ORCID Profile
0000-0002-0791-0950
Current Organisations
University of Oxford
,
University of Tasmania
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Publisher: Oxford University Press (OUP)
Date: 03-10-2015
DOI: 10.1093/BRAIN/AWU283
Publisher: SAGE Publications
Date: 09-07-2023
DOI: 10.1177/17474930231189135
Abstract: This article is temporarily under embargo.
Publisher: SAGE Publications
Date: 21-09-2020
Abstract: The popularity of pericyte research is increasing, and this was not more evident than at the recent 2019 Brain meeting in Yokohama which featured a large number of presentations focused on brain pericyte research, including the Presidential Symposium. In this article, we will provide a history of brain pericyte research, present the results of our analysis showing a substantial increase in brain pericyte research presented at Brain meetings since 2005, suggest reasons for their increased popularity, and comment on what the future holds for brain pericyte research.
Publisher: American Medical Association (AMA)
Date: 05-2014
DOI: 10.1001/JAMANEUROL.2013.6299
Abstract: Preclinical stroke research has had a remarkably low translational success rate, and the clinical need for novel neuroprotective therapeutics has gone largely unmet, especially in light of the severe underuse of thrombolysis in acute ischemic stroke. In this review, we aim to provide a brief overview of the commonly used stroke models, their merits and shortcomings, and how these have contributed to translational failures. We review some recent developments in preclinical stroke, providing ex les of how improved study quality and the use of novel methods can facilitate translation into the clinical setting. This is a narrative review of ischemic stroke neuroprotection based on electronic database searches, references of previous publications, and personal libraries. The stroke research community has not been complacent in its response to criticism: preclinical stroke studies now demonstrate considerable rigor, standardization, and emphasis on minimization of experimenter bias. In addition, numerous innovative methods and strategies are providing novel avenues for investigating neuroprotection, as well as more extensive characterization of established models. The improvements in preclinical stroke models and methods will make stroke research a good ex le for preclinical medicine, in general, and will hopefully instill greater confidence in the clinical community regarding which compounds are worthy of further investigation in a clinical setting.
Publisher: SAGE Publications
Date: 18-10-2019
Abstract: The significant morbidity that accompanies stroke makes it one of the world's most devastating neurological disorders. Currently, proven effective therapies have been limited to thrombolysis and thrombectomy. The window for the administration of these therapies is narrow, h ered by the necessity of rapidly imaging patients. A therapy that could extend this window by protecting neurons may improve outcome. Endogenous neuroprotection has been shown to be, in part, due to changes in mTOR signalling pathways and the instigation of productive autophagy. Inducing this effect pharmacologically could improve clinical outcomes. One such therapy already in use in transplant medicine is the mTOR inhibitor rapamycin. Recent evidence suggests that rapamycin is neuroprotective, not only via neuronal autophagy but also through its broader effects on other cells of the neurovascular unit. This review highlights the potential use of rapamycin as a multimodal therapy, acting on the blood–brain barrier, cerebral blood flow and inflammation, as well as directly on neurons. There is significant potential in applying this old drug in new ways to improve functional outcomes for patients after stroke.
Publisher: Frontiers Media SA
Date: 10-09-2020
Publisher: Wiley
Date: 24-05-2011
Publisher: Elsevier BV
Date: 2007
DOI: 10.1016/J.NEULET.2006.10.053
Abstract: Until recently the cannabinoid CB2 receptor was believed to be absent from the central nervous system. In this study we have identified CB2 expressing cells that appear in the rat brain following stroke and hypoxic-ischemia. At 3 days following surgery CB2-positive macrophages, deriving from resident microglia and/or invading monocytes appear on the lesioned side of the brain. By day 7, a mixed population of CB2-positive cells is present. Microglia-derived macrophages are the key cells in the first stages of brain inflammation, and a pivotal step in the neurodegeneration that follows the acute stage of injury. Thus, CB2 may be important in the brain during injury, and in inflammatory neurodegenerative disorders. The presence of CB2-positive cells in the brain following stroke may provide a novel strategy for cannabinoid-mediated intervention into stroke induced neurodegeneration without the psychoactive effects of CB1 receptor stimulation.
Publisher: Bentham Science Publishers Ltd.
Date: 04-2013
DOI: 10.2174/18715273113129990057
Abstract: Despite advances in the diagnosis and treatment of acute ischaemic stroke in the past two decades, stroke has remained the third cause of mortality and the single leading cause of disability worldwide. The immediate goal of acute ischaemic stroke therapy is to salvage the ischaemic penumbra through recanalisation of the occluded cerebral blood vessel. This is currently achieved through thrombolytics, which are pharmacological agents that can break up a clot blocking the flow of blood. To date, the only approved thrombolytic for treatment of acute ischaemic stroke is recombinant tissue plasminogen activator (alteplase, rt-PA), however, alteplase is substantially underused because of concerns regarding adverse bleeding risk. This limitation has fuelled the search for other thrombolytic agents, which display greater fibrin dependence and selectivity, but lack detrimental effects within the central nervous system. Development of alternative fibrinolytic agents that might be easier and safer to administer could lead to wider acceptance and use of thrombolytic therapy for stroke. Although other thrombolytic agents (e.g. streptokinase) have failed to show benefit over alteplase, there is still on-going research in search of alternative agents with higher target specificity and better safety profile. The potential thrombolytic agents with trials in progress include desmoteplase, tenecteplase, reteplase, plasmin and microplasmin. This review summarises current therapies with thrombolytics (e.g. alteplase and urokinase), their limitations and side effects, and also discusses ongoing clinical studies with the various potential emerging thrombolytic agents.
Publisher: Medknow
Date: 20-04-2023
Publisher: Elsevier BV
Date: 06-2022
DOI: 10.1016/J.TAAP.2022.116025
Abstract: Capillary pericytes have numerous functions important for tissue maintenance. Changes in pericyte function are implicated in diseases such as cancer, where pericyte-mediated angiogenesis contributes to the blood supply that tumors use to survive. Some anti-cancer agents, like imatinib, target platelet-derived growth factor receptor-beta (PDGFRβ). Healthy pericytes rely on PDGFRβ phosphorylation for their survival. Therefore, we hypothesised that pharmacological agents that block PDGFRβ phosphorylation could be used to kill pericytes. We treated human brain vascular pericytes, which express PDGFRβ, with three receptor tyrosine kinase inhibitors: imatinib, sunitinib and orantinib. Imatinib and sunitinib, but not orantinib, inhibited PDGFRβ phosphorylation in pericytes. Imatinib and sunitinib also reduced viability, prevented proliferation, and induced death, while orantinib only blocked pericyte proliferation. Overall, we found that receptor tyrosine kinase inhibitors that block PDGFRβ phosphorylation cause healthy pericytes to die in vitro. While useful in cancer to limit tumor growth, these agents could impair healthy brain pericyte survival and impact brain function.
