Delayed neuronal death in the rat hippocampus following transient forebrain ischemia

Summary An unusual, slowly progressing neuronal damage has been reported to occur in the gerbil hippocampus following ischemia (Kirino 1982). Delayed neuronal death following ischemia has also been noticed in the rat four-vessel occlusion model (Pulsinelli et al. 1982). By light microscopy this slow neuronal injury in the rat was not different from the previously known neuronal ischemic cell change. This report lead us to the question as to whether neurons in the rat hippocampus are damaged rapidly following an initial latent period or deteriorate slowly and progressively until they display overt changes. To clarify this point, observation was done on the hippocampal CA1 sector of the rat following ischemia. Rats were subjected to four-vessel occlusion, and those which developed ischemic symptoms were perfusion-fixed. Although the change appeared very slowly and lacked microvacuolation of the cytoplasm, neuronal alteration was practically not different from classical ischemic cell change. By electron microscopy, however, the change was detectable when the neurons still appeared intact by light microscopy. An increase in the membranous organelles and deposition of dark substances were the initial manifestations. It seemed that the CA1 neurons deteriorated very slowly and progressively, and that they retained partial viability in the initial phase of the change. In spite of the difference in light-microscopic findings, the mechanisms underlying delayed neuronal death in the rat and gerbil hippocampus seemed to be identical.     

Neuroprotection and glutamate attenuation by acetylsalicylic acid in temporary but not in permanent cerebral ischemia

To assess the effects of acetylsalicylic acid (ASA) on glutamate and interleukin-6 (IL-6) release in the striatum of rats suffering from cerebral ischemia, we used the microdialysis technique with probes implanted 2 h prior to stroke onset. A total of 36 rats were randomly assigned to either temporary (90 min, n=18) or permanent (n=18) middle cerebral artery occlusion (MCAO). Animals received either a bolus of 40 mg/kg ASA or saline as control 30 min after stroke onset. Permanent MCAO led to large infarct volumes with no differences between treatment with ASA (239.8+/-4.1 mm3) and saline (230.1+/-3.9 mm3, p=0.15). In contrast, ASA therapy in temporary ischemia (87.2+/-6.2 mm3) reduced infarct size significantly compared to placebo (155.6+/-4.8 mm3, p<0.0001). Only in temporary ischemia, ASA application reduced glutamate significantly at the time points 90, 120, and 150 min after MCAO. Pooled post-ischemic microdialysate concentrations of IL-6 in temporary MCAO were significantly higher after ASA treatment (215+/-81 pg/mL, p=0.0297) than in saline-treated rats (80+/-13 pg/mL). In the permanent MCAO group, no difference in IL-6 between the ASA (125+/-21 pg/mL) and saline group (68+/-34 pg/mL) was noted. No differences were seen for c-fos positive neurons in the penumbra and hippocampus between all groups. These results suggest that the neuroprotective effect of ASA is reflected by glutamate attenuation and IL-6 induction even if given after stroke onset, but only if reperfusion is achieved.     

The role of remaining presynaptic terminals in the hippocampal CA1 after selective neuronal death: ischemia-induced glutamate efflux

Following selective neuronal death, numerous presynaptic terminals maintain their structural integrity in the brain region. The role that these remaining presynaptic terminals play in the brain region showing selective neuronal death is not known. In the present study, we investigated the possibility that brief transient ischemia induces an excessive release of glutamate from the remaining presynaptic terminals, which then spreads by diffusion. The glutamate could act as an excitotoxin and be a pathogenic factor in the local injured brain region. Transient ischemia of 3.5 min duration was used in the gerbil as a pretreatment to obtain hippocampal CA1 in which most of postsynaptic neurons were eliminated but numerous presynaptic terminals remained normal. At 10–14 days after the pretreatment, brain microdialysis experiments were performed in vivo in the CA1 to measure the levels of extracellular glutamate induced by 5 min ischemia. Prior to 5 min ischemia the basal concentration of glutamate in the CA1 was the same as that observed in gerbils that had been subjected to sham pretreatment. During 5 min ischemia, no significant increase in glutamate was induced in the CA1 which showed selective neuronal death. However, a massive increase in glutamate was induced in the CA1 of the sham-pretreated gerbils. These results suggest that the remaining presynaptic terminals are unlikely to play a pathogenic role in the CA1 after selective neuronal death has occurred. Received: 6 June 1995 / Revised, accepted: 4 August 1995     

