, but their absence could induce subtle developmental changes in the sensitivity of hippoc al circuits to develop this behaviour.
Interleukin‐1β has trophic effects in microglia and its release is mediated by P2X7R pore
Publisher: Wiley
Date: 05-2017
DOI: 10.1111/IMJ.5_13457
Classification of antiseizure drugs in cultured neuronal networks using multielectrode arrays and unsupervised learning
Publisher: Wiley
Date: 10-05-2022
DOI: 10.1111/EPI.17268
Abstract: Antiseizure drugs (ASDs) modulate synaptic and ion channel function to prevent abnormal hypersynchronous or excitatory activity arising in neuronal networks, but the relationship between ASDs with respect to their impact on network activity is poorly defined. In this study, we first investigated whether different ASD classes exert differential impact upon network activity, and we then sought to classify ASDs according to their impact on network activity. We used multielectrode arrays (MEAs) to record the network activity of cultured cortical neurons after applying ASDs from two classes: sodium channel blockers (SCBs) and γ‐aminobutyric acid type A receptor‐positive allosteric modulators (GABA PAMs). A two‐dimensional representation of changes in network features was then derived, and the ability of this low‐dimensional representation to classify ASDs with different molecular targets was assessed. A two‐dimensional representation of network features revealed a separation between the SCB and GABA PAM drug classes, and could classify several test compounds known to act through these molecular targets. Interestingly, several ASDs with novel targets, such as cannabidiol and retigabine, had closer similarity to the SCB class with respect to their impact upon network activity. These results demonstrate that the molecular target of two common classes of ASDs is reflected through characteristic changes in network activity of cultured neurons. Furthermore, a low‐dimensional representation of network features can be used to infer an ASDs molecular target. This approach may allow for drug screening to be performed based on features extracted from MEA recordings.
KCNT1 gain of function in 2 epilepsy phenotypes is reversed by quinidine.
Publisher: Wiley
Date: 04-2014
DOI: 10.1002/ANA.24128
Spontaneous release from mossy fiber terminals inhibits Ni2+ -sensitive T-type Ca2+ channels of CA3 pyramidal neurons in the rat organotypic hippocampal slice
Publisher: Wiley
Date: 07-2008
DOI: 10.1002/HIPO.20419
Abstract: Mossy fibers (axons arising from dentate granule cells) form large synaptic contacts exclusively onto the proximal apical dendrites of CA3 pyramidal neurons. They can generate large synaptic currents that occur in close proximity to the soma. These properties mean that active conductance in the proximal apical dendrite could have a disproportionate influence on CA3 pyramidal neuron excitability. Ni(2+)-sensitive T-type Ca(2+) channels are important modulators of dendritic excitability. Here, we use an optical approach to determine the contribution of Ni(2+) (100 microM)-sensitive Ca(2+) channels to action potential (AP) elicited Ca(2+) flux in the soma, proximal apical and distal apical dendrites. At resting membrane potentials Ni(2+)-sensitive Ca(2+) channels do not contribute to the Ca(2+) signal in the proximal apical dendrite, but do contribute in the other cell regions. Spontaneous release from mossy fiber terminals acting on 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX)-sensitive postsynaptic channels underlies a tonic inhibition of Ni(2+)-sensitive channels. Chelating Zn(2+) with CaEDTA blocks CNQX-sensitive changes in Ca(2+) flux implicating a mechanistic role of this ion in T-type Ca(2+) channel block. To test if this inhibition influenced excitability, progressively larger depolarizing pulses were delivered to CA3 pyramidal neurons. CNQX significantly reduced the size of the depolarizing step required to generate APs and increased the absolute number of APs per depolarizing step. This change in AP firing was completely reversed by the addition of Ni(2+). This mechanism may reduce the impact of T-type Ca(2+) channels in a region where large synaptic events are common.