Publisher: Elsevier BV
Date: 12-2009
DOI: 10.1016/J.NEURES.2009.08.007
Abstract: The regional and cellular distribution of heme oxygenase (HO)-1 and -2 following cerebral ischemia has not been ascertained. Employing the transient middle cerebral artery occlusion (MCAO) and hypoxia-ischemia (HI) models of unilateral brain injury, the aim was to elucidate immunolocalization of HO-1 and HO-2. Animals were sacrificed 3 days post-ischemia and immunohistochemistry and Western blotting were utilized to determine HO-1 and HO-2 expression. In the ipsilateral hemisphere following HI, HO-1 immunoreactivity was significantly upregulated in many neuronal and glial populations (including the cortex, hippoc us and thalamus). HO-1 was also detected in macrophages/microglia within the infarct. In addition to widespread neuronal HO-2 labelling, HO-2 was also expressed in vascular endothelial cells. Inflammatory cells within the infarct of MCAO and HI animals were surprisingly immunoreactive for HO-2, but only HI animals had significantly elevated HO-2 protein expression in the ipsilateral hemisphere. This may be due to the presence of global hypoxia in the HI model which can upregulate vascular endothelial growth factor and subsequent proliferation of endothelial cells. This report of HO-2 protein expression upregulation following HI coupled with an increase in HO-1 immunoreactivity suggests that this response may be implicated in reducing cell death or repairing damage induced by cerebral ischemia.
Publisher: SAGE Publications
Date: 14-10-2023
Publisher: Wiley
Date: 26-10-2020
DOI: 10.1002/MRM.28565
Publisher: Wiley
Date: 11-05-2023
DOI: 10.1111/NAN.12904
Abstract: Selective neuronal vulnerability of hippoc al Cornu Ammonis (CA)‐1 neurons is a pathological hallmark of Alzheimer's disease (AD) with an unknown underlying mechanism. We interrogated the expression of tuberous sclerosis complex‐1 (TSC1 hamartin) and mTOR‐related proteins in hippoc al CA1 and CA3 subfields. A human post‐mortem cohort of mild ( n = 7) and severe ( n = 10) AD and non‐neurological controls ( n = 9) was used for quantitative and semi‐quantitative analyses. We also developed an in vitro TSC1 knockdown model in rat hippoc al neurons, and transcriptomic analyses of TSC1 knockdown neuronal cultures were performed. We found a selective increase of TSC1 cytoplasmic inclusions in human AD CA1 neurons with hyperactivation of one of TSC1's downstream targets, the mammalian target of rapamycin complex‐1 (mTORC1), suggesting that TSC1 is no longer active in AD. TSC1 knockdown experiments showed accelerated cell death independent of amyloid‐beta toxicity. Transcriptomic analyses of TSC1 knockdown neuronal cultures revealed signatures that were significantly enriched for AD‐related pathways. Our combined data point to TSC1 dysregulation as a key driver of selective neuronal vulnerability in the AD hippoc us. Future work aimed at identifying targets amenable to therapeutic manipulation is urgently needed to halt selective neurodegeneration, and by extension, debilitating cognitive impairment characteristic of AD.
Publisher: Bio-Protocol, LLC
Date: 2022
Publisher: SAGE Publications
Date: 17-02-2020
Abstract: Direct and real-time assessment of cerebral hemodynamics is key to improving our understanding of cerebral blood flow regulation in health and disease states such as stroke. While a number of sophisticated imaging platforms enable assessment of cerebral perfusion, most are limited either spatially or temporally. Here, we applied transcranial contrast-enhanced ultrasound (CEU) to measure cerebral perfusion in real-time through the intact rat skull before, during and after ischemic stroke, induced by intraluminal filament middle cerebral artery occlusion (MCAO). We demonstrate expected decreases in cortical and striatal blood volume, flow velocity and perfusion during MCAO. After filament retraction, blood volume and perfusion increased two-fold above baseline, indicative of acute hyperperfusion. Adjacent brain regions to the ischemic area and the contralateral hemisphere had increased blood volume during MCAO. We assessed our data using wavelet analysis to demonstrate striking vasomotion changes in the ischemic and contralateral cortices during MCAO and reperfusion. In conclusion, we demonstrate the application of CEU for real-time assessment of cerebral hemodynamics and show that the ischemic regions exhibit striking hyperemia post-MCAO. Whether this post-stoke hyperperfusion is sustained long-term and contributes to stroke severity is not known.
Publisher: SAGE Publications
Date: 04-08-2018
Abstract: Cornu ammonis 3 (CA3) hippoc al neurons are resistant to global ischemia, whereas cornu ammonis (CA1) 1 neurons are vulnerable. Hamartin expression in CA3 neurons mediates this endogenous resistance via productive autophagy. Neurons lacking hamartin demonstrate exacerbated endoplasmic reticulum stress and increased cell death. We investigated endoplasmic reticulum stress responses in CA1 and CA3 regions following global cerebral ischemia, and whether pharmacological modulation of endoplasmic reticulum stress or autophagy altered neuronal viability . In vivo: male Wistar rats underwent sham or 10 min of transient global cerebral ischemia. CA1 and CA3 areas were microdissected and endoplasmic reticulum stress protein expression quantified at 3 h and 12 h of reperfusion. In vitro: primary neuronal cultures (E18 Wistar rat embryos) were exposed to 2 h of oxygen and glucose deprivation or normoxia in the presence of an endoplasmic reticulum stress inducer (thapsigargin or tunicamycin), an endoplasmic reticulum stress inhibitor (salubrinal or 4-phenylbutyric acid), an autophagy inducer ([4′-(N-diethylamino) butyl]-2-chlorophenoxazine (10-NCP)) or autophagy inhibitor (3-methyladenine). In vivo, decreased endoplasmic reticulum stress protein expression (phospho-eIF2α and ATF4) was observed at 3 h of reperfusion in CA3 neurons following ischemia, and increased in CA1 neurons at 12 h of reperfusion. In vitro, endoplasmic reticulum stress inducers and high doses of the endoplasmic reticulum stress inhibitors also increased cell death. Both induction and inhibition of autophagy also increased cell death. Endoplasmic reticulum stress is associated with neuronal cell death following ischemia. Neither reduction of endoplasmic reticulum stress nor induction of autophagy demonstrated neuroprotection in vitro, highlighting their complex role in neuronal biology following ischemia.
