ORCID Profile
0000-0002-3883-5682
Current Organisations
Utrecht University
,
Netherlands Institute for Neuroscience
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Publisher: Springer Science and Business Media LLC
Date: 07-06-2021
DOI: 10.1038/S41467-021-23647-2
Abstract: Single-Molecule Localization Microscopy (SMLM) provides the ability to determine molecular organizations in cells at nanoscale resolution, but in complex biological tissues, where s le-induced aberrations h er detection and localization, its application remains a challenge. Various adaptive optics approaches have been proposed to overcome these issues, but the exact performance of these methods has not been consistently established. Here we systematically compare the performance of existing methods using both simulations and experiments with standardized s les and find that they often provide limited correction or even introduce additional errors. Careful analysis of the reasons that underlie this limited success enabled us to develop an improved method, termed REALM (Robust and Effective Adaptive Optics in Localization Microscopy), which corrects aberrations of up to 1 rad RMS using 297 frames of blinking molecules to improve single-molecule localization. After its quantitative validation, we demonstrate that REALM enables to resolve the periodic organization of cytoskeletal spectrin of the axon initial segment even at 50 μm depth in brain tissue.
Publisher: Society for Neuroscience
Date: 06-05-2015
DOI: 10.1523/JNEUROSCI.4747-14.2015
Abstract: Myelination and voltage-gated ion channel clustering at the nodes of Ranvier are essential for the rapid saltatory conduction of action potentials. Whether myelination influences the structural organization of the axon initial segment (AIS) and action potential initiation is poorly understood. Using the cuprizone mouse model, we combined electrophysiological recordings with immunofluorescence of the voltage-gated Nav1.6 and Kv7.3 subunits and anchoring proteins to analyze the functional and structural properties of single demyelinated neocortical L5 axons. Whole-cell recordings demonstrated that neurons with demyelinated axons were intrinsically more excitable, characterized by increased spontaneous suprathreshold depolarizations as well as antidromically propagating action potentials ectopically generated in distal parts of the axon. Immunofluorescence examination of demyelinated axons showed that βIV-spectrin, Nav1.6, and the Kv7.3 channels in nodes of Ranvier either dissolved or extended into the paranodal domains. In contrast, while the AIS in demyelinated axons started more closely to the soma, ankyrin G, βIV-spectrin, and the ion channel expression were maintained. Structure–function analysis and computational modeling, constrained by the AIS location and realistic dendritic and axonal morphologies, confirmed that a more proximal onset of the AIS slightly reduced the efficacy of action potential generation, suggesting a compensatory role. These results suggest that oligodendroglial myelination is not only important for maximizing conduction velocity, but also for limiting hyperexcitability of pyramidal neurons.
Publisher: Cold Spring Harbor Laboratory
Date: 17-01-2021
DOI: 10.1101/2021.01.15.426022
Abstract: The complement system is implicated in synapse loss in the MS hippoc us, but the functional consequences of synapse loss remain poorly understood. Here, in post-mortem MS hippoc i with demyelination we find that deposits of the complement component C1q are enriched in the CA2 subfield, are linked to loss of inhibitory synapses and are significantly higher in MS patients with cognitive impairments compared to those with preserved cognitive functions. Using the cuprizone mouse model of demyelination, we corroborated that C1q deposits are highest within the demyelinated dorsal hippoc al CA2 pyramidal layer, and co-localized with inhibitory synapses engulfed by microglia/macrophages. In agreement with the loss of inhibitory perisomatic synapses, we further found that Schaffer collateral feedforward inhibition but not excitation was impaired in CA2 pyramidal neurons and accompanied by a reduced spike output. Ultimately, we show that these electrophysiological changes were associated with an impaired encoding of social memories. Together, our findings identify CA2 as a critical circuit in demyelinated intrahippoc al lesions and memory dysfunctions in MS.
Publisher: Cold Spring Harbor Laboratory
Date: 02-12-2022
DOI: 10.1101/2022.11.29.518317
Abstract: Human cortical pyramidal neurons are large, have extensive dendritic trees, and yet have surprisingly fast input-output properties: rapid subthreshold synaptic membrane potential changes are reliably encoded in timing of action potentials (APs). Here, we tested whether biophysical properties of voltage-gated sodium (Na + ) and potassium (K + ) currents in human pyramidal neurons can explain their fast input-output properties. Human Na + and K + currents exhibited more depolarized voltage-dependence, slower inactivation and faster recovery from inactivation compared with their mouse counterparts. Computational modeling showed that despite lower Na + channel densities in human neurons, the biophysical properties of Na + channels resulted in higher channel availability and contributed to fast AP kinetics stability. Finally, human Na + channel properties also resulted in a larger dynamic range for encoding of subthreshold membrane potential changes. Thus, biophysical adaptations of voltage-gated Na + and K + channels enable fast input-output properties of large human pyramidal neurons. Biophysical properties of Na + and K + ion channels enable human neurons to reliably encode fast inputs into output.
