Early recovery of protein synthesis following ischemia in hippocampal neurons with induced tolerance in the gerbil

Summary Following brief cerebral ischemia, tolerance to subsequent ischemia is induced in the hippocampal neurons. In this experiment, recovery of protein synthesis was investigated autoradiographically in gerbils with induced tolerance. The animals were subjected to single forebrain ischemia for 5 min (5-min ischemia group) or 2 min (2-min ischemia group). To observe the effect of tolerance acquisition, double forebrain ischemia (double ischemia group), 2-min ischemia followed by 5-min ischema was induced 2 days later. At various recircultion periods (90 min, 6 h, 1 day, and 4 days following ischemia), animals received a single dose of Lxxx-[2,3-³H]valine. In the 5-min ischemia group, protein synthesis in the CA1 sector was severely suppressed during the period from 90 min to 1 day of recirculation and never returned to the normal level even at 4 day of recirculation. In the 2-min ischemia group, protein synthesis recovered gradually and returned to near normal at 4 days of recirculation. On the other hand, in the double ischemia group, recovery of protein synthesis in the CA1 sector was rapid. At 1 day of recirculation, protein synthesis returned to near normal. Protein synthesis in the CA2 sector was inhibited during the 4 days of recirculation in this group. The present study revealed an early recovery of protein synthesis in the hippocampal CA1 neurons in the gerbil with induced tolerance. We suggest that recovery of protein synthesis is essential for the survival of neurons exposed to transient ischemia.Supported by a Grant-in Aid for Scientific Research on Priority Areas, Ministry of Education, Science and Culture, Japan, and by a research grant for cardiovascular diseases from the Ministry of Health and Welfare, Japan     

Melatonin administration protects CA1 hippocampal neurons after transient forebrain ischemia in rats

Melatonin administered at the beginning of cerebral reperfusion protected CA1 neurons against 10, 20 and 30 min of transient forebrain ischemia. Intraperitoneal injections of saline or melatonin (10 mg/kg) were given after 0, 2 and 6 h, or 1, 2 and 6 h of cerebral reperfusion, or 30 min prior to ischemia. One week later, quantitative histological analysis demonstrated that CA1 neuronal density was significantly increased in the melatonin groups that were treated at 0, 2, 6 h compared to the saline-treated controls. Ischemic protection of CA1 was lost in the animals in which the melatonin treatment was delayed by 1 h, or given 30 min prior to the ischemia.     

Regional impairment of protein synthesis following brief cerebral ischemia in the gerbil

Summary Regional cerebral protein synthesis following brief ischemia was investigated in the Mongolian gerbil, utilizing l-[methyl-¹⁴C]methionine autoradiography. Transient ischemia was induced for 1,2 or 3 min. At various recirculation periods up to 48 h, animals received a single dose of l-[methyl-¹⁴C]-methionine and then were terminated 35 min later. Sham-operated animals showed a normal pattern of amino acid incorporation into the proteins of the brain. Following 1-min ischemia, the pattern of protein synthesis was similar to that in the sham-operated gerbils. Ischemia for 2 min, however, caused marked inhibition of protein synthesis in the neocortex, striatum, hippocampal CA1 sector and the thalamus at 1 h of recirculation. Extensive recovery of protein synthesis was found in the neocortex, the striatum, the hippocampal CA1 sector and the thalamus at 5–24 h of recirculation, but, a slight inhibition was detectable in the hippocampal CA1 sector in one of six animals. This inhibition had fully recovered at 48 h of recirculation. Following 3-min ischemia, severe impairment of protein synthesis was found in the neocortex, striatum, the whole hippocampus and the thalamus. After 5–24 h of recirculation, the protein synthesis in these regions had gradually recovered, except that complete lack of amino acid incorporation was seen in the hippocampal CA1 subfield. This impairment of protein synthesis in the hippocampal CA1 sector was not recovered at 48h of recirculation. Morphological study indicated that 2-min ischemia did not produce any significant neuronal damage in the brain, whereas gerbils subjected to 3-min ischemia revealed a mild neuronal damage in the hippocampal CA1 sector. The present study indicates that even non-lethal ischemia can produce a severe inhibition of protein synthesis in the selectively vulnerable regions during the early stage of recirculation.     