Moderate hypothermia mitigates neuronal damage in the rat brain when initiated several hours following transient cerebral ischemia

Intraischemic moderate hypothermia generally protects the brain against ischemic cell death, while hypothermia instigated several hours into the reperfusion phase is considered to be less effective. Here we report the effect of hypothermia (32.5°–33.5°C) of 5-h duration, initiated at 2, 6, 12, 24 and 36 h into the recirculation phase following 10 min of transient cerebral ischemia, on ischemic neuronal injury in the hippocampus and striatum of the rat. Hypothermia induced at 2 h, and 6 h postischemia reduces neuronal damage in the entire hippocampal CA1 region by approximately 50%. In the lateral CA1 region hypothermia induced at 12 h postischemia, significantly mitigates necrosis. When initiated at 2 h postischemia, but not later, protection was also observed in the striatum. Hypothermia induced 24 and 36 h postischemia was ineffective. A period of hypothermia of 5 h, initiated 2 h postischemia, was required for marked neuronal protection in the CA1 region, while 3.5-h hypothermia decreased neuronal damage by approximately 10% and 30 min hypothermia was ineffective. The clinical implications of the data are that extended period of hypothermia initiated long into the recovery phase following ischemia may prove beneficial. Hypothermia protects brain regions displaying rapid as well as delayed neuronal damage, and a minimal time of hypothermia is required for effective neuronal protection. Also, strict temperature control for up to 24 h postischemia may be required for proper assessment of the efficacy of cerebro-protective drugs.Supported by the Swedish Medical Research Council (grant no. 08644), The Medical Faculty at Lund University, The Segerfalk Foundation, The Crafoord Foundation, Åke Wibergs Foundation, and the CNPq (Brazilian Council for Development of Science and Technology)     

脑缺血再灌注后海马CA1区谷氨酸的表达变化及氟桂利嗪的影响

目的　观察暂短性脑缺血再灌注后沙土鼠海马区谷氨酸的表达变化以及氟桂利嗪干预的影响。方法　按照Kirino的方法 ,制作缺血再灌注模型。于缺血再灌注后 1、2、7天采取免疫组化方法检测谷氨酸表达 ,并于 7天在电镜和光镜下观察组织学变化。结果　缺血再灌注组 1天及 2天海马CA1区谷氨酸表达增高 (P <0 .0 1) ,7天恢复正常。光镜及电镜可见给药组存活的神经元数目明显多于缺血再灌注组 (P <0 .0 1)。结论　谷氨酸表达增高可能是鼠脑海马区迟发性神经元死亡的原因之一 ,氟桂利嗪可抑制谷氨酸的表达 ,对缺血的神经元起保护作用。     

Temporal changes in extracellular acetylcholine and CA1 pyramidal cells in gerbil hippocampus following transient cerebral ischemia

Temporal changes in cholinergic functions following transient cerebral ischemia (10 min) were studied in the hippocampus of awake unrestrained gerbils using in vivo microdialysis. These data were compared with the results for temporal change in the area of each CA1 cell soma, measured with a microcomputer imaging device. KCl-induced release of acetylcholine (ACh) tended to be lower within 1 day after recirculation, and was significantly lower on the 4th, 7th and 14th days. Atropine-induced release of ACh gradually decreased over the test period. In histological estimation, no differences were observed within the 1st day, but a significant decrease of the area of CA1 cell soma was observed from the 4th to 14th days. Moreover, ischemia over 2 min decreased KCl- and atropine-induced ACh release on the 14th day without significant changes of hippocampal CA1 pyramidal cell. From these results, it is clear that ischemia produced dysfunction of hippocampal cholinergic neurons, and that dysfunction of the hippocampal cholinergic system following transient ischemia precedes pyramidal cell damage in the hippocampal CA1 subfield.     