Publisher: Wiley
Date: 07-03-2022
DOI: 10.1002/MRM.29187
Abstract: In chemical exchange saturation transfer imaging, saturation effects between 2 to 5 ppm (nuclear Overhauser effects, NOEs) have been shown to exhibit contrast in preclinical stroke models. Our previous work on NOEs in human stroke used an analysis model that combined NOEs and semisolid MT however their combination might feasibly have reduced sensitivity to changes in NOEs. The aim of this study was to explore the information a 4‐pool Bloch–McConnell model provides about the NOE contribution in ischemic stroke, contrasting that with an intentionally approximate 3‐pool model. MRI data from 12 patients presenting with ischemic stroke were retrospectively analyzed, as well as from six animals induced with an ischemic lesion. Two Bloch–McConnell models (4 pools, and a 3‐pool approximation) were compared for their ability to distinguish pathological tissue in acute stroke. The association of NOEs with pH was also explored, using pH phantoms that mimic the intracellular environment of naïve mouse brain. The 4‐pool measure of NOEs exhibited a different association with tissue outcome compared to 3‐pool approximation in the ischemic core and in tissue that underwent delayed infarction. In the ischemic core, the 4‐pool measure was elevated in patient white matter () and in animals (). In the naïve brain pH phantoms, significant positive correlation between the NOE and pH was observed. Associations of NOEs with tissue pathology were found using the 4‐pool metric that were not observed using the 3‐pool approximation. The 4‐pool model more adequately captured in vivo changes in NOEs and revealed trends depending on tissue pathology in stroke.
Publisher: Springer International Publishing
Date: 2021
Publisher: Elsevier BV
Date: 03-2023
Publisher: Wiley
Date: 21-11-2020
Abstract: The matching of capillary blood flow to metabolic rate of the cells within organs and tissues is a critical microvascular function which ensures appropriate delivery of hormones and nutrients, and the removal of waste products. This relationship is particularly important in tissues where local metabolism, and hence capillary blood flow, must be regulated to avoid a mismatch between nutrient demand and supply that would compromise normal function. The consequences of a mismatch in microvascular blood flow and metabolism are acutely apparent in the brain and heart, where a sudden cessation of blood flow, for ex le following an embolism, acutely manifests as stroke or myocardial infarction. Even in more resilient tissues such as skeletal muscle, a short-term mismatch reduces muscle performance and exercise tolerance, and can cause intermittent claudication. In the longer-term, a microvascular-metabolic mismatch in skeletal muscle reduces insulin-mediated muscle glucose uptake, leading to disturbances in whole-body metabolic homeostasis. While the notion that capillary blood flow is fine-tuned to meet cellular metabolism is well accepted, the mechanisms that control this function and where and how different parts of the vascular tree contribute to capillary blood flow regulation remain poorly understood. Here, we discuss the emerging evidence implicating pericytes, mural cells that surround capillaries, as key mediators that match tissue metabolic demand with adequate capillary blood flow in a number of organs, including skeletal muscle.
Publisher: Wiley
Date: 30-08-2011
Publisher: Society for Neuroscience
Date: 12-10-2021
DOI: 10.1523/ENEURO.0177-21.2021
Abstract: Whole slide scanning technology has enabled the generation of high-resolution images from complete tissue sections. However, commonly used analysis software is often unable to handle the large data files produced. Here, we present a method using the open-source software QuPath to detect, classify and quantify fluorescently-labeled cells (microglia and pericytes) in whole coronal brain tissue sections. Whole-brain sections from both male and female NG2DsRed x CX 3 CR1 +/GFP mice were analyzed. Small regions of interest were selected and manual counts were compared with counts generated from an automated approach, across a range of detection parameters. The optimal parameters for detecting cells and classifying them as microglia or pericytes in each brain region were determined and applied to annotations corresponding to the entire somatosensory and motor cortices, hippoc us, thalamus, and hypothalamus in each section. 3.74% of all detected cells were classified as pericytes however, this proportion was significantly higher in the thalamus (6.20%) than in other regions. In contrast, microglia (4.51% of total cells) were more abundant in the cortex (5.54%). No differences were detected between male and female mice. In conclusion, QuPath offers a user-friendly solution to whole-slide image analysis which could lead to important new discoveries in both health and disease.
Publisher: SAGE Publications
Date: 26-08-2015
DOI: 10.1111/IJS.12618
Abstract: Acute ischemic strokes involving occlusion of large vessels usually recanalize poorly following treatment with intravenous thrombolysis. Recent studies have shown higher recanalization and higher good outcome rates with endovascular therapy compared with best medical management alone. A systematic review and meta-analysis investigating the benefits of all randomized controlled trials of endovascular thrombectomy where at least 25% of patients were treated with a thrombectomy device for the treatment of acute ischemic stroke compared with best medical treatment have yet to be performed. To perform a systematic review and a meta-analysis evaluating the effectiveness of endovascular thrombectomy compared with best medical care for treatment of acute ischemic stroke. Our search identified 437 publications, from which eight studies (totaling 2423 patients) matched the inclusion criteria. Overall, endovascular thrombectomy was associated with improved functional outcomes (modified Rankin Scale 0–2) [odds ratio 1·56 (1·32–1·85), P 0·00001]. There was a tendency toward decreased mortality [odds ratio 0·84 (0·67–1·05), P = 0·12], and symptomatic intracerebral hemorrhage was not increased [odds ratio 1·03 (0·71–1·49), P = 0·88] compared with best medical management alone. The odds ratio for a favorable functional outcome increased to 2·23 (1·77–2·81, P 0·00001) when newer generation thrombectomy devices were used in greater than 50% of the cases in each trial. There is clear evidence for improvement in functional independence with endovascular thrombectomy compared with standard medical care, suggesting that endovascular thrombectomy should be considered the standard effective treatment alongside thombolysis in eligible patients.
Publisher: Oxford University Press (OUP)
Date: 13-05-2022
Abstract: To match the metabolic demands of the brain, mechanisms have evolved to couple neuronal activity to vasodilation, thus increasing local cerebral blood flow and delivery of oxygen and glucose to active neurons. Rather than relying on metabolic feedback signals such as the consumption of oxygen or glucose, the main signalling pathways rely on the release of vasoactive molecules by neurons and astrocytes, which act on contractile cells. Vascular smooth muscle cells and pericytes are the contractile cells associated with arterioles and capillaries, respectively, which relax and induce vasodilation. Much progress has been made in understanding the complex signalling pathways of neurovascular coupling, but issues such as the contributions of capillary pericytes and astrocyte calcium signal remain contentious. Study of neurovascular coupling mechanisms is especially important as cerebral blood flow dysregulation is a prominent feature of Alzheimer’s disease. In this article we will discuss developments and controversies in the understanding of neurovascular coupling and finish by discussing current knowledge concerning neurovascular uncoupling in Alzheimer’s disease.
