Expression of glial fibrillary acidic protein in areas of focal cerebral ischemia accompanies neuronal expression of 72-kDa heat shock protein

Delayed Chronic Acidic Postconditioning Improves Poststroke Motor Functional Recovery and Brain Tissue Repair by Activating Proton-Sensing TDAG8

Acidic postconditioning by transient CO2 inhalation applied within minutes after reperfusion has neuroprotective effects in the acute phase of stroke. However, the effects of delayed chronic acidic postconditioning (DCAPC) initiated during the subacute phase of stroke or other acute brain injuries are unknown. Mice received daily DCAPC by inhaling 5%/10%/20% CO2 for various durations (three cycles of 10- or 20-min CO2 inhalation/10-min break) at days 3-7, 7-21, or 3-21 after photothrombotic stroke. Grid-walk, cylinder, and gait tests were used to assess motor function. DCAPC with all CO2 concentrations significantly promoted motor functional recovery, even when DCAPC was delayed for 3-7 days. DCAPC enhanced the puncta density of GAP-43 (a marker of axon growth and regeneration) and synaptophysin (a marker of synaptogenesis) and reduced the amoeboid microglia number, glial scar thickness and mRNA expression of CD16 and CD32 (markers of proinflammatory M1 microglia) compared with those of the stroke group. Cerebral blood flow (CBF) increased in response to DCAPC. Furthermore, the mRNA expression of TDAG8 (a proton-activated G-protein-coupled receptor) was increased during the subacute phase of stroke, while DCAPC effects were blocked by systemic knockout of TDAG8, except for those on CBF. DCAPC reproduced the benefits by re-expressing TDAG8 in the peri-infarct cortex of TDAG8-/- mice infected with HBAAV2/9-CMV-TDAG8-3flag-ZsGreen. Taken together, we first showed that DCAPC promoted functional recovery and brain tissue repair after stroke with a wide therapeutic time window of at least 7 days after stroke. Brain-derived TDAG8 is a direct target of DCAPC that induces neuroreparative effects.

Differential effects of the cell cycle inhibitor, olomoucine, on functional recovery and on responses of peri-infarct microglia and astrocytes following photothrombotic stroke in rats

Background

Following stroke, changes in neuronal connectivity in tissue surrounding the infarct play an important role in both spontaneous recovery of neurological function and in treatment-induced improvements in function. Microglia and astrocytes influence this process through direct interactions with the neurons and as major determinants of the local tissue environment. Subpopulations of peri-infarct glia proliferate early after stroke providing a possible target to modify recovery. Treatment with cell cycle inhibitors can reduce infarct volume and improve functional recovery. However, it is not known whether these inhibitors can influence neurological function or alter the responses of peri-infarct glia without reducing infarction. The present study aimed to address these issues by testing the effects of the cell cycle inhibitor, olomoucine, on recovery and peri-infarct changes following photothrombotic stroke.

Methods

Stroke was induced by photothrombosis in the forelimb sensorimotor cortex in Sprague-Dawley rats. Olomoucine was administered at 1 h and 24 h after stroke induction. Forelimb function was monitored up to 29 days. The effects of olomoucine on glial cell responses in peri-infarct tissue were evaluated using immunohistochemistry and Western blotting.

Results

Olomoucine treatment did not significantly affect maximal infarct volume. Recovery of the affected forelimb on a placing test was impaired in olomoucine-treated rats, whereas recovery in a skilled reaching test was substantially improved. Olomoucine treatment produced small changes in aspects of Iba1 immunolabelling and in the number of CD68-positive cells in cerebral cortex but did not selectively modify responses in peri-infarct tissue. The content of the astrocytic protein, vimentin, was reduced by 30% in the region of the lesion in olomoucine-treated rats.

Conclusions

Olomoucine treatment modified functional recovery in the absence of significant changes in infarct volume. The effects on recovery were markedly test dependent, adding to evidence that skilled tasks requiring specific training and general measures of motor function can be differentially modified by some interventions. The altered recovery was not associated with specific changes in key responses of peri-infarct microglia, even though these cells were considered a likely target for early olomoucine treatment. Changes detected in peri-infarct reactive astrogliosis could contribute to the altered patterns of functional recovery.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02208-w.

A1/A2 astrocytes in central nervous system injuries and diseases: Angels or devils?

Astrocytes play a pivotal role in maintaining the central nervous system (CNS) homeostasis and function. In response to CNS injuries and diseases, reactive astrocytes are triggered. By purifying and genetically profiling reactive astrocytes, it has been now found that astrocytes can be activated into two polarization states: the neurotoxic or pro-inflammatory phenotype (A1) and the neuroprotective or anti-inflammatory phenotype (A2). Although the simple dichotomy of the A1/A2 phenotypes does not reflect the wide range of astrocytic phenotypes, it facilitates our understanding of the reactive state of astrocytes in various CNS disorders. This article reviews the recent evidences regarding A1/A2 astrocytes, including (a) the specific markers and morphological characteristics, (b) the effects of A1/A2 astrocytes on the neurovascular unit, and (c) the molecular mechanisms involved in the phenotypic switch of astrocytes. Although many questions remain, a deeper understanding of different phenotypic astrocytes will eventually help us to explore effective strategies for neurological disorders by targeting astrocytes.

Intra- and intergenerational changes in the cortical DNA methylome in response to therapeutic intermittent hypoxia in mice

Recent evidence from our laboratory documents functional resilience to retinal ischemic injury in untreated mice derived from parents exposed to repetitive hypoxic conditioning (RHC) before breeding. To begin to understand the epigenetic basis of this intergenerational protection, we used methylated DNA immunoprecipitation and sequencing to identify genes with differentially methylated promoters (DMGPs) in the prefrontal cortex of mice treated directly with the same RHC stimulus (F0-RHC) and in the prefrontal cortex of their untreated F1-generation offspring (F1-*RHC). Subsequent bioinformatic analyses provided key mechanistic insights into how changes in gene expression secondary to promoter hypo- and hypermethylation might afford such protection within and across generations. We found extensive changes in DNA methylation in both generations consistent with the expression of many survival-promoting genes, with twice the number of DMGPs in the cortex of F1*RHC mice relative to their F0 parents that were directly exposed to RHC. In contrast to our hypothesis that similar epigenetic modifications would be realized in the cortices of both F0-RHC and F1-*RHC mice, we instead found relatively few DMGPs common to both generations; in fact, each generation manifested expected injury resilience via distinctly unique gene expression profiles. Whereas in the cortex of F0-RHC mice, predicted protein-protein interactions reflected activation of an anti-ischemic phenotype, networks activated in F1-*RHC cortex comprised networks indicative of a much broader cytoprotective phenotype. Altogether, our results suggest that the intergenerational transfer of an acquired phenotype to offspring does not necessarily require the faithful recapitulation of the conditioning-modified DNA methylome of the parent.

The Antiapoptosis Effect of Geum japonicum Thunb. var. chinense Extracts on Cerebral Ischemia Reperfusion Injury via PI3K/Akt Pathway

Geum japonicum Thunb. var. chinense (GJ) is a type of wild vegetable found in China and other Asian countries; it has been reported that its extracts possess a neuroprotective effect against cerebral ischemia reperfusion (CIR) injury. The aim of this study is to explore the effect GJ extracts on transient focal CIR injury and neurons apoptosis and to clarify its possible underlying mechanisms in vivo. Our results indicated that pretreatment with GJ extracts significantly ameliorated the infarct volume, decreased neurological deficits, lessened neural cells apoptosis, downregulated GFAP activity level, and increased surviving neurons. Moreover, GJ extracts preadministration increased Bcl-2 levels and attenuated the increase in the expressions of Bax and it also lowered the cleaved caspase-3 activity in ischemic cortex tissues which was caused by CIR and increased the expression of PI3K and p-Akt. The above effects of high dose of GJ (GJ-H) group were much better than those of low dose of GJ (GJ-L), which indicated that GJ extracts may be helpful in the suppression of CIR injury with a dose-dependent manner.

The roles of astrocyte in the brain pathologies following ischemic stroke

Aim: In this work, we systematically explored the physiological functions of astrocytes and their roles following ischemic stroke, additionally, the potential therapy strategy targeting the astrocytes was also discussed. Methods: This work searched the PubMed database (including MEDLINE) until 14 Feb 2018, and furthermore, the studies were identified through cross-referencing and by consulting the experts in this field. Results: This study indicated that the astrocytes can not only play harmful roles following ischemic stroke through release of inflammatory factors and formation of glial scar but also have protective effects through quenching glutamate excitotoxicity and maintaining the clearance function of glymphatic system in brain. Conclusion: Owing to their important roles in physiological functions of brain and in the pathological conditions following ischemic stroke, the astrocytes might be a potential but promising therapeutic target for treating the ischemic stroke in the future.

Strain-specific differential expression of astrocytes and microglia in the mouse hippocampus

INTRODUCTION

Genetic background influences neurotransmitter expression and function of the hippocampus. Genetic background influences the phenotype of the hippocampus, but expression of neuroglia in hippocampus has not been well established dependent on various mouse strains.