Publisher: Wiley
Date: 06-2004
Publisher: eLife Sciences Publications, Ltd
Date: 09-09-2019
DOI: 10.7554/ELIFE.42766
Abstract: Hyperpolarization-activated cyclic-nucleotide-gated (HCN) channels control electrical rhythmicity and excitability in the heart and brain, but the function of HCN channels at the subcellular level in axons remains poorly understood. Here, we show that the action potential conduction velocity in both myelinated and unmyelinated central axons can be bidirectionally modulated by a HCN channel blocker, cyclic adenosine monophosphate (cAMP), and neuromodulators. Recordings from mouse cerebellar mossy fiber boutons show that HCN channels ensure reliable high-frequency firing and are strongly modulated by cAMP (EC50 40 µM estimated endogenous cAMP concentration 13 µM). In addition, immunogold-electron microscopy revealed HCN2 as the dominating subunit in cerebellar mossy fibers. Computational modeling indicated that HCN2 channels control conduction velocity primarily by altering the resting membrane potential and are associated with significant metabolic costs. These results suggest that the cAMP-HCN pathway provides neuromodulators with an opportunity to finely tune energy consumption and temporal delays across axons in the brain.
Publisher: Springer Science and Business Media LLC
Date: 05-10-2008
DOI: 10.1038/NN.2203
Abstract: Action potential threshold is thought to be lowest in the axon, but when measured using conventional techniques, we found that action potential voltage threshold of rat cortical pyramidal neurons was higher in the axon than at other neuronal locations. In contrast, both current threshold and voltage threshold of the isolated somato-dendritic spike were substantially higher at the soma. These data indicate that action potential threshold is indeed lowest in the axon.
Publisher: eLife Sciences Publications, Ltd
Date: 10-01-2022
DOI: 10.7554/ELIFE.73827
Abstract: Parvalbumin-positive (PV + ) γ-aminobutyric acid (GABA) interneurons are critically involved in producing rapid network oscillations and cortical microcircuit computations, but the significance of PV + axon myelination to the temporal features of inhibition remains elusive. Here, using toxic and genetic mouse models of demyelination and dysmyelination, respectively, we find that loss of compact myelin reduces PV + interneuron presynaptic terminals and increases failures, and the weak phasic inhibition of pyramidal neurons abolishes optogenetically driven gamma oscillations in vivo. Strikingly, during behaviors of quiet wakefulness selectively theta rhythms are lified and accompanied by highly synchronized interictal epileptic discharges. In support of a causal role of impaired PV-mediated inhibition, optogenetic activation of myelin-deficient PV + interneurons attenuated the power of slow theta rhythms and limited interictal spike occurrence. Thus, myelination of PV axons is required to consolidate fast inhibition of pyramidal neurons and enable behavioral state-dependent modulation of local circuit synchronization.
Publisher: Elsevier BV
Date: 08-2007
DOI: 10.1016/J.NEURON.2007.07.031
Abstract: Action potentials are binary signals that transmit information via their rate and temporal pattern. In this context, the axon is thought of as a transmission line, devoid of a role in neuronal computation. Here, we show a highly localized role of axonal Kv1 potassium channels in shaping the action potential waveform in the axon initial segment (AIS) of layer 5 pyramidal neurons independent of the soma. Cell-attached recordings revealed a 10-fold increase in Kv1 channel density over the first 50 microm of the AIS. Inactivation of AIS and proximal axonal Kv1 channels, as occurs during slow subthreshold somatodendritic depolarizations, led to a distance-dependent broadening of axonal action potentials, as well as an increase in synaptic strength at proximal axonal terminals. Thus, Kv1 channels are strategically positioned to integrate slow subthreshold signals, providing control of the presynaptic action potential waveform and synaptic coupling in local cortical circuits.
Publisher: Elsevier BV
Date: 2004
Publisher: Cold Spring Harbor Laboratory
Date: 10-04-2022
DOI: 10.1101/2022.04.07.487496
Abstract: Parvalbumin-expressing (PV + ) basket cells are fast-spiking interneurons that exert critical control over local neuronal circuit activity and oscillations. PV + interneuron axons are partially myelinated but the electrical and metabolic roles of myelin in axonal functions remain poorly understood. Here, we developed Cre-dependent AAV vectors for cell type-specific investigation of mitochondria with genetically encoded fluorescent probes. Single-cell reconstructions and mining of ultrastructural data revealed that mitochondria selectively cluster to myelinated segments of PV + basket cell axons. Cuprizone-induced demyelination abolished mitochondrial clustering in PV + axons but increased axonal mitochondrial densities in excitatory axons. The internodal clustering of mitochondria was preserved with genetic deletion of myelin basic protein, suggesting that noncompacted myelin is sufficient. Finally, two-photon imaging of action potential-evoked mitochondrial calcium (mt-Ca 2+ ) responses showed that internodal mitochondria did not contribute in buffering activity-dependent Ca 2+ influx. These findings suggest that oligodendrocyte-PV + axon signaling assembles mitochondria to branch selectively fine-tune metabolic demands.