Ion Channels in Genetic Epilepsy: From Genes and Mechanisms to Disease-Targeted Therapies
Publisher: American Society for Pharmacology & Experimental Therapeutics (ASPET)
Date: 20-12-2018
Biophysical analysis of an HCN1 epilepsy variant suggests a critical role for S5 helix Met-305 in voltage sensor to pore domain coupling
Publisher: Elsevier BV
Date: 11-2021
DOI: 10.1016/J.PBIOMOLBIO.2021.07.005
Abstract: Hyperpolarization-gated, cyclic nucleotide-activated (HCN1-4) channels are inwardly rectifying cation channels that display voltage dependent activation and de-activation. Pathogenic variants in HCN1 are associated with severe developmental and epileptic encephalopathies including the de novo HCN1 M305L variant. M305 is located in the S5 domain that is implicated in coupling voltage sensor domain movement to pore opening. This variant lacks voltage-dependent activation and de-activation and displays normal cation selectivity. To elucidate the impact of the mutation on the channel structure-function relations, molecular dynamics simulations of the wild type and mutant homotetramers were compared and identified a sulphur-aromatic interaction between M305 and F389 that contributes to the coupling of the voltage-sensing domain to the pore domain. To mimic the heterozygous condition as a heterotetrameric channel assembly, Xenopus oocytes were co-injected with various ratios of wild-type and mutant subunit cRNAs and the biophysical properties of channels with different subunit stoichiometries were determined. The results showed that a single mutated subunit was sufficient to significantly disrupt the voltage dependence of activation. The functional data were qualitatively consistent with predictions of a model that assumes independent activation of the voltage sensing domains allosterically controlling the closed to open transition of the pore. Overall, the M305L mutation results in an HCN1 channel that lacks voltage dependence and facilitates excitatory cation flow at membrane potentials that would normally close the channel. Our findings provide molecular insights into HCN1 channels and reveal the structural and biophysical basis of the severe epilepsy phenotype associated with the M305L mutation.
Sub region-specific modulation of synchronous neuronal burst firing after a kainic acid insult in organotypic hippocampal cultures
Publisher: Springer Science and Business Media LLC
Date: 02-07-2008
Antidepressant-like activity of a brain penetrant HCN channel inhibitor in mice
Publisher: Frontiers Media SA
Date: 10-05-2023
DOI: 10.3389/FPHAR.2023.1159527
Abstract: Changes in Hyperpolarization-Activated Cyclic Nucleotide-Gated (HCN) channel function have been linked to depressive-like traits, making them potential drug targets. However, there is currently no peer-reviewed data supporting the use of a small molecule modulator of HCN channels in depression treatment. Org 34167, a benzisoxazole derivative, has been patented for the treatment of depression and progressed to Phase I trials. In the current study, we analysed the biophysical effects of Org 34167 on HCN channels in stably transfected human embryonic kidney 293 (HEK293) cells and mouse layer V neurons using patch-cl electrophysiology, and we utilised three high-throughput screens for depressive-like behaviour to assess the activity of Org 34167 in mice. The impact of Org 34167 on locomotion and coordination were measured by performing rotarod and ledged beam tests. Org 34167 is a broad-spectrum inhibitor of HCN channels, slowing activation and causing a hyperpolarising shift in voltage-dependence of activation. It also reduced I h -mediated sag in mouse neurons. Org 34167 (0.5 mg/kg) reduced marble burying and increased the time spent mobile in the Porsolt swim and tail suspension tests in both male and female BALB/c mice, suggesting reduced depressive-like behaviour. Although no adverse effects were seen at 0.5 mg/kg, an increase in dose to 1 mg/kg resulted in visible tremors and impaired locomotion and coordination. These data support the premise that HCN channels are valid targets for anti-depressive drugs albeit with a narrow therapeutic index. Drugs with higher HCN subtype selectivity are needed to establish if a wider therapeutic window can be obtained.
