Exercise preconditioning exhibits neuroprotective effects on hippocampal CA1 neuronal damage after cerebral ischemia

Recent evidence has suggested the neuroprotective effects of physical exercise on cerebral ischemic injury. However, the role of physical exercise in cerebral ischemia-induced hippocampal damage remains controversial. The aim of the present study was to evaluate the effects of pre-ischemia treadmill training on hippocampal CA1 neuronal damage after cerebral ischemia. Male adult rats were randomly divided into control, ischemia and exercise + ischemia groups. In the exercise + ischemia group, rats were subjected to running on a treadmill in a designated time schedule(5 days per week for 4 weeks). Then rats underwent cerebral ischemia induction th rough occlusion of common carotids followed by reperfusion. At 4 days after cerebral ischemia, rat learning and memory abilities were evaluated using passive avoidance memory test and rat hippocampal neuronal damage was detected using Nissl and TUNEL staining. Pre-ischemic exercise significantly reduced the number of TUNEL-positive cells and necrotic cell death in the hippocampal CA1 region as compared to the ischemia group. Moreover, pre-ischemic exercise significantly prevented ischemia-induced memory dysfunction. Pre-ischemic exercise mighct prevent memory deficits after cerebral ischemia through rescuing hippocampal CA1 neurons from ischemia-induced degeneration.     

Systemic administration of MK-801 protects against ischemia-induced hippocampal neurodegeneration in the gerbil

The neuroprotective effects of MK-801, a noncompetitive antagonist of N-methyl-D-aspartate (NMDA) receptors, were evaluated in models of cerebral ischemia using Mongolian gerbils. Bilateral occlusion of the carotid arteries for a period of 5 min resulted in a consistent pattern of degeneration of hippocampal CA1 and CA2 pyramidal neurons, which was quantified using an image analyzer. Systemic administration of MK-801 (0.01-10 mg/kg, i.p.) 1 hr prior to the occlusion caused a dose-dependent protection of the CA1 and CA2 neurons. The ED50 value for neuroprotection by MK-801 was calculated to be 0.3 mg/kg, and at doses greater than or equal to 3 mg/kg the majority of animals were completely protected against the ischemic insult. Systemic administration of MK-801 (1 or 10 mg/kg, i.p.) 1 hr prior to unilateral occlusion of the right carotid artery resulted in significant protection against hippocampal neurodegeneration following 10 min of occlusion, and increased the survival rate after 30 min of occlusion. The potent neuroprotective effects of MK-801 in these cerebral ischemia models add further weight to the evidence that NMDA receptors are involved in the mechanism of ischemia-induced neuronal degeneration.     

Neuronal damage and calcium accumulation following repeated brief cerebral ischemia in the gerbil

We investigated the distribution of neuronal damage following brief cerebral transient ischemia and repeated ischemia at 1-h intervals in the gerbil, using light microscopy and 45Ca autoradiography as a marker for detection of ischemic damage. The animals were allowed to survive for 7 days after ischemia induced by bilateral carotid artery occlusion. Following 2-min ischemia, neuronal damage determined by abnormal calcium accumulation was not observed in the forebrain regions. Following 3-min ischemia, however, abnormal calcium accumulation was recognized only in the hippocampal CA1 sector and part of the striatum. Two 2-min ischemic insults caused extensive abnormal calcium accumulation in the dorsolateral part of striatum, the hippocampal CA1 sector, the thalamus, the substantia nigra and the inferior colliculus. The ischemic insults were more severe than that of a single 3-min ischemia. However, three 1-min ischemic insults caused abnormal calcium accumulation only in the striatum. On the other hand, three 2-min ischemic insults caused severe abnormal calcium accumulation in the brain. The abnormal calcium accumulation was found in the dorsolateral part of striatum, the hippocampal CA1 sector, the thalamus, the medial geniculate body, the substantia nigra and the inferior colliculus. Gerbils subjected to three 3-min ischemic insults revealed most severe abnormal calcium accumulation. Marked calcium accumulation was seen not only in the above sites, but also spread in the neocortex, the septum and the hippocampal CA3 sector. Morphological study after transient or repeated ischemia indicated that the distribution and frequency of the neuronal damage was found in the sites corresponding to most of the regions of abnormal calcium accumulation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Protective effect of a prosaposin-derived, 18-mer peptide on slowly progressive neuronal degeneration after brief ischemia.