Publisher: Wiley
Date: 12-01-2007
Publisher: Wiley
Date: 09-2002
DOI: 10.1046/J.1460-9568.2002.02136.X
Abstract: Recent hypotheses on the action of antidepressants imply a modulation of excitatory amino acid transmission. Here, the effects of long-term antidepressant application in rats with the drug tianeptine were examined at hippoc al CA3 commissural associational (c/a) glutamate receptor ion channels, employing the whole-cell patch-cl technique. The drug's impact was tested by subjecting rats to daily restraint stress for three weeks in combination with tianeptine treatment (10 mg/kg/day). Whereas stress increased the deactivation time-constant and litude of the N-methyl-d-aspartate (NMDA) receptor-mediated excitatory postsynaptic currents (EPSCs), it did not affect the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)/kainate receptor-mediated EPSCs. Concomitant pharmacological treatment of stressed animals with tianeptine resulted in a normalized scaling of the litude ratio of NMDA receptor to AMPA/kainate receptor-mediated currents and prevented the stress-induced attenuation of NMDA-EPSCs deactivation. Both paired-pulse-facilitation and frequency-dependent plasticity remained unchanged. Both in control and stressed animals, however, tianeptine treatment strengthened the slope of the input-output relation of EPSCs. The latter was mimicked by exposing hippoc al slices in vitro with 10 micro m tianeptine, which rapidly increased the litudes of NMDA- and AMPA/kainate EPSCs. The enhancement of EPSCs could be blocked by the intracellular presence of the kinase inhibitor staurosporine (1 micro m), suggesting the involvement of a postsynaptic phosphorylation cascade rather then presynaptic release mechanisms at CA3 c/a synapses. These results indicate that tianeptine targets the phosphorylation-state of glutamate receptors at the CA3 c/a synapse. This novel signal transduction mechanism for tianeptine may provide a mechanistic resolution for its neuroprotective properties and, moreover, a pharmacological trajectory for its memory enhancing and/or antidepressant activity.
Publisher: Springer Science and Business Media LLC
Date: 03-06-2012
DOI: 10.1038/NN.3132
Abstract: Action potential generation and conduction requires large quantities of energy to restore Na(+) and K(+) ion gradients. We investigated the subcellular location and voltage dependence of this metabolic cost in rat neocortical pyramidal neurons. Using Na(+)/K(+) charge overlap as a measure of action potential energy efficiency, we found that action potential initiation in the axon initial segment (AIS) and forward propagation into the axon were energetically inefficient, depending on the resting membrane potential. In contrast, action potential backpropagation into dendrites was efficient. Computer simulations predicted that, although the AIS and nodes of Ranvier had the highest metabolic cost per membrane area, action potential backpropagation into the dendrites and forward propagation into axon collaterals dominated energy consumption in cortical pyramidal neurons. Finally, we found that the high metabolic cost of action potential initiation and propagation down the axon is a trade-off between energy minimization and maximization of the conduction reliability of high-frequency action potentials.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 15-09-2023
Publisher: Elsevier BV
Date: 07-2001
DOI: 10.1016/S0304-3940(01)01926-7
Abstract: This study tested the time-of-day dependence of the intrinsic postsynaptic properties of hippoc al CA3 pyramidal neurons. High-voltage-activated Ca2+ currents and the Ca(2+)- and voltage-dependent afterhyperpolarizations were examined in slices of rat brains obtained at four distinct time periods. Just after onset of the dark phase, the steady-state litude of the Ca2+ current (-1.24+/-0.11 nA) was significantly greater (P<0.03) than that of the light phase (-0.84+/-0.06 nA). Over the entire time range, the litude of the Ca2+ current correlated with plasma corticosterone levels in a U-shaped function. Furthermore, depolarization-induced excitability during the dark phase exhibited an increased spike after depolarization (3.1+/-0.1 mV) and a slower adaptation of the firing frequency (146+/-18%). These findings point to a dynamic time-of-day dependence of the CA3 neuronal properties and postsynaptic Ca2+ currents.
Publisher: Cold Spring Harbor Laboratory
Date: 09-11-2022
DOI: 10.1101/2022.11.09.515770
Abstract: Activity-dependent plasticity of the axon initial segment (AIS) endows neurons with the ability to adapt action potential output to changes in network activity. Action potential initiation at the AIS highly depends on the clustering of voltage-gated sodium channels, however the molecular mechanisms regulating their plasticity remain largely unknown. Here, we used novel genetic tools to endogenously label sodium channels and their scaffolding protein, to reveal their nanoscale organization and longitudinally image AIS plasticity in hippoc al neurons, in slices and primary cultures. We find that induction of NMDA receptor-mediated long-term synaptic depression is linked to a rapid and local endocytosis of sodium channels from the distal AIS. These data reveal a novel fundamental mechanism for rapid activity-dependent AIS reorganization sharing conserved features with synaptic plasticity.
