Neurons In Penumbra Research Articles

Delayed recanalization at 3 days after permanent MCAO attenuates neuronal apoptosis through FGF21/FGFR1/PI3K/Caspase-3 pathway in rats

Reperfusion exceeded time window may induce ischemia/reperfusion injury, increase hemorrhagic transformation, and deteriorate neurological outcomes in ischemic stroke models. However, the increasing clinical evidences supported that reperfusion even within 6–24 h may salvage ischemic tissue and improve neurological outcomes in selected large vessel occlusion patients, without inducing serious ischemia/reperfusion injury and hemorrhagic transformation. The underlying molecular mechanisms are less clear. In present study, we demonstrated that delayed recanalization at 3 days after permanent middle cerebral artery occlusion (MCAO) decreased infarct volumes and improved neurobehavioral deficits in rats, with no increasing animal mortality and intracerebral hemorrhage. Meanwhile, we observed that endogenous neuroprotective agent fibroblast growth factor 21 (FGF21) significantly increased in serum after MCAO, but which did not synchronously increase in penumbra due to permanent MCAO. Recanalization dramatically increased the endogenous FGF21 expression on neurons in penumbra after MCAO. We confirmed that FGF21 activated the FGFR1/PI3K/Caspase-3 signaling pathway, which attenuated neuronal apoptosis in penumbra. Conversely, knockdown of FGFR1 via FGFR1 siRNA abolished the anti-apoptotic effects of FGF21, and in part abrogated beneficial effects of recanalization on neurological outcomes. These findings suggested that delayed recanalization at 3 days after MCAO improved neurological outcomes in rats via increasing endogenous FGF21 expression and activating FGFR1/PI3K/Caspase-3 pathway to attenuate neuronal apoptosis in penumbra. Delayed recanalization at 3 days after ischemic stroke onset may be a promising treatment strategy in selected patients.

Normobaric hyperoxia markedly reduces brain damage and sensorimotor deficits following brief focal ischaemia.

'True' transient ischaemic attacks are characterized not only clinically, but also radiologically by a lack of corresponding changes on magnetic resonance imaging. During a transient ischaemic attack it is assumed that the affected tissue is penumbral but rescued by early spontaneous reperfusion. There is, however, evidence from rodent studies that even brief focal ischaemia not resulting in tissue infarction can cause extensive selective neuronal loss associated with long-lasting sensorimotor impairment but normal magnetic resonance imaging. Selective neuronal loss might therefore contribute to the increasingly recognized cognitive impairment occurring in patients with transient ischaemic attacks. It is therefore relevant to consider treatments to reduce brain damage occurring with transient ischaemic attacks. As penumbral neurons are threatened by markedly constrained oxygen delivery, improving the latter by increasing arterial O2 content would seem logical. Despite only small increases in arterial O2 content, normobaric oxygen therapy experimentally induces significant increases in penumbral O2 pressure and by such may maintain the penumbra alive until reperfusion. Nevertheless, the effects of normobaric oxygen therapy on infarct volume in rodent models have been conflicting, although duration of occlusion appeared an important factor. Likewise, in the single randomized trial published to date, early-administered normobaric oxygen therapy had no significant effect on clinical outcome despite reduced diffusion-weighted imaging lesion growth during therapy. Here we tested the hypothesis that normobaric oxygen therapy prevents both selective neuronal loss and sensorimotor deficits in a rodent model mimicking true transient ischaemic attack. Normobaric oxygen therapy was applied from the onset and until completion of 15 min distal middle cerebral artery occlusion in spontaneously hypertensive rats, a strain representative of the transient ischaemic attack-prone population. Whereas normoxic controls showed normal magnetic resonance imaging but extensive cortical selective neuronal loss associated with microglial activation (present both at Day 14 in vivo and at Day 28 post-mortem) and marked and long-lasting sensorimotor deficits, normobaric oxygen therapy completely prevented sensorimotor deficit (P < 0.02) and near-completely Day 28 selective neuronal loss (P < 0.005). Microglial activation was substantially reduced at Day 14 and completely prevented at Day 28 (P = 0.002). Our findings document that normobaric oxygen therapy administered during ischaemia nearly completely prevents the neuronal death, microglial inflammation and sensorimotor impairment that characterize this rodent true transient ischaemic attack model. Taken together with the available literature, normobaric oxygen therapy appears a promising therapy for short-lasting ischaemia, and is attractive clinically as it could be started at home in at-risk patients or in the ambulance in subjects suspected of transient ischaemic attack/early stroke. It may also be a straightforward adjunct to reperfusion therapies, and help prevent subtle brain damage potentially contributing to long-term cognitive and sensorimotor impairment in at-risk populations.

