'Ischemic tolerance' phenomenon found in the brain

We investigated the possibility that neuronal cells given a mild ischemic treatment sufficient to perturb the cellular metabolism acquired tolerance to a subsequent, and what would be lethal, ischemic stress in vivo. Cerebral ischemia was produced in the gerbils by occlusion of both common carotids for 5 min, which consistently resulted in delayed neuronal death in the CA1 region of the hippocampus. Minor 2-min ischemia in this model depletes high-energy phosphate compounds and perturbs the protein synthesis, but never causes neuronal necrosis, and therefore was chosen as mild ischemic treatment. Single 2-min ischemia 1 day or 2 days before 5 min ischemia exhibited only partial protective effects against delayed neuronal death. However, two 2-min ischemic treatments at 1 day intervals 2 days before 5 min ischemia exhibited drastically complete protection against neuronal death. The duration and intervals of ischemic treatment, enough to perturb cellular metabolism and cause protein synthesis, were needed respectively, because neither 1-min ischemia nor 2-min ischemia received twice at short intervals exhibited protective effects. This 'ischemic tolerance' phenomenon induced by ischemic stress--which is unquestionably important--and frequent stress in clinical medicine, is intriguing and may open a new approach to investigate the pathophysiology of ischemic neuronal damage.     

‘Ischemic tolerance’ phenomenon found in the brain

We investigated the possibility that neuronal cells given a mild ischemic treatment sufficient to perturb the cellular metabolism acquired tolerance to a subsequent, and what would be lethal, ischemic stress in vivo. Cerebral ischemia was produced in the gerbils by occlusion of both common carotids for 5 min, which consistently resulted in delayed neuronal death in the CA1 region of the hippocampus. Minor 2-min ischemia in this model depletes high-energy phosphate compounds and perturbs the protein synthesis, but nerver causes neuronal necrosis, and therefore was chosen as mild ischemic treatment. Single 2-min ischemia 1 day or 2 days before 5 min ischemia exhibited only partial protective effects against delayed neuronal death. However, two 2-min ischemic treatments at 1 day intervals 2 days before 5 min ischemia exhibited drastically complete protection against neuronal death. The duration and intervals of ischemic treatment, enough to perturb cellular metabolism and cause protein syhthesis, were needed respectively, because neither 1-min ischemia nor 2-min ischemia received twice at short intervals exhibited protective effects. This ‘ischemic tolerance’ phenomenon induced by ischemic stress — which is unquestionably important — and frequent stress in clinical medicine, is intriguing and may open a new approach to investigate the pathophysiology of ischemic neuronal damage.     

Effect of hyperthermia on calbindin-D 28k immunoreactivity in the hippocampal formation following transient global cerebral ischemia in gerbils

Calbindin D-28K(CB), a Ca2+-binding protein, maintains Ca2+ homeostasis and protects neurons against various insults. Hyperthermia can exacerbate brain damage produced by ischemic insults. However, little is reported about the role of CB in the brain under hyperthermic condition during ischemic insults. We investigated the effects of transient global cerebral ischemia on CB immunoreactivity as well as neuronal damage in the hippocampal formation under hyperthermic condition using immunohistochemistry for neuronal nuclei(Neu N) and CB, and Fluoro-Jade B histofluorescence staining in gerbils. Hyperthermia(39.5 ± 0.2°C) was induced for 30 minutes before and during transient ischemia. Hyperthermic ischemia resulted in neuronal damage/death in the pyramidal layer of CA1–3 area and in the polymorphic layer of the dentate gyrus at 1, 2, 5 days after ischemia. In addition, hyperthermic ischemia significantly decreaced CB immunoreactivity in damaged or dying neurons at 1, 2, 5 days after ischemia. In brief, hyperthermic condition produced more extensive and severer neuronal damage/death, and reduced CB immunoreactivity in the hippocampus following transient global cerebral ischemia. Present findings indicate that the degree of reduced CB immunoreactivity might be related with various neuronal damage/death overtime and corresponding areas after ischemic insults.     