Publisher: Oxford University Press (OUP)
Date: 14-09-2013
DOI: 10.1093/BRAIN/AWT201
Abstract: The science of metric-based patient stratification for intravenous thrombolysis, revolutionized by the landmark National Institute of Neurological Disorders and Stroke trial, has transformed acute ischaemic stroke therapy. Recanalization of an occluded artery produces tissue reperfusion that unequivocally improves outcome and function in patients with acute ischaemic stroke. Recanalization can be achieved mainly through intravenous thrombolysis, but other methods such as intra-arterial thrombolysis or mechanical thrombectomy can also be employed. Strict guidelines preclude many patients from being treated by intravenous thrombolysis due to the associated risks. The quiet art of informed patient selection by careful assessment of patient baseline factors and brain imaging could increase the number of eligible patients receiving intravenous thrombolysis. Outside of the existing eligibility criteria, patients may fall into therapeutic 'grey areas' and should be evaluated on a case by case basis. Important factors to consider include time of onset, age, and baseline blood glucose, blood pressure, stroke severity (as measured by National Institutes of Health Stroke Scale) and computer tomography changes (as measured by Alberta Stroke Programme Early Computed Tomography Score). Patients with traditional contraindications such as wake-up stroke, malignancy or dementia may have the potential to receive benefit from intravenous thrombolysis if they have favourable predictors of outcome from both clinical and imaging criteria. A proportion of patients experience complications or do not respond to intravenous thrombolysis. In these patients, other endovascular therapies or a combination of both may be used to provide benefit. Although an evidence-based approach to intravenous thrombolysis for acute ischaemic stroke is pivotal, it is imperative to examine those who might benefit outside of protocol-driven practice.
Publisher: Cold Spring Harbor Laboratory
Date: 11-08-2022
DOI: 10.1101/2022.08.08.503250
Abstract: Cerebral blood flow is important for the maintenance of brain function and its dysregulation has been implicated in Alzheimer’s disease (AD). Subpopulations of microglia have well-characterised associations with the vasculature in the central nervous system but the precise relationship between microglia and cells which exist on the vasculature is not yet clear. In this study we explored the relationship between microglia and pericytes, a vessel-resident cell type that has a major role in the regulation of cerebral blood flow and maintenance of the blood brain barrier. Using fixed tissue sections and in vivo live imaging, we discovered a subset of microglia that closely associated with pericytes, termed PE ricyte-associated M icroglia (PEM). PEM are present throughout all regions of the brain and spinal cord in NG2DsRed x CX 3 CR1 +/GFP mice, and in the human frontal cortex. They reside adjacent to pericytes at all levels of the capillary tree and can maintain their position for at least 28 days. PEM associate with pericytes lacking astroglial endfeet coverage but are segregated from pericytes by capillary basement membranes and capillary vessel width is similarly increased beneath pericytes with or without an associated PEM. Deletion of the microglia fractalkine receptor (CX 3 CR1) did not disrupt the association between pericytes and PEM, suggesting the association is not reliant on fractalkine signalling. Finally, we found that the proportion of microglia that are capillary-associated and PEM declines in the superior frontal gyrus (SFG) in AD, which is exacerbated by the APOE ε3/ε4 genotype. In summary, we identify and characterise a subpopulation of microglia that specifically associate with pericytes and find this population is reduced in the SFG in AD. This reduction may be a novel mechanism contributing to vascular dysfunction in diseases such as AD.
Publisher: Frontiers Media SA
Date: 22-09-2021
Publisher: Springer US
Date: 2023
Publisher: SAGE Publications
Date: 20-07-2017
Abstract: Pericytes are contractile vascular mural cells overlying capillary endothelium, and they have been implicated in a variety of functions including regulation of cerebral blood flow. Recent work has suggested that both in vivo and ex vivo, ischaemia causes pericytes to constrict and die, which has implications for microvascular reperfusion. Assessing pericyte contractility in tissue slices and in vivo is technically challenging, while in vitro techniques remain unreliable. Here, we used isolated cultures of human brain vascular pericytes to examine their contractile potential in vitro using the iCelligence electrical impedance system. Contraction was induced using the vasoactive peptide endothelin-1, and relaxation was demonstrated using adenosine and sodium nitroprusside. Endothelin-1 treatment also resulted in increased proliferation, which we were able to monitor in the same cell population from which we recorded contractile responses. Finally, the observation of pericyte contraction in stroke was reproduced using chemical ischaemia, which caused a profound and irreversible contraction clearly preceding cell death. These data demonstrate that isolated pericytes retain a contractile phenotype in vitro, and that it is possible to quantify this contraction using real-time electrical impedance recordings, providing a significant new platform for assessing the effects of vasoactive and vasculoprotective compounds on pericyte contractility.
Publisher: Elsevier BV
Date: 04-2021
Publisher: SAGE Publications
Date: 19-12-2014
DOI: 10.1111/IJS.12237
Publisher: SAGE Publications
Date: 25-08-2010
Abstract: Alteplase is the only drug licensed for acute ischemic stroke, and in this formulation, the thrombolytic agent recombinant tissue plasminogen activator (rtPA) is stabilized in a solution of L-arginine. Improved functional outcomes after alteplase administration have been shown in clinical trials, along with improved histological and behavioral measures in experimental models of embolic stroke. However, in animal models of mechanically induced ischemia, alteplase can exacerbate ischemic damage. We have systematically reviewed the literature of both rtPA and L-arginine administration in mechanical focal ischemia. The rtPA worsens ischemic damage under certain conditions, whereas L-arginine can have both beneficial and deleterious effects dependent on the time of administration. The interaction between rtPA and L-arginine may be leading to the production of nitric oxide, which can cause direct neurotoxicity, altered cerebral blood flow, and disruption of the neurovascular unit. We suggest that alternative formulations of rtPA, in the absence of L-arginine, would provide new insight into rtPA neurotoxicity, and have the potential to offer more efficacious thrombolytic therapy for ischemic stroke patients.
Publisher: Portico
Date: 03-2022
Publisher: Elsevier BV
Date: 04-2011
DOI: 10.1016/J.JNEUMETH.2011.02.002
Abstract: Perinatal and early childhood asphyxia is common, debilitating and has few efficacious treatments. A hypoxia ischemia (HI) rat model that involves a unilateral ligation of the common carotid artery followed by a 60 min period of 8% oxygen hypoxia is often used to test proposed treatments. However, this HI protocol produces inconsistent infarction volumes due to the variability of in idual rats to compensate for the ligated artery and hypoxia. Therefore, this HI model is problematic for experiments that prevent measurement of infarction volume, such as those that require analysis of homogenised brain tissue. We therefore aimed to find a simple and non-invasive predictor of infarction volume. Observations made prior, during and following HI in p26 rats showed that weight change 24 h following surgery was a strong predictor of infarction volume. The occurrence of a tonic clonic seizure during hypoxia was highly correlated with success of inducing an infarction, and for this reason we assessed whether ceasing the hypoxia for each rat following a tonic clonic seizure would produce a more consistent infarction volume. Using this procedure, infarction volumes measured at 3 and 15 days after surgery were significantly less variable, resulting in considerable improvements in statistical power compared with the original model.