SUMMARY: Slowly progressive degeneration of the hippocampal CA1 neurons was induced by 3-minute transient global ischemia in gerbils. Sustained degeneration of hippocampal CA1 neurons was evident 1 month after ischemia. To investigate the effects of an 18-mer peptide comprising the hydrophilic sequence of the rat saposin C domain (18MP) on this sustained neuronal degeneration, an intracerebroventricular 18MP infusion was initiated 3 days after ischemia. Histopathologic and behavior evaluations were conducted 1 week and 1 month after induction of ischemia. When compared with the vehicle infusion, 18MP treatment significantly increased the response latency time in a passive avoidance task. Increased neuronal density was also evident, as was the number of intact synapses in the hippocampal CA1 region at 1 week and 1 month after ischemia. 18MP treatment also significantly decreased the number of TUNEL-positive CA1 neurons 1 week after ischemia. Subsequent in vitro experiments using cultured neurons demonstrated that the 18MP at optimal extracellular concentrations of 1 to 100 fg/mL prevented nitric oxide-induced neuronal damage as expected and significantly up-regulated the expressions of bcl-x(L) mRNA and its translated protein. These results suggest that the gerbil model of 3-minute ischemia is useful in studying the pathogenesis of slowly progressive neuronal degeneration after stroke and in evaluating effects of novel therapeutic agents. It is likely that the 18MP at low extracellular concentrations prevents neuronal apoptosis possibly through up-regulation of the mitochondrial antiapoptotic factor Bcl-x(L).     

Ischemia-induced neuronal cell death, calcium accumulation, and glial response in the hippocampus of the Mongolian gerbil and protection by propentofylline (HWA 285)

The localization and timing of cellular calcium loading and glial cell reaction in relation to selective death of hippocampal neurons was studied in Mongolian gerbils following transient forebrain ischemia. Two days after a 5-min period of ischemia, heavy calcium staining was histochemically demonstrated in circumscribed groups of nerve cells, located in the transition zone between the CA1 and CA3 areas. This preceded complete neuronal cell death that was quantitatively assessed by measuring the intensity of Nissl staining. After a 12-min period of ischemia, extensive calcium loading was observed in conjunction with severe neuronal damage throughout the CA1 region as well in the dorsal nuclei of the thalamus. The extent of calcium staining decreased with time and was not seen at stages later than 7 days. Already at 2 days after a 5-min period of ischemia, a strong increase of glial fibrillary acidic protein immunoreactivity was seen. This indicates a marked and early hypertrophy of astrocytes that was not accompanied by an obvious proliferation. Neither the astrocytic response nor the neuronal calcium accumulation were observed in gerbils pretreated with propentofylline, HWA 285 (10 mg/kg, i.p.) 15 min before bilateral carotid artery occlusion. Also, the decrease of Nissl staining in the CA1 area after 5 and 12 min of ischemia was considerably less pronounced and did not significantly differ from sham-operated controls.     

Ginseng root prevents learning disability and neuronal loss in gerbils with 5-minute forebrain ischemia

The present study was designed to investigate the possible neuroprotective activity of ginseng roots in 5-min ischemic gerbils using a step-down passive avoidance task and subsequent neuron and synapse counts in the hippocampal CA1 region. The following drugs were administered for 7 days before the induced ischemia: red ginseng powder (RGP), crude ginseng saponin (CGS), crude ginseng non-saponin (CGNS), and pure ginsenosides Rb₁, Rg₁ and Ro. Oral administration of RGP significantly prevented the ischemia-induced decrease in response latency, as determined by the passive avoidance test, and rescued a significant number of ischemic hippocampal CA1 pyramidal neurons in a dose-dependent manner. Intraperitoneal injections of CGS exhibited a similar neuroprotective effect. CGNS had a significant but less potent protective effect against impaired passive avoidance task and degeneration of hippocampal CA1 neurons. Ginsenoside Rb₁ significantly prolonged the response latency of ischemic gerbils and rescued a significant number of ischemic CA1 pyramidal neurons, whereas ginisenosides Rg₁ and Ro were ineffective. Postischemic treatment with RGP, CGS or ginsenoside Rb₁ was ineffective. The neuroprotective activities of RGP, CGS and ginsenoside Rb₁ were confirmed by electron microscopy counts of synapses in individual strata of the CA1 field of ischemic gerbils pretreated with the drugs. These findings suggest that RGP and CGS are effective in the prevention of delayed neuronal death, and that ginsenoside Rb₁ is one of the neuroprotective molecules within ginseng root. Received: 22 May 1995 / Revised, accepted: 14 August 1995     