Publisher: Springer Science and Business Media LLC
Date: 12-2016
Abstract: The patch-cl technique allows investigation of the electrical excitability of neurons and the functional properties and densities of ion channels. Most patch-cl recordings from neurons have been made from the soma, the largest structure of in idual neurons, while their dendrites, which form the majority of the surface area and receive most of the synaptic input, have been relatively neglected. This protocol describes techniques for recording from the dendrites of neurons in brain slices under direct visual control. Although the basic technique is similar to that used for somatic patching, we describe refinements and optimizations of slice quality, microscope optics, setup stability and electrode approach that are required for maximizing the success rate for dendritic recordings. Using this approach, all configurations of the patch-cl technique (cell-attached, inside-out, whole-cell, outside-out and perforated patch) can be achieved, even for relatively distal dendrites, and simultaneous multiple-electrode dendritic recordings are also possible. The protocol--from the beginning of slice preparation to the end of the first successful recording--can be completed in 3 h.
Publisher: Society for Neuroscience
Date: 08-02-2006
DOI: 10.1523/JNEUROSCI.3664-05.2006
Abstract: The hyperpolarization-activated cation current ( I h ) plays an important role in regulating neuronal excitability, yet its native single-channel properties in the brain are essentially unknown. Here we use variance-mean analysis to study the properties of single I h channels in the apical dendrites of cortical layer 5 pyramidal neurons in vitro . In these neurons, we find that I h channels have an average unitary conductance of 680 ± 30 fS ( n = 18). Spectral analysis of simulated and native I h channels showed that there is little or no channel flicker below 5 kHz. In contrast to the uniformly distributed single-channel conductance, I h channel number increases exponentially with distance, reaching densities as high as ∼550 channels/μm 2 at distal dendritic sites. These high channel densities generate significant membrane voltage noise. By incorporating a stochastic model of I h single-channel gating into a morphologically realistic model of a layer 5 neuron, we show that this channel noise is higher in distal dendritic compartments and increased threefold with a 10-fold increased single-channel conductance (6.8 pS) but constant I h current density. In addition, we demonstrate that voltage fluctuations attributable to stochastic I h channel gating impact on action potential output, with greater spike-timing precision in models with the experimentally determined single-channel conductance. These data suggest that, in the face of high current densities, the small single-channel conductance of I h is critical for maintaining the fidelity of action potential output.
Publisher: Elsevier BV
Date: 05-2022
DOI: 10.1016/J.NEURON.2022.04.014
Abstract: Cortical pyramidal neurons receive thousands of synaptic inputs and transform these into action potential output. In this issue of Neuron, Lafourcade et al. (2022) demonstrate that distinct long-range projections to retrosplenial cortex pyramidal neurons are coupled to erse modes of dendritic integration.
Publisher: Springer Science and Business Media LLC
Date: 25-06-2021
DOI: 10.1007/S00401-021-02338-8
Abstract: The complement system is implicated in synapse loss in the MS hippoc us, but the functional consequences of synapse loss remain poorly understood. Here, in post-mortem MS hippoc i with demyelination we find that deposits of the complement component C1q are enriched in the CA2 subfield, are linked to loss of inhibitory synapses and are significantly higher in MS patients with cognitive impairments compared to those with preserved cognitive functions. Using the cuprizone mouse model of demyelination, we corroborated that C1q deposits are highest within the demyelinated dorsal hippoc al CA2 pyramidal layer and co-localized with inhibitory synapses engulfed by microglia/macrophages. In agreement with the loss of inhibitory perisomatic synapses, we found that Schaffer collateral feedforward inhibition but not excitation was impaired in CA2 pyramidal neurons and accompanied by intrinsic changes and a reduced spike output. Finally, consistent with excitability deficits, we show that cuprizone-treated mice exhibit impaired encoding of social memories. Together, our findings identify CA2 as a critical circuit in demyelinated intrahippoc al lesions and memory dysfunctions in MS.
Publisher: Oxford University Press (OUP)
Date: 05-05-2023
Abstract: Brain oedema is a life-threatening complication of various neurological conditions. Understanding molecular mechanisms of brain volume regulation is critical for therapy development. Unique insight comes from monogenic diseases characterized by chronic brain oedema, of which megalencephalic leukoencephalopathy with subcortical cysts (MLC) is the prototype. Variants in MLC1 or GLIALCAM, encoding proteins involved in astrocyte volume regulation, are the main causes of MLC. In some patients, the genetic cause remains unknown. We performed genetic studies to identify novel gene variants in MLC patients, diagnosed by clinical and MRI features, without MLC1 or GLIALCAM variants. We determined subcellular localization of the related novel proteins in cells and in human brain tissue. We investigated functional consequences of the newly identified variants on volume regulation pathways using cell volume measurements, biochemical analysis and electrophysiology. We identified a novel homozygous variant in AQP4, encoding the water channel aquaporin-4, in two siblings, and two de novo heterozygous variants in GPRC5B, encoding the orphan G protein-coupled receptor GPRC5B, in three unrelated patients. The AQP4 variant disrupts membrane localization and thereby channel function. GPRC5B, like MLC1, GlialCAM and aquaporin-4, is expressed in astrocyte endfeet in human brain. Cell volume regulation is disrupted in GPRC5B patient-derived lymphoblasts. GPRC5B functionally interacts with ion channels involved in astrocyte volume regulation. In conclusion, we identify aquaporin-4 and GPRC5B as old and new players in genetic brain oedema. Our findings shed light on the protein complex involved in astrocyte volume regulation and identify GPRC5B as novel potentially druggable target for treating brain oedema.