Publisher: Wiley
Date: 22-11-2023
DOI: 10.1002/JNR.25146
Abstract: Stroke therapy has largely focused on preventing damage and encouraging repair outside the ischemic core, as the core is considered irreparable. Recently, several studies have suggested endogenous responses within the core are important for limiting the spread of damage and enhancing recovery, but the role of blood flow and capillary pericytes in this process is unknown. Using the Rose Bengal photothrombotic model of stroke, we illustrate blood vessels are present in the ischemic core and peri-lesional regions 2 weeks post stroke in male mice. A FITC-albumin gel cast of the vasculature revealed perfusion of these vessels, suggesting cerebral blood flow (CBF) may be partially present, without vascular leakage. The length of these vessels is significantly reduced compared to uninjured regions, but the average width is greater, suggesting they are either larger vessels that survived the initial injury, smaller vessels that have expanded in size (i.e., arteriogenesis), or that neovascularization begins with larger vessels. Concurrently, we observed an increase in platelet-derived growth factor receptor beta (PDGFRβ, a marker of pericytes) expression within the ischemic core in two distinct patterns, one which resembles pericyte-derived fibrotic scarring at the edge of the core, and one which is vessel associated and may represent blood vessel recovery. We find little evidence for iding cells on these intralesional blood vessels 2 weeks post stroke. Our study provides evidence flow is present in PDGFRβ-positive vessels in the ischemic core 2 weeks post stroke. We hypothesize intralesional CBF is important for limiting injury and for encouraging endogenous repair following cerebral ischemia.
Publisher: SAGE Publications
Date: 10-11-2015
DOI: 10.1111/IJS.12197
Abstract: Disruption of the neurovascular unit following cerebral ischemia affects protetive function of the blood-brain barrier, thus contributing to vasogenic edema and hemorrhagic transformation. This study explored the effects of mediators released from neurovascular unit cells on death of brain endothelial cells, astrocytes, pericytes, and microglia during oxygen glucose deprivation. Rat primary cell cultures were exposed either to oxygen glucose deprivation or control conditions. Cell death and released angiogenic factors were assessed from media collected from cultures. For some experiments, astrocyte-conditioned media, pericyte-conditioned media, and microglia-conditioned media, collected from the corresponding cell culture after six-hour oxygen glucose deprivation, were added to the media during oxygen glucose deprivation incubations. Brain endothelial cells were more susceptible to death following oxygen glucose deprivation than other neurovascular unit cells. Neither astrocyte-conditioned media nor vascular endothelial growth factor165 were protective for pericytes or brain endothelial cells during oxygen glucose deprivation. Vascular endothelial growth factor receptor antagonist significantly reduced cell death of brain endothelial cells treated with astrocyte-conditioned media or vascular endothelial growth factor165. Pericyte-conditioned media were protective for brain endothelial cells and microglia, but this was not mediated by pericyte-released angiopoietin 1. Soluble angiopoietin 1/angiopoietin 2 receptor Tie2 was protective for brain endothelial cells. Microglia-conditioned media were protective for astrocytes and brain endothelial cells, possibly through transforming growth factor β1 or interleukin 6. Microglia-derived signaling molecules, but not angiogenic factors, were protective for neurovascular unit cells during oxygen glucose deprivation. This finding could identify a potential therapeutic target for ischemic stroke.
Publisher: Medknow
Date: 2023
Publisher: Elsevier
Date: 2017
Publisher: Springer Science and Business Media LLC
Date: 2005
DOI: 10.1163/156856005774382797
Abstract: Inflammatory processes are made up of a multitude of complex cascades. Under physiological conditions these processes aid in tissue repair. However, under pathophysiological environments, such as wound healing and hypoxia-ischaemia (HI), inflammatory mediators become imbalanced, resulting in tissue destruction. This review addresses the changes in reactive oxygen species (ROS), L-arginine and arachidonic acid metabolism in wound healing and HI and subsequent treatments with promising anti-oxidants. Even though these models may appear ergent, anti-oxidant treatments are nevertheless still having favourable effects. On the basis of recent findings, it is apparent that protection with anti-oxidants is not solely attributed to scavenging of ROS. In addition, the actions of anti-oxidants must be considered in light of the inflammatory process being assessed. To this end, there does not appear to be any universally applicable single mechanism to explain the actions of anti-oxidants.
Publisher: SAGE Publications
Date: 29-11-2019
Abstract: Amplifying endogenous neuroprotective mechanisms is a promising avenue for stroke therapy. One target is mammalian target of rapamycin (mTOR), a serine/threonine kinase regulating cell proliferation, cell survival, protein synthesis, and autophagy. Animal studies investigating the effect of rapamycin on mTOR inhibition following cerebral ischemia have shown conflicting results. To conduct a systematic review and meta-analysis evaluating the effectiveness of rapamycin in reducing infarct volume in animal models of ischemic stroke. Our search identified 328 publications. Seventeen publications met inclusion criteria (52 comparisons: 30 reported infarct size and 22 reported neurobehavioral score). Study quality was modest (median 4 of 9) with no evidence of publication bias. The point estimate for the effect of rapamycin was a 21.6% (95% CI, 7.6%–35.7% p 0.01) improvement in infarct volume and 30.5% (95% CI 17.2%–43.8%, p 0.0001) improvement in neuroscores. Effect sizes were greatest in studies using lower doses of rapamycin. Low-dose rapamycin treatment may be an effective therapeutic option for stroke. Modest study quality means there is a potential risk of bias. We recommend further high-quality preclinical studies on rapamycin in stroke before progressing to clinical trials.