Delayed neuronal death in hippocampal CA1 pyramidal neurons after forebrain ischemia in hyperglycemic gerbils: amelioration by indomethacin

Hyperglycemia worsens ischemic-induced neuronal damage. Many reports argue the delayed neuronal cell death (DND) after forebrain ischemia in gerbils is due to apoptosis. We examined the effects of hyperglycemia and indomethacin on DND after forebrain ischemia in gerbils. Complete occlusion of both common carotid arteries was performed for 3.5 min followed by declamping and reperfusion. Blood glucose levels were maintained at 25-30 mmol/1 for 24 h after reperfusion in the hyperglycemic groups. We examined morphological changes consistent with DND using Nissel-stained sections and DNA fragmentation using TUNEL staining, at 12, 24, 36, 48, 60, 72, 84, 96, 108, 120 h, and 7 days after reperfusion. DND was noted 96-120 h after ischemia in normoglycemic group. Hyperglycemia enhanced the development of DND at an earlier stage (48-84 h after ischemia). TUNEL positive neurons were detected 72-108 h after reperfusion in normoglycemic group, but very few TUNEL positive neurons were detected in hyperglycemic group at 36-48 h. Indomethacin reduced the number of TUNEL-positive cells in normoglycemia and completely inhibited the appearance of TUNEL-positive cells under hyperglycemia. The number of viable neurons at 7 days after ischemia was markedly higher in indomethacin-treated groups than vehicle-treated group. Our results indicate that hyperglycemia worsens DND after forebrain ischemia in gerbils but such process is not associated with DNA fragmentation. Our results also showed that indomethacin provides a neuroprotective effect in normo- and hyperglycemic conditions.     

Nitrotyrosine immunoreactivity in gerbil hippocampal CA1 region after transient forebrain ischemia

We examined whether or not nitration of tyrosine residues takes place in the gerbil hippocampal CA1 region after transient forebrain ischemia. The nitration of tyrosine residues to produce nitrotyrosine is a footprint of peroxynitrite, a reaction product of nitric oxide (NO) with superoxide. Nitrotyrosine immunoreactivity had been detected in the CA1 region from the early stage in a reperfused brain at 30 min after transient ischemia until DNA fragmentation and neuronal death appeared at 4 days after transient ischemia. In electron microscopy, we detected, prominently, nitrotyrosine immunoreactivity after transient ischemia in the cytoplasm of the CA1 neurons. Therefore, it is considered that the nitration of tyrosine residues by peroxynitrite may be closely related to apoptosis after transient ischemia.     

Transport of fragmented DNA in apical dendrites of gerbil CA1 pyramidal neurons following transient forebrain ischemia

Transport of fragmented DNA in apical dendrites of the CA1 pyramidal neurons of gerbil hippocampus is observed in the apoptotic process following transient forebrain ischemia. The time-course of specific DNA fragmentation was examined after the ischemic insult by in situ nick-end-labeling method and fluorescence detection technique by DAPI. Although the role of the fragmented DNA movement is unclear, the transport mechanism of fragmented DNA is still active in the late phase of apoptotic process.     

Release of cytochrome c from mitochondria to cytosol in gerbil hippocampal CA1 neurons after transient forebrain ischemia

We examined cytosolic cytochrome c in gerbil hippocampal CA1 and CA3 regions after induction of 5-min ischemia by immunoblotting. In the CA1 region, cytochrome c was detected in the cytosolic fraction from 1 to 6 h after ischemia by Western blotting, while it was not detected in the CA3 region. Following intraventricular administration of cyclosporin A (CsA), detectable cytosolic cytochrome c was dramatically decreased, and about 80% of CA1 neurons survived after ischemia. The present studies demonstrate that cytochrome c is translocated from mitochondria to the cytosol in the early stage of delayed neuronal cell death, and suggest the involvement of the mitochondrial permeability transition.     