Publisher: eLife Sciences Publications, Ltd
Date: 22-05-2019
Publisher: Springer Science and Business Media LLC
Date: 09-12-2022
DOI: 10.1038/S41467-022-35350-X
Abstract: Parvalbumin-expressing (PV + ) basket cells are fast-spiking inhibitory interneurons that exert critical control over local circuit activity and oscillations. PV + axons are often myelinated, but the electrical and metabolic roles of interneuron myelination remain poorly understood. Here, we developed viral constructs allowing cell type-specific investigation of mitochondria with genetically encoded fluorescent probes. Single-cell reconstructions revealed that mitochondria selectively cluster to myelinated segments of PV + basket cells, confirmed by analyses of a high-resolution electron microscopy dataset. In contrast to the increased mitochondrial densities in excitatory axons cuprizone-induced demyelination abolished mitochondrial clustering in PV + axons. Furthermore, with genetic deletion of myelin basic protein the mitochondrial clustering was still observed at internodes wrapped by noncompacted myelin, indicating that compaction is dispensable. Finally, two-photon imaging of action potential-evoked calcium (Ca 2+ ) responses showed that interneuron myelination attenuates both the cytosolic and mitochondrial Ca 2+ transients. These findings suggest that oligodendrocyte ensheathment of PV + axons assembles mitochondria to branch selectively fine-tune metabolic demands.
Publisher: Elsevier BV
Date: 2012
DOI: 10.1016/J.NEURON.2012.01.007
Abstract: The axon initial segment (AIS) is a specialized membrane region in the axon of neurons where action potentials are initiated. Crucial to the function of the AIS is the presence of specific voltage-gated channels clustered at high densities, giving the AIS unique electrical properties. Here we review recent data on the physiology of the AIS. These data indicate that the role of the AIS is far richer than originally thought, leading to the idea that it represents a dynamic signal processing unit within neurons, regulating the integration of synaptic inputs, intrinsic excitability, and transmitter release. Furthermore, these observations point to a critical role of the AIS in disease.
Publisher: Cold Spring Harbor Laboratory
Date: 21-04-2023
DOI: 10.1101/2023.04.21.537780
Abstract: Detailed characterization of interneuron subtypes in primary visual cortex (V1) has greatly contributed to understanding visual perception, yet the role of chandelier cells (ChCs) in visual processing remains poorly characterized. Using viral tracing we found that V1 ChCs predominantly receive monosynaptic input from local layer 5 pyramidal cells and higher-order cortical regions. Two-photon calcium imaging and convolutional neural network modelling revealed that ChCs are visually responsive but weakly selective for stimulus content. In mice running in a virtual tunnel, ChCs respond strongly to locomotion and halting visual flow, suggesting arousal-related activity. Visuomotor experience in the tunnel diminished visual responses of ChCs and induced structural plasticity of ChC boutons and axon initial segment length. Finally, ChCs only weakly inhibited pyramidal cells. These findings suggest that ChCs provide an arousal-related signal to layer 2/3 pyramidal cells that may modulate their activity and/or gate plasticity of their axon initial segments during behaviorally relevant events.
Publisher: Cold Spring Harbor Laboratory
Date: 07-09-2021
DOI: 10.1101/2021.09.07.459122
Abstract: Parvalbumin-positive (PV + ) γ-aminobutyric acid (GABA) interneurons are critically involved in producing rapid network oscillations and cortical microcircuit computations but the significance of PV + axon myelination to the temporal features of inhibition remains elusive. Here using toxic and genetic models of demyelination and dysmyelination, respectively, we find that loss of compact myelin reduces PV + interneuron presynaptic terminals, increases failures and the weak phasic inhibition of pyramidal neurons abolishes optogenetically driven gamma oscillations in vivo . Strikingly, during periods of quiet wakefulness selectively theta rhythms are lified and accompanied by highly synchronized interictal epileptic discharges. In support of a causal role of impaired PV-mediated inhibition, optogenetic activation of myelin-deficient PV + interneurons attenuated the power of slow theta rhythms and limited interictal spike occurrence. Thus, myelination of PV axons is required to consolidate fast inhibition of pyramidal neurons and enable behavioral state-dependent modulation of local circuit synchronization.
Publisher: Frontiers Media SA
Date: 27-02-2017
Publisher: eLife Sciences Publications, Ltd
Date: 12-05-2020
Publisher: eLife Sciences Publications, Ltd
Date: 23-10-2023
Publisher: Springer Science and Business Media LLC
Date: 04-01-2021
DOI: 10.1038/S41467-020-20232-X
Abstract: The axon initial segment (AIS) is a critical microdomain for action potential initiation and implicated in the regulation of neuronal excitability during activity-dependent plasticity. While structural AIS plasticity has been suggested to fine-tune neuronal activity when network states change, whether it acts in vivo as a homeostatic regulatory mechanism in behaviorally relevant contexts remains poorly understood. Using the mouse whisker-to-barrel pathway as a model system in combination with immunofluorescence, confocal analysis and electrophysiological recordings, we observed bidirectional AIS plasticity in cortical pyramidal neurons. Furthermore, we find that structural and functional AIS remodeling occurs in distinct temporal domains: Long-term sensory deprivation elicits an AIS length increase, accompanied with an increase in neuronal excitability, while sensory enrichment results in a rapid AIS shortening, accompanied by a decrease in action potential generation. Our findings highlight a central role of the AIS in the homeostatic regulation of neuronal input-output relations.