Neuroprotection of GST, an extract of traditional Chinese herb, against ischemic brain injury induced by transient brain ischemia and reperfusion in rat hippocampus

In this study, we investigated the effect of GST, an extract of Chinese traditional herb, on transient brain ischemia/reperfusion-induced neuronal cell death. Immunoblotting was used to detect the phosphorylation of MLK, JNK and c-jun. Transient (15 minutes) brain ischemia was induced by the four-vessel occlusion in Sprague-Dawley rats. GST was administrated to the SD rats 20 minutes before ischemia or 1 hour after ischemia. Our data showed that the pretreatment of GST could inhibit phosphorylation of MLK, JNK and c-jun. Moreover, GST showed potent neuroprotective effects on ischemic brain damage in vivo and administration of it 1 hour after ischemia also achieved the protective effects. These results indicate that GST has a prominent neuroprotection action against brain ischemic damage and provides a promising therapeutic approach for ischemic brain injury.     

'Ischemic tolerance' phenomenon detected in various brain regions.

We investigated the effects of mild and non-lethal ischemic insult on neuronal death following subsequent lethal ischemic stress in various brain regions, using a gerbil model of bilateral cerebral ischemia. Single 10-min ischemia consistently caused neuronal damage in the hippocampal CA1, CA2, CA3 and CA4, layer III/IV of the cerebral cortex, dorsolateral part of the caudoputamen and ventrolateral part of the thalamus. On the other hand, in double ischemia groups, 2-min ischemic insult 2 days before 10-min ischemia exhibited significant protection in the CA1 and CA3 of the hippocampus, the cerebral cortex, the caudoputamen and the thalamus. Five-min ischemic insult 2 days before 10-min ischemia also showed protective effect in the same areas as those of 2-min ischemia except for the CA1 region of the hippocampus, while 1-min ischemic insult exhibited no protective effect in any brain regions. In the immunoblot analysis, both 2- and 5-min ischemia caused increased synthesis of heat shock protein 72 (HSP 72) in the hippocampus, but 1-min ischemia did not. The present study demonstrated that the 'ischemic tolerance' phenomenon was widely found in the brain and also suggested that ischemic treatment severe enough to cause HSP 72 synthesis might be needed for induction of 'ischemic tolerance'.     

Severe global cerebral ischemia-induced programmed necrosis of hippocampal CA1 neurons in rat is prevented by 3-methyladenine: a widely used inhibitor of autophagy

The true programmed mechanisms of delayed neuronal death induced by global cerebral ischemia/reperfusion injury remain incompletely characterized. Autophagic cell death and programmed necrosis are 2 kinds of programmed cell death distinct from apoptosis. Here, we studied the death mechanisms of hippocampal cornu ammonis 1 neuronal death after a 20-minute severe global ischemia/reperfusion injury in young adult rats and the effects of 3-methyladenine (3-MA), a widely used inhibitor of autophagy. The morphological changes detected by electron microscopy, together with the activation of autophagy, transferase-mediated UTP nick end-labeling-positive neurons, and delayed death, demonstrated that cornu ammonis 1 neuronal death induced in this paradigm was programmed necrosis. No significant activation of caspase-3 after injury was detected by Western blot and immunohistochemistry. Treatment with 3-MA provided time-dependent protection against cornu ammonis 1 neuronal death at 7 days of reperfusion when it was administered before ischemia; administration 60 minutes after reperfusion was not beneficial. The redistribution of the lysosomal enzyme cathepsin B after injury was inhibited by 3-MA administered before ischemia, suggesting that this might be another important mechanism for the protective effect of 3-MA in ischemic neuronal injury.     

‘Ischemic tolerance’ phenomenon detected in various brain regions

We investigated the effects of mild and non-lethal ischemic insult on neuronal death following subsequent lethal ischemic stress in various brain regions, using a gerbil model of bilateral cerebral ischemia. Single 10-min ischemia consistently caused neuronal damage in the hippocampal CA1, CA2, CA3 and CA4, layer III/IV of the cerebral cortex, dorsolateral part of the caudoputamen and ventrolateral part of the thalamus. On the other hand, in double ischemia groups, 2-min ischemic insult 2 days before 10-min ischemia exhibited significant protection in the CA1 and CA3 of the hippocampus, the cerebral cortex, the caudoputamen and the thalamus. Five-min ischemic insult 2 days before 10-min ischemia also showed protective effect in the same areas as those of 2-min ischemia except for the CA1 region of the hippocampus, while 1-min ischemic insult exhibited no protective effect in any brain regions. In the immunoblot analysis, both 2- and 5-min ischemia caused increased synthesis of heat shock protein 72 (HSP 72) in the hippocampus, but 1-min ischemia did not. The present study demonstrated that the ‘ischemic tolerance’ phenomenon was widely found in the brain and also suggested that ischemic treatment severe enough to cause HSP 72 synthesis might be needed for induction of ‘ischemic tolerance’.     