Dietary fats significantly influence the survival of penumbral neurons in a rat model of chronic ischemic by modifying lipid mediators, inflammatory biomarkers, NOS production, and redox-dependent apoptotic signals

ObjectiveBrain stroke is the third most important cause of death in developed countries. We studied the effect of different dietary lipids on the outcome of a permanent ischemic stroke rat model. MethodsWistar rats were fed diets containing 7% commercial oils (S, soybean; O, olive; C, coconut; G, grape seed) for 35 d. Stroke was induced by permanent middle cerebral artery occlusion. Coronal slices from ischemic brains and sham-operated animals were supravitally stained. Penumbra and core volumes were calculated by image digitalization after 24, 48, and 72 h poststroke. Homogenates and mitochondrial fractions were prepared from different zones and analyzed by redox status, inflammatory markers, ceramide, and arachidonate content, phospholipase A2, NOS, and proteases. ResultsSoybean (S) and G diets were mainly prooxidative and proinflammatory by increasing the liberation of arachidonate and its transformation into prostaglandins. O was protective in terms of redox homeostatic balance, minor increases in lipid and protein damage, conservation of reduced glutathione, protective activation of NOS in penumbra, and net ratio of anti-to proinflammatory cytokines. Apoptosis (caspase-3, milli- and microcalpains) was less activated by O than by any other diet. ConclusionDietary lipids modulate NOS and PLA2 activities, ceramide production, and glutathione import into the mitochondrial matrix, finally determining the activation of the two main protease systems involved in programmed cell death. Olive oil appears to be a biological source for the isolation of protective agents that block the expansion of brain core at the expense of penumbral neurons.

Proliferative and Synthetic Activity of Nerve Cells after Combined or Individual Exposure to Hypoxia and Hypercapnia.

We compared synthetic and proliferative activity of brain cells in rats exposed hypoxia, hypercapnia, or both prior to experimental focal stroke. The mean number of nucleolus organizer regions in penumbra neurons did not change after normobaric hypoxia, but increased after permissive hypercapnia or hypercapnic hypoxia. These data attest to activation of proliferative and synthetic functions in nerve cells, which plays an important role in the neuroprotective mechanisms under conditions of combined exposure to hypoxia and hypercapnia.

Abstract 113: Nuclear Translocation of Neuronal Histone Deacetylase 4 (HDAC4) is Detrimental in Stroke

HDAC4 has been identified as a transcriptional corepressor that catalyzes local histone deacetylation. It is highly expressed in neurons and usually trapped in cytosol. In vitro, translocation of HDAC4 from cytosol into nucleus induced neuronal death in response to glutamate toxicity. Here we assessed the hypothesis that accumulation of nuclear HDAC4 occurs after stroke, this translocation is detrimental in stroke outcome and regulated by calcium/calmodulin-dependent protein kinase IV (CaMK IV). Wild type (WT) and CaMK IV knockout (KO) mice were subjected to transient middle cerebral artery occlusion and were sacrificed 6 hours for molecule assessments or 72 hours post stroke for outcome assessments. Primary cortical neurons underwent oxygen-glucose deprivation (OGD) and viability was measured 24 hours after OGD. Lentiviral vectors were utilized in culture and mice. Stroke induced HDAC4 nuclear translocation in WT mice as assessed by both Western blots and immunohistochemistry. Knockdown of HDAC4 improved cell viability after OGD (HDAC4 SiRNA: 87.19±7.57% vs. control: 68.09±3.83%, p&lt;0.05, n=6). Expression of a nuclear restricted HDAC4 mutant (Nuc) reduced cell viability after OGD (p&lt;0.05), in contrast, no effect was seen for a cytoplasmic mutant HDAC4 (Cyto) (Nuc: 50.32±1.36% and Cyto: 68.95±2.17% vs. GFP control: 73.25±1.28%, n=6). In vivo nuclear HDAC4 mutant expression increased hemispheric infarcts (Nuc: 57.54±1.67% vs. Cyto: 36.98±3.26%) and worsened mice performance in rotarod test (Nuc: 12.38±3.50 seconds vs. Cyto: 33.65±2.98 seconds) compared with expression of cytoplasmic HDAC4 mutant after stroke (p&lt;0.05, n=8-10). Percentage of nuclear HDAC4 positive neurons in penumbra was increased in CaMK IV KO mice (KO: 66.28±4.28% vs. WT: 37.08±2.44%, p&lt;0.05, n=4) when compared to WT after stroke. Finally, overexpression of CaMK IV increased neuronal viability after OGD; however, this effect was lost when HDAC4 was inhibited by SiRNA. In conclusion, we showed that ischemia induces HDAC4 nuclear shuttling in neurons and this translocation is deleterious in stroke outcome. Our data suggested CaMK IV inhibits HDAC4 nuclear accumulation in stroke.