Publisher: Wiley
Date: 28-11-2008
Publisher: American Association for the Advancement of Science (AAAS)
Date: 13-10-2023
Publisher: Elsevier BV
Date: 2019
Publisher: Oxford University Press (OUP)
Date: 04-10-2012
Abstract: Central nervous system (CNS) inflammation involves the generation of inducible cytokines such as interferons (IFNs) and alterations in brain activity, yet the interplay of both is not well understood. Here, we show that in vivo elevation of IFNs by viral brain infection reduced hyperpolarization-activated currents (Ih) in cortical pyramidal neurons. In rodent brain slices directly exposed to type I IFNs, the hyperpolarization-activated cyclic nucleotide (HCN)-gated channel subunit HCN1 was specifically affected. The effect required an intact type I receptor (IFNAR) signaling cascade. Consistent with Ih inhibition, IFNs hyperpolarized the resting membrane potential, shifted the resonance frequency, and increased the membrane impedance. In vivo application of IFN-β to the rat and to the mouse cerebral cortex reduced the power of higher frequencies in the cortical electroencephalographic activity only in the presence of HCN1. In summary, these findings identify HCN1 channels as a novel neural target for type I IFNs providing the possibility to tune neural responses during the complex event of a CNS inflammation.
Publisher: Wiley
Date: 22-01-2020
DOI: 10.1002/ACN3.50975
Publisher: eLife Sciences Publications, Ltd
Date: 23-10-2023
DOI: 10.7554/ELIFE.91153
Publisher: Society for Neuroscience
Date: 05-03-2014
DOI: 10.1523/JNEUROSCI.4206-13.2014
Abstract: Rapid energy-efficient signaling along vertebrate axons is achieved through intricate subcellular arrangements of voltage-gated ion channels and myelination. One recently appreciated ex le is the tight colocalization of K v 7 potassium channels and voltage-gated sodium (Na v ) channels in the axonal initial segment and nodes of Ranvier. The local biophysical properties of these K v 7 channels and the functional impact of colocalization with Na v channels remain poorly understood. Here, we quantitatively examined K v 7 channels in myelinated axons of rat neocortical pyramidal neurons using high-resolution confocal imaging and patch-cl recording. K v 7.2 and 7.3 immunoreactivity steeply increased within the distal two-thirds of the axon initial segment and was mirrored by the conductance density estimates, which increased from ∼12 (proximal) to 150 pS μm −2 (distal). The axonal initial segment and nodal M-currents were similar in voltage dependence and kinetics, carried by K v 7.2/7.3 heterotetramers, 4% activated at the resting membrane potential and rapidly activated with single-exponential time constants (∼15 ms at 28 mV). Experiments and computational modeling showed that while somatodendritic K v 7 channels are strongly activated by the backpropagating action potential to attenuate the afterdepolarization and repetitive firing, axonal K v 7 channels are minimally recruited by the forward-propagating action potential. Instead, in nodal domains K v 7.2/7.3 channels were found to increase Na v channel availability and action potential litude by stabilizing the resting membrane potential. Thus, K v 7 clustering near axonal Na v channels serves specific and context-dependent roles, both restraining initiation and enhancing conduction of the action potential.
Publisher: Wiley
Date: 10-2013
Publisher: eLife Sciences Publications, Ltd
Date: 17-06-2020
DOI: 10.7554/ELIFE.54566
Abstract: Calcium ions (Ca 2+ ) are essential for many cellular signaling mechanisms and enter the cytosol mostly through voltage-gated calcium channels. Here, using high-speed Ca 2+ imaging up to 20 kHz in the rat layer five pyramidal neuron axon we found that activity-dependent intracellular calcium concentration ([Ca 2+ ] i ) in the axonal initial segment was only partially dependent on voltage-gated calcium channels. Instead, [Ca 2+ ] i changes were sensitive to the specific voltage-gated sodium (Na V ) channel blocker tetrodotoxin. Consistent with the conjecture that Ca 2+ enters through the Na V channel pore, the optically resolved I Ca in the axon initial segment overlapped with the activation kinetics of Na V channels and heterologous expression of Na V 1.2 in HEK-293 cells revealed a tetrodotoxin-sensitive [Ca 2+ ] i rise. Finally, computational simulations predicted that axonal [Ca 2+ ] i transients reflect a 0.4% Ca 2+ conductivity of Na V channels. The findings indicate that Ca 2+ permeation through Na V channels provides a submillisecond rapid entry route in Na V -enriched domains of mammalian axons.