OBJECTIVES

In this study, we investigated the effects of genetic background on cell population of astrocytes and microglia in eight widely used inbred strains (C57BL/6J, A/J, BALB/c, C3H/HeJ, FVB, 129/SvJ, DBA/1, and DBA/2) and one outbred strain (ICR).

METHODS

In all mouse strains, glial fibrillary acidic protein (GFAP)-immunoreactive astrocytes and ionized calcium-binding adaptor molecule 1 (Iba-1)-immunoreactive microglia were found in almost all layers of hippocampal CA1-4 regions and the dentate gyrus.

RESULTS

We observed significant differences in the number of astrocytes and microglia. In the CA1 and CA3 regions, the number of GFAP-immunoreactive astrocytes was highest in the C3H/HeJ strain, and lowest in the 129/SvJ and FVB strains. In the polymorphic layer of the dentate gyrus, the number was highest in the DBA/1 strain and lowest in the 129/SvJ strain. Among the nine mouse strains, the number of Iba-1-immunoreactive microglia was highest in the CA1 and CA3 regions in the ICR and in the dentate gyrus of the C57BL/6 strain. The CA1 region of the FVB strain and the CA3 region and dentate gyrus of DBA/2 had the lowest number of Iba-1-immunoreactive microglia.

CONCLUSION

These results suggest that the numbers of astrocytes and microglia differ depending on the mouse strain and these differences may be related to strain-dependent function of astrocytes.

S1PR3 is essential for phosphorylated fingolimod to protect astrocytes against oxygen-glucose deprivation-induced neuroinflammation via inhibiting TLR2/4-NFκB signalling

Fingolimod (FTY720) is used as an immunosuppressant for multiple sclerosis. Numerous studies indicated its neuroprotective effects in stroke. However, the mechanism remains to be elucidated. This study was intended to investigate the mechanisms of phosphorylated FTY720 (pFTY720), which was the principle active molecule in regulating astrocyte‐mediated inflammatory responses induced by oxygen‐glucose deprivation (OGD). Results demonstrated that pFTY720 could protect astrocytes against OGD‐induced injury and inflammatory responses. It significantly decreased pro‐inflammatory cytokines, including high mobility group box 1 (HMGB1) and tumour necrosis factor‐α (TNF‐α). Further, studies displayed that pFTY720 could prevent up‐regulation of Toll‐like receptor 2 (TLR2), phosphorylation of phosphoinositide 3‐kinase (PI3K) and nuclear translocation of nuclear factor kappa B (NFκB) p65 subunit caused by OGD. Sphingosine‐1‐phosphate receptor 3 (S1PR3) knockdown could reverse the above change. Moreover, administration of TLR2/4 blocker abolished the protective effects of pFTY720. Taken together, this study reveals that pFTY720 depends on S1PR3 to protect astrocytes against OGD‐induced neuroinflammation, due to inhibiting TLR2/4‐PI3K‐NFκB signalling pathway.

Astrocytes and the Warning Signs of Intracerebral Hemorrhagic Stroke

Two decades into the two thousands, intracerebral hemorrhagic stroke (ICH) continues to reap lives across the globe. In the US, nearly 12,000 people suffer from ICH every year. Half of them survive, but many are left with permanent physical and cognitive disabilities, the severity of which depends on the location and broadness of the brain region affected by the hemorrhage. The ongoing efforts to identify risk factors for hemorrhagic stroke have been instrumental for the development of new medical practices to prevent, aid the recovery and reduce the risk of recurring ICH. Recent efforts approach the study of ICH from a different angle, providing information on how we can limit brain damage by manipulating astrocyte receptors. These results provide a novel understanding of how astrocytes contribute to brain injury and recovery from small ICH. Here, we discuss current knowledge on the risk factors and molecular pathology of ICH and the functional properties of astrocytes and their role in ICH. Last, we discuss candidate astrocyte receptors that may prove to be valuable therapeutic targets to treat ICH. Together, these findings provide basic and clinical scientists useful information for the future development of strategies to improve the detection of small ICH, limit brain damage, and prevent the onset of more severe episodes of brain hemorrhage.

Use of 2,3,5-triphenyltetrazolium chloride-stained brain tissues for immunofluorescence analyses after focal cerebral ischemia in rats

The middle cerebral artery occlusion (MCAO) model in rodents has been widely used as model for studying brain ischemic stroke. TTC (2,3,5-triphenyltetrazolium chloride) staining in fresh tissues is used to evaluate the size of the infarct in MCAO model, and TTC-stained brain tissues are considered to be possible to bring a damage to the anatomical structure of neuronal cells and unsuitable for immunofluorescence analyses of cytology, and discarded after evaluation of infarct volume. Another group of models with in vivo fixation was required to the pathological or histological analyses of the infarct brains, which lead to double the numbers of animals in researches. However, some evidences indicate that if we properly optimized staining protocol, TTC-stained brain tissues might be suitable for cytological analyses. In this work, we have optimized the immunofluorescent staining methods of TTC-stained brain slices, and found that TTC-stained brain tissues are suitable for quantitative and qualitative analyses of microglia, astrocytes and neuroblasts, the morphology of theses cell were nearly identical to the in-vivo fixed models. Our optimized-protocol provide two advantages over traditional methods one of them is providing the precise the infarct region, which reduces the differences within groups, the other one is decreasing the total number of animals in research dramatically.

α-Endosulfine (ARPP-19e) Expression in a Rat Model of Stroke

In nutrient restricted environments, the yeast endosulfines Igo1/2 are activated via TORC1 inhibition and function critically to initiate and coordinate the cellular stress response that promotes survival. We examined expression of αEnsa, the mammalian homolog of yeast endosulfines, in rat stroke. Prominent neuronal upregulation of αEnsa was identified in 3 patterns within the ischemic gradient: (1) neurons in GFAP-/HSF1+ cortex showed upregulation and near-complete nuclear translocation of αEnsa protein within hours of ischemic onset; (2) neurons in GFAP+/HSF1+ cortex showed upregulation in cytoplasm and nuclei that persisted for days; (3) neurons in GFAP+/HSF1- cortex showed delayed cytosolic-only upregulation that persisted for days. Findings were corroborated using in situ hybridization for ENSA mRNA. Rapamycin treatment was found to reduce infarct size and behavioral deficits and, in GFAP+/HSF1+ zones, enhance αEnsa neuronal nuclear translocation and mitigate cell death, relative to controls. Based on the conservation of TOR signaling across species, and on the finding that the Rim15-Igo1/2-PP2A module is triggered by substrate deprivation in eukaryotic yeast, we speculate that αEnsa is activated by substrate deprivation, functioning through the homologous MASTL-αEnsa/ARPP19-PP2A module to promote neuronal survival. In conjunction with recent studies suggesting a neuroprotective role, our data highlight a potential function for αEnsa within ischemic brain.

Reactive astrogliosis in stroke: Contributions of astrocytes to recovery of neurological function

Alterations in neuronal connectivity, particularly in the "peri-infarct" tissue adjacent to the region of ischemic damage, are important contributors to the spontaneous recovery of function that commonly follows stroke. Peri-infarct astrocytes undergo reactive astrogliosis and play key roles in modulating the adaptive responses in neurons. This reactive astrogliosis shares many features with that induced by other forms of damage to the central nervous system but also differs in details that potentially influence neurological recovery. A subpopulation of astrocytes within a few hundred micrometers of the infarct proliferate and are centrally involved in the development of the glial scar that separates the damaged tissue in the infarct from surrounding normal brain. The intertwined processes of astrocytes adjacent to the infarct provide the core structural component of the mature scar. Interventions that cause early disruption of glial scar formation typically impede restoration of neurological function. Marked reactive astrogliosis also develops in cells more distant from the infarct but these cells largely remain in the spatial territories they occupied prior to stroke. These cells play important roles in controlling the extracellular environment and release proteins and other molecules that are able to promote neuronal plasticity and improve functional recovery. Treatments manipulating aspects of reactive astrogliosis can enhance neuronal plasticity following stroke. Optimising these treatments for use in human stroke would benefit from a more complete characterization of the specific responses of peri-infarct astrocytes to stroke as well as a better understanding of the influence of other factors including age, sex, comorbidities and reperfusion of the ischemic tissue.

Histidine provides long-term neuroprotection after cerebral ischemia through promoting astrocyte migration

The formation of glial scar impedes the neurogenesis and neural functional recovery following cerebral ischemia. Histamine showed neuroprotection at early stage after cerebral ischemia, however, its long-term effect, especially on glial scar formation, hasn’t been characterized. With various administration regimens constructed for histidine, a precursor of histamine, we found that histidine treatment at a high dose at early stage and a low dose at late stage demonstrated the most remarkable long-term neuroprotection with decreased infarct volume and improved neurological function. Notably, this treatment regimen also robustly reduced the glial scar area and facilitated the astrocyte migration towards the infarct core. In wound-healing assay and transwell test, histamine significantly promoted astrocyte migration. H2 receptor antagonists reversed the promotion of astrocyte migration and the neuroprotection provided by histidine. Moreover, histamine upregulated the GTP-bound small GTPase Rac1, while a Rac1 inhibitor, NSC23766, abrogated the neuroprotection of histidine and its promotion of astrocyte migration. Our data indicated that a dose/stage-dependent histidine treatment, mediated by H2 receptor, promoted astrocyte migration towards the infarct core, which benefited long-term post-cerebral ischemia neurological recovery. Therefore, targeting histaminergic system may be an effective therapeutic strategy for long-term cerebral ischemia injury through its actions on astrocytes.