Intraventricular administration of the neurotrophic factor midkine ameliorates hippocampal delayed neuronal death following transient forebrain ischemia in gerbils

Midkine (MK) is a growth factor with neurotrophic activities, and is expressed during the early stages of experimental cerebral infarction in rats in the zone surrounding the infarct. To evaluate in vivo activity of MK in preventing neuronal death, MK produced in yeast (Pichia pastoris) was administered into the brain ventricle immediately before occlusion of the bilateral common carotid artery of Mongolian gerbils. MK administration at the dose of 0.5-2 microg immediately before occlusion was found to ameliorate delayed neuronal death in the hippocampal CA1 region caused by transient ischemia 7 days after the insult. The hippocampal neurons of the MK-administered gerbils tended to degenerate 14 and 21 days after the insult, but their numbers remained higher than those in saline-administered controls; however, the hippocampal neurons were degenerated 28 days after the insult. MK administration at 2 h after occlusion did not ameliorate the neuronal death. These findings suggested that the therapeutic time window was narrow. The two to four times repeated administration of 2 microg MK immediately before and at 1, 2, or 3 weeks after the occlusion were not significantly different for the hippocampal neuronal death at 28 days after the insult compared with a single injection, but were significantly effective compared with vehicle administration alone. These findings suggested that the therapeutic time window was relatively narrow. The potent neuroprotective activity of MK observed in vivo suggested that MK might be useful as a therapeutic reagent for prevention of neuronal death in neurodegenerative diseases.     

Selective vulnerability of hippocampus and disturbances of memory storage after mild unilateral ischemia of gerbil brain

The effect of selective injury of hippocampal neurons on the consolidation of memory traces was studied in gerbils (meriones unguiculatus) after production of mild cerebral ischemia. The right carotid artery was permanently ligated, and animals without gross neurological deficits ("symptom-negative" gerbils) were selected. Eight days and eight weeks after vascular ligation, cell counts of hippocampal neurons were carried out and correlated with regional blood flow and the acquisition of operant behaviour. Eight days after carotid artery occlusion, learning behaviour was significantly impaired although the number of hippocampal neurons had not changed and blood flow had even increased above normal. After eight weeks, learning behaviour and blood flow were normal but now a significant loss of pyramidal neurons was present in the CA1 and CA2 sectors of the hippocampus. Our observations demonstrate that it is possible to detect subtle functional disturbances by appropriate behavioural investigation before manifestation of selective injury of the hippocampus. Recovery of integrative function, despite persistent cellular damage, provides further evidence for central nervous plasticity.     

Oxypurinol attenuates ischemia-induced hippocampal damage in the gerbil

Oxypurinol, an inhibitor of the enzyme xanthine oxidase, reduced ischemic hippocampal damage and the associated hypermotility in Mongolian gerbils. Cerebral ischemia was induced in unanesthetized gerbils by a bilateral 5-min occlusion of the carotid arteries. Oxypurinol (40 mg/kg, IP), administered 20 min prior to carotid occlusion, prevented the increase in locomotor activity observed in saline-injected ischemic animals and significantly reduced the damage to, and loss of, CA1 hippocampal neurons observed 5 days postischemia. These findings suggest that oxypurinol may be useful for the prevention of cerebral ischemic damage.     