No enhancement by nitric oxide of glutamate release from P2 and P3 synaptosomes of rat hippocampus

Effects of nitric oxide on glutamate (Glu) release in long-term potentiation (LTP) were investigated by superfusion of conventional (P2) and large (P3) synaptosomes prepared from the rat hippocampus. Basal releasing rates of endogenous Glu from P2 and P3 fractions were 103.6 and 85.2 pmol/min/mg protein, respectively. Exposure to a depolarizing concentration of KCl (30 mM) evoked 3.58- and 4.52-fold increases in releasing rates of Glu from P2 and P3 fractions, respectively. Although the perfusion with sodium nitroprusside (NP, 10⁻³ M), a nitric oxide-releasing agent, failed to augment the K⁺-evoked releases of Glu from P2 and P3 synaptosomes, NP enhanced that from slices of the hippocampus by 39% without changing basal release. Similarly, 8-bromoguanosine3′ : 5′-cyclic monophosphate (10⁻⁴ M) increased the K⁺-evoked release of Glu from slices by 30%, but not from either synaptosomes. When synaptosomes were prepared from the hippocampus which was pretreated with two trains of electrical field stimulation (100 Hz, 0.1 ms, for 2 s), K⁺-evoked releases of Glu from P2 and P3 synaptosomes were increased by 15% and 23%, respectively. Although nitric oxide is postulated to function as a retrograde messenger to maintain LTP, present results suggest that nitric oxide may not directly act upon nerve terminals to enhance glutamate release, but that interventions of glias and short neurons may be involved in the presynaptic mechanism of LTP.     

Lubeluzole inhibits accumulation of extracellular glutamate in the hippocampus during transient global cerebral ischemia

Increases in extracellular glutamate during cerebral ischemia may play an important role in neuronal injury. Lubeluzole is a novel neuroprotective drug, which in previous in vitro and focal ischemia studies has been shown to inhibit nitric oxide synthesis, to block voltage-gated Na+-ion channels, and to inhibit glutamate release. In this study, we investigated the ability of lubeluzole to inhibit glutamate accumulation during episodes of transient global cerebral ischemia. Twenty-five New Zealand white rabbits were randomized to one of four groups: a normothermic control group; a hypothermic group; a 1.25 mg/kg lubeluzole group; or a 2.5 mg/kg lubeluzole group. The animals were anesthetized, intubated, and ventilated before microdialysis probes were placed in the hippocampus. Lubeluzole was given intravenously 90 min before the onset of ischemia. Esophageal temperature was maintained at 38 degrees C in the control, and lubeluzole treated groups, while the animals in the hypothermia group were cooled to 30 degrees C. A 15-min period of global cerebral ischemia was produced by inflating a neck tourniquet. Glutamate concentrations in the microdialysate were determined using high-performance liquid chromatography (HPLC). During ischemia and early reperfusion, glutamate concentrations increased significantly in the control group and returned to baseline after 15 min of reperfusion. In the lubleuzole 2.5 mg/kg and hypothermia groups, glutamate levels were significantly lower (P<0.05) than in the control group and there was no significant change from baseline levels during the entire experiment. This study suggests that lubeluzole is effective in inhibiting extracellular glutamate accumulation during global cerebral ischemia, and has the potential to produce potent neuroprotection when instituted prior to an ischemic event.     

Region-selective stress-induced increase of glutamate uptake and release in rat forebrain

The study describes stress-induced changes in high-affinity uptake and release of glutamate by synaptosomal preparations from several regions of rat brain. The results demonstrate that restraint stress can lead to increased glutamate uptake and release in limbic forebrain regions (frontal cortex, hippocampus and septum) but not in the striatum. The increase in glutamate uptake was evident after 30 min of stress. A plateau (140–150% of unhandled controls) was reached after 1 h and was maintained after 4 h of continuous stress. The stress-induced increase in glutamate uptake was observed with glutamate concentrations of up to 10 μM, but not with 500 μM. The results indicate that forebrain glutamatergic terminals are activated by stressful stimuli in a regionally selective manner, and suggest that enhanced high-affinity uptake is important in clearing increased levels of released glutamate.     

Glutamate neurotoxicity in the developing rat cochlea is antagonized by kynurenic acid and MK-801

Glutamate (Glu) is neurotoxic in the neonatal rat cochlea, producing hearing impairment which is largely due to the death of spiral ganglion cells, whereas the receptor hair cells are spared. Dendritic processes of the spiral ganglion are postsynaptic to the primary afferent synapse of the auditory system. The experiments reported here were designed to test whether this apparent excitotoxicity can be blocked by Glu antagonist. The broad-spectrum antagonist kynurenic acid (KYNA) was coadministered with Glu initially to determine whether the high-frequency hearing deficit caused by Glu may be mediated by excitatory amino acid receptors. Subsequently, the (NMDA)-specific receptor blocker MK-801 was used to test whether NMDA receptors may be involved in the effect. Both antagonists partially blocked the high-frequency hearing impairment caused by Glu. The blocker-alone control groups exhibited mid-frequency effects of unknown origin. The significant antagonism of Glu-induced impairment is consistent with the hypothesis that Glu or a similar excitatory amino acid is an important afferent transmitter in the cochlea.     