Publisher: Informa UK Limited
Date: 07-2014
DOI: 10.4161/CHAN.29965
Publisher: Cold Spring Harbor Laboratory
Date: 12-06-2020
DOI: 10.1101/2020.06.12.147884
Abstract: Performing Single-Molecule Localization Microscopy (SMLM) in complex biological tissues, where s le-induced aberrations h er detection and localization, has remained a challenge. Here we establish REALM (Robust and Effective Adaptive Optics in Localization Microscopy), which corrects aberrations of ≤1 rad RMS using 297 frames of blinking molecules to improve single-molecule localization. We demonstrate this method by resolving the periodic cytoskeleton of the axon initial segment at 50 μm depth in brain tissue.
Publisher: Proceedings of the National Academy of Sciences
Date: 05-12-2016
Abstract: Neurons generate highly reliable and temporally precise action potentials with a spatial onset in the axon initial segment. The axon initial segment location relative to the soma is, however, highly variable across neurons within the same cell class. Here, we experimentally and theoretically investigated the structure–function relationship of axon distances in neocortical pyramidal neurons. We discovered a scaling principle between the size of the dendritic tree and the axon distance supported by the cable properties and electrophysiological recordings. The work reveals that axons are not randomly positioned but covary with dendrites normalizing the somatic action potential in the face of erse cellular morphologies.
Publisher: Elsevier BV
Date: 12-2004
DOI: 10.1016/J.EURONEURO.2004.09.002
Abstract: Early hypotheses on the pathophysiology of major depression were based on aberrant intrasynaptic concentrations of mainly the neurotransmitters serotonin and norepinephrine. However, recent neuroimaging studies have demonstrated selective structural changes across various limbic and nonlimbic circuits in the brains of depressed patients. In addition, postmortem morphometric studies revealed decreased glial and neuron densities in selected brain structures supporting the idea that major depression may be related to impairments of structural plasticity. Stressful life events are among the major predisposing risk factors for developing depression. Using the chronic psychosocial stress paradigm in male tree shrews, an animal model with a high validity for the pathophysiology of depressive disorders, we found that 1 month of stress reduced the in vivo concentrations of the brain metabolites N-acetyl-aspartate, choline-containing compounds, and (phospho)-creatine, as well as the proliferation rate in the dentate gyrus and the hippoc al volume. Even though long-lasting social conflict does not lead to a loss of principal cells, the hippoc al changes were accompanied by modifications in the incidence of apoptosis. Notably, these suppressive effects of social conflict on hippoc al structure could be counteracted by treatment with the antidepressant tianeptine. These findings support current theories proposing that major depressive disorders may be associated with impairment of structural plasticity and neural cellular resilience, and that antidepressants may act by correcting this dysfunction.
Publisher: Wiley
Date: 2004
DOI: 10.1002/HIPO.10212
Abstract: The experience of chronic stress induces a reversible regression of hippoc al CA3 apical neuron dendrites. Although such postsynaptic membrane reduction will obviously diminish the possibility of synaptic input, the consequences for the functional membrane properties of these cells are not well understood. We tested the hypothesis that chronic stress affects the input-output characteristics and excitability of CA3 pyramidal cells. Somatic whole-cell current-cl recording with parallel intracellular biocytin labeling was performed on CA3 neurons from in vitro hippoc al slices from male tree shrews, which were collected after 28 days of psychosocial stress exposure and compared to recordings obtained from control animals. Post hoc morphometric analysis of biocytin-labeled CA3 cells revealed branch regression, by fewer dendritic crossings and length, limited to a distance of approximately 280-340 microm from the soma only. The results from whole-cell recording indicate that chronic stress surprisingly reduced the apparent membrane time constant and input resistance 20-25%, accompanied by increased litude of the hyperpolarization-induced voltage "sag." All active membrane properties, including depolarization-induced action potential kinetics, complex spiking patterns, and afterhyperpolarization voltages, were indistinguishable from control recordings. Although linear association analysis confirmed that differences in geometry, such as apical length or branch number, were correlated to functional variability in properties of the AP current and voltage threshold, these changes were too marginal to be reflected in the group differences. However, the in idual adrenal hormone status was associated significantly with the selective changes in subthreshold excitability. Taken together, the data provide evidence that despite long-term stress induces morphological changes, upregulates cortisol release and shifts the intrinsic membrane properties, the efficacy of somatic excitability of CA3 pyramidal neurons is largely preserved.
Publisher: Wiley
Date: 12-2001
Publisher: Elsevier BV
Date: 08-2011
DOI: 10.1016/J.NEURON.2011.06.024
Abstract: In central neurons the first node of Ranvier is located at the first axonal branchpoint, ∼ 100 μm from the axon initial segment where synaptic inputs are integrated and converted into action potentials (APs). Whether the first node contributes to this signal transformation is not well understood. Here it was found that in neocortical layer 5 axons, the first branchpoint is required for intrinsic high-frequency (≥ 100 Hz) AP bursts. Furthermore, block of nodal Na(+) channels or axotomy of the first node in intrinsically bursting neurons depolarized the somatic AP voltage threshold (∼ 5 mV) and eliminated APs selectively within a high-frequency cluster in response to steady currents or simulated synaptic inputs. These results indicate that nodal persistent Na(+) current exerts an anterograde influence on AP initiation in the axon initial segment, revealing a computational role of the first node of Ranvier beyond conduction of the propagating AP.