Indomethacin ameliorates ischemic neuronal damage in the gerbil hippocampal CA1 sector

The purpose of our experiment was to examine whether the cyclooxygenase inhibitor indomethacin ameliorates neuronal injury in the gerbil hippocampal CA1 sector following 5 minutes of forebrain ischemia. Thirty minutes before bilateral carotid artery occlusion, Mongolian gerbils were injected intraperitoneally with 1 (n = 10), 2 (n = 10), 5 (n = 12), or 10 (n = 7) mg/kg of indomethacin. Seven days after occlusion, the gerbils were perfusion-fixed and neuronal density in the hippocampal CA1 sector was assessed. The mean +/- SEM neuronal density in nine unoperated normal gerbils was 307 +/- 9/mm, in 10 untreated ischemic gerbils 55 +/- 21/mm, and in seven vehicle-treated ischemic gerbils 15 +/- 9/mm. The mean +/- SEM neuronal density in ischemic gerbils treated with 1, 2, 5, or 10 mg/kg indomethacin was 132 +/- 28/mm, 154 +/- 29/mm, 176 +/- 30/mm, and 136 +/- 39/mm, respectively. Indomethacin at any dose significantly ameliorated ischemic neuronal damage in the gerbil hippocampal CA1 sector.     

Calpain inhibitor entrapped in liposome rescues ischemic neuronal damage

Transient forebrain ischemia induces activation of calpain and proteolysis of a neuronal cytoskeleton, fodrin, in gerbil hippocampus. This phenomenon precedes delayed neuronal death in hippocampal CA1 neurons. We examined effects of a calpain inhibitor on delayed neuronal death after transient forebrain ischemia. In gerbils, a selective calpain inhibitor entrapped in liposome was given transvenously and 30 min later, 5-min forebrain ischemia was produced by occlusion of both common carotid arteries. On day 7, CA1 neuronal damage was examined in the hippocampal slices stained with cresyl violet. Calpain-induced proteolysis of fodrin was also examined by immunohistochemistry and immunoblot. Additionally, to assure entrapment of the inhibitor by CA1 neurons, the inhibitor-liposome complex was labeled with FITC and given to gerbils. Fluorescence in the hippocampal slices was examined by confocal laser scanning microscope. Selective CA1 neuronal damage induced by forebrain ischemia was prevented by administration of the inhibitor in a dose-dependent manner. Calpain-induced proteolysis of fodrin was also extinguished by the calpain inhibitor in a dose-dependent manner. Bright fluorescence of the FITC-labeled inhibitor was observed in the CA1 neurons. The data show an important role of calpain in the development of the ischemic delayed neuronal death. Calpain seems to produce neuronal damage by degrading neuronal cytoskeleton. Our data also show a palliative effect of the calpain inhibitor on the neurotoxic damage, which offers a new and potent treatment of transient forebrain cerebral ischemia.     

Quantitative analysis of effects of kappa-opioid agonists on postischemic hippocampal CA1 neuronal necrosis in gerbils

The ability of the kappa-opioid receptor agonists U50488H and U62066E (spiradoline mesylate) compared with the non-kappa close structural analogue U54494A to affect postischemic necrosis of the selectively vulnerable hippocampal CA1 neurons was examined in male Mongolian gerbils. The gerbils were treated with either saline vehicle or 10 mg/kg i.p. of one of the test drugs 30 minutes before and again 2 hours after a 10-minute period of bilateral carotid artery occlusion or sham occlusion under light methoxyflurane anesthesia. Seven days after ischemia and reperfusion the brains were perfusion-fixed, and hippocampal CA1 cells were counted in a blind fashion. In ischemic gerbils that received only vehicle, there was a 78.9% loss of CA1 neurons compared with sham-occluded gerbils. In contrast, in U50488H-treated gerbils, mean cell loss was reduced to 33.9% (p less than 0.01 vs. vehicle-treated group). U62066E was even more effective in reducing postischemic CA1 degeneration to only 20.7% (p less than 0.0001 vs. vehicle-treated group). However, treatment with the non-kappa analogue U54494A did not cause any apparent protection; the gerbils in this group showed an 80.7% loss of CA1 neurons. Our results are consistent with the hypothesis that kappa-receptor stimulation is associated with improved postischemic neuronal preservation.     