Postischemic alterations of spontaneous activities in rat hippocampal CA1 neurons

Changes of spontaneous impulse discharges in rat hippocampal neurons during and after transient forebrain ischemia were investigated electrophysiologically. Spontaneous impulse frequencies of CA1 neurons before ischemia were varied from 0.4 to 20.0 impulses/s and its average was5.8 ± 1.2 (means±S.E., n = 36). These spontaneous discharges were completely suppressed during forebrain ischemia exept for the transient hyperactivity observed just after the beginning of ischemia. Recovery of spontaneous discharges of CA1 neurons from suppression induced by 5 min ischemia started at 5 min, and neuronal activities were restored to pre-ischemic levels approximately 30 min after reperfusion. On the other hand, spontaneous impulse frequencies at all time points recorded after 20 min ischemia were less than 40% of the pre-ischemic levels. These continuous suppression of spontaneous activity after 20 min ischemia may suggest that neuronal function is impaired during and/or in the early stages of reperfusion, and functional disorders precede morphological degeneration.     

Effects of adenosine agonists and an antagonist on excitatory transmitter release from the ischemic rabbit hippocampus

The purpose of this study was to determine the effects of adenosine agonists and an antagonist on ischemia-induced extracellular glutamate concentrations in an animal model of transient cerebral ischemia using in vivo cerebral microdialysis. Fifty New Zealand white rabbits were randomly assigned to one of five groups (normothermia, hypothermia, cyclopentyladenosine (CPA), theophylline, or propentofylline). Microdialysis probes were stereotactically placed in the dorsal hippocampus. Twenty minutes before the onset of ischemia, either 1 mg/kg CPA, 5 mg/kg propentofylline, or 20 mg/kg theophylline were administered intravenously. Esophageal temperature was maintained at 38 degrees C, except in the hypothermic animals, which were cooled to 30 degrees C throughout the entire experiment. Two 12-min periods of cerebral ischemia, separated by a 105-min interval of reperfusion, were produced by inflating a neck tourniquet. High-performance liquid chromatography was used to determine the glutamate concentration in the microdialysate. There were no significant increases in glutamate concentrations during the first ischemic period in any of the five groups. During the second ischemic episode, glutamate concentrations in the normothermic group peaked at levels approximately three times higher than the initial values. A similar pattern of changes in glutamate concentrations was observed in the CPA, propentofylline, and theophylline groups. In the hypothermic group, the concentrations of glutamate remained at baseline levels during the entire experiment. Contrary to expectations, neither the adenosine agonists (CPA, propentofylline) nor the antagonist (theophylline) had any effect on extracellular glutamate concentrations in the peri-ischemic period. Although adenosine and its analogs may be cerebroprotective agents, their mechanism of action is not fully understood. The data derived from this study indicates that the acute administration of such agents had no effect on ischemia-induced glutamate release within the hippocampus under these experimental conditions. Based on these results, further work is needed to compare in vivo versus in vitro experimental results in acute and long-term treatment studies with adenosine receptor agonists and antagonists.     

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.     

Time profile of calcium accumulation in hippocampus,striatum and frontoparietal cortex after transient forebrain ischemia in the gerbil

Summary The topical and temporal relationship between neuronal injury and calcium loading was investigated in gerbils following bilateral carotid artery occlusion for 5 or 10 min and recirculation times from 15 min to 7 days. The association of histochemically visible calcium deposits with neuronal death was assessed by combining two calcium stains, alizarin red and arsenazo III, with conventional histological techniques. Neuronal calcium accumulation was evaluated morphometrically in the striatum, the frontoparietal cortex and the CA1 and CA4 sectors of the hippocampus. After 5-min ischemia and 1–2 days of recirculation numerous calcium-containing neurons appeared in the CA4 sector but only a few were present in the CA1 sector. After 4 days of recirculation calcium accumulation was visible in the whole CA1 sector and the dorso-lateral part of striate nucleus. After 10-min ischemia calcium accumulation started in these regions, as well as in the cortex, already after 1 day. In the CA1 sector calcium accumulation followed a typical time course: on day 2 only the lateral parts were affected, while on day 4 the whole CA1 neuronal band was calcium positive. The regional distribution of histological lesions matched that of calcium loading and, furthermore, the lesions appeared after a corresponding delay in the respective regions. Morphometric evaluations of calcium staining and histological lesions in the CA1 sector revealed a high correlation, indicating that calcium accumulation and neuronal death are closely associated both topically and temporally. This suggests that disturbances of calcium homeostasis such as those measured by this histochemical technique are the consequence of and not the reason for ischemic cell death.     

