Hypothermia inhibits ischemia-induced efflux of amino acids and neuronal damage in the hippocampus of aged rats

Brain hypothermia has been reported to protect against ischemic damages in adult animals. Our goal in this study was to examine whether brain hypothermia attenuates ischemic neuronal damages in the hippocampus of aged animals. We also determined effects of hypothermia on ischemia-induced releases of amino acids in the hippocampus. Temperature in the hippocampus of aged rats (19-23 months) was maintained at 36 degrees C (normothermia), 33 degrees C (mild hypothermia) or 30 degrees C (moderately hypothermia) using a thermoregulator during 20 min of transient forebrain ischemia. Cerebral ischemia increased extracellular concentrations of glutamate and aspartate by 6- and 5-fold, respectively, in the normothermic group. Mild and moderate hypothermia, however, markedly inhibited the rise of these amino acids to less than 2-fold. Elevation of extracellular taurine, a putative inhibitory amino acid, was 16-fold in the normothermic rats. Mild hypothermia attenuated ischemia-induced increase in taurine (10-fold), and moderate hypothermia inhibited the increase. Ischemic damages, evaluated by histopathological grading of hippocampal CA1 area 7 days after ischemia, was significantly ameliorated in the mild (1.3+/-0.5, mean+/-S.E.M.) and moderate hypothermic rats (0.8+/-0.3) compared with the normothermic ones (3.4+/-0.4). These results suggest that brain hypothermia protects against ischemic neuronal damages even in the aged animals, and the protection is associated with inhibition of excessive effluxes of both excitatory and inhibitory amino acids.     

Differential temperature sensitivity of ischemia-induced glutamate release and eicosanoid production in rats

The effect of mild and moderate hypothermia on ischemia-induced glutamate release and eicosanoid production was evaluated in WKY rats subjected to incomplete forebrain ischemia. Under isoflurane anesthesia, microdialysis probes were inserted into the hippocampus and caudate nucleus. In four groups of rats, the intraischemic temperature was maintained at either 38°C (normothermia), 36°C, 34°C (mild hypothermia) and 30°C (moderate hypothermia). In these groups, normothermia was restored immediately upon reperfusion. In two additional groups, both intra- and post-ischemic temperatures were maintained at either 34°C or 30°C. The levels of glutamate were measured in the dialysate collected during ischemia and the levels of TxB₂, 6-keto-PGF₁ and PGF₂ were measured in dialysate collected prior to and after ischemia. As expected, hypothermia reduced ischemia-induced glutamate release in both structures. However, the application of mild hypothermia did not attenuate post-ischemic levels of all eicosanoids measured. Moderate hyothermia (30°C) attenuated the post-ischemic increase in the levels of PGF₂. The data suggest that the processes that lead to eicosanoid formation are less sensitive to temperature reduction than those that lead to glutamate release.     

Effects of the anion channel blocker DIDS on ouabain- and high K(+)-induced release of amino acids from the rat cerebral cortex

Amino acid release from the rat cerebral cortex was analyzed using an in vivo cortical cup perfusion model. Topical applications of ouabain or high extracellular K(+) were used to mimic two dimensions of ischemic conditions which promote cell swelling and amino acid release. Ouabain (30 microM) induced significant releases of taurine, gamma-aminobutyric acid (GABA), aspartate, glutamate and phosphoethanolamine. The anion channel blocker, 4, 4'-diisothiocyanatostilbene-2, 2'-disulfonic acid (DIDS; 1 mM), inhibited ouabain-induced release of all these amino acids except for glutamate. Exposure to high extracellular K(+) (75 mM) induced a delayed rise in the levels of taurine in the superfusates and an immediate increase in GABA levels. There were no significant releases of other amino acids. The release of taurine and GABA was sensitive to the blocking of anion channels with DIDS. Both ouabain- and high K(+)-induced taurine release is likely to be mediated by DIDS sensitive anion channels. The extracellular accumulation of the other amino acids, where insensitive to DIDS, may be mediated by mechanisms other than swelling-induced anion channels.     

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.     