缺血预处理后海马CA1区反应性星形胶质细胞增生与迟发性神经元缺血耐受性的关系

目的 探讨缺血预处理后海马CA1区反应性星形胶质细胞增生与迟发性神经元缺血耐受性的关系。方法 实验动物被随机分为手术组、缺血组、预缺血组、预缺血后再缺血组。阴断沙土鼠双侧颈总动脉造成前脑缺血模型。采用细胞特异性抗原胶质纤维酸性蛋白（GFAP）免疫组化法标记星形胶质细胞。结果 预缺血后1－7天,海马CA1区GFAP阳性的星形胶质细胞数轻度增加,至28天时增生非常显著（P＜0．01）。预缺血后1－7天再缺血,海马CA1区存活正常神经元数逐渐下降,预缺血后28天再缺血又显著增加（P＜0．01）。结论 缺血预处理后,神经元可出现迟发性缺血耐受,反应性星形胶质细胞增生可能起了重要作用。     

Postischemic inhibition of GABA reuptake by tiagabine slows neuronal death in the gerbil hippocampus

The neuroprotective effects of enhancing neuronal inhibition with a γ-aminobutyric acid (GABA) uptake inhibitor were studied in gerbil hippocampus following transient ischemia. We used in vivo microdialysis to determine a suitable dosing regimen for tiagabine (NNC 328) to elevate extracellular levels of GABA within the hippocampus. In anesthetized (normothermic) gerbils, tiagabine (45 mg/kg, i. p.) selectively elevated extracellular GABA levels 450% in area CA1 of the hippocampus. In gerbils subjected to cerebral ischemia via 5-min bilateral carotid occlusion, extracellular GABA levels increased 13-fold in area CA1, returning to baseline within 30–45 min. When tiagabine was injected 10 min following onset of reperfusion, GABA levels remained elevated (200–470%) for 90 min. In addition, tiagabine significantly reduced the ischemic-induced elevation of glutamate levels in area CA1 during the postischemic period when GABA levels were elevated. There was no effect of postischemic tiagabine on aspartate or six other amino acids. Using the same dosing regimen, we evaluated the degree of neuroprotection in the hippocampus of gerbils 4 and 21 days after ischemia. Tiagabine decreased body temperature a maximum of 2.7°C beginning 30 min into reperfusion and lasting 90 min. In untreated gerbils sacrificed 4 and 21 days after ischemia, there was severe necrosis (99%) of the pyramidal cell layer in area CA1. Whereas tiagabine significantly protected the CA1 pyramidal cell layer in ischemic gerbils at 4 days (overt necrosis confined to about 17% of area CA1), the protection diminished significantly 21 days postischemia. When normothermia was maintained both during and after ischemia in a separate group of tiagabine-treated animals, approximately 77% of the CA1 pyramidal cell layer was necrotic at 4 days. Based on these findings, we suggest that (1) tiagabine slows the development of hippocampal degeneration following ischemia, and (2) that mild, postischemic hypothermia is responsible, in large part, for the neuroprotective actions of this drug. We conclude that the histological outcome after administration of cerebral neuroprotectants should be assessed following long-term survival. © 1995 Wiley-Liss, Inc.     

Riluzole, a novel antiglutamate, prevents memory loss and hippocampal neuronal damage in ischemic gerbils

The neuroprotective effects of riluzole, a novel antiglutamate, has been demonstrated in a model of ischemia induced in female Mongolian gerbils by transient bilateral carotid occlusion. Riluzole was administered at a dose of 4 mg/kg, i.p., just before, 4 hr after, and for the 14 d following the transient bilateral carotid occlusion (10 min). The functional sequelae of ischemic damage were assessed using a memory test (passive avoidance) and the extent of neuronal damage by histological examination and quantitative autoradiography of muscarinic cholinergic receptors in the hippocampus. The performance of the ischemic gerbils in the memory test was about half that of control animals. This memory deficit was completely reversed in animals treated with riluzole. This protective effect of riluzole was confirmed by histological and autoradiographic studies. The neuronal degeneration of CA1 pyramidal cells in the hippocampus observed in the ischemic group was not seen in the riluzole-treated animals, which resembled the control group. This neuronal degeneration in the CA1 area was confirmed by a quantitative measurement of muscarinic receptors: The binding was decreased by a third in the lacunosum moleculare, the stratum oriens, and the stratum radiatum. By contrast in riluzole-treated gerbils, this decrease was reversed by 50%. Finally, a clear-cut correlation was found between the deficit in the memory test and the decrease in muscarinic receptor binding in the CA1 fields. These results are compatible with the idea that glutamic acid may be involved in the neuronal degeneration of the hippocampus following ischemia, and could be foreseeable.(ABSTRACT TRUNCATED AT 250 WORDS)     