Chemical preconditioning with 3-nitropropionic acid: lack of induction of neuronal tolerance in gerbil hippocampus subjected to transient forebrain ischemia

Chemical preconditioning using the mitochondrial toxin, 3-nitropropionic acid (3-NP) has been reported to induce neuroprotection against subsequent global ischemia. To investigate the underlying mechanisms, Mongolian gerbils were pretreated with either vehicle or 3-NP at the dose of 3 or 10 mg/kg, intraperitoneal, 3 days prior to a 5-min bilateral carotid artery occlusion followed by either 48 h or 7 days of blood recirculation. Neuronal damage was assessed by a cresyl violet/fuchsin acid staining. Induction of heat shock protein 72 (HSP72) and manganese superoxide dismutase (MnSOD) expression was evaluated by Western blotting. Astroglial and microglial activation was detected by immunohistochemistry (glial fibrillary acid protein) and by histochemistry (isolectin B4 staining), respectively. Present data show that the hippocampal neuronal damage induced by ischemia were of similar extent between the vehicle- and 3-NP-treated gerbils, whatever the dose tested, indicating that 3-NP did not induce tolerance to transient forebrain ischemia under our experimental conditions. The lack of difference in the post-ischemic level of HSP72 and MnSOD protein expression and in the intensity of astroglial and microglial activation represents further indirect indications of the absence of 3-NP preconditioning effect. In conclusion, although chemical preconditioning with 3-NP is a well-established phenomenon at least in vitro and in models of focal ischemia, the relevance of 3-NP as a preconditioning molecule towards global brain ischemia remains an open question.     

Increased extracellular ascorbate release reflects glutamate re-uptake during the early stage of reperfusion after forebrain ischemia in rats

Ascorbate is highly concentrated in neuropils, and its extracellular release is closely related to that of the excitatory neurotransmitters. Thus, the extracellular release of ascorbate and glutamate was measured during the early stage of forebrain ischemia-reperfusion in the rat hippocampus using a microdialysis biosensor system. Male Wistar rats were anesthetized with halothane under mechanical ventilation and normothermia. Two probes of the microdialysis biosensor electrode were inserted in the hippocampus bilaterally. One probe was perfused with phosphate-buffered saline (PBS) and the oxidation signal of dialyzed ascorbate was recorded. A second electropolymerized probe was perfused with PBS containing glutamate oxidase for glutamate measurement. Forebrain ischemia-reperfusion was performed by bilateral carotid artery occlusion with hemorrhagic hypotension (MAP=30 mmHg) for 10 min (Group 10, n=10) or 15 min (Group 15, n=10), followed by reperfusion for 60 min. The release of glutamate increased significantly to 294% (Group 10) and 334% (Group 15) during ischemia, and then decreased rapidly. In Group 15, however, it remained significantly higher after reperfusion than in Group 10. The release of ascorbate increased significantly to 504% (Group 10) and 334% (Group 15) after reperfusion. In Group 10, it was significantly higher for 5-15 min after reperfusion than in Group 15. The marked increase of ascorbate during reperfusion was associated with the rapid decrease in glutamate. The extended time of ischemia significantly inhibited glutamate re-uptake and ascorbate release during reperfusion. These findings suggest the extracellular ascorbate release during reperfusion after global ischemia as a marker of glutamate re-uptake.     