Persistent inhibition of protein synthesis precedes delayed neuronal death in postischemic gerbil hippocampus

Summary Regional cerebral protein synthesis was investigated in the Mongolian gerbil during recovery from forebrain ischemia produced by bilateral common carotid artery occlusion for 5 min. At various recirculation periods up to 72 h animals received a single dose ofl-(3,5-³H)tyrosine and were killed 30 min later. Brains were processed for autoradiography using the stripping film technique. During the initial 30 min of recirculation autoradiographs revealed an almost complete inhibition of protein synthesis in all forebrain structures with the exception of the medio-dorsal thalamic nuclei. Between 30 min and 12 h of recirculation amino acid incorporation was completely restored in neurons of the cerebral cortex, basal ganglia, hippocampal CA3 and CA4 zones and the dentate gyrus. In CA1, early (90-min postischemia) and progressive recovery of a few irregularly dispersed neurons was observed, but the vast majority of pyramidal cells never regained their normal biosynthetic activity. Between 3 and 6 h of recirculation CA1 neurons showed faint labeling, followed by a secondary deterioration resulting in complete lack of incorporation within 12 h after restoration of blood flow. Autoradiographs at all subsequent time points exhibited persistent inhibition of protein synthesis in CA1 until neuronal necrosis occurred 2–3 days later. Thus, in contrast to ischemia-resistant cell populations with rapid progressive and complete restoration of protein synthesis, hippocampal neurons undergoing delayed necrosis are characterized by an early incomplete recovery immediately followed by a secondary persistent inhibition.Supported by the Deutsche Forschungsgemeinschaft (SFB 70)     

Selective proteasomal dysfunction in the hippocampal CA1 region after transient forebrain ischemia.

Delayed neuronal death in the hippocampal CA1 region after transient forebrain ischemia may share its underlying mechanism with neurodegeneration and other modes of neuronal death. The precise mechanism, however, remains unknown. In the postischemic hippocampus, conjugated ubiquitin accumulates and free ubiquitin is depleted, suggesting impaired proteasome function. The authors measured regional proteasome activity after transient forebrain ischemia in male Mongolian gerbils. At 30 minutes after ischemia, proteasome activity was 40% of normal in the frontal cortex and hippocampus. After 2 hours of reperfusion, it had returned to normal levels in the frontal cortex, CA3 region, and dentate gyrus, but remained low for up to 48 hours in the CA1 region. Thus, the 26S proteasome was globally impaired in the forebrain during transient ischemia and failed to recover only in the CA1 region after reperfusion. The authors also measured 20S and 26S proteasome activities directly after decapitation ischemia (at 5 and 20 minutes) by fractionating the extracts with glycerol gradient centrifugation. Without adenosine triphosphate (ATP), only 20S proteasome activity was detected in extracts from both the hippocampus and frontal cortex. When the extracts were incubated with ATP in an ATP-regenerating system, 26S proteasome activity recovered almost fully in the frontal cortex but only partially in the hippocampus. Thus, after transient forebrain ischemia, ATP-dependent reassociation of the 20S catalytic and PA700 regulatory subunits to form the active 26S proteasome is severely and specifically impaired in the hippocampus. The irreversible loss of proteasome function underlies the delayed neuronal death induced by transient forebrain ischemia in the hippocampal CA1 region.     

Influence of oxidative stress on induced tolerance to ischemia in gerbil hippocampal neurons

We investigated whether reversible oxidative stress induced by the administration of the superoxide dismutase inhibitor, diethyldithiocarbamate, could induce tolerance to subsequent cerebral ischemia in gerbil hippocampal neurons. Mature male gerbils received intraperitoneal injections of diethyldithiocarbamate (1.0 g/kg), which led to reduced superoxide dismutase activity and increases in thiobarbituric acid-reactive substance in the brain. Cerebral ischemia was produced by occluding the bilateral common carotid arteries for 5 min, either 2 or 4 days after diethyldithiocarbamate injection. One week after ischemia, samples from each brain were stained with hematoxylin-eosin to evaluate ischemic neuronal damage in the hippocampal CA1 sector. Diethyldithiocarbamate treatment 4 days before ischemia had significant protective effects against cerebral ischemia, while diethyldithiocarbamate 2-day pretreatment and vehicle treatment failed to show neuroprotection. Biochemical examinations showed a clear induction of heat shock protein 72 and a significant increase in manganese-containing superoxide dismutase in the hippocampus in animals treated with diethyldithiocarbamate 4 days prior to ischemia. These results suggested that the oxidative stress caused by diethyldithiocarbamate could induced tolerance to ischemia in the gerbil brain, and that the increase in the biosynthesis of manganese-containing superoxide dismutase and heat shock protein 72 could provide a biochemical explanation of the tolerance induced under these conditions.     