Keratinocyte growth factor prevents ischemia-induced delayed neuronal death in the hippocampal CA1 field of the gerbil brain

Fibroblast growth factors (FGFs) are polypeptides with various biological activities in vivo and in vitro, and their receptors are expressed in the widespread and specific neuronal populations of the brain. In this study, we asked whether keratinocyte growth factor (KGF), one of the FGF superfamily, would express in the brain, and have neuroprotective against ischemic brain injury. In situ hybridization analysis revealed that intense silver grains for KGF mRNA are observed in the neuronal cells of the cerebral cortex, hippocampus and amygdala in gerbil brain. Continuous cerebroventricular infusion of KGF (20 microg) for a 7 day period to gerbils starting 2 days before temporary right carotid artery occlusion (20 min) resulted in a higher survival rate than seen in vehicle-treated ischemic animals. Subsequent histological examinations showed that KGF effectively prevented delayed neuronal death of the hippocampal CA1 region. In situ detection of DNA fragmentation (TUNEL staining) revealed that ischemic animals infused with KGF contained fewer TUNEL-positive neurons in the hippocampal CA1 field than those infused with vehicle alone at the forth and seventh day after ischemia. KGF-treated brain showed over-expression of KGF mRNA in the neuronal cells of the cerebral cortex, hippocampus only in the right hemisphere, which was the side of carotid artery occlusion, 8-10 h after ischemia. These findings suggest that KGF has a protective effect against ischemic hippocampal neuronal damage in vivo, which may provide a new therapeutic strategy in the survival and reconstruction of neurons in response to cerebral injury.     

Protective effect of pitavastatin, a 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor, on ischemia-induced neuronal damage

We investigated the neuroprotective effects of a novel 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor (pitavastatin) on ischemic neuronal damage in gerbils using immunohistochemistry. The animals were allowed to survive for 14 days after 5 min of ischemia induced by bilateral occlusion of the common carotid arteries. Five days after ischemia, severe neuronal cell loss was observed in the hippocampal CA1 sector. Prophylactic treatment with pitavastatin dose-dependently prevented the hippocampal CA1 neuronal cell loss 5 days after ischemia. Immunohistochemical study did not show the change of nNOS and iNOS expression in the hippocampus except for, in a few regions, up to 1 day after ischemia. Thereafter, the expression of iNOS was observed in the hippocampal CA1 sector 5 and 14 days after ischemia. In contrast, the expression of nNOS and eNOS gradually decreased in the hippocampal CA1 sector up to 14 days after ischemia. Prophylactic treatment with pitavastatin also prevented the expression of iNOS and the decrease of eNOS expression and the number of nNOS-positive cells in the hippocampal CA1 sector 5 days after ischemia. However, prophylactic treatment with pitavastatin at a dose of 10 mg kg(-1) did not change the immunoreactivity of iNOS and nNOS in the hippocampus at an early phase after ischemia. In contrast, this drug prevented the reduction of eNOS immunoreactivity in the hippocampal CA1 neurons at an early phase after ischemia. These findings demonstrate that the HMG-CoA reductase inhibitor pitavastatin can protect hippocampal CA1 neurons after transient forebrain ischemia through up-regulation of eNOS expression in this region. Thus pharmacological modulation of eNOS expression may offer a novel therapeutic strategy for cerebral ischemic stroke.     