Astrocytes, therapeutic targets for neuroprotection and neurorestoration in ischemic stroke

Astrocytes are the most abundant cell type within the central nervous system. They play essential roles in maintaining normal brain function, as they are a critical structural and functional part of the tripartite synapses and the neurovascular unit, and communicate with neurons, oligodendrocytes and endothelial cells. After an ischemic stroke, astrocytes perform multiple functions both detrimental and beneficial, for neuronal survival during the acute phase. Aspects of the astrocytic inflammatory response to stroke may aggravate the ischemic lesion, but astrocytes also provide benefit for neuroprotection, by limiting lesion extension via anti-excitotoxicity effects and releasing neurotrophins. Similarly, during the late recovery phase after stroke, the glial scar may obstruct axonal regeneration and subsequently reduce the functional outcome; however, astrocytes also contribute to angiogenesis, neurogenesis, synaptogenesis, and axonal remodeling, and thereby promote neurological recovery. Thus, the pivotal involvement of astrocytes in normal brain function and responses to an ischemic lesion designates them as excellent therapeutic targets to improve functional outcome following stroke. In this review, we will focus on functions of astrocytes and astrocyte-mediated events during stroke and recovery. We will provide an overview of approaches on how to reduce the detrimental effects and amplify the beneficial effects of astrocytes on neuroprotection and on neurorestoration post stroke, which may lead to novel and clinically relevant therapies for stroke.

Ciliary neurotrophic factor (CNTF) activation of astrocytes decreases spreading depolarization susceptibility and increases potassium clearance

Waves of spreading depolarization (SD) have been implicated in the progressive expansion of acute brain injuries. SD can persist over several days, coincident with the time course of astrocyte activation, but little is known about how astrocyte activation may influence SD susceptibility. We examined whether activation of astrocytes modified SD threshold in hippocampal slices. Injection of a lentiviral vector encoding Ciliary neurotrophic factor (CNTF) into the hippocampus in vivo, led to sustained astrocyte activation, verified by up-regulation of glial fibrillary acidic protein (GFAP) at the mRNA and protein levels, as compared to controls injected with vector encoding LacZ. In acute brain slices from LacZ controls, localized 1M KCl microinjections invariably generated SD in CA1 hippocampus, but SD was never induced with this stimulus in CNTF tissues. No significant change in intrinsic excitability was observed in CA1 neurons, but excitatory synaptic transmission was significantly reduced in CNTF samples. mRNA levels of the predominantly astrocytic Na(+) /K(+) -ATPase pump α2 subunit were higher in CNTF samples, and the kinetics of extracellular K(+) transients during matched synaptic activation were consistent with increased K(+) uptake in CNTF tissues. Supporting a role for the Na(+) /K(+) -ATPase pump in increased SD threshold, ouabain, an inhibitor of the pump, was able to generate SD in CNTF tissues. These data support the hypothesis that activated astrocytes can limit SD onset via increased K(+) clearance and suggest that therapeutic strategies targeting these glial cells could improve the outcome following acute brain injuries associated with SD.

Therapeutic time window and dose dependence of xenon delivered via echogenic liposomes for neuroprotection in stroke

AIMS

Neurologic impairment following ischemic injury complicates the quality of life for stroke survivors. Xenon (Xe) has favorable neuroprotective properties to modify stroke. Xe delivery is hampered by a lack of suitable administration strategies. We have developed Xe-containing echogenic liposomes (Xe-ELIP) for systemic Xe delivery. We investigated the time window for Xe-ELIP therapeutic effect and the most efficacious dose for neuroprotection. Molecular mechanisms for Xe neuroprotection were investigated.

METHODS

Xenon-containing echogenic liposomes were created by a previously developed pressurization-freezing method. Following right middle cerebral artery occlusion (2 h), animals were treated with Xe-ELIP at 2, 3, or 5 h to determine time window of therapeutic effect. The neuroprotectant dosage for optimal effect was evaluated 3 h after stroke onset. Expression of brain-derived neurotrophic factor (BDNF), protein kinase B (Akt), and mitogen-activated protein kinases (MAPK) was determined.

RESULTS

Xenon-containing echogenic liposomes administration for up to 5 h after stroke onset reduced infract size. Treatment groups given 7 and 14 mg/kg of Xe-ELIP reduced infarct size. Behavioral outcomes corresponded to changes in infarct volume. Xe-ELIP treatment reduced ischemic neuronal cell death via activation of both MAPK and Akt. Elevated BDNF expression was shown following Xe-ELIP delivery.

CONCLUSION

This study demonstrates the therapeutic efficacy of Xe-ELIP administered within 5 h after stroke onset with an optimal dosage range of 7-14 mg/kg for maximal neuroprotection.

Prenatal hypoxia is associated with long-term retinal dysfunction in rats

Background

Intra-uterine growth restriction (IUGR) has been associated with increased predisposition to age-related complications. We tested the hypothesis that rat offspring models of IUGR would exhibit exacerbated, age-related retinal dysfunction.

Methods

Female Sprague-Dawley rats (maintained at 11.5% O₂ from gestational day 15 to 21 to induce IUGR) and control offspring (maintained at 21% O₂ throughout pregnancy) had retinal function assessed at 2 months (young) and 14 months of age (aged) with electroretinogram (ERG) recordings. Retinal anatomy was assessed by immunofluorescence.

Results

Deficits in rod-driven retina function were observed in aged IUGR offspring, as evidenced by reduced amplitudes of dark-adapted mixed a-wave V_max (by 49.3%, P<0.01), b-wave V_max (by 42.1%, P<0.001) and dark-adapted peak oscillatory potentials (by 42.3%, P<0.01). In contrast to the rod-driven defects specific to aged IUGR offspring, light adapted ERG recordings revealed cone defects in young animals, that were stationary until old age. At 2 months, IUGR offspring had amplitude reductions for both b-wave (V_max by 46%, P<0.01) and peak oscillatory potential (V_max by 38%, P<0.05). Finally, defects in cone-driven responses were further confirmed by reduced maximal photopic flicker amplitudes at 2 (by 42%, P<0.001) and 14 months (by 34%, P = 0.06) and critical flicker fusion frequencies at 14 months (Control: 42±1 Hz, IUGR: 35±2 Hz, P<0.05). These functional changes were not paralleled by anatomical losses in IUGR offspring retinas.

Conclusions

These data support that the developing retina is sensitive to stressors, and that pathways governing cone- and rod-driven function differ in their susceptibilities. In the case of prenatal hypoxia, cone- and rod-driven dysfunction manifest at young and old ages, respectively. We must, therefore, take into account the specific impact that fetal programming might exert on age-related retinal dystrophies when considering related diagnoses and therapeutic applications.

Cognitive deficits and delayed neuronal loss in a mouse model of multiple microinfarcts

Microinfarcts are a common clinical feature of the aging brain, particularly in patients with cognitive decline or vascular or Alzheimer's dementia. However, the natural history of these lesions remains largely unexplored. Here we describe a mouse (C57BL/6J) model of multiple diffuse microinfarcts induced by unilateral internal carotid artery injection of cholesterol crystals (40-70 μm). Microinfarcts were spread throughout the deep cortex, subcortical tissue, and hippocampus and were comprised of a core positive for CD68 (a marker for reactive microglia and macrophages), surrounded by large regions of glial fibrillary acidic protein-positive reactive astrogliosis. Widespread reactive gliosis, including mislocalization of the astrocytic water channel aquaporin 4 persisted long after injury, recovering only after 1 month after stroke. Within the cortex, neuronal cell death progressed gradually over the first month, from ∼35% at 3 d to 60% at 28 d after stroke. Delayed demyelination was also observed in lesions, beginning 28 d after stroke. These findings demonstrate that microinfarct development follows a distinct course compared to larger regional infarcts such as those induced by middle cerebral artery occlusion. The long-lasting gliosis, delayed neuronal loss, and demyelination suggest that the therapeutic window for microinfarcts may be much wider (perhaps days to weeks) than for larger strokes.