Publisher: Oxford University Press (OUP)
Date: 10-04-2014
DOI: 10.1093/BRAIN/AWU066
Publisher: SAGE Publications
Date: 21-08-2013
Abstract: Recanalization of an occluded vessel with recombinant tissue plasminogen activator is an effective strategy for treating acute ischemic stroke. Recombinant tissue plasminogen activator is administered as alteplase, a formulation containing many excipients including L-arginine, the substrate for nitric oxide production. Most studies fail to compare the effects of alteplase on brain injury to its L-arginine carrier solution. This study aimed to verify the previously reported detrimental effects of alteplase after cerebral ischemia and delineate the contribution of L-arginine. Male Wistar rats, subjected to 90 minutes of intraluminal middle cerebral artery occlusion (MCAO), were administered alteplase, the carrier solution or saline upon reperfusion. Neither alteplase nor the carrier affected cerebral blood flow (CBF) restoration throughout the first 60 minutes of reperfusion. Alteplase treatment was associated with increased mortality after MCAO. Twenty-four hours after MCAO, neurologic function and infarct volume did not differ between rats treated with alteplase, the carrier solution, or saline. Irrespective of treatment group, infarct volume was correlated with CBF during reperfusion, neuroscore, and peri-infarct depolarizations. These results suggest that alteplase treatment, independent of thrombolysis, does not cause increased ischemic injury compared with its appropriate carrier solution, supporting the continued use of alteplase in eligible ischemic stroke patients.
Publisher: Bentham Science Publishers Ltd.
Date: 04-2013
DOI: 10.2174/18715273112119990050
Abstract: Intravenous recombinant human tissue plasminogen activator (rtPA, formulated as alteplase) is the primary therapy for acute ischaemic stroke by breaking down a clot of an occluded vessel. There are several randomised controlled trials and observational studies that support the use of rtPA to improve functional outcome following acute ischaemic stroke. However, thrombolytic therapy with rtPA can be associated with a number of complications. Many of the rtPArelated complications result from its thrombolytic action including bleeding (intracerebral and systemic haemorrhage), reperfusion injury with oedema, and angioedema. Other rtPA complications such as reocclusion and secondary embolisation are related to ineffective thrombolysis or redistribution of the lysed clot. In addition to its thrombolytic properties, rtPA can act upon the brain parenchyma leading to seizures and neurotoxicity. Many of these complications have been reported in both pre-clinical experiments and in clinical trials. In animal studies, these complications of rtPA can confound the experimental results achieved, and have to be taken into account in future experiments. In the clinical setting, these complications are not always life-threatening, but can be serious and often lead to prolonged stays in intensive care units, increase the need for medical treatment, lengthen hospital stays, delay rehabilitation and increase morbidity and mortality. Some of these complications could be prevented through adherence to treatment guidelines or at least minimised through early detection and proper management. It is imperative that physicians caring for stroke patients have knowledge of these complications associated with rtPA treatment, and their management.
Publisher: Elsevier BV
Date: 05-2006
DOI: 10.1016/J.JNUTBIO.2005.10.005
Abstract: Catechins are dietary polyphenolic compounds associated with a wide variety of beneficial health effects in vitro, in vivo and clinically. These therapeutic properties have long been attributed to the catechins' antioxidant and free radical scavenging effects. Emerging evidence has shown that catechins and their metabolites have many additional mechanisms of action by affecting numerous sites, potentiating endogenous antioxidants and eliciting dual actions during oxidative stress, ischemia and inflammation. Catechins have proven to modulate apoptosis at various points in the sequence, including altering expression of anti- and proapoptotic genes. Their anti-inflammatory effects are activated through a variety of different mechanisms, including modulation of nitric oxide synthase isoforms. Catechins' actions of attenuating oxidative stress and the inflammatory response may, in part, account for their confirmed neuroprotective capabilities following cerebral ischemia. The versatility of the mechanisms of action of catechins increases their therapeutic potential as interventions for numerous clinical disorders. However, more epidemiological and clinical studies need to be undertaken for their efficacy to be fully elucidated.
Publisher: MDPI AG
Date: 18-09-2012
Publisher: Elsevier BV
Date: 04-2023
Publisher: Georg Thieme Verlag KG
Date: 13-12-2019
Abstract: Stroke is a leading cause of death and disability worldwide. The classification of stroke subtypes is difficult but critical for the prediction of clinical course and patient management, and limited treatment options are available. There is an urgent need for improvements in both diagnosis and therapy. Strokes have rapidly evolving phases of damage involving unique compartments of the brain, which imposes severe limitations for current diagnostic and treatment procedures. The rapid development of nanotechnology in other areas of modern medicine has ignited a widespread interest in its potential for the field of stroke. An important feature of nanoparticles is the relative ease in which their structures and surface chemistries can be modified for specific and potentially multiple, simultaneous purposes. Nanoparticles can be synthesized to carry and deliver therapeutics to specific cellular or subcellular compartments they can be engineered to provide enhanced contrast for imaging based on the detection of changes in the blood flow or possess ligand-specific chemistries which can facilitate diagnosis and monitor the treatment response. More specifically for a stroke, nanoparticles can be engineered to release their payload in response to the distinct extracellular processes occurring around the clot and in the ischemic penumbra, as well as aid in the detection of pathological hallmarks present at various stages of stroke progression. These capacities allow targeted release of disease-modifying agents in the affected brain tissue, increasing treatment efficacy, and limiting unwanted side effects. While nanospheres, liposomes, and mesoporous nanostructures all emerge as future prospects for stroke treatment and diagnosis, much of this potential is yet to be clinically realized. This review outlines aspects of nanotechnology identified as having potential to revolutionize the field of stroke.
Publisher: Wiley
Date: 11-06-2023
DOI: 10.1002/GLIA.24208
Publisher: SAGE Publications
Date: 06-03-2012
DOI: 10.1111/J.1747-4949.2012.00770.X
Abstract: Neuroprotection seeks to restrict injury to the brain parenchyma following an ischaemic insult by preventing salvageable neurons from dying. The concept of neuroprotection has shown promise in experimental studies, but has failed to translate into clinical success. Many reasons exist for this including the heterogeneity of human stroke and the lack of methodological agreement between preclinical and clinical studies. Even with the proposed Stroke Therapy Academic Industry Roundtable criteria for preclinical development of neuroprotective agents for stroke, we have still seen limited success in the clinic, an ex le being NXY-059, which fulfilled nearly all the Stroke Therapy Academic Industry Roundtable criteria. There are currently a number of ongoing trials for neuroprotective strategies including hypothermia and albumin, but the outcome of these approaches remains to be seen. Combination therapies with thrombolysis also need to be fully investigated, as restoration of oxygen and glucose will always be the best therapy to protect against cell death from stroke. There are also a number of promising neuroprotectants in preclinical development including haematopoietic growth factors, and inhibitors of the nicotinamide adenine dinucleotide phosphate oxidases, a source of free radical production which is a key step in the pathophysiology of acute ischaemic stroke. For these neuroprotectants to succeed, essential quality standards need to be adhered to however, these must remain realistic as the evidence that standardization of procedures improves translational success remains absent for stroke.