Expresgions of nerve growth factor and p75 low affinity receptor after transient forebrain ischemia in gerbil hippocampal CA1 neurons

Expressions of nerve growth factor (NGF) and low affinity p75 NGF receptor (p75 NGFR) in gerbil hippocampal neurons after 3.5-min transient forebrain ischemia were studied. Most hippocampal CAI neurons were lost (neuronal density = 44 ± 12/mm) at 7 days after recirculation, while no cell death was found in the sham-control neurons (220 ± 27/min). NGF immunoreactivity was normally present in the sham-control hippocampal neurons. However, it decreased in hippocampal CAI neurons, and slightly decreased in the neurons of CA3 and dentate gyrus areas from 3 hr after recirculation. By 7 days, NGF immunoreactivity returned almost completely to the sham-control level in the CA3 and dentate gyrus neurons but decreased markedly in the CAI neurons. In contrast, p75 NGFR immunoreactivity was scarcely present in the sham-control hippocampal neurons but was induced from 1 hr after recirculation in the CAI and CA3 neurons and from 3 hr in the dentate gyrus. At 7 days, p75 NGFR immunoreactivity was expressed greatly in the surviving CAI neurons and the reactive astrocytes but was not seen in the other hippocampal neurons. The markedly decreased NGF and greatly induced p75 NGFR immunoreactivity found in the CAI neurons after transient forebrain ischemia suggests that NGF and p75 NGFR may be involved in the mechanism of delayed neuronal death. © 1995 Wiley-Liss, Inc.     

DNA fragmentation in the CA2 sector of gerbil hippocampus following transient forebrain ischemia

It has been reported that following transient forebrain ischemia in the gerbil, "delayed neuronal death" and "reactive change" occur in hippocampal CA1 and CA2 sectors, respectively. In the present study, using the gerbil transient forebrain ischemia model, we examined brain sections after various recirculation periods and demonstrated, employing the in situ nick-end labeling (TUNEL) method, a nuclear DNA fragmentation in the damaged CA2 neurons.     

Elevation of Na+-K+ ATPase immunoreactivity in GABAergic neurons in gerbil CA1 region following transient forebrain ischemia

In a previous study, we suggested that GABAergic neurons might be resistant to ischemic insult, because of the maintenance of the GABA shunt, which is one of the ATP synthetic pathways in neurons. In the present study, we identified Na(+)-K(+) ATPase immunoreactivity in the gerbil hippocampus in order to determine whether changes in Na(+)-K(+) ATPase immunoreactivity correlate with GABA shunt following ischemic insult. At 12 h after ischemia-reperfusion, Na(+)-K(+) ATPase immunoreactivity accumulated in some neurons in the CA1 region. However, the protein content of Na(+)-K(+) ATPase was not altered. Interestingly, the density of Na(+)-K(+) ATPase immunoreactivity in neurons and the protein content in the CA1 region was intensified in the 24 h post-ischemic group. As a result of double immunofluorescence study, Na(+)-K(+) ATPase immunoreactive neurons were identified with GABAergic neurons. Therefore, our findings suggest that the increase of Na(+)-K(+) ATPase in GABAergic neurons may be able to explain the resistance of these cells to ischemic insult, and support our previous hypothesis that GABA may play an important role as a metabolite in the survival of GABAergic neurons after ischemic insult.     

Effect of transient forebrain ischemia on superoxide dismutases in gerbil hippocampus

Substantial generation of oxygen-derived free radicals has been implicated in pathophysiology of ischemic brain damage. Immunoreactive mitochondrial manganese and cytosolic copper-zinc superoxide dismutases, initial and essential enzymes to scavenge superoxide radical anions, increased in the gerbil hippocampal neurons after transient forebrain ischemia. Neuronal cells responded to oxidative stress in ischemia and induced the protective mechanism to increase superoxide dismutases.     

Effect of ischemic preconditioning on antioxidant status in the gerbil hippocampal CA1 region after transient forebrain ischemia