MRNA redistribution during permanent focal cerebral ischemia.

Translation arrest occurs in neurons following focal cerebral ischemia and is irreversible in penumbral neurons destined to die. Following global cerebral ischemia, mRNA is sequestered away from 40S ribosomal subunits as mRNA granules, precluding translation. Here, we investigated mRNA granule formation using fluorescence in situ histochemistry out to 8 h permanent focal cerebral ischemia using middle cerebral artery occlusion in Long Evans rats with and without diabetes. Neuronal mRNA granules colocalized with PABP, HuR, and NeuN, but not 40S or 60S ribosomal subunits, or organelle markers. The volume of brain with mRNA granule-containing neurons decreased exponentially with ischemia duration, and was zero after 8 h permanent focal cerebral ischemia or any duration of ischemia in diabetic rats. These results show that neuronal mRNA granule response has a limited range of insult intensity over which it is expressed. Identifying the limits of effective neuronal stress response to ischemia will be important for developing effective stroke therapies.

In vivo imaging of induction of heat-shock protein-70 gene expression with fluorescence reflectance imaging and intravital confocal microscopy following brain ischaemia in reporter mice

Stroke induces strong expression of the 72-kDa heat-shock protein (HSP-70) in the ischaemic brain, and neuronal expression of HSP-70 is associated with the ischaemic penumbra. The aim of this study was to image induction of Hsp-70 gene expression in vivo after brain ischaemia using reporter mice. A genomic DNA sequence of the Hspa1b promoter was used to generate an Hsp70-mPlum far-red fluorescence reporter vector. The construct was tested in cellular systems (NIH3T3 mouse fibroblast cell line) by transient transfection and examining mPlum and Hsp-70 induction under a challenge. After construct validation, mPlum transgenic mice were generated. Focal brain ischaemia was induced by transient intraluminal occlusion of the middle cerebral artery and the mice were imaged in vivo with fluorescence reflectance imaging (FRI) with an intact skull, and with confocal microscopy after opening a cranial window. Cells transfected with the Hsp70-mPlum construct showed mPlum fluorescence after stimulation. One day after induction of ischaemia, reporter mice showed a FRI signal located in the HSP-70-positive zone within the ipsilateral hemisphere, as validated by immunohistochemistry. Live confocal microscopy allowed brain tissue to be visualized at the cellular level. mPlum fluorescence was observed in vivo in the ipsilateral cortex 1day after induction of ischaemia in neurons, where it is compatible with penumbra and neuronal viability, and in blood vessels in the core of the infarction. This study showed in vivo induction of Hsp-70 gene expression in ischaemic brain using reporter mice. The fluorescence signal showed in vivo the induction of Hsp-70 in penumbra neurons and in the vasculature within the ischaemic core.