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     

Ischemic tolerance and extracellular amino acid concentrations in gerbil hippocampus measured by intracerebral microdialysis

Preconditioning of the brain with sublethal ischemia induces tolerance to subsequent longer periods of ischemia. To elucidate the role of excitatory and inhibitory amino acids in the induction of ischemic tolerance, we measured the extracellular concentrations of the amino acids in the gerbil hippocampus with intracerebral microdialysis. Mongolian gerbils were subjected to 3 min of forebrain ischemia 4 days after preconditioning with 2 min of ischemia or sham operation. Microdialysis probes were implanted into the hippocampus before the second ischemia and the amino acid concentrations in the dialysates were measured with HPLC. During and immediately after 3 min of ischemia without preconditioning, the concentrations of glutamate, glycine, γ-aminobutyric acid, and taurine, but not glutamine, increased significantly. The increased amino acid levels rapidly returned to baseline after reperfusion. Preconditioning of the brain did not alter the amount of any amino acid released during and after the second ischemia. The excitotoxic index also unchanged in the preconditioned hippocampus. Thus, the results clearly show that ischemic tolerance is not induced through the alteration of the amounts of excitatory and inhibitory amino acids released during subsequent ischemia.     

鼠脑反复缺血再灌注海马6种氨基酸、单胺递质及其代谢产物变化的研究

目的：研究脑反复缺血后海马细胞外液氨基酸和单胺递质及其代谢产物的变化规律。方法：采用Ｐｕｌｓｉｎｅｌｌｉ和Ｂｒｉｅｒｌｅｙ４血管闭塞的方法,使鼠脑反复缺血,海马微管透极与高压液相电化学检测,观察细胞外谷氨酸（Ｇｌｕ）,天门冬氨酸（Ａｓｐ）,谷氨酰胺,牛磺酸、丙氨酸,丝氨酸,多巴胺（ＤＡ）,５－羟色胺（５－ＨＴ）及其代谢产物浓度的变化。结果：缺血期,Ｇｌｕ和Ａｓｐ骤然增高５０倍和３０倍。缺血期ＤＡ和５－ＨＴ含量分别增加３０倍和５０倍,随后逐渐下降,再灌注１００ｍｉｎ恢复到基线水平,与此同时,其酸性代谢产物３,４－二羟苯乙酸（ＤＯＰＡＣ）,高香草酸（ＨＶＡ）,５－羟吲哚乙酸（５－ＨＩＡＡ）在缺血期明显下降。结论：缺血期海马细胞外液兴奋性氨基酸和单胺递质急剧大量释放并触发膜离子通道改变。Ｃａ＾＋超载,自由基反应,共同     

Effect of ibuprofen on regional eicosanoid production and neuronal injury after forebrain ischemia in rats

Post-ischemic metabolism of arachidonic acid by cyclooxygenase results in the elaboration of numerous eicosanoids and in the generation of free radicals. Accordingly, the effect of cyclooxygenase inhibition by ibuprofen on post-ischemic eicosanoid production and delayed neuronal death was evaluated in Wistar-Kyoto rats subjected to incomplete forebrain ischemia. In control (C) and ibuprofen-treated groups (n = 5 each), pre- and post-ischemic eicosanoid production in the caudate nucleus (CN) and dorsal hippocampus (HPC) were evaluated by microdialysis. The ibuprofen-treated animals were given ibuprofen, 15 mg/kg i.v., prior to insertion of microdialysis probes. Forebrain ischemia was induced by bilateral carotid artery occlusion (BCAO) for 10 min with simultaneous hypotension to 35 Torr. The concentrations of thromboxane B₂ (TxB₂), 6-keto-PGF_1α and PGF_2α in the microdialysate were measured by radioimmunoassay. In two additional concurrent groups of rats (>n = 10 each), neuronal injury in the HPC, CN and cortex (parietal, temporal and entorhinal regions) was evaluated histologically three days after 10 min of forebrain ischemia with and without pre-ischemic ibuprofen administration. In the control microdialysis group, levels of TxB₂, 6-keto-PGF_1α and PGF_2α increased in both CN and HPC after probe insertion. These probe related increases were substantially reduced in the ibuprofen group. After ischemia and reperfusion in the control group, the levels of TxB₂ and PGF_2α increased in both CN and HPC. Levels of 6-keto-PGF_1α increased in the CN but not in the HPC. The administration of ibuprofen substantially reduced post-ischemic TxB₂ and PGF_2α levels in both CN and HPC and decreased 6-keto-PGF_1α levels in the CN. The results of these initial microdialysis studies left the possibility that, in the ibuprofen group, the reduction in eicosanoid levels after probe penetration might have influenced the subsequent post-ischemic eicosanoid production. Therefore, in an additional group of animals (n = 5), ibuprofen was administered after probe insertion. Only PGF_2α levels were measured in this group. Increased levels of PGF_2α comparable to the original control group were detected after probe penetration. Nonetheless, after ibuprofen administration, the pre- and post-ischemic levels of PGF_2α were again significantly reduced. In the histologic evaluation groups, overall neuronal injury was significantly less in the ibuprofen treated animals. This protective effect of ibuprofen was most clearly evident in the CA3 sector of the HPC. The data suggest that metabolism of arachidonic acid by cylooxygenase may contribute to post-ischemic neuronal injury, though the relative contributions of eicosanoids per se and of free radicals remains undefined.     