Ischemic preconditioning (IPC) is a condition of sublethal transient global ischemia and exhibits neuro-protective effects against subsequent lethal ischemic insult. We, in this study, examined the neuroprotective effects of IPC and its effects on immunoreactive changes of antioxidant enzymes including superoxide dismutase (SOD) 1 and SOD2, catalase (CAT) and glutathione peroxidase (GPX) in the gerbil hippocampal CA1 region after transient forebrain ischemia. Pyramidal neurons of the stratum pyramidale (SP) in the hippocampal CA1 region of animals died 5 days after lethal transient ischemia without IPC (8.6%(ratio of remanent neurons) of the sham-operated group);however, IPC prevented the pyramidal neurons from subsequent lethal ischemic injury (92.3%(ratio of remanent neurons) of the sham-operated group). SOD1, SOD2, CAT and GPX immunoreactivities in the sham-operated animals were easily detected in pyramidal neurons in the stratum pyramidale (SP) of the hippocampal CA1 region, while all of these immunoreac-tivities were rarely detected in the stratum pyramidale at 5 days after lethal transient ischemia without IPC. Meanwhile, their immunoreactivities in the sham-operated animals with IPC were similar to (SOD1, SOD2 and CAT) or higher (GPX) than those in the sham-operated animals without IPC. Furthermore, their immunoreactivities in the stratum pyramidale of the ischemia-operated animals with IPC were steadily maintained after lethal ischemia/reperfusion. Results of western blot analysis for SOD1, SOD2, CAT and GPX were similar to immunohistochemical data. In conclusion, IPC maintained or increased the expression of antioxidant enzymes in the stratum pyramidale of the hippocampal CA1 region after subsequent lethal transient forebrain ischemia and IPC exhibited neuroprotective effects in the hippocampal CA1 region against transient forebrain ischemia.     

Antioxidant-like protein 1 is altered in non-pyramidal cells and expressed in astrocytes in the gerbil hippocampal CA1 region after transient forebrain ischemia

In the present study, we observed chronological changes of antioxidant-like protein 1 (AOP-1) in the gerbil hippocampal CA1 region after 5 min of transient forebrain ischemia using immunohistochemistry and western blot. AOP-1 was significantly altered in the CA1 region after transient ischemia. In the sham-operated group, AOP-1 immunoreactivity was detected in pyramidal and non-pyramidal cells of the CA1 region. At 30 min after ischemic insult, AOP-1 immunoreactivity and protein level was decreased in the CA1 region. At 12 h after ischemic insult, AOP-1 immunoreactivity and protein level was highest in this region. At this time, after ischemia, AOP-1 immunoreactivity in non-pyramidal cells was high compared to the sham-operated group. Based on double immunofluorescence study, AOP-1-immunoreactive neurons were identified as GABAergic, which were stained with GAD or parvalbumin. Thereafter, AOP-1 immunoreactivity and protein levels were decreased time-dependently. From 4 days after ischemic insult, AOP 1 immunoreactivity was generally expressed in astrocytes. Five days after ischemic insult, AOP-1 immunoreactivity and protein level was increased again to 1.4 folds compared to that of the sham-operated group. In brief, AOP-1 immunoreactivity was increased in GABAergic non-pyramidal cells in the hippocampal CA1 region at early time after ischemic insult and was expressed in astrocytes at late time after ischemia. This result suggests that AOP-1 may be important role in homeostasis of GABAergic neurons because these neurons are resistant to ischemic damage.     

Cholinergic deafferentation prevents delayed neuronal death of the hippocampal CA1 pyramidal neurons after transient forebrain ischaemia

Abstract

The relation between CA1 neurons, fimbria-fornix and cholinergic neurons of the basal forebrain was examined with the aid of Acetylcholine esterase (AChE) staining, Woelcke's staining and immunohistochemistry of Choline-acetyl transferase (ChAT). The transected side of the hippocampus was poorly stained by AChE two weeks after the transection, when the ipsilateral medial septum ChAT-positive neurons were reduced, but showed good recovery with AChE six weeks later.’ Nerve growth factor (NGF) was added at a dose of 10 jig/100 \i\ immediately after the aspiration>, and after that once per week with cisternal puncture. As a result, ipsilateral medial septum ChAT-positive neurons were preserved, but cross innervation with relation to hypertrophy of the cholinergic neurons was not detectable even six weeks after the transection. Furthermore, delayed CA1 neuronal death on the transected side of the hippocampus following occlusion of four vessels for 30 minutes was not detectable two weeks after the operation, although neuronal density was reduced after six weeks. The density of neurons on the transected side of the hippocampus in the CA1 subfield with treated NGF had not decreased significantly six weeks later. Therefore, we suspect that the input from cholinergic fibres must be transported to the hippocampal pyramidal neurons responding to NCF, and it was confirmed that cholinergic deafferentation prevents the delayed neuronal death of CA1 pyramidal neurons during transient ischaemia. [Neurol Res 1992; 14: 340-344]     