Role of the NMDA receptor and iron on free radical production and brain damage following transient middle cerebral artery occlusion

Excess activation of ionotropic glutamate receptors and iron is believed to contribute to free radical production and neuronal death following hypoxic ischemia. We examined the possibility that both NMDA receptor activation and iron overload determine spatial and temporal patterns of free radical production after transient middle cerebral artery occlusion (tMCAO) in male Sprague–Dawley rats. Mitochondrial free radical (MFR) levels were maximally increased in neurons in the core at 1h and 24h after tMCAO. Early MFR production was blocked by administration of MK-801, an NMDA receptor antagonist, but not deferoxamine, an iron chelator. Neither MK-801 nor deferoxamine attenuated late MFR production in the core. Increased MFRs were observed in penumbral neurons within 6h and gradually increased over 24h after tMCAO. Slowly-evolving MFRs in the core and penumbra were accompanied by iron overload. Deferoxamine blocked iron overload but reduced MFR production only in the penumbra. Combined MK-801/deferoxamine reduced late MFR production in both core and penumbra in an additive manner. Combination therapy significantly ameliorated infarction compared with monotherapy. These findings suggest that the NMDA receptor activation and iron overload mediate late MFR production and infarction after tMCAO.

An in vitro ischemic penumbral mimic perfusate increases NADPH oxidase-mediated superoxide production in cultured hippocampal neurons

The currently accepted scheme for reactive oxygen species production during ischemia/reperfusion injury is characterized by a deleterious mitochondria-derived burst of radical generation during reperfusion; however, recent examination of the penumbra suggests a central role for NADPH-oxidase (Nox)-mediated radical generation during the ischemic period. Therefore, we utilized a novel in vitro model of the penumbra to examine the free radical profile of ischemic murine hippocampal neurons using electron paramagnetic resonance spectroscopy, and also the role of Nox in this generation and in cell fate. We report that free radical production increased ~75% at 2h of ischemia, and this increase was abolished by: (1) scavenging of extracellular free radicals with superoxide dismutase (SOD), (2) a general anion channel antagonist, or (3) the Nox inhibitor apocynin. Similarly, at 24h of ischemia, [ATP] decreased >95% and vital dye uptake increased 6-fold relative to controls; whereas apocynin, the Cl− channel antagonist 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB), or the free radical scavenger N-acetyl cysteine (NAC) each provided moderate neuroprotection, ameliorating 13–32% of [ATP]-depletion and 19–56% of vital dye uptake at 24h. Our results support a cytotoxic role for Nox-mediated free radical production from penumbral neurons during the ischemic period.

The role of Leptin on neuron apoptosis in mice with cerebral ischemia/reperfusion injury

To study the effect of Leptin on neuron apoptosis in mice with cerebral ischemia injury and its mechanism. Seventy-five mice were randomly divided into three groups. Focal cerebral ischemia/reperfusion injury model in mice was reproduced by middle cerebral artery occlusion for 2 hours followed by reperfusion. In Leptin intervention group mice were given Leptin 1 μg/g during cerebral ischemia by intraperitoneal injection. Mice in the model group were given equal amount of phosphate buffer saline. After reperfusion for 24 hours, the neuron apoptosis was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining. The mRNA and protein expression of apoptosis relative gene caspase-3 and bcl-2 were determined by reverse transcription-polymerase chain reaction (RT-PCR) and immuno histochemistry. Most of neuron necrosis was observed in cerebral ischemia center in model group. Compared with sham-operation group, neuron apoptosis rate, mRNA and protein expression of caspase-3 and bcl-2 in model group increased significantly [apoptosis rate: (68.65 ± 0.79)% vs. (4.40 ± 0.00)%, caspase-3 mRNA: 2.563 ± 0.250 vs. 0.153 ± 0.020, bcl-2 mRNA: 0.337 ± 0.100 vs. 0.125 ± 0.030, caspase-3 protein (absorbance value, A value): 0.57 ± 0.05 vs. 0.37 ± 0.03, bcl-2 protein (A value): 0.51 ± 0.04 vs. 0.35 ± 0.01, all P<0.01]. The apoptosis rate of penumbra neurons was reduced in Leptin intervention group significantly compared with model group [(42.30 ± 8.45)% vs. (68.65 ± 0.79)%, P<0.01]. Compared with model group, the mRNA and protein expression of caspase-3 in Leptin intervention group were reduced significantly [caspase-3 mRNA: 2.267 ± 0.040 vs. 2.563 ± 0.250, caspase-3 protein (A value): 0.45 ± 0.04 vs. 0.57 ± 0.05, P>0.05 and P<0.01], and the mRNA and protein expression of bcl-2 in Leptin intervention group upregulated significantly [bcl-2 mRNA: 0.662 ± 0.040 vs. 0.337 ± 0.100, bcl-2 protein (A value): 0.76 ± 0.09 vs. 0.51 ± 0.04, both P<0.01]. Leptin could reduce apoptosis of neurons through down-regulation of the expression of caspase-3 and up-regulation of the expression of bcl-2. The results suggest that Leptin plays a neuroprotective role in cerebral ischemia injury.