Publisher: eLife Sciences Publications, Ltd
Date: 24-12-2021
Publisher: Springer Science and Business Media LLC
Date: 20-01-2008
DOI: 10.1038/NN2040
Abstract: The axon initial segment (AIS) is a specialized region in neurons where action potentials are initiated. It is commonly assumed that this process requires a high density of voltage-gated sodium (Na(+)) channels. Paradoxically, the results of patch-cl studies suggest that the Na(+) channel density at the AIS is similar to that at the soma and proximal dendrites. Here we provide data obtained by antibody staining, whole-cell voltage-cl and Na(+) imaging, together with modeling, which indicate that the Na(+) channel density at the AIS of cortical pyramidal neurons is approximately 50 times that in the proximal dendrites. Anchoring of Na(+) channels to the cytoskeleton can explain this discrepancy, as disruption of the actin cytoskeleton increased the Na(+) current measured in patches from the AIS. Computational models required a high Na(+) channel density (approximately 2,500 pS microm(-2)) at the AIS to account for observations on action potential generation and backpropagation. In conclusion, action potential generation requires a high Na(+) channel density at the AIS, which is maintained by tight anchoring to the actin cytoskeleton.
Publisher: Springer Science and Business Media LLC
Date: 30-10-2020
DOI: 10.1038/S41467-020-19152-7
Abstract: Myelinating oligodendrocytes enable fast propagation of action potentials along the ensheathed axons. In addition, oligodendrocytes play erse non-canonical roles including axonal metabolic support and activity-dependent myelination. An open question remains whether myelination also contributes to information processing in addition to speeding up conduction velocity. Here, we analyze the role of myelin in auditory information processing using paradigms that are also good predictors of speech understanding in humans. We compare mice with different degrees of dysmyelination using acute multiunit recordings in the auditory cortex, in combination with behavioral readouts. We find complex alterations of neuronal responses that reflect fatigue and temporal acuity deficits. We observe partially discriminable but similar deficits in well myelinated mice in which glial cells cannot fully support axons metabolically. We suggest a model in which myelination contributes to sustained stimulus perception in temporally complex paradigms, with a role of metabolically active oligodendrocytes in cortical information processing.
Publisher: Wiley
Date: 05-01-2023
DOI: 10.1002/ANA.26585
Abstract: Changes in the normal‐appearing white matter (NAWM) in multiple sclerosis (MS) may contribute to disease progression. Here, we systematically quantified ultrastructural and subcellular characteristics of the axon–myelin unit in MS NAWM and determined how this correlates with low‐grade inflammation. Human brain tissue obtained with short postmortem delay and fixation at autopsy enables systematic quantification of ultrastructural characteristics. In this study, we performed high‐resolution immunohis tochemistry and quantitative transmission electron microscopy to study inflammation and ultrastructural characteristics of the axon–myelin unit in MS NAWM (n = 8) and control white matter (WM) in the optic nerve. In the MS NAWM, there were more activated and phagocytic microglia cells (HLA + P2RY12 − and Iba1 + CD68 + ) and more T cells (CD3 + ) compared to control WM, mainly located in the perivascular space. In MS NAWM compared to control WM, there were, as expected, longer paranodes and juxtaparanodes and larger overlap between paranodes and juxtaparanodes. There was less compact myelin wrapping, a lower g‐ratio, and a higher frequency of axonal mitochondria. Changes in myelin and axonal mitochondrial frequency correlated positively with the number of active and phagocytic microglia and lymphocytes in the optic nerve. These data suggest that in MS NAWM myelin detachment and uncompact myelin wrapping occurs, potassium channels are unmasked at the nodes of Ranvier, and axonal energy demand is increased, or mitochondrial transport is stagnated, accompanied by increased presence of activated and phagocytic microglia and T cells. These subclinical alterations to the axon–myelin unit in MS NAWM may contribute to disease progression. ANN NEUROL 2023 :856–870
Publisher: Elsevier BV
Date: 05-1999
DOI: 10.1016/S0006-8993(99)01257-3
Abstract: The effects of a single rapid-rate transcranial magnetic stimulation (rTMS) exposure on neurotransmitter binding sites in the rat brain 24 h after the stimulation were examined. Quantification by in vitro-autoradiography showed no differences for 3H-paroxetine binding (5-HT uptake sites) between rTMS-treated, sham and control animals. In contrast, the number of 5-HT1A binding sites (labeled with 3H-8-OH-DPAT) were selectively increased in the rTMS-group with significantly higher BMAX values in the frontal cortex, the cingulate cortex, and the anterior olfactory nucleus. A non-specific increase in NMDA binding sites (labeled with 125I-MK-801) in rTMS and sham animals was observed in the hippoc al formation. A selective increase of these binding sites after rTMS was detected in the ventromedial hypothalamus, the basolateral amygdala and layers 5-6 of the parietal cortex. These findings imply that a single rTMS exposure can result in persistent effects on NMDA and 5-HT1A binding sites even 24 h after stimulation and therefore may be of relevance with respect to the therapeutic action of rTMS reported from clinical studies.
No related grants have been discovered for Maarten Kole.