Nitric oxide synthase inhibitor reduces delayed neuronal death in gerbil hippocampal CA1 neurons after transient global ischemia without reduction of brain temperature or extracellular glutamate concentration

We planned a study to determine whether or not the mechanism of nitric oxide (NO) neurotoxicity involves the elevation of extracellular glutamate or changes of brain temperature in the pathogenesis of delayed neuronal death of gerbil hippocampal CA1 neurons following 5-min transient forebrain ischemia. Intraventricular injection of 5 μl of 5.0 mg/ml N^ω-nitro-l-arginine (LNNA) significantly preserved neuronal density in the central part of the CAI region examined 7 days after 5-min ischemia [188.5 ± 8.5/mm: 90.0% of the 209.5 ± 11.1 /mm density in the sham-operated controls vs. 16.7 ± 6.4/mm in those injected with artificial cerebrospinal fluid (CSF) only]. There was no difference between these two groups in hippocampal temperature before, during or after 5-min ischemia. The glutamate concentration ([Glu.]) during 5-min ischemia measured by a microdialysis technique was similar in the two groups (peak [Glu.] = 2.76 ± 0.62 pmol/μl dialysate in the artificial CSF group and = 2.93 ± 0.64 pmol/μ1 dialysate in the LNNA group). It was found that the neuronal toxicity of NO does not involve hyperthermia or the increase of extracellular glutamate concentration in the hippocampal CA1 region during 5-min ischemia.     

Temporal profile of interneuron and pyramidal cell protein synthesis in rat hippocampus following cerebral ischemia

Summary Cellular protein synthesis was investigated in the rat hippocampus 2–100 h following 20 min of cerebral ischemia induced by four-vessel occlusion. [³H]-Phenylalanine was retrogradely infused through the external carotid artery for 30 min. This method limited the distribution of the tracer to one hemisphere and required 1/50th of the tracer amount used for intravenous tracer infusion. Cellular [³H]phenylalanine incorporation was examined in hematoxyline and eosin-stained sections coated with nuclear emulsion. A score for relative protein synthesis was estimated from counts of silver grains across neuron somata with undamaged morphology. Shortly after ischemia a generalized complete arrest of protein synthesis was observed. In CA1 pyramidal cells, this was followed by a transient incomplete regeneration (9–20 h) and later (46–100 h) persistent cessation of protein synthesis. By contrast protein synthesis in interneurons, CA3c pyramidal cells and granule cells recovered to preischemic levels 9–100 h after ischemia, as did the CA3ab pyramidal cells 46–100 h postischemia. Moreover, eosinophilic cell changes were seen in hilar and CA3c neurons at all postischemic stages and in CA1 pyramidal cells 46–72 h after ischemia. [³H]Phenylalanine incorporation was absent in neurons demonstrating eosinophilic cell changes. From the rapid recovery of protein synthesis in hippocampal interneurons, we conclude that changes in interneuronal protein synthesis per se are not involved in the pathophysiology of the delayed ischemic CA1 pyramidal cell death.Supported by research grants from The Danish Research Council and the Danish Biotechnology Program     

In vitro ischemia and protein synthesis in the rat hippocampal slice: the role of calcium and NMDA receptor activation

The rat hippocampal slice was developed as a model for investigating the effects of ischemia on protein synthesis in different cell types, as synthesis is an early functional indicator of cell damage. Five min of in vitro ischemia inhibited protein synthesis in CA1 pyramidal and subicular neurons 3 h later, despite recovery of the energy charge. Morphology of these neurons was also affected. In contrast, glia and capillary endothelial cells showed increased synthesis at this time point, and no apparent structural changes. Exposure of slices to buffer lacking calcium and containing the non-competitive NMDA receptor blocker ketamine, during the 5 min ischemia, prevented both the inhibition of protein synthesis and the morphologic changes in the neurons. However, if buffer only lacked calcium, or only contained ketamine, both forms of ischemic damage occurred. Thus, the neuronal protein synthesis inhibition and the impaired morphology appear to be mediated by either extracellular calcium or NMDA receptor activation. In contrast to the neurons, the ischemia-induced stimulation of protein synthesis in glia and capillary endothelial cells was not affected by the above treatments, indicating that neither NMDA receptor activation nor extracellular calcium is necessary for this effect.