Effect of decompressive craniectomy on expression of NF-κB and apoptosis in brain of rats with hypoxic-ischemic brain damage

Objective To investigate the effect of decompressive craniectomy on the expression of NF-κB and apoptosis in the brain of rats with hypoxic-ischemic brain damage.Methods Sixty adult sprague-dawley rats were randomly divided into 3 groups(n=20,each):cerebral isehemia group(IS),cerebral ischemia and decompressive cranieetomy group(IS+DC),and decompressive craniectomy group (DC).The brains were collected to observe the scope of cerebral infarction by TTC staining,to examine the uhrastrueture of ischemic penumbra by an electronic microscope,to detect the expression of NF-κB by immunohistochemistry and to test the apoptosis by TUNEL.Results Compared with the other groups,the infarction volume was decreased,the damage of ischemic penumbra neurons was relieved.the expression of NF-κB was attenuated remarkably(0.0621±0.0101,P＜0.05),and the apoptotie cells were decreased significantly(0.0621±0.0101,P＜0.05)in IS+DC group.Conclusion Deeompressive craniectomy may protect the brain by increasing the expression of NF-κB and decreasing the apoptotie cells in cerebral iscbemie penumbra. Key words: Brain isehemia; Decompression,snrsical; NF-κB; Apoptosis

Preconditioning as a method of neuroprotection in a model of brain infarct

Preconditioning of ischemic and hypoxic type was investigated as a method of protecting brain against acute ischemic injury. The preconditioning methods were applied to experimental rats 24 h before the time when local brain infarct was done by middle cerebral artery occlusion (MCAO). It was found that the ischemic and hypoxic preconditioning resulted in three general morphological changes: 1) the size of infarct zone was reduced by 2.2–3.8 times compared with rats that had not been treated with the preconditioning before MCAO; 2) the preconditioning treatment retained the number of living neurons in penumbra at the level of control rats, while without the preconditioning neuronal count in the penumbra after MCAO was 29% lower; 3) the number of glial cells in penumbra was increased after MCAO by 38% compared with the control level, and continued to increase under the preconditioning treatment up to 60%, that suggests an important role of neuroglia in neuroprotection. Selective blockers of ATP2dependant K+2channels (52hydroxydecanoate and glibenclamide) completely abolished the neuroprotective effects of the preconditioning.

Dynamics of morphological changes after transplantation of mesenchymal stem cells in rat brain provoked by stroke

The study of the dynamic of morphological changes in the brain after ischemic stroke is very important for the preclinical trial of mesenchymal stem cell (MSC) therapy for this widespread disease. Experiments were carried out in inbred Wistar-Kyoto rats. MSCs were isolated, expanded in culture, and labeled with the vital fluorescent dye PKH-26. Animals were subjected to middle cerebral artery occlusion (MCAO), followed by an injection of 5 × 106 rat MSCs into the tail vein on the day of MCAO. Control group animals received PBS injection (negative control). Animals were sacrificed at 1, 2, 3, and 5 days and 1, 2, 4, and 6 weeks after the operation. MSCs were revealed in the brain on the third day after transplantation as being distributed around brain vessels both in the ipsilateral and contralateral hemispheres. This pattern of distribution remained unchanged throughout six weeks of observation. It was demonstrated that the inflammation process and scar formation in the cell therapy group were progressing at a rate 25–30% faster than in the control group. MSC transplantation stimulated endogenous stem cell proliferation in the subependimal zone of lateral ventricles (subventricular zone). In addition, MSC injection caused a neuroprotecting effect; most penumbra neurons retained their structure in cell therapy group, whereas in control group, animal penumbra neurons died or showed signs of serious damage.