Publisher: Cold Spring Harbor Laboratory
Date: 10-2023
Publisher: Springer International Publishing
Date: 2017
Publisher: Elsevier BV
Date: 08-2015
Publisher: SAGE Publications
Date: 02-10-2016
Abstract: The clinical relevance of the transient intraluminal filament model of middle cerebral artery occlusion (tMCAO) has been questioned due to distinct cerebral blood flow profiles upon reperfusion between tMCAO (abrupt reperfusion) and alteplase treatment (gradual reperfusion), resulting in differing pathophysiologies. Positive results from recent endovascular thrombectomy trials, where the occluding clot is mechanically removed, could revolutionize stroke treatment. The rapid cerebral blood flow restoration in both tMCAO and endovascular thrombectomy provides clinical relevance for this pre-clinical model. Any future clinical trials of neuroprotective agents as adjuncts to endovascular thrombectomy should consider tMCAO as the model of choice to determine pre-clinical efficacy.
Publisher: Springer Science and Business Media LLC
Date: 16-06-2023
DOI: 10.1007/S10565-023-09814-9
Abstract: Pericytes play several important functions in the neurovascular unit including contractile control of capillaries, maintenance of the BBB, regulation of angiogenesis, and neuroinflammation. There exists a continuum of pericyte subtypes along the vascular tree which exhibit both morphological and transcriptomic differences. While different functions have been associated with the pericyte subtypes in vivo, numerous recent publications have used a primary human brain vascular pericytes (HBVP) cell line where this pericyte heterogeneity has not been considered. Here, we used primary HBVP cultures, high-definition imaging, cell motility tracking, and immunocytochemistry to characterise morphology, protein expression, and contractile behaviour to determine whether heterogeneity of pericytes also exists in cultures. We identified five distinct morphological subtypes that were defined using both qualitative criteria and quantitative shape analysis. The proportion of each subtype present within the culture changed as passage number increased, but pericytes did not change morphological subtype over short time periods. The rate and extent of cellular and membrane motility differed across the subtypes. Immunocytochemistry revealed differential expression of alpha-smooth muscle actin (αSMA) across subtypes. αSMA is essential for cell contractility, and consequently, only subtypes with high αSMA expression contracted in response to physiological vasoconstrictors endothelin-1 (ET1) and noradrenaline (NA). We conclude that there are distinct morphological subtypes in HBVP culture, which display different behaviours. This has significance for the use of HBVP when modelling pericyte physiology in vitro where relevance to in vivo pericyte subtypes along the vascular tree must be considered. Graphical abstract
Publisher: Elsevier BV
Date: 07-2019
DOI: 10.1016/J.NEULET.2019.05.023
Abstract: Hamartin, a component of the tuberous sclerosis complex (TSC) that actively inhibits the mammalian target of rapamycin (mTOR), may mediate the endogenous resistance of Cornu Ammonis 3 (CA3) hippoc al neurons following global cerebral ischemia. Pharmacological compounds that selectively inhibit mTOR may afford neuroprotection following ischemic stroke. We hypothesize that AZD2014, a novel mTORC1/2 inhibitor, may protect neurons following oxygen and glucose deprivation (OGD). Primary neuronal cultures from E18 Wistar rat embryos were exposed to 2 h OGD or normoxia. AZD2014 was administered either during OGD, 24 h prior to OGD or for 24 h following OGD. Cell death was quantified by lactate dehydrogenase assay. We characterized the expression of mTOR pathway proteins following exposure to AZD2014 using western blotting. Following 2 h OGD +24 h recovery, AZD2014 increased neuronal death when present during OGD. Rapamycin, the archetypal mTOR inhibitor, had no effect on cell death. Treatment with AZD2014 24 h prior to OGD and 24 h after OGD also enhanced cell death. While Western blotting showed a trend towards decreased expression levels of phospho-Akt relative to total Akt with increasing AZD2014 concentration, hamartin expression was also significantly decreased leading to activation of mTOR. AZD2014 was detrimental to neurons that underwent ischemia. AZD2014 appeared to reduce hamartin, a known neuroprotective mediator, thereby preventing any beneficial effects of mTOR inhibition. Further characterization of the role of in idual mTOR complexes (mTORC1 and mTORC2) and their upstream and downstream regulators are necessary to reveal whether these pathways are neuroprotective targets for stroke.
Publisher: Frontiers Media SA
Date: 28-06-2019
Publisher: Frontiers Media SA
Date: 03-02-2022
DOI: 10.3389/FPHYS.2021.793741
Abstract: The study of stroke has historically made use of traditional spectroscopy techniques to provide the ground truth for parameters like pH. However, techniques like 31 P spectroscopy have limitations, in particular poor temporal and spatial resolution, coupled with a need for a high field strength and specialized coils. More modern magnetic resonance spectroscopy (MRS)-based imaging techniques like chemical exchange saturation transfer (CEST) have been developed to counter some of these limitations but lack the definitive gold standard for pH that 31 P spectroscopy provides. In this perspective, both the traditional ( 31 P spectroscopy) and emerging (CEST) techniques in the measurement of pH for ischemic imaging will be discussed. Although each has its own advantages and limitations, it is likely that CEST may be preferable simply due to the hardware, acquisition time and image resolution advantages. However, more experiments on CEST are needed to determine the specificity of endogenous CEST to absolute pH, and 31 P MRS can be used to calibrate CEST for pH measurement in the preclinical model to enhance our understanding of the relationship between CEST and pH. Combining the two imaging techniques, one old and one new, we may be able to obtain new insights into stroke physiology that would not be possible otherwise with either alone.
Publisher: SAGE Publications
Date: 10-2017
Abstract: Hyperacute changes in cerebral blood flow during cerebral ischaemia and reperfusion are important determinants of injury. Cerebral blood flow is regulated by neurovascular coupling, and disruption of neurovascular coupling contributes to brain plasticity and repair problems. However, it is unknown how neurovascular coupling is affected hyperacutely during cerebral ischaemia and reperfusion. We have developed a remote middle cerebral artery occlusion model in the rat, which enables multi-modal assessment of neurovascular coupling immediately prior to, during and immediately following reperfusion. Male Wistar rats were subjected to remote middle cerebral artery occlusion, where a long filament was advanced intraluminally through a guide cannula in the common carotid artery. Transcallosal stimulation evoked increases in blood flow, tissue oxygenation and neuronal activity, which were diminished by middle cerebral artery occlusion and partially restored during reperfusion. These evoked responses were not affected by administration of the thrombolytic alteplase at clinically used doses. Evoked cerebral blood flow responses were fully restored at 24 h post–middle cerebral artery occlusion indicating that neurovascular dysfunction was not sustained. These data show for the first time that the rat remote middle cerebral artery occlusion model coupled with transcallosal stimulation provides a novel method for continuous assessment of hyperacute neurovascular coupling changes during ischaemia and reperfusion, and offers unique insight into hyperacute ischaemic pathophysiology.