Neuroprotective effects of bilobalide, a component of Ginkgo biloba extract (EGb 761) in global brain ischemia and in excitotoxicity-induced neuronal death

In this study, we compared the protective effect of bilobalide, a purified terpene lactone component of ginkgo biloba extract EGb 761, (definition see editorial) and EGb 761 against ischemic injury and against glutamate-induced excitotoxic neuronal death. In ischemic injury, we measured neuronal loss and the levels of mitochondrial DNA (mtDNA)-encoded cytochrome oxidase (COX) subunit III mRNA in vulnerable hippocampal regions of gerbils. At 7 days of reperfusion after 5 min of transient global ischemia, a significant increase in neuronal death and a significant decrease in COX III mRNA were observed in the hippocampal CA1 neurons. Oral administration of EGb 761 at 25, 50 and 100 mg/kg/day and bilobalide at 3 and 6 mg/kg/day for 7 days before ischemia progressively protected CA1 neurons from death and from ischemia-induced reductions in COX III mRNA. In rat cerebellar neuronal cultures, addition of bilobalide or EGb 761 protected in a dose-dependent manner against glutamate-induced excitotoxic neuronal death (effective concentration [EC (50)] = 5 microg/ml (12 microM) for bilobalide and 100 microg/ml for EGb 761. These results suggest that both EGb 761 and bilobalide are protective against ischemia-induced neuronal death in vivo and glutamate-induced neuronal death in vitro by synergistic mechanisms involving anti-excitotoxicity, inhibition of free radical generation, scavenging of reactive oxygen species, and regulation of mitochondrial gene expression.     

异丙酚对全脑缺血大鼠海马CA_1区锥体神经元的保护作用

目的 观察不同剂量、给药时间点及给药方式的异丙酚对全脑缺血大鼠海马CA_1区锥体细胞的保护作用.方法 80只雄性Wistar大鼠按照不同的给药剂量、给药时间点及方式随机分组.采用4血管闭塞法制造大鼠全脑缺血模型,硫堇染色下对锥体细胞的死亡进行评估.结果 异丙酚可剂量依赖性地保护锥体细胞,给药时间点越接近脑缺血,异丙酚的神经保护作用越明显.持续静脉输注异丙酚的神经保护作用较好.结论 在脑缺血前后的"有效时间窗"内,静脉持续输注麻醉剂量的异丙酚可有效地保护神经元.     

Prevention of delayed neuronal death in gerbil hippocampus by a novel vinca alkaloid derivative (Vinconate)

We investigated the effect of vinconate, a novel vinca alkaloid derivative, on delayed neuronal death using Mongolian gerbils. The animals were allowed to survive for 7 d after 3 or 5 min of forebrain ischemia induced by bilateral occlusion of the common carotid arteries. Morphological changes and calcium (⁴⁵Ca) accumulation were evaluated in the CA1 sector of the hippocampus after ischemia. Vinconate (50, 100, and 300 mg/kg) showed protective effects against neuronal death in a dose-dependent manner when administered intraperitoneally (ip) 10 min before 5 min of ischemia. However, the administration of vinconate (100 and 300 mg/kg, ip) immediately after 5 min of ischemia showed no therapeutic effect, whereas a marked therapeutic effect of vinconate (50 and 100 mg/kg, ip) was observed when administered immediately after 3 min of ischemia. An anesthetic dose of pentobarbital (40 mg/kg, ip) also produced significant protection against neuronal death. Furthermore, a⁴⁵Ca autoradiographic study indicated that a marked calcium accumulation was found in the CA1 sector at 7 d after 5 min of ischemia, which was consistent with the extent of histological neuronal damage. When vinconate (100 and 300 mg/kg, ip) was administered 10 min before 5 min of ischemia, the abnormal calcium accumulation was not detected in the CA1 sector. These data indicate that suppression of abnormal neuronal activity may be owing to the antagonistic action of vinconate on calcium accumulation.     