亚低温对大鼠短暂全脑缺血后神经元凋亡的影响

目的 探讨亚低温对大鼠脑缺血后神经元凋亡的影响，揭示亚低温的部分神经保护机制。方法 采用“双侧颈总动脉阻断＋全身低血压”方法来建立大鼠短暂性全脑缺血模型。用神经元尼氏体亚甲兰特殊染色法观察大鼠脑缺血后海马CA1区神经元损害情况；原位细胞凋亡检测法（TUNEL染色）及电镜观察脑缺血后CA1区神经元凋亡情况。结果 与假手术组、低温缺血组相比，常温缺血组海马CA1区神经元缺失明显（P＜0．01）。常温及低温缺血组海马CA1区均存在神经元凋亡，但低温缺血组海马CA1区凋亡神经元数明显少于缺血组（P＜0．01）。结论 经“双侧颈总动脉阻断＋全身低血压”方法建立的大鼠短暂全脑缺血模型证实了亚低温的脑保护作用。全脑缺血后的迟发性神经元死亡很可能经由凋亡途径，而亚低温可通过抑制缺血性神经元凋亡而发挥一定的神经保护作用。     

A model of global cerebral ischemia in C57 BL/6 mice.

A reproducible model of global cerebral ischemia in mice is essential for elucidating the molecular mechanism of ischemic neuronal injury. Such a model is particularly important in the mouse because many genetically engineered mutant animals are available. In C57BL/6 and SV129/EMS mice, we evaluated a three-vessel occlusion model. Occlusion of the basilar artery with a miniature clip was followed by bilateral carotid occlusion. The mean cortical cerebral blood flow was reduced to less than 10% of the preischemic value, and the mean anoxic depolarization was attained within 1 minute. In C57BL/6 mice, there was CA1 hippocampal neuronal degeneration 4 days after ischemia. Neuronal damage depended upon ischemic duration: the surviving neuronal count was 78.5 +/- 8.5% after 8-minute ischemia and 8.4 +/- 12.7% after 14-minute ischemia. In SV129/EMS mice, similar neuronal degeneration was not observed after 14-minute ischemia. The global ischemia model in C57BL/6 mice showed high reproducibility and consistent neuronal injury in the CA1 sector, indicating that comparison of ischemic outcome between wild-type and mutant mice could provide meaningful data using the C57BL/6 genetic background. Strain differences in this study highlight the need for consideration of genetic background when evaluating ischemia experiments in mice.     

Ischemic tolerance to memory impairment associated with hippocampal neuronal damage after transient cerebral ischemia in rats

When rats were trained preoperatively with a three-panel runway task and were then exposed to 10-min ischemia by the method of 4-vessel occlusion, they showed no increase in the number of errors (attempts to pass through two incorrect panels of the three panel-gates at four choice points), having normal retention of memory performance learned before the ischemic insult. Next, we investigated the abilities of ischemic rats to acquire the three-panel runway task and to learn a subsequent reversal task, where the correct panel-gate locations were changed. Rats with 5-min ischemia exhibited performance as good as that of control rats, but rats exposed to 10- and 20-min ischemia showed more errors than control rats during 10 acquisition sessions and 5 subsequent reversal sessions, each of which (consisting of 6 trials) was given once a day. Marked neuronal degeneration was observed in the hippocampal CA1 sector from the rats with 10- and 20-min ischemia. Exposure to sublethal 5-min ischemia followed by 10-min ischemia at a 2-h interval had no effect on either the memory impairment during acquisition and reversal tests or the hippocampal CA1 damage. When rats were exposed to 5-min ischemia 2 days before lethal 10-min ischemia, they showed acquisition and subsequent reversal learning as good as that of control rats. Preconditioning with sublethal 5-min ischemia followed by 2 days of reperfusion also prevented the neuronal destruction of the hippocampal CA1 sector induced by 10-min ischemia. These findings suggest that postischemic hippocampal CA1 neuronal damage does not affect retention of spatial memory acquired before ischemia, but produces a significant impairment of acquisition and subsequent reversal learning. The present results also demonstrate that preconditioning with sublethal ischemia can develop tolerance to subsequent lethal ischemia to prevent the learning impairment related to the hippocampal CA1 neuronal damage.