Glial neuronal ratio: a novel index for differentiating injury type in patients with severe traumatic brain injury

Neurobiochemical marker levels in blood after traumatic brain injury (TBI) may reflect structural changes detected by neuroimaging. This study evaluates whether correlations between neuronal (ubiquitin carboxy-terminal hydrolase-L1 [UCH-L1]) and glial (glial fibrillary acidic protein [GFAP]) biomarkers may be used as an indicator for differing intracranial pathologies after brain trauma. In 59 patients with severe TBI (Glasgow Coma Scale [GCS] score≤8) serum samples were obtained at the time of hospital admission and analyzed for UCH-L1 and GFAP. Glial neuronal ratio (GNR) was evaluated as the ratio between GFAP and UCH-L1 concentrations. A logistic regression analysis was used to identify variables associated with type of injury. GNR had a median of 0.85 and was positively correlated with age (R=0.45, p=0.003). Twenty-nine patients presented with diffuse injury and 30 with focal mass lesions as assessed by CT scan at admission and classified according to the Marshall Classification. GNR was significantly higher in the focal mass lesion group compared with the diffuse injury group (1.77 versus 0.48, respectively; p=0.003). Receiver operating characteristic curve analysis showed that GNR discriminated between types of injury (area under the curve [AUC]=0.72; p=0.003). GNR was more accurate earlier (≤12 h after injury) than later (AUC=0.80; p=0.002). Increased GNR was independently associated with type of injury, but not age, gender, GCS score, or mechanism of injury. GNR was significantly higher in patients who died, but was not an independent predictor of death. The data from the present study indicate that GNR provides valuable information about different injury pathways, which may be of diagnostic significance. In addition, GNR may help to identify different pathophysiological mechanisms following different types of brain trauma, with implications for therapeutic interventions.

Astrocytes: targets for neuroprotection in stroke

In the past two decades, over 1000 clinical trials have failed to demonstrate a benefit in treating stroke, with the exception of thrombolytics. Although many targets have been pursued, including antioxidants, calcium channel blockers, glutamate receptor blockers, and neurotrophic factors, often the focus has been on neuronal mechanisms of injury. Broader attention to loss and dysfunction of non-neuronal cell types is now required to increase the chance of success. Of the several glial cell types, this review will focus on astrocytes. Astrocytes are the most abundant cell type in the higher mammalian nervous system, and they play key roles in normal CNS physiology and in central nervous system injury and pathology. In the setting of ischemia astrocytes perform multiple functions, some beneficial and some potentially detrimental, making them excellent candidates as therapeutic targets to improve outcome following stroke and in other central nervous system injuries. The older neurocentric view of the central nervous system has changed radically with the growing understanding of the many essential functions of astrocytes. These include K+ buffering, glutamate clearance, brain antioxidant defense, close metabolic coupling with neurons, and modulation of neuronal excitability. In this review, we will focus on those functions of astrocytes that can both protect and endanger neurons, and discuss how manipulating these functions provides a novel and important strategy to enhance neuronal survival and improve outcome following cerebral ischemia.

The effect of age and cerebral ischemia on diffusion-weighted proton MR spectroscopy of the human brain

BACKGROUND AND PURPOSE

DW-MRS is a promising tool for the noninvasive identification of the cellular response to cerebral ischemia. To date, the potential confounding effects of aging and the stage of ischemia are unknown. We, therefore, examined the cross-sectional effects of age and different stages of cerebral ischemia on the diffusion of brain metabolites.

MATERIALS AND METHODS

The ADCs of 3 major metabolites, including Cho, Cr, and NAA were measured by DW-MRS in healthy younger (n = 26, 24 ± 2.2 years of age) and older (n = 17, 63 ± 7.0 years of age) adults, as well as in patients with acute (n = 7, 57 ± 4.0 years of age) and subacute (n = 12, 62 ± 7.8 years of age) cerebral ischemia.

RESULTS

Compared with younger adults, healthy older adults presented with significantly reduced ADC values of NAA (P = .000052), Cr (P = .000018), and Cho (P = .00075). Meanwhile, the ADC values of NAA (F(2,36) = 6.057, P = .006), Cr (F(2,36) = 5.634, P = .008), and Cho (F(2,36) = 8.167, P = .001) were significantly different among the acute cerebral ischemia group, subacute cerebral ischemia group, and healthy older controls. These metabolites decreased in the acute stage of cerebral ischemia but increased in the subacute stage, compared with age-matched controls.

CONCLUSIONS

The effect of age should be considered when analyzing diffusion of cerebral metabolites with DW-MRS. Our observations also suggest that metabolite diffusion data may be used to reveal changes in the intracellular environment, depending on the pathologic status of ischemia.

Live imaging of neuroinflammation reveals sex and estrogen effects on astrocyte response to ischemic injury

BACKGROUND AND PURPOSE

We sought to develop a model system for live analysis of brain inflammatory response in ischemic injury.

METHODS

Using a reporter mouse-expressing luciferase gene under transcriptional control of the murine glial fibrillary acidic protein (GFAP) promoter (GFAP-luc mice) and biophotonic/bioluminescent imaging as tools, we developed a model system for in vivo analysis of astrocyte activation/response in cerebral ischemia.

RESULTS

Analysis of photon emissions from the brains of living animals revealed marked sex differences in astrocyte response to ischemic injury. The increase in GFAP signals was significantly higher in female mice in the metestrus/diestrus period compared with male transgenic mice (1.71 x 10(7)+/-0.19 x 10(7) vs 0.92 x 10(7)+/-0.15 x 10(7), P<0.001). Similar results were obtained by quantitative immunohistochemistry (males vs females: 13.4+/-0.5 vs 16.96+/-0.64, P<0.0001). However, astrocyte activation/GFAP signals showed cyclic, estrus-dependent variations in response to ischemic injury. Physiologically higher levels of estrogen and application of pharmacologic doses of estrogen during replacement therapy attenuated GFAP upregulation after stroke. Interestingly, contrary to a positive correlation between the intensities of GFAP signals and infarct size in male mice, no such correlation was observed in any of the experimental groups of female GFAP-luc mice.

CONCLUSIONS

Our results suggest that GFAP upregulation in ischemic injury may have different functional significance in female and male experimental animals and may not directly reflect the extent of ischemia-induced neuronal damage in female GFAP-luc mice. Using a novel live imaging approach, we demonstrated that the early-phase brain inflammatory response to ischemia may be associated with sex-specific biomarkers of brain damage.

Increased expression of cysteinyl leukotriene receptor-1 in the brain mediates neuronal damage and astrogliosis after focal cerebral ischemia in rats

Cysteinyl leukotrienes are potent pro-inflammatory mediators. Cysteinyl leukotriene receptor 1 is one of the two cysteinyl leukotriene receptors cloned. We recently reported that cysteinyl leukotriene receptor 1 antagonists protected against cerebral ischemic injury, and an inducible expression of cysteinyl leukotriene receptor 1 was found in neuron- and glial-appearing cells after traumatic injury in human brain. To determine the role of cysteinyl leukotriene receptor 1 in ischemic brain injury, we investigated the temporal and spatial profile of cysteinyl leukotriene receptor 1 expression in rat brain from 3 h to 14 days after 30 min of middle cerebral artery occlusion, and observed the effect of pranlukast, a cysteinyl leukotriene receptor 1 antagonist, on the ischemic injury. We found that cysteinyl leukotriene receptor 1 mRNA expression was up-regulated in the ischemic core both 3-12 h and 7-14 days, and in the boundary zone 7-14 days after reperfusion. In the ischemic core, cysteinyl leukotriene receptor 1 was primarily localized in neurons 24 h, and in macrophage/microglia 14 days after reperfusion; while in the boundary zone it was localized in proliferated astrocytes 14 days after reperfusion. Pranlukast attenuated neurological deficits, reduced infarct volume and ameliorated neuron loss in the ischemic core 24 h after reperfusion; it reduced infarct volume, ameliorated neuron loss and inhibited astrocyte proliferation in the boundary zone 14 days after reperfusion. Thus, we conclude that cysteinyl leukotriene receptor 1 mediates acute neuronal damage and subacute/chronic astrogliosis after focal cerebral ischemia.

The metabolism of C-glucose by neurons and astrocytes in brain subregions following focal cerebral ischemia in rats

To provide insights into the effects of temporary focal ischemia on the function of neurons and astrocytes in vivo, we measured the incorporation of radiolabel from [U-14C]glucose into both glutamate and glutamine in brain subregions at 1 h of reperfusion following occlusion of the middle cerebral artery for 2 or 3 h. Under the experimental conditions used, 14C-glutamate is mainly produced in neurons whereas 14C-glutamine is generated in astrocytes from 14C-glutamate of both neuronal and astrocytic origin. Radiolabel incorporation into both amino acids was greatly decreased. The change in 14C-glutamate accumulation provides strong evidence for substantial reductions in neuronal glucose metabolism. The resulting decrease in delivery of 14C-glutamate from the neurons to astrocytes was probably also the major contributor to the change in 14C-glutamine content. These alterations probably result in part from a marked depression of glycolytic activity in the neurons, as suggested by previous studies assessing deoxyglucose utilization. Alterations in 14C-glucose metabolism were not restricted to tissue that would subsequently become infarcted. Thus, these changes did not inevitably lead to death of the affected cells. The ATP : ADP ratio and phosphocreatine content were essentially preserved during recirculation following 2 h of ischemia and showed at most only moderate losses in some subregions following 3 h of ischemia. This retention of energy reserves despite the decreases in 14C-glucose metabolism in neurons suggests that energy needs were substantially reduced in the post-ischemic brain. Marked increases in tissue lactate accumulation during recirculation, particularly following 3 h of ischemia, provided evidence that impaired pyruvate oxidation probably also contributed to the altered 14C-glucose metabolism. These findings indicate the presence of complex changes in energy metabolism that are likely to greatly influence the responses of neurons and astrocytes to temporary focal ischemia.