The density and distribution of ischemic brain injury in the rat following 2–10 min of forebrain ischemia

Summary The density and distribution of brain damage after 2–10 min of cerebral ischemia was studied in the rat. Ischemia was produced by a combination of carotid clamping and hypotension, followed by 1 week recovery. The brains were perfusion-fixed with formaldehyde, embedded in paraffin, subserially sectioned, and stained with acid fuchsin/cresyl violet. The number of necrotic neurons in the cerebral cortex, hippocampus, and caudate nucleus was assessed by direct visual counting.Somewhat unexpectedly, mild brain damage was observed in some animals already after 2 min, and more consistently after 4 min of ischemia. This damage affected CA4 and CA1 pyramids in the hippocampus, and neurons in the subiculum. Necrosis of neocortical cells began to appear after 4 min and CA3 hippocampal damage after 6 min of ischemia, while neurons in the caudoputamen were affected first after 8–10 min.Selective neuronal necrosis of the cerebral cortex worsened into infarction after higher doses of insult. Damage was worst over the superolateral convexity of the hemisphere, in the middle laminae of the cerebral cortex. The caudate nucleus showed geographically demarcated zones of selective neuronal necrosis, damage to neurons in the dorsolateral portion showing an all-or-none pattern. Other structures involved included the amygdaloid, the thalamic reticular nucleus, the septal nuclei, the pars reticularis of the substantia nigra, and the cerebellar vermis.Supported by the Swedish Medical Research Council (projects 12X-03020, 14X-263) and the National Institutes of Health of the United States Public Health Service (grant no. 5 R01 NS07838). Dr. Auer is the recipient of a Medical Research Council of Canada Fellowship.     

Progressive expression of immunomolecules on microglial cells in rat dorsal hippocampus following transient forebrain ischemia

Summary We show a differential up-regulation of immunomolecules in the rat dorsal hippocampus accompanying neuronal cell death as a consequence of transient forebrain ischemia (four-vessel occlusion model). Using a panel of monoclonal antibodies (mAbs), we have examined the time course of expression of major histocompatibility complex (MHC) antigens class I (OX-18) and class II (OX-6), leukocyte common antigen (OX-1), CD4 (W3/25) and CD8 (OX-8) antigens, CR3 complement receptor (OX-42), as well as brain macrophage antigen (ED2). The study was performed at time intervals ranging from 1 to 28 days after reperfusion. Throughout all post-ischemic time periods, strongly enhanced immunoreactivity on microglial cells in the CA1 region and dentate hilus and, to a lesser extent, in CA3 was demonstrated with mAb OX-42. MHC class I-positive cells (OX-18) appeared on day 2, whereas cells immunoreactive with OX-1 and W3/25 became evident in the CA1 and hilar regions on post-ischemic day 6. In contrast, MHC class II (Ia) antigen was first detected on indigenous microglia by day 13. In some animals, the OX-8 antibody resulted in the labelling of scattered CD8-positive lymphocytes, but perivascular inflammatory infiltrates were absent. No changes in the expression of ED2 immunoreactivity on perivascular cells could be observed. The results show that following ischemic injury, microglial cells demonstrate a timedependent up-regulation and de novo expression of certain immunomolecules, indicative of their immunocompetence. The findings are compared with those obtained in other models of brain injury.Supported in part by NIH/NINCDS PO 1 NS27511     

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.     

Ultrastructural investigation of the CA1 region of the hippocampus after transient cerebral ischemia in gerbils

Summary Ultrastructural damage leading to delayed neuronal death was investigated in the mid-CA1 region of the hippocampus from the stratum (str.) moleculare to oriens after transient bilateral forebrain ischemia in Mongolian gerbils. After ischemia for 5 min without recirculation, mild swelling of the peripheral part of the apical and basal dendrites was already apparent in the str. moleculare and str. oriens. Mitochondria in the dendrites were also swollen in the same area. During recirculation for 12 h to 3 days, swelling of the dendritic cytoplasm persisted with formation of microvacuoles, but swelling of mitochondria receded. Microvacuolation and loss of microtubules were also observed in the proximal part of the dendrites during this period, and swelling and disruption of internal cristae were observed in mitochondria after recirculation for 3 days. The dendrites became severely degenerated after recirculation for 4 days. In the pyramidal cell bodies, no abnormality was observed at the end of ischemia for 5 min, but disaggregation of polyribosomes and swelling of the endoplasmic reticulum were observed 12 h after recirculation. Proliferation of the endoplasmic reticulum in parallel arrays occurred after recirculation for 1 day and persisted. Severe degeneration of the pyramidal cell bodies was obvious after recirculation for 4 days. The findings observed in the present investigation suggested that the neuronal structure most vulnerable to ischemia was the peripheral part of the dendrites and postischemic neuronal damage occurred early in this part of the dendrites.Supported by the grant NS-06663 from the National Institutes of Health, U.S. Public Health Service