Prolactin is involved in glial responses following a focal injury to the juvenile rat brain

A cerebral growth hormone axis is activated following brain injury in the rat and treatment with growth hormone is neuroprotective. We have now investigated whether the closely related prolactin axis has similar properties following injury to the developing rat brain. From one day following a unilateral hypoxic ischemic injury, prolactin immunoreactivity was increased in the affected cortex parallel to the development of the injury ( P<0.001). Initial prolactin and prolactin receptor staining on penumbral neurons progressively decreased whereas astrocytes remained strongly immunopositive. Reactive microglia also became strongly prolactin immunoreactive. Unlike growth hormone, central treatment with prolactin failed to rescue neurons in this paradigm. This was confirmed in vitro; rat prolactin failed to protect neurons under conditions for which growth hormone was neuroprotective. However, prolactin had trophic and pro-proliferative effects on glia ( P<0.001). We confirmed the expression of the prolactin receptor in vitro by reverse transcriptase polymerase chain reaction, and show its strong association with astrocytes as compared with neurons by immunocytochemistry. In summary, we show for the first time that hypoxia ischemia induces a robust activation of the prolactin axis in regions of the cerebral cortex affected by injury. The lack of neuroprotective properties in vivo and in vitro indicates that, unlike growth hormone, prolactin is not directly involved in neuronal rescue in the injured brain. Its strong relation to glial reactions and its gliatrophic effects suggest that the prolactin axis is primarily involved in a gliogenic response during recovery from cerebral injury.

Irreversible aggregation of protein synthesis machinery after focal brain ischemia

Focal brain ischemia leads to a slow type of neuronal death in the penumbra that starts several hours after ischemia and continues to mature for days. During this maturation period, blood flow, cellular ATP and ionic homeostasis are gradually recovered in the penumbral region. In striking contrast, protein synthesis is irreversibly inhibited. This study used a rat focal brain ischemia model to investigate whether or not irreversible translational inhibition is due to abnormal aggregation of translational complex components, i.e. the ribosomes and their associated nascent polypeptides, protein synthesis initiation factors and co-translational chaperones. Under electron microscopy, most rosette-shaped polyribosomes were relatively evenly distributed in the cytoplasm of sham-operated control neurons, but clumped into large abnormal aggregates in penumbral neurons subjected to 2 h of focal ischemia followed by 4 h of reperfusion. The abnormal ribosomal protein aggregation lasted until the onset of delayed neuronal death at 24-48 h of reperfusion after ischemia. Biochemical study further suggested that translational complex components, including small ribosomal subunit protein 6 (S6), large subunit protein 28 (L28), eukaryotic initiation factors 2alpha, 4E and 3eta, and co-translational chaperone heat-shock cognate protein 70 (HSC70) and co-chaperone Hdj1, were all irreversibly clumped into large abnormal protein aggregates after ischemia. Translational complex components were also highly ubiquitinated. This study clearly demonstrates that focal ischemia leads to irreversible aggregation of protein synthesis machinery that contributes to neuronal death after focal brain ischemia.

Cyclophilin C-Associated Protein and Cyclophilin C mRNA are Upregulated in Penumbral Neurons and Microglia after Focal Cerebral Ischemia

Immunophilin ligands, such as cyclosporin A and FK506, have neuroprotective effects in experimental stroke models, although the precise mechanism is unclear. Cyclophilin C-associated protein (CyCAP) is a natural cellular ligand for the immunophilin, cyclophilin C, and has a protective effect against endotoxins by downmodulating the proinflammatory response. Expressions of CyCAP and cyclophilin C mRNA in a rat middle cerebral artery (MCA) occlusion ischemia model were investigated by Northern blotting and in situ hybridization. Both CyCAP and cyclophilin C mRNAs were ubiquitously distributed in the neurons of the normal brain. Expression increased in neurons of the periinfarct zone up to 7 days after MCA occlusion. The neuronal distribution was confirmed by counterimmunostaining of NeuN. Both mRNAs were predominantly expressed in microglia of the ischemic core at 7 days, confirmed by immunostaining with the microglial marker, ED1. The quantification of CyCAP and cyclophilin C mRNAs at 7 days by Northern blot analysis showed the 8.5-fold increase (P<0.005, n=6) and 6.8-fold increase (P<0.005, n=6), respectively, in ischemic core compared with control. The coincidence of CyCAP and cyclophilin C expression in neurons and microglia suggests distinct roles in each cellular population. In particular, the early increase in penumbral neurons might be related to protection in periinfarct neurons.