沙鼠脑缺血耐受的组织学变化及HSP在其中的作用

目的 :观察脑缺血耐受时的组织学变化及 HSP在其中的作用。方法 :通过 HE染色观察脑缺血耐受时的组织学变化 ,并通过免疫组化染色 ,了解 HSP70及 HSP2 7在其中的作用。结果 :一次性 5分钟缺血后 7天海马 CA1区神经元大多坏死 ,若在缺血前给予 2分钟的缺血预处理 ,该区神经元大多保留 ,表现出明显的保护作用。只给一次性 5分钟缺血 ,海马 CA1区神经元无 HSP70染色。若在缺血前给予预处理 ,海马 CA1区神经元可见明显 HSP70染色。而HSP2 7主要在胶质细胞表达 ,海马区的神经元未见其表达。结论 :缺血前给予预处理对以后的缺血有保护作用 ;在缺血耐受过程中 ,HSP70表达出一定的保护作用。     

Neuroprotective effects of riluzole: an electrophysiological and histological analysis in an in vitro model of ischemia.

The protective effects of riluzole against the neuronal damage caused by O2 and glucose deprivation (ischemia) was investigated in rat cortical slices by recording electrophysiologically the cortico-cortical field potential and by evaluating histologically the severity of neuronal death. Five minutes of ischemia determined an irreversible depression of the amplitude of the field potential. In addition, this insult caused a clear enhancement of the number of death cells that were specifically colored with trypan blue (a vital colorant which stains altered cells). We found that riluzole, which by itself depressed the synaptic transmission, neuroprotected when perfused 15-20 min before and during ischemia. In fact, due to the treatment with riluzole, the ischemia-induced irreversible depression of the field potential recovered and less cells were stained with trypan blue. These findings demonstrate that riluzole prevents neuronal death in an in vitro model of ischemia and suggest a therapeutic use of this drug in order to reduce the pathophysiological outcomes of stroke.     

Hyperthermic pre-conditioning protects retinal neurons from N-methyl-D-aspartate (NMDA)-induced apoptosis in rat

Glutamate-induced excitotoxicity is associated with a selective loss of retinal neurons after retinal ischemia and possibly in glaucoma. Since heat shock protein (HSP) 70 is known to play a protective role against ischemic neuronal injury, which is also linked to excitotoxicity, we studied the expression of inducible (HSP72) and constitutive (HSC70) forms of HSP70 in apoptosis of retinal ganglion cells (RGCs) after intravitreal injection of 8 nmoles N-methyl-D-aspartate (NMDA), a glutamate receptor agonist. Approximately 18 h after NMDA injection, there were increased numbers of TUNEL-positive cells and cells with elevated HSP72 immunoreactivity in the retinal ganglion cell layer (RGCL), but there were no noticeable changes in HSC70 immunoreactivity. These HSPs positive cells were also Thy-1 positive, a marker for RGCs. Hyperthermic pre-conditioning, which is known to induce HSPs, given 6 or 12 h prior to NMDA injection ameliorated neuronal loss in the RGCL as counted 7 days after NMDA injection but pre-conditioning at 18 h prior to NMDA injection did not have any ameliorative effect. Quercetin, an inhibitor of HSP synthesis, abolished the ameliorative effect of hyperthermic pre-conditioning. Pre-conditioning elevated HSP72 but not HSC70 immunoreactivity and reduced the number of TUNEL-positive cells in the RGCL at 18 h. Our results suggest that intravitreal injection of NMDA induces an up-regulation of HSP72 in a time-dependent manner but not HSC70 in RGCs, indicating a stress response of HSP72 in RGCs and other inner retinal neurons after exposure to NMDA. Hyperthermic pre-conditioning given within a therapeutic window is neuroprotective to the retina against NMDA-induced excitotoxicity, likely by inhibiting apoptosis through the modulation of HSP72 expression.     