Bongkrekic acid ameliorates ischemic neuronal death in the cortex by preventing cytochrome c release and inhibiting astrocyte activation

Mitochondrial release of cytochrome c (cyt-c) plays a critical role in initiating cell death after cerebral ischemia. The objective of this study was to determine whether bongkrekic acid (BKA) ameliorates ischemic neuronal damage by inhibiting the release of cyt-c. These results showed that a 10min period of global ischemia caused neuronal death, increased the release of cyt-c and activated astrocytes in the cortex and CA1. BKA treatment reduced ischemic-induced neuronal death, prevented cyt-c release and inhibited astrocyte activation in the cortex, but not in the CA1. These results suggest that the neuroprotective effect of BKA is associated with its ability to prevent cyt-c release and to inhibit astrocyte activation.

Astrocytic function assessed from 1-14C-acetate metabolism after temporary focal cerebral ischemia in rats

Astrocytes play many roles essential for normal brain activity. The ability of these cells to recover after temporary focal cerebral ischemia is likely to be one important determinant of the extent of brain dysfunction and tissue damage. We have assessed astrocytic function based on the incorporation of radiolabel from 1-14C-acetate into glutamine at 1 hour of recirculation after middle cerebral artery occlusion for 2 or 3 hours in rats. There were marked differences in the response between subregions within the tissue subjected to ischemia, but the overall pattern of changes was similar after each ischemic period. The striatum, which forms part of the severely ischemic focal tissue during arterial occlusion, showed a large (44% to 68%) decrease in glutamine labeling compared with equivalent tissue from the contralateral hemisphere. In contrast, 14C-glutamine content was not significantly altered in perifocal tissue in the cerebral cortex, which was subjected to more moderate ischemia. Cortical focal tissue also was not significantly affected, but the response was much more variable between rats. In these brain subregions, the extent of recovery of the 14C-acetate metabolism after ischemia was not a good predictor of the likelihood of subsequent infarct development. Interestingly, a similar pattern of responses persisted when recirculation was extended to 4 hours. These results indicate that many astrocytes, particularly in the cortex, remain viable and capable of at least some complex oxidative metabolism during the first few hours of recirculation.

Spinal implantation of hNT neurons and neuronal precursors: graft survival and functional effects in rats with ischemic spastic paraplegia

Transient spinal ischemia, a complication associated with aortic cross-clamp may lead to spastic paraplegia. Once fully developed this deficit is permanent. Quantitative histopathological assessments and pharmacological studies show that the ischemic spasticity is secondary to the loss of lumbar GABA and glycinergic inhibitory interneurons. In the present study, we investigated whether human hNT neurons or committed Sprague-Dawley rat spinal neuronal precursors (SNPs) when grafted into previously ischemic spinal segments depleted of inhibitory neurons would restore local inhibitory tone and ameliorate spasticity. Rats with functionally and electrophysiologically defined spasticity that received spinal graft of hNT neurons or neuronal precursors and immunosuppressive treatment displayed a progressive recovery of motor function that correlated with the improvement of otherwise exacerbated peripheral motor response evoked by stimulation of motor cortex. In contrast, in control, medium-injected or oligodendrocyte-grafted animals no significant therapeutic effect was seen. Stereological quantification of grafted neurons revealed 1-2% survival at three months after transplantation. These surviving neurons displayed a robust axo-dendritic sprouting and expression of markers typical of mature neurons including NSE, NeuN and synaptophysin. In both treatment groups a subpopulation of grafted neurons developed GABA immunoreactivity. These data provide evidence that a region specific grafting of hNT neurons or other neuronally committed cells, which have a potential to develop inhibitory neurotransmitter phenotype, represent an effective treatment modality to modulate ischemia-induced spastic paraplegia.

Losses of NG2 and NeuN immunoreactivity but not astrocytic markers during early reperfusion following severe focal cerebral ischemia

The ability of glia to recover essential functions following a period of focal cerebral ischemia is likely to be one important factor influencing the severity of tissue damage that subsequently develops. In this study, we have compared changes in immunoreactivity of markers specific for astrocytes, NG2-positive glia and neurons in tissue subregions during early reperfusion following 3 h of middle cerebral artery occlusion to provide insights into possible differential susceptibility of these cell populations. Under the conditions used, infarction ultimately encompasses most of the perfusion territory of the occluded artery. Nonetheless, alterations in immunoreactivity during the first 3 h of recirculation were restricted to brain regions that had been subjected to severe ischemia. In the striatum, cellular immunoreactivity for NG2 and neuronal markers, NeuN and microtubule-associated protein 2, was greatly reduced by 1 h of reperfusion and declined further at 3 h. NG2 labeling of blood vessels in the striatum appeared post-ischemically, mimicking expression of this protein during development. Less severe changes were seen in the neuronal markers in overlying cerebral cortex. In contrast to the losses of other cellular proteins, immunoreactivity for the astrocytic marker, glial fibrillary acidic protein, was preserved in all tissue that had been subjected to severe ischemia and labeling of another astrocytic protein, glutamine synthetase, was increased by 3 h of reperfusion. These findings provide the first evidence of marked sensitivity of NG2-immunoreactivity to severe ischemia and suggest a greater initial resistance of astrocytes compared with neurons and NG2-positive glia to ischemia-reperfusion damage.

HSP70 constitutive expression in rat central nervous system from postnatal development to maturity

We studied the level of the basal (constitutive) HSP70 expression (inducible and constitutive forms) in the central nervous system (CNS) of male and female rats from the postnatal period to maturity. HSP70 levels were analyzed by immunoblotting in five different areas (cortex, hippocampus, hypothalamus, cerebellum, and spinal cord). The highest levels of HSP70 were found in juvenile rats and decreased progressively until reaching baseline levels between 2 and 4 months. A slight and nonsignificant increase in aged (2-year-old) rats compared with adult subjects was observed in some cerebral areas (cerebral cortex, hippocampus, and cerebellum). In the first weeks of postnatal development, HSP70 immunoreactivity was distributed throughout CNS sections and no specific immunopositive cells could be clearly determined. In adult animals, strong immunostaining was observed in some large neurons (Purkinje neurons and mesencephalic and spinal cord motor neurons), some perivascular and subpial astrocytes, and ependymocytes. Immunoelectron microscopy revealed that HSP70 in these cells is located in the perinuclear area and in mitochondria, rough endoplasmic reticulum, and microtubules. In neurons, strong immunolabeling was also observed in synaptic membranes. The postnatal time course of HSP70 levels and the location and size of HSP70-immunopositive cells suggest that HSP70 constitutively expressed in the rat CNS may be mainly determined by the degree of development and metabolic activity of the neural cells.

Correlation between changes in apparent diffusion coefficient and induction of heat shock protein, cell-specific injury marker expression, and protein synthesis reduction on diffusion-weighted magnetic resonance images after temporary focal cerebral ischemia in rats

OBJECT

The authors investigated the relationship between the time course of apparent diffusion coefficient (ADC) changes and stress protein induction, ischemic neuroglial damage, and cerebral protein synthesis (CPS) after temporary focal cerebral ischemia in rats.

METHODS

In Group I, ADC changes were measured on magnetic resonance (MR) images obtained during the second half of a 1-hour middle cerebral artery (MCA) occlusion, during a 1-hour reperfusion, and after 23 hours of reperfusion in rats. Immunohistochemical studies for heat shock protein (hsp) 70, glial fibrillary acidic protein (GFAP), and neuronal nuclear (NeuN) protein were performed. In Group II, CPS was assessed using autoradiographic studies obtained after occlusion. At 36 minutes of occlusion, MR imaging demonstrated significantly less ADC reduction in the frontoparietal cortex (82 +/- 9% of the contralateral hemisphere) than in the striatum (64 +/- 11%; p < 0.05). After 1 hour of reperfusion, the lesion resolved and the difference between cortex and striatum was no longer evident. After 23 hours of reperfusion, the ADC lesion recurred in striatum (76 +/- 12%) compared with frontoparietal cortex (100 +/- 11%; p < 0.05). Immunohistochemical studies showed hsp 70 expression and an increased GFAP reactivity localized in the frontoparietal cortex of the ischemic hemisphere, along with a significant drop in striatal NeuN immunoreactivity. A trend toward greater reduction in striatal CPS (53 +/- 15%) than in frontoparietal cortex CPS (78 +/- 23%) was also observed.

CONCLUSIONS

Sequential ADC maps correlate with the expression of neuroglial stress and injury markers after temporary focal ischemia in rats, distinguishing the striatum (infarct core) from the cortex (ischemic penumbra). A greater reduction in striatal CPS further supports the conclusion that the striatum is more susceptible to temporary MCA occlusion than the cortex.