Neuroprotective and thrombolytic agents: advances in stroke treatment.

Acute ischemic stroke is a complex, heterogeneous and debilitating disorder, which leads to death or disability. Recent research into the mechanism of stroke has identified a relatively short window of opportunity, during which a population of neurons surrounding the ischemic core remain viable for a number of hours following stroke onset. These penumbral neurons can be salvaged if treatment is begun within 3-6 hours following the onset of ischemia. This understanding of stroke mechanisms has lead to the development of promising new therapies currently under study. To maximize the potential benefits of these new therapies, neurologists, neuroscience nurses and other healthcare professionals need to assume the responsibility of effectively implementing treatment and to educate their peers and the public about the symptoms of stroke and the need to seek immediate medical assistance.

A putative role for platelet-derived growth factor in angiogenesis and neuroprotection after ischemic stroke in humans.

Growth factors control two important processes in infarcted tissue, ie, angiogenesis and gliosis. We recently reported that transforming growth factor-beta1 (TGF-beta1) might be involved in angiogenesis after ischemic stroke in humans; here we present data of an extensive study on platelet-derived growth factor (PDGF) and its receptors. We studied brain samples from patients who suffered from ischemic stroke for the expression of mRNA encoding PDGF-A, PDGF-B, and PDGF receptors (PDGF-R). Proteins were examined by Western blotting and immunohistochemistry using the antibodies to PDGF-AB, PDGF-BB, PDGF-R alpha, and PDGF-R beta. At the mRNA level, PDGF-A and PDGF-B were expressed mainly in neurons in penumbra. PDGF-R mRNA was strongly expressed in some astrocytes but mainly in type III/IV neurons in infarct and penumbra. The least expression was seen in the contralateral hemisphere (P<.001). In contrast, both PDGF-AB and PDGF-BB immunoreactive products were present in most cell types: PDGF-R alpha and PDGF-R beta mainly on neurons, and PDGF-R beta on some endothelial cells, with less staining of all the isoforms in the contralateral hemisphere. On Western blots, PDGF-AB and -BB were expressed more within white matter than gray matter of infarct/penumbra, whereas both isoforms of receptor were expressed mainly in gray matter compared with contralateral hemisphere. There was no or very weak expression of the receptor in white matter. PDGF proteins are highly expressed in white matter, suggesting that PDGF may exert its function in white matter participating either in regeneration of damaged axons or in glial scar formation. PDGF-BB and its receptor expressed on microvessel endothelial cells might be involved in angiogenesis after stroke. Thus, PDGF is likely to be angiogenic and neuroprotective in stroke.

The effect of non-competitive N-methyl-D-aspartate receptor antagonism on cerebral oedema and cerebral infarct size in the aging ischaemic brain.

Although vulnerability to ischemic neuronal injury is enhanced with age, the aging brain may be less amenable to neuroprotection as a result of quantitative and qualitative changes in the NMDA receptor. In addition, the elderly may be less tolerant of adverse effects of neuroprotective drugs and this might ultimately limit therapeutic potential in human stroke. However, antagonism of the excitotoxic effects of glutamate by parenteral administration of the non competitive NMDA antagonist magnesium has been well tolerated and has shown to be neuroprotective in young animal models of stroke and head injury. We therefore evaluated the potential of magnesium chloride to reduce ischemic neuronal injury in aged rodents subjected to permanent occlusion of the middle cerebral artery. Treatment with magnesium chloride induced hypotension and hyperglycaemia in both adult and aged rats and did not reduce ischemic neuronal injury or cerebral edema. However, despite these adverse haemodynamic and biochemical effects, which may augment cerebral infarct size, ischemic damage was not exacerbated in the treated groups, suggesting that magnesium has the potential to salvage penumbral neurons and that inotropic support and maintenance of normoglycaemia may permit realisation of its neuroprotective potential. This may have important implications for future clinical stroke trials.