Publisher: Medknow
Date: 2020
Publisher: Wiley
Date: 29-12-2004
Abstract: (-)-Epigallocatechin gallate (EGCG) is a potent antioxidant that is neuroprotective against ischemia-induced brain damage. However, the neuroprotective effects and possible mechanisms of action of EGCG after hypoxia-ischemia (HI) have not been investigated. Therefore, we used a modified "Levine" model of HI to determine the effects of EGCG. Wistar rats were treated with either 0.9% saline or 50 mg/kg EGCG daily for 1 day and 1 h before HI induction and for a further 2 days post-HI. At 26-days-old, both groups underwent permanent left common carotid artery occlusion and exposure to 8% oxygen/92% nitrogen atmosphere for 1 h. Histological assessment showed that EGCG significantly reduced infarct volume (38.0+/-16.4 mm(3)) in comparison to HI + saline (99.6+/-15.6 mm(3)). In addition, EGCG significantly reduced total (622.6+/-85.8 pmol L-[(3)H]citrulline/30 min/mg protein) and inducible nitric oxide synthase (iNOS) activity (143.2+/-77.3 pmol L-[(3)H]citrulline/30 min/mg protein) in comparison to HI+saline controls (996.6+/-113.6 and 329.7+/-59.6 pmol L-[(3)H]citrulline/30 min/mg protein for total NOS and iNOS activity, respectively). Western blot analysis demonstrated that iNOS protein expression was also reduced. In contrast, EGCG significantly increased endothelial and neuronal NOS protein expression compared with HI controls. EGCG also significantly preserved mitochondrial energetics (complex I-V) and citrate synthase activity. This study demonstrates that the neuroprotective effects of EGCG are, in part, due to modulation of NOS isoforms and preservation of mitochondrial complex activity and integrity. We therefore conclude that the in vivo neuroprotective effects of EGCG are not exclusively due to its antioxidant effects but involve more complex signal transduction mechanisms.
Publisher: Wiley
Date: 30-03-2023
DOI: 10.1002/GLIA.24371
Abstract: Cerebral blood flow (CBF) is important for the maintenance of brain function and its dysregulation has been implicated in Alzheimer's disease (AD). Microglia associations with capillaries suggest they may play a role in the regulation of CBF or the blood–brain‐barrier (BBB). We explored the relationship between microglia and pericytes, a vessel‐resident cell type that has a major role in the control of CBF and maintenance of the BBB, discovering a spatially distinct subset of microglia that closely associate with pericytes. We termed these pericyte‐associated microglia (PEM). PEM are present throughout the brain and spinal cord in NG2DsRed × CX 3 CR1 +/GFP mice, and in the human frontal cortex. Using in vivo two‐photon microscopy, we found microglia residing adjacent to pericytes at all levels of the capillary tree and found they can maintain their position for at least 28 days. PEM can associate with pericytes lacking astroglial endfeet coverage and capillary vessel width is increased beneath pericytes with or without an associated PEM, but capillary width decreases if a pericyte loses a PEM. Deletion of the microglia fractalkine receptor (CX 3 CR1) did not disrupt the association between pericytes and PEM. Finally, we found the proportion of microglia that are PEM declines in the superior frontal gyrus in AD. In summary, we identify microglia that specifically associate with pericytes and find these are reduced in number in AD, which may be a novel mechanism contributing to vascular dysfunction in neurodegenerative diseases.
Publisher: Springer Science and Business Media LLC
Date: 26-03-2014
DOI: 10.1038/NATURE13165
Publisher: Society for Neuroscience
Date: 30-01-2017
DOI: 10.1523/JNEUROSCI.0005-16.2016
Abstract: Cerebral blood flow (CBF) is controlled by arterial blood pressure, arterial CO 2 , arterial O 2 , and brain activity and is largely constant in the awake state. Although small changes in arterial CO 2 are particularly potent to change CBF (1 mmHg variation in arterial CO 2 changes CBF by 3%–4%), the coupling mechanism is incompletely understood. We tested the hypothesis that astrocytic prostaglandin E 2 (PgE 2 ) plays a key role for cerebrovascular CO 2 reactivity, and that preserved synthesis of glutathione is essential for the full development of this response. We combined two-photon imaging microscopy in brain slices with in vivo work in rats and C57BL/6J mice to examine the hemodynamic responses to CO 2 and somatosensory stimulation before and after inhibition of astrocytic glutathione and PgE 2 synthesis. We demonstrate that hypercapnia (increased CO 2 ) evokes an increase in astrocyte [Ca 2+ ] i and stimulates COX-1 activity. The enzyme downstream of COX-1 that synthesizes PgE 2 (microsomal prostaglandin E synthase-1) depends critically for its vasodilator activity on the level of glutathione in the brain. We show that, when glutathione levels are reduced, astrocyte calcium-evoked release of PgE 2 is decreased and vasodilation triggered by increased astrocyte [Ca 2+ ] i in vitro and by hypercapnia in vivo is inhibited. Astrocyte synthetic pathways, dependent on glutathione, are involved in cerebrovascular reactivity to CO 2 . Reductions in glutathione levels in aging, stroke, or schizophrenia could lead to dysfunctional regulation of CBF and subsequent neuronal damage. SIGNIFICANCE STATEMENT Neuronal activity leads to the generation of CO 2 , which has previously been shown to evoke cerebral blood flow (CBF) increases via the release of the vasodilator PgE 2 . We demonstrate that hypercapnia (increased CO 2 ) evokes increases in astrocyte calcium signaling, which in turn stimulates COX-1 activity and generates downstream PgE 2 production. We demonstrate that astrocyte calcium-evoked production of the vasodilator PgE 2 is critically dependent on brain levels of the antioxidant glutathione. These data suggest a novel role for astrocytes in the regulation of CO 2 -evoked CBF responses. Furthermore, these results suggest that depleted glutathione levels, which occur in aging and stroke, will give rise to dysfunctional CBF regulation and may result in subsequent neuronal damage.
Publisher: Springer New York
Date: 2014
DOI: 10.1007/978-1-4939-0320-7_20
Abstract: Laser Doppler flowmetry (LDF) is a method by which relative cerebral blood flow (CBF) of the cortex can be measured. Although the method is easy to employ, LDF only measures relative CBF, while absolute CBF cannot be quantified. LDF is useful for investigating CBF changes in a number of different applications including neurovascular and stroke research. This chapter will prepare the reader for rodent experiments using LDF with two preparations. The closed skull preparation can be used to monitor CBF with an intact skull, but in adult rats, thinning of the skull is required to obtain an accurate cortical CBF signal. The open skull preparation requires a craniotomy to expose the surface of the brain and the LDF probe is held close to the surface to measure cerebral perfusion.
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Brad Sutherland.