High sensitivity of protoplasmic cortical astroglia to focal ischemia

The generally accepted concept that astrocytes are highly resistant to hypoxic/ischemic conditions has been challenged by an increasing amount of data. Considering the differences in functional implications of protoplasmic versus fibrous astrocytes, the authors have investigated the possibility that those discrepancies come from specific behaviors of the two cell types. The reactivity and fate of protoplasmic and fibrous astrocytes were observed after permanent occlusion of the medial cerebral artery in mice. A specific loss of glial fibrillary acidic protein (GFAP) immunolabeling in protoplasmic astrocytes occurred within minutes in the area with total depletion of regional CBF (rCBF) levels, whereas "classical" astrogliosis was observed in areas with remaining rCBF. Severe disturbance of cell function, as suggested by decreased GFAP content and increased permeability of the blood-brain barrier to macromolecules, was rapidly followed by necrotic cell death, as assessed by ultrastructure and by the lack of activation of the apoptotic protease caspase-3. In contrast to the response of protoplasmic astrocytes, fibrous astrocytes located at the brain surface and in deep cortical layers displayed a transient and limited hypertrophy, with no conspicuous cell death. These results point to a differential sensitivity of protoplasmic versus fibrous cortical astrocytes to blood deprivation, with a rapid demise of the former, adding to the suggestion that protoplasmic astrocytes play a crucial role in the pathogenesis of ischemic injury.

Cerebellar alterations induced by chronic hypoxia: an immunohistochemical study using a chick embryonic model

A model of fetal aerogenic hypoxia was developed in which fertilized chicken eggs were half-painted with melted wax and incubated under normal conditions. The cerebellum of the hypoxic chick embryos at a later stage of development (E18-20) was analyzed immunochemically. Hypoxic insult resulted in considerable neurocytological deficits of the Purkinje cells and altered glial fibrillary acid protein (GFAP) immunoreactivity in the fetal cerebellum. Purkinje cells in the hypoxic embryos were marked by small cell size, poorly developed dendrites, low cell density, deletion and ectopia. On the other hand, enhanced GFAP immunoreactivity was found in astrocytes and Bergmann glia of the hypoxic embryos. Our results indicate that chronic hypoxia in the chick fetus can cause severe disorders of neuronal development as well as glial activation. We suggest that our hypoxic model of chick embryos could be an accessible animal model for further elucidating fetal hypoxia.

Matrix remodeling after stroke. De novo expression of matrix proteins and integrin receptors

Following an ischemic insult to the central nervous system a reorganization of cells and tissue takes place as the surrounding cells attempt to limit the injury, repair the damage, and restore normal architecture of the brain. This tissue remodeling requires de novo synthesis of genes and proteins which enables cells to actively change their relationship with the existing extracellular matrix and with other cells to reorganize the damaged tissue. We have identified two key molecular components of the matrix remodeling process after focal ischemia: osteopontin (OPN) and its integrin receptor alpha v beta 3 (alpha v beta 3). OPN is initially expressed by activated macrophages and microglia in the periinfarct region (24-48 hr) and at later times (5-15 days) in the core infarct. After focal stroke the alpha v beta 3 was upregulated by astrocytes in the periinfarct region. Spatial and temporal analyses demonstrated that at 5 days after injury the alpha v beta 3-positive astrocytes were at a distance from the osteopontin-expressing macrophages; by 15 days the alpha v beta 3-expressing astrocytes were localized within an osteopontin-rich matrix. In vitro OPN was shown to induce migration of astrocytes in a Boyden chamber system. These data suggest that OPN derived from microglia at the infarct border zone (and possible macrophages in the infarct core) may serve as an "astrokine" (suggested term for astrocyte chemoattractant) to organize the astrocyte scar after focal stroke. Our data demonstrate profound changes in brain matrix remodeling after focal ischemic stroke, including the synthesis and release of matrix proteins alien to the normal brain, the expression of integrin receptors that ligate these proteins, and possibly a novel function for microglial-derived OPN in astrocyte migration after focal ischemia that may drive glial activation, organization, and repair functions.

Transcription factor nuclear factor-kappa B is activated in neurons after focal cerebral ischemia

Nuclear factor-kappa B (NF-kappaB) is a multisubunit transcription factor that when activated induces the expression of genes encoding acute-phase proteins, cell adhesion molecules, cell surface receptors, and cytokines. NF-kappaB is composed of a variety of protein subunits of which p50-and p65-kDa (RelA) are the most widely studied. Under resting conditions, these subunits reside in the cytoplasm as an inactive complex bound by inhibitor proteins, IkappaB alpha and IkappaB beta. On activation, IkappaB is phosphorylated by IkappaB kinase and ubiquitinated and degraded by the proteasome; simultaneously, the active heterodimer translocates to the nucleus where it can initiate gene transcription. In the periphery, NF-kappaB is involved in inflammation through stimulation of the production of inflammatory mediators. The role of NF-kappaB in the brain is unclear. In vitro, NF-kappaB activation can be either protective or deleterious. The role of NF-kappaB in ischemic neuronal cell death in vivo was investigated. Adult male rats were subjected to 2 hours of focal ischemia induced by middle cerebral artery occlusion (MCAO). At 2, 6, and 12 hours after reperfusion, the expression and transactivation of NF-kappaB in ischemic versus nonischemic cortex and striatum were determined by immunocytochemistry and by electrophoretic mobility gel-shift analysis. At all time points studied, p50 and p65 immunoreactivity was found exclusively in the nuclei of cortical and striatal neurons in the ischemic hemisphere. The contralateral nonischemic hemisphere showed no evidence of nuclear NF-kappaB immunoreactivity. Double immunofluorescence confirmed expression of p50 in nuclei of neurons. Increased NF-kappaB DNA-binding activity in nuclear extracts prepared from the ischemic hemisphere was further substantiated by electrophoretic mobility gel-shift analysis. Because the activation of NF-kappaB by many stimuli can be blocked by antioxidants in vitro, the effect of the antioxidant, LY341122, previously shown to be neuroprotective, on NF-kappaB activation in the MCAO model was evaluated. No significant activation of NF-kappaB was found by electrophoretic mobility gel-shift analysis in animals treated with LY341122. These results demonstrate that transient focal cerebral ischemia results in activation of NF-kappaB in neurons and supports previous observations that neuroprotective antioxidants may inhibit neuronal death by preventing the activation of NF-kappaB.

Three-dimensional measurement of cerebral microvascular plasma perfusion, glial fibrillary acidic protein and microtubule associated protein-2 immunoreactivity after embolic stroke in rats: a double fluorescent labeled laser-scanning confocal microscopic study

Early astroglial response to post-ischemic microvascular hypoperfusion may contribute to progressive cerebral microcirculatory impairment and ischemic neuronal injury. Using laser-scanning confocal microscopy and three fluorescent probes, we measured in three-dimensions cerebral microvascular plasma perfusion, astrocytic reactivity, and neuronal injury assessed by fluorescein isothiocyanate (FITC)-dextran, GFAP immunoreactivity, and microtubule associated protein-2 (MAP2) immunoreactivity, respectively, in rats subjected to 2 h of middle cerebral artery occlusion. Three-dimensional quantitative analysis revealed that 2 h of embolic ischemia resulted in a significant (P<0.05) reduction of cerebral microvascular plasma perfusion in the ipsilateral cortex and subcortex. Tissue within the ipsilateral cortex and subcortex with low plasma perfusion exhibited a significant (P<0.05) increase in GFAP immunoreactivity compared with the homologous contralateral tissue. Three-dimensional re-constructed images showed that prominent GFAP immunoreactive astrocytes surrounded large vessels with decreased plasma perfusion in downstream capillaries in the ipsilateral MCA territory when compared to the vessels in the contralateral homologous tissue. Triple fluorescence probe-stained sections showed that tissue with decreased plasma perfusion and with increased GFAP immunoreactivity was accompanied by a reduction of MAP2 immunoreactivity. The present study demonstrates that an impairment of microvascular perfusion induces an early increase in GFAP immunoreactivity, and reactive astrocytes may contribute to a further reduction of cerebral microvascular plasma perfusion. The three-dimensional quantitative imaging analysis used in the present study provides a means to investigate parenchymal cellular responses to changes of cerebral microvascular plasma perfusion after MCA occlusion.