Effects of hyperthermia on the effectiveness of MK-801 treatment in the gerbil hippocampus following transient forebrain ischemia

The effects of dizocilipine maleate (MK-801), a noncompetitive N-methyl-D-aspartate (NMDA) receptor/channel antagonist, were tested on the dysfunction of neurotransmitter and signal transduction systems and morphological damage 7 days after transient forebrain ischemia in gerbils. Neurotransmitter system (adenosine A1, muscarinic cholinergic receptor) and signal transduction system (inositol 1,4,5-trisphosphate receptor: IP3, protein kinase C: PKC, L-type calcium channels) binding sites were mapped by in vitro quantitative receptor autoradiography. All ligands used in the present study decreased significantly in the CA1 subfield 7 days after ischemia. In normothermic animals, pretreatment with MK-801 failed to protect against decreased receptor binding in the hippocampus 7 days after ischemia. Moreover, in a morphological study, pre- and posttreatment of MK-801 failed to show protective effects against ischemic neuronal damage. On the other hand, pretreatment of MK-801, without maintaining body temperature, prevented the neuronal death of CA1 subfield 7 days after ischemia. These results weaken the hypothesis that NMDA receptor/channel may play a pivotal role in the pathogenesis of neuronal damage after transient forebrain ischemia.     

Resveratrol prevents CA1 neurons against ischemic injury by parallel modulation of both GSK‐3β and CREB through PI3‐K/Akt pathways

Accumulating evidence indicates that resveratrol potently protects against cerebral ischemia damage due to its oxygen free radicals scavenging and antioxidant properties. However, cellular mechanisms that may underlie the neuroprotective effects of resveratrol in brain ischemia are not fully understood yet. This study aimed to investigate the potential association between the neuroprotective effect of resveratrol and the apoptosis/survival signaling pathways, in particular the glycogen synthase kinase 3 (GSK‐3β) and cAMP response element‐binding protein (CREB) through phosphatidylinositol 3‐kinase (PI3‐K)‐dependent pathway. An experimental model of global cerebral ischemia was induced in rats by the four‐vessel occlusion method for 10 min and followed by different periods of reperfusion. Nissl staining indicated extensive neuronal death at 7 days after ischemia/reperfusion. Administration of resveratrol by i.p. injections (30 mg/kg) for 7 days before ischemia significantly attenuated neuronal death. Both GSK‐3β and CREB appear to play a critical role in resveratrol neuroprotection through the PI3‐K/Akt pathway, as resveratrol pretreatment increased the phosphorylation of Akt, GSK‐3β and CREB in 1 h in the CA1 hippocampus after ischemia/reperfusion. Furthermore, administration of LY294002, an inhibitor of PI3‐K, compromised the neuroprotective effect of resveratrol and decreased the level of p‐Akt, p‐GSK‐3β and p‐CREB after ischemic injury. Taken together, the results suggest that resveratrol protects against delayed neuronal death in the hippocampal CA1 by maintaining the pro‐survival states of Akt, GSK‐3β and CREB pathways. These data suggest that the neuroprotective effect of resveratrol may be mediated through activation of the PI3‐K/Akt signaling pathway, subsequently downregulating expression of GSK‐3β and CREB, thereby leading to prevention of neuronal death after brain ischemia in rats.     

Protective effects of serotonin reuptake inhibitors, citalopram and clomipramine, against hippocampal CA1 neuronal damage following transient ischemia in the gerbil

To clarify the role of serotonin in cerebral ischemia, we examined the effects of selective serotonin reuptake inhibitors, citalopram and clomipramine, on ischemic neuronal damage in the gerbil. Pretreatment with citalopram (40 mg/kg i.p.) and clomipramine (20 mg/kg i.p.) protected against neuronal destruction of hippocampal CA1 pyramidal cells following 5 min of forebrain ischemia. Furthermore, microdialysis assays showed that a striking increase in extracellular excitatory amino acid levels during ischemia was significantly inhibited by pretreatment with citalopram and clomipramine. However, citalopram (40 mg/kg i.p.) did not alter the extracellular amino acid concentrations in normal gerbils. Thus, serotonin reuptake inhibitors have a protective effect against ischemic neuronal damage. Furthermore, the present result suggests that the protective effect is mediated through prevention of the accumulation of extracellular excitatory amino acids during and after ischemia.     