Rhythmic neuronal activity in S2 somatosensory and insular cortices contribute to the initiation of absence-related spike-and-wave discharges.
Publisher: Wiley
Date: 22-10-2012
DOI: 10.1111/J.1528-1167.2012.03720.X
Abstract: The origin of bilateral synchronous spike-and-wave discharges (SWDs) that underlie absence seizures has been widely debated. Studies in genetic rodent models suggest that SWDs originate from a restricted region in the somatosensory cortex. The properties of this initiation site remain unknown. Our goal was to characterize the interictal, preictal and ictal neuronal activity in the primary and secondary cortical regions (S1, S2) and in the adjacent insular cortex (IC) in Genetic Absence Epilepsy Rats from Strasbourg (GAERS). We performed electroencephalography (EEG) recordings in combination with multisite local field potential (LFP) and single cell juxtacellular recordings, and cortical electrical stimulations, in freely moving rats and those under neurolept-anesthesia. The onset of the SWDs was preceded by 5-9 Hz field potential oscillations, which were detected earlier in S2 and IC than in S1. Sustained SWDs could be triggered by a 2-s train of 7-Hz electrical stimuli at a lower current intensity in S2 than in S1. In S2 and IC, subsets of neurons displayed rhythmic firing (5-9 Hz) in between seizures. S2 and IC layers V and VI neurons fired during the same time window, whereas in S1 layer VI, neurons fired before layer V neurons. Just before the spike component of each SW complex, short-lasting high-frequency oscillations consistently occurred in IC ∼20 msec before S1. Our findings demonstrate that the S2/IC cortical areas are a critical component of the macro-network that is responsible for the generation of absence-related SWDs.
Reduced dendritic arborization and hyperexcitability of pyramidal neurons in a Scn1b-based model of Dravet syndrome
Publisher: Oxford University Press (OUP)
Date: 17-04-2014
DOI: 10.1093/BRAIN/AWU077
Abstract: Epileptic encephalopathies, including Dravet syndrome, are severe treatment-resistant epilepsies with developmental regression. We examined a mouse model based on a human β1 sodium channel subunit (Scn1b) mutation. Homozygous mutant mice shared phenotypic features and pharmaco-sensitivity with Dravet syndrome. Patch-cl analysis showed that mutant subicular and layer 2/3 pyramidal neurons had increased action potential firing rates, presumably as a consequence of their increased input resistance. These changes were not seen in L5 or CA1 pyramidal neurons. This raised the concept of a regional seizure mechanism that was supported by data showing increased spontaneous synaptic activity in the subiculum but not CA1. Importantly, no changes in firing or synaptic properties of gamma-aminobutyric acidergic interneurons from mutant mice were observed, which is in contrast with Scn1a-based models of Dravet syndrome. Morphological analysis of subicular pyramidal neurons revealed reduced dendritic arborization. The antiepileptic drug retigabine, a K+ channel opener that reduces input resistance, d ened action potential firing and protected mutant mice from thermal seizures. These results suggest a novel mechanism of disease genesis in genetic epilepsy and demonstrate an effective mechanism-based treatment of the disease.
KCTD12 modulation of GABA(B) receptor function
Publisher: Wiley
Date: 07-06-2017
DOI: 10.1002/PRP2.319
Related Organisations
Florey Institute Of Neuroscience And Mental Health
Location: Australia
Related Funding Activities
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End Date: 01-2016
Amount: $300,000.00
Funder: Australian Research Council
View Funded ActivityDiscovery Projects - Grant ID: DP120104112
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Amount: $310,000.00
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View Funded ActivityDiscovery Projects - Grant ID: DP0449696
Start Date: 01-2004
End Date: 12-2007
Amount: $285,000.00
Funder: Australian Research Council
View Funded ActivityARC Future Fellowships - Grant ID: FT0990628
Start Date: 01-2010
End Date: 01-2014
Amount: $658,400.00
Funder: Australian Research Council
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