NMDA receptor antagonism, but not AMPA receptor antagonism attenuates induced ischaemic tolerance in the gerbil hippocampus

Recent studies have shown that a brief 'pre-conditioning' ischaemic insult reduces the hippocampal cell death caused by a subsequent more severe test insult. In the present studies, we have examined the effects of the non-competitive NMDA receptor antagonist ((5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5, 10-imine, MK-801) a competitive NMDA receptor antagonist, LY202157, AMPA receptor antagonist ((3S,4aR,6R,8aR)-6-[2-(1(2)H-tetrazole-5-yl)]decahydroiso quinoline-3-carboxylic acid, LY293558), a non-competitive AMPA receptor antagonist ((-)-1-(4-amino-phenyl)-4-methyl-7,8-methylenedioxy-4,5-dihydro-3-acetyl -2,3-benzodiazepine, LY300164), and a mixed NMDA/AMPA receptor antagonist, LY246492, in a gerbil model of ischaemic tolerance. Ischaemic tolerance was induced by subjecting gerbils to a 2-min 'pre-conditioning' ischaemia (bilateral carotid occlusion) 2 days prior to a 3-min test ischaemia. The effects of MK-801 (2 mg/kg i.p.), LY293558 (20 mg/kg i.p., followed by 4 x 10 mg/kg at 3 h intervals), LY300164 (4 x 10 mg/kg i.p. at 1 h intervals), LY246492 (40 mg/kg i.p., followed by 4 x 20 mg/kg i.p. at 3 h intervals) and LY202157 (30 mg/kg i.p., followed by 4 x 15 mg/kg i.p. at 2 h intervals) were then examined in this model. Initial dosing commenced 30 min prior to the 2-min 'pre-conditioning' ischaemia. Results indicated that a 2-min 'pre-conditioning' ischaemia produced ischaemic tolerance in all cases. The non-competitive NMDA receptor antagonist, MK-801, produced a significant (P < 0.01) reduction in the induced tolerance, while the competitive NMDA receptor antagonist, LY202157, also attenuated (P < 0.05) the induction of tolerance. In contrast, two AMPA receptor antagonists (LY293558 and LY300164) and a mixed NMDA/AMPA receptor antagonist (LY246492) had no effect on the induction of tolerance. These results suggest that NMDA receptor activation, but not AMPA receptor activation is involved in the phenomenon of ischaemic tolerance.

Astrocytic demise precedes delayed neuronal death in focal ischemic rat brain

Active neuronal-glial interaction is important in the maintenance of brain homeostasis and is vital for neuronal survival following brain injury. The time course of post-ischemic astroglial dysfunction and neuronal death was studied in the spontaneously hypertensive rat (SHR) brain following permanent middle cerebral artery occlusion (MCAO). In situ hybridization with 35S-labeled riboprobes for GFAP and GLUT3 was used to monitor mRNA expression in glia and neurons. Astrocytic proteins GFAP, vimentin, S100, Glutathione-S-Transferase Yb (GST Yb) and neuronal protein TG2 were detected by immunofluorescence. Cells were co-stained with in situ end labeling (ISEL) to detect DNA fragmentation, a hallmark of cell death. GFAP mRNA expression declined rapidly in the ischemic region of the cortex and was almost absent by 12 h. Immunohistochemical studies revealed a parallel decline in the corresponding protein: a reduction in GFAP staining was apparent in the infarct after 3 h and by 24 h, there was essentially no remaining GFAP. Three other glial proteins (vimentin, S100 and GST Yb) disappeared from infarct over a similar time course. A few ISEL positive cells were observed in the infarct at 6 h, but maximal detection was not seen until 24-48 h. Most of the ISEL-positive cells were neurons, identified by co-staining with the neuronal marker TG2. Few cells expressing GFAP or other glial markers were positive at any time point. Neuronal GLUT3 mRNA declined more slowly than GFAP mRNA in the ischemic core and disappeared during the period of neuronal death. Concurrent with the loss of GFAP mRNA and protein expression in the infarct, there was a rapid rise in GFAP mRNA in the peri-infarct region of ipsilateral hemisphere and proximal region of the contralateral hemisphere. This was followed by the enhanced GFAP protein expression characteristic of reactive astrocytes, but over a significantly slower time course. These studies show that MCAO leads to a rapid decline of GFAP mRNA and glial proteins, which appears to precede the decline in neuronal mRNA and neuronal death within the infarct. Early astroglial dysfunction may play a critical role in determining the outcome of acute hypoxic-ischemic injury by compromising neuronal-glial interactions.

Neuronal death and survival in two models of hypoxic-ischemic brain damage

Two unilateral hypoxic-ischemia (HI) models (moderate and severe) in immature rat brain have been used to investigate the role of various transcription factors and related proteins in delayed neuronal death and survival. The moderate HI model results in an apoptotic-like neuronal death in selectively vulnerable regions of the brain while the more severe HI injury consistently produces widespread necrosis resulting in infarction, with some necrosis resistant cell populations showing evidence of an apoptotic type death. In susceptible regions undergoing an apoptotic-like death there was not only a prolonged induction of the immediate early genes, c-jun, c-fos and nur77, but also of possible target genes amyloid precursor protein (APP751) and CPP32. In contrast, increased levels of BDNF, phosphorylated CREB and PGHS-2 were found in cells resistant to the moderate HI insult suggesting that these proteins either alone or in combination may be of importance in the process of neuroprotection. An additional feature of both the moderate and severe brain insults was the rapid activation and/or proliferation of glial cells (microglia and astrocytes) in and around the site of damage. The glial response following HI was associated with an upregulation of both the CCAAT-enhancer binding protein alpha (microglia only) and NFkappaB transcription factors.

Osteopontin and its integrin receptor alpha(v)beta3 are upregulated during formation of the glial scar after focal stroke

BACKGROUND AND PURPOSE

Microglia and astrocytes in the peri-infarct region are activated in response to focal stroke. A critical function of activated glia is formation of a protective barrier that ultimately forms a new glial-limiting membrane. Osteopontin, a provisional matrix protein expressed during wound healing, is induced after focal stroke. The present study was performed to determine the spatial and temporal expression of osteopontin and its integrin receptor alpha(v)beta3 during formation of the peri-infarct gliotic barrier and subsequent formation of a new glial-limiting membrane.

METHODS

Spontaneously hypertensive rats (n = 19) were subjected to permanent occlusion of the middle cerebral artery and killed 3, 6, and 24 hours and 2, 5, and 15 days after occlusion. The spatial and temporal expression of osteopontin mRNA was determined by in situ hybridization, and that of osteopontin ligand and its integrin receptor alpha(v)beta3 was determined by immunohistochemistry.

RESULTS

Osteopontin mRNA was expressed de novo in the peri-infarct region from 3 to 48 hours; by 5 days osteopontin mRNA expression was restricted to the infarct. Osteopontin protein was expressed by peri-infarct microglia beginning at 24 hours and by microglia/macrophages at 48 hours in the infarct. Integrin receptor alpha(v)beta3 was expressed in peri-infarct astrocytes at 5 and 15 days.

CONCLUSIONS

Early microglial/macrophage expression of osteopontin mRNA defines the borders and final infarct area at 24 hours. At 5 days osteopontin ligand is at a distance from the peri-infarct astrocytes expressing integrin receptor alpha(v)beta3. By 15 days astrocytes expressing integrin receptor alpha(v)beta3 are localized in an osteopontin-rich region concomitant with formation of the new glial-limiting membrane. The de novo expression and interaction of osteopontin ligand with its receptor integrin alpha(v)beta3 suggest a role in wound healing after focal stroke.

The influence of delayed postischemic hyperthermia following transient focal ischemia: alterations of gene expression

We have recently shown that moderate hyperthermia, even if delayed, markedly enlarges the volume of an acute ischemic infarct. In the current study, we used in situ hybridization autoradiography to assess the effects of delayed hyperthermia on the regional expression of messenger RNA (mRNA) for the immediate early genes c-fos and c-jun, the inducible heat-shock protein 70 (hsp70) and glial fibrillary acid protein (GFAP) following 1 h of transient middle cerebral artery occlusion (MCAo) produced in rats by the insertion of an intraluminal suture. Sham-occluded rats were also studied. One day after MCAo, rats were placed into a heating chamber, where cranial temperature was either maintained at 37-38 degrees C (normothermic group) or was elevated to 40 degrees C (hyperthermic group) for 3 h. At either 2 or 24 h thereafter, brains were studied by in situ hybridization. Low-level constitutive c-fos and c-jun expression in sham-occluded rats was unaffected by delayed temperature manipulation. Prior MCAo decreased c-fos and c-jun mRNA in the affected striatum and overlying cortex. In rats studied 2 h after delayed hyperthermia, however, c-fos mRNA was markedly increased in ipsilateral cingulate cortex. By contrast, the pattern of c-jun mRNA was similar in rats with prior MCAo irrespective of delayed normothermia or hyperthermia: increased expression involved ipsilateral cingulate and paramedian cortical areas. Bilateral increases in hsp70 expression were produced by hyperthermia alone, and hsp70 mRNA was densely increased throughout the ischemic cortex and striatum following MCAo, while delayed hyperthermia altered this pattern by extending the zone of increased hsp70 message to cingulate and paramedian cortical areas at 2 h. GFAP mRNA was decreased within the previously ischemic field but increased in surrounding regions. The induction of c-fos and hsp70 message in tissue regions abutting zones of enhanced injury in brains with delayed postischemic hyperthermia indicates that these zones have been additionally stressed: these gene responses may possibly contribute to the protection of these threatened regions.