Temporal profile of the effects of pretreatment with brief cerebral ischemia on the neuronal damage following secondary ischemic insult in the gerbil: cumulative damage and protective effects

We examined the response of the gerbil brain to secondary ischemic insult following pretreatment with brief ischemia at intervals of 5 min, 1 and 6 h, 1, 2, 4, 7 and 14 days. Two minutes of bilateral carotid artery occlusion produced no histopathological brain damage, whereas 3 min of occlusion caused a moderate to severe reduction in the number of hippocampal CA1 pyramidal cells. Two-minute occlusion followed by 3-min occlusion at 5-min, 1- and 6-h intervals resulted in almost complete destruction of CA1 neurons. Additional neuronal damage was observed in the striatum at a 1-h interval and in the thalamus and the neocortex at 1- and 6-h intervals. The neuronal damage was most severe at a 1-h interval. Two-minute ischemia followed by 3-min ischemia at intervals of 1, 2, 4 and 7 days, however, caused a marked protective effect, and the hippocampal CA1 neurons were preserved. The protective effect was not observed at a 14-day interval and following pretreatment with 1-min ischemia. Thus, pretreatment with brief ischemia leads to complex responses of the brain to secondary ischemic insult; cumulative damage at intervals of 1-6 h and protective effects at intervals of 1-7 days.     

MRS Metabolic Markers of Seizures and Seizure-Induced Neuronal Damage

Summary: Purpose: Proton magnetic resonance spectroscopy (MRS) was used to identify specific in situ metabolic markers for seizures and seizure-induced neuronal damage. Kainic acid (KA)-induced seizures lead to histopathologic changes in rat brain. The protective effect of cycloheximide treatment against neuronal damage caused by KA-induced seizures was studied, using in situ proton MRS imaging technique.
Methods: Rats were pretreated with placebo or cycloheximide 1 h before KA injection. Rat brains (n = 25) were scanned at the level of the hippocampus before, during, and 24 h after seizures. Spectra were recorded and the relative ratios of N-acetylaspartate (NAA), choline (cho), and lactate (Lac) to creatine (Cr) were calculated and compared between groups.
Results: A significant increase in Lac ratios was observed in KA-treated rats during and 24 h after seizure onset and this increase was prevented by cycloheximide pretreatment. NAA ratios were significantly higher during the ictal phase following KA treatment and this effect was not affected by cycloheximide pretreatment. Nissl staining confirmed previously reported prevention of KA-induced neuronal loss in CA1 and CA areas of the hippocampus by cycloheximide pretreatment.
Conclusions: Our results suggest that in situ Lac increase is a marker of seizure-induced neuronal damage, whereas N-acetylaspartate (NAA) changes during and after status epilepticus may be a reflection of neuronal activity and damage, respectively.     

Acetoacetate protects neuronal cells from oxidative glutamate toxicity

Glutamate cytotoxicity contributes to neuronal degeneration in many central nervous system (CNS) diseases, such as epilepsy and ischemia. We previously reported that a high-fat and low-carbohydrate diet, the ketogenic diet (KD), protects against kainic acid-induced hippocampal cell death in mice. We hypothesized based on these findings that ketosis resulting from KD might inhibit glutamate cytotoxicity, resulting in inhibition of hippocampal neuronal cell death. Therefore, we investigated the role of ketone bodies [acetoacetate (AA) and beta-hydroxybutyrate (beta-OHB)] both in a mouse hippocampal cell line (HT22) and in rat primary hippocampal neurons. As a result, we found that pretreatment with 5 mM lithium AA and 4 mM Na beta-OHB protected the HT22 hippocampal cell line and primary hippocampal neuronal culture against 5 mM glutamate toxicity and that up to 2 hr of pretreatment with 5 mM AA had a protective effect against 5 mM glutamate toxicity in the HT22 cell line. Pretreatment with 5 mM AA decreased ROS production of HT22 cell line at 2 and 8 hr exposure of glutamate, and it decreased the appearance of annexin V-positive HT22 cells, which are indicative of an early stage of apoptosis, and propidium iodide-positive HT22 cells, which are indicative of necrosis.     

神经生长因子对大鼠脑缺血再灌注海马神经细胞损伤的影响

目的 :观察神经生长因子 (NGF)对脑缺血再灌注后海马CA1区神经细胞损伤的影响。方法 :采用大鼠脑缺血再灌注模型 ,在光镜和透射电镜下观察NGF治疗组和缺血再灌组动物脑缺血 3 0min再灌注 2 4h和 72h时海马组织学及超微结构的改变。结果 :在缺血 3 0min再灌注 2 4h和 72h时 ,NGF治疗组海马CA1区神经细胞的结构损伤与缺血再灌组比较显著减轻 ;NGF可以减轻海马迟发性神经细胞死亡 (DND)性损伤。结论 :NGF对缺血再灌注所致的神经细胞损伤可能具有一定的保护作用