Expression of c-jun, hsp72 and gfap following repeated unilateral common carotid artery occlusion in gerbils-correlates of delayed ischemic injury

The relationship between gene responses and cumulative ischemic damage, as induced by two 10 min episodes of unilateral common carotid artery (CCA) occlusion separated by 5 h, was examined by in situ hybridization histochemistry and terminal transferase biotinylated-dUTP nick end labeling (TUNEL) in the gerbil brain. Intense cell death was noticed starting from 5 h after the second ischemic insult, reaching maximum levels in the nucleus caudate-putamen and thalamus at 12-24 h, but in the cortex and hippocampus at 2 days post-ischemia. Although tissue damage developed gradually, the region of progressive infarction could be delineated as an area deficient in gfap mRNA starting from 12 h, more apparent 24 h after repeated ischemic insults. Hsp72 mRNA was strongly increased in the cortex, caudate-putamen, ventrolateral thalamus, CA1-CA4 fields and dentate gyrus in the early stages, i.e., 15 min-5 h post-ischemia. C-jun mRNA was also elevated in these structures except for the CA1 field, where mRNA levels remained low. In the caudate-putamen and thalamus, where DNA fragmentation occurred rapidly, c-jun and hsp72 mRNAs declined to almost basal levels within 12 h after repeated ischemia, whereas in the other structures, c-jun and hsp72 mRNAs decreased in a more delayed fashion by 24-48 h. The close association between the c-jun and hsp72 mRNA decline and the onset of injury may reflect a more general disruption of the transcription process probably as the consequence of secondary metabolic deterioration. The dissociation between c-jun and hsp72 mRNA expression in the CA1 field may indicate severe ischemic injury, surpassing the range of tissue salvage.

Redox control of neuronal damage during brain ischemia after middle cerebral artery occlusion in the rat: immunohistochemical and hybridization studies of thioredoxin

Thioredoxin (TRX) is a small, multifunctional protein with a redox-active site and multiple biological functions that include reducing activity for reactive oxygen intermediates. We assayed TRX and TRX mRNA by immunohistochemical methods and hybridization experiments in the rat brain after middle cerebral artery (MCA) occlusion. During ischemia, the immunoreactivity for TRX decreased; it disappeared after MCA occlusion in the ischemic regions. It rapidly decreased and nearly disappeared at 4 and 16 hours after MCA occlusion in the lateral striatum and frontoparietal cortex, respectively. On the other hand, in the perifocal ischemic region, the penumbra, TRX immunoreactivity began to increase 4 hours after MCA occlusion and continued to increase until 24 hours after occlusion. In hybridization experiments, TRX mRNA decreased and nearly disappeared 4 hours after MCA occlusion in the lateral striatum. In the frontoparietal cortex, it decreased until 24 hours after MCA occlusion. In the perifocal ischemic region, TRX mRNA began to increase 4 hours after MCA occlusion and continued to increase until 24 hours. Northern blot analysis showed that total TRX mRNA in the operated hemispheres was induced from 8 hours and increased until 24 hours after the surgical procedures. We previously reported that recombinant TRX promotes the in vitro survival of primary cultured neurons. We now suggest that TRX in the penumbra has neuroprotective functions and that decreased levels of TRX in the ischemic core modify neuronal damage during focal brain ischemia.

Effects of chronic placental insufficiency on brain development in fetal sheep

Clinical evidence has linked intrauterine compromise such as fetal hypoxemia to poor neurologic outcome in the newborn. In this study we examined the effects of inducing chronic fetal hypoxemia by impairment of placental function on brain development in fetal sheep. Placental insufficiency was induced from 120 to 140 d of gestation (term = 145-148 d) by injection of microspheres into the umbilical circulation in five fetal sheep. Fetal partial pressure of oxygen, PaO2, was reduced from 24.1 +/- 0.5 mm Hg before embolization to 14.8 +/- 0.4 mm Hg after embolization (p < 0.05). In another three fetuses a similar level of hypoxemia (PaO2, 13.8 +/- 0.4 mm Hg) occurred spontaneously. At 140 d of gestation the fetal brains were perfused with fixatives and compared with five control fetuses for the assessment of structural and immunohistochemical alterations. Hypoxemic fetuses demonstrated severe gliosis in the cerebral cortex and reduced myelination of subcortical white matter as visualized by glial fibrillary acidic protein and myelin basic protein staining, respectively (p < 0.05). White matter lesions were observed in two fetuses. The diameter of cerebral capillaries was increased in hypoxemic fetuses (p < 0.05), but there was no change in the number of nitric oxide synthase immunoreactive cells. Growth of neuronal processes was affected in the cerebellum, where there was also a reduction in the number of Purkinje neurons (p < 0.05). These results show that a prolonged period of placental insufficiency, resulting in moderate fetal hypoxemia during the last third of gestation, can affect neurodevelopmental processes that occur late in gestation such as myelination and growth of the cerebellum. This prenatal damage could affect neural connectivity and have functional consequences after birth.

Immunoreactivity of cyclin D1/cdk4 in neurons and oligodendrocytes after focal cerebral ischemia in rat

We investigated the expression of cyclin D1 and its kinase, cdk4, after induction of focal cerebral ischemia in the rat. Brain from rats (n = 6) subjected to 2 hours of transient middle cerebral artery occlusion and 46 hours of reperfusion, and control sham-operated (n = 3) and normal (n = 2) rats were processed for dual label immunohistochemical study for cellular identification of the expression of these cell cycle proteins. Antibodies raised against microtubule-associated protein 2 and neuronal specific enolase for neurons, glial fibrillary acidic protein for astrocytes, myelin basic protein for oligodendrocytes and lectin histochemical study with the B4-isolectin for microglia were used for cell type identification. Double staining for DNA fragmentation detection (TUNEL) and expression of cyclin D1 and cdk4 also was performed. Cyclin D1 and cdk4 were selectively expressed in morphologically intact or altered neurons and oligodendrocytes localized to the ischemic tissue. Apoptotic cells were not immunoreactive to cyclin D1 and cdk4 at 46 hours after 2 hours of middle cerebral artery occlusion. The selective expression of cell cycle proteins observed in nonapoptotic ischemic postmitotic neurons and oligodendrocytes suggests a role for these proteins in cell survival after transient focal cerebral ischemia.

Induction of macrophage inflammatory protein MIP-1alpha mRNA on glial cells after focal cerebral ischemia in the rat

The distribution and cell source of macrophage inflammatory protein-1alpha (MIP-1alpha) mRNA induced by transient and permanent middle cerebral artery occlusion (MCAO) were investigated by a double in situ hybridization technique. The distribution and time course of the induction of MIP-1alpha mRNA were similar in the two MCAO models. MIP-1alpha mRNA was not detected in the sham-operated rat brain. MIP-1alpha mRNA was induced by MCAO with the peak of expression at 4-6 h after the onset of occlusion, and the signals of MIP-1alpha mRNA were observed in the ischemic core region at an earlier time point, and thereafter intensely in the penumbra of the ischemic area. The signals of MIP-1alpha mRNA were evident on Mac-1alpha mRNA-positive cells, but not on glial fibrillary acidic protein (GFAP) mRNA-positive cells, indicating that MIP-1alpha mRNA was induced in microglia/macrophages of the rat brain after focal cerebral ischemia.

Hypoxia-induced ABR change and heat shock protein expression in the pontine auditory pathway of young rabbits

The auditory brainstem response (ABR) was compared with the immunohistochemical expression of heat shock protein (HSP-72) and microtubule-associated protein 2 (MAP-2) of the brainstem auditory pathway in young rabbits subjected to hypoxic stress. Severe hypoxia for 2 h produced significant prolongation and decreased amplitude of the later component of ABR. HSP-72 expression was distinctly increased in the cochlear nucleus, but there was less induction in the inferior colliculus under severe hypoxia. MAP-2 immunostaining of neuropiles in the inferior collicular nucleus was decreased slightly after severe-long hypoxia, but cytoplasmic staining did not change. The present ABR change, which was produced by brainstem hypoxia-ischemia and acidosis, may be due to the neural cytoarchitectural derangement and less induction of stress proteins in the upper brainstem.

The heat shock stress response after brain lesions: induction of 72 kDa heat shock protein (cell types involved, axonal transport, transcriptional regulation) and protein synthesis inhibition

The cerebral stress response is examined following a variety of pathological conditions such as focal and global ischemia, administration of excitotoxins, and hyperthermia. Expression of 72 kDa heat shock protein (Hsp70) and hsp70 mRNA, the mechanism underlying induction of hsp70 mRNA involving activation of heat shock factor 1, and inhibition of cerebral protein synthesis are different aspects of the stress response considered here. The results are compared with those in the literature on induction, transcriptional regulation, expression, and cellular location of Hsp70, with a view to getting more insight into the function of the stress response in the injured brain. The present results illustrate that Hsp70 can be expressed in cells affected at various degrees following an insult that will either survive or dic as the brain lesion develops, depending on the severity of cell injury. This indicates that, under certain circumstances, synthesized Hsp70 might be necessary but not sufficient to ensure cell survival. Other situations involve uncoupling between synthesis of hsp70 mRNA and protein, probably due to very strict protein synthesis blockade, and often result in cell loss. Cells eventually will die if protein synthesis rates do not go back to normal after a period of protein synthesis inhibition. The stress response is a dynamic event that is switched on in neural cells sensitive to a brain insult. The stress response is, however, tricky, as affected cells seem to need it, have to deal transiently with it, but eventually be able to get rid of it, in order to survive. Putative therapeutic treatments can act either selectively, potentiating the synthesis of Hsp70 protein and recovery of protein synthesis, or preventing the stress response by deadening the insult severity.