Re-evaluation of ischemia-induced neuronal damage in hippocampal regions in the normothermic gerbil

Summary It has not been discussed whether transient forebrain ischemia of 5-min duration, which is a model frequently used to evaluate pharmacological protection against ischemic injury, is an optimal model in the CA1 field of this animal whose brain temperature is maintained at normothermic levels. The temperature of the brain during an ischemic insult strongly affects the extent of the resulting neuronal injury. If the brain temperature is not regulated, it usually falls in the gerbil by 2°–4°C during 5-min ischemia. However, the brain temperature during ischemic insult was not regulated in many previous studies. In the present study, the effects of transient (1 to 5 min) forebrain ischemia on the development of neuronal degeneration in hippocampal regions of the gerbil whose brain temperature was maintained at 37°C were examined. In the CA1 field of the hippocampus, transient ischemia of 3- and 4-min duration caused almost the same maximal damage (88%–91% neuronal loss) as observed in the gerbils subjected to 5-min ischemia. Transient ischemia of 2-and 2.5-min duration provoked substantial neuronal damage in 25% and 55% of experimental gerbils, respectively. These results indicate that 5-min bilateral forebrain ischemia is more than is necessary to examine ischemiainduced neuronal degeneration in hippocampal CA1 field of the gerbil whose brain temperature is maintained at normothermic levels. In the normothermic gerbil brain, an ischemic period of 3-min already induces extensive neuronal death in the CA1 and, thus, constitutes a sensitive model to evaluate faint protective effects of drugs against ischemic injury in the normothermic gerbil.Supported by Grant-in-Aid for Encouragement of Young Scientist (03857019) from the Ministry of Education, Science and Culture of Japan and the Sasakawa Health Science Foundation to A.M., and Grants-in-Aid for General Scientific Research (01400004 and 03557007) from the Ministry of Education, Science and Culture of Japan, Japan Foundation for Aging and Health and Mitsui Life Social Welfare Foundation to K.K.     

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.     

17β-雌二醇对新生大鼠缺氧缺血性脑损伤的保护作用

目的　研究 17β 雌二醇 (17β E2 )对新生大鼠缺氧缺血脑损伤 (HIBD)后谷氨酸 (Glu)释放的影响 ,探讨 17β E2 是否对HIBD有保护作用。方法　 7日龄Wistar大鼠随机分为三组 ,A、B组为分别在HIBD模型制作前、后腹腔注射 17β E2 (10 0 μg·kg-1) ,C组在HIBD模型制作前腹腔注射等量的生理盐水。注射17β E2 后的不同时间取血检测 17β E2 的浓度。HIBD后 4h处死大鼠 ,用氨基酸分析仪检测脑组织匀浆上清液中Glu的含量。结果　 17β E2 血浓度在注射后 5min达到高峰 ,随后下降。A、B组较C组Clu含量明显下降 (P <0 .0 5 ) ,A、B两组Glu含量没有显著差异 (P >0 .0 5 )。结论　 17β E2 能明显降低HIBD后Glu的释放 ,减轻神经元损伤     

脑缺血选择性海马CA1区神经元损害的实验研究

采用Ｐｕｌｓｉｎｅｌｉ－Ｂｒｉｅｒｌｅｙ４血管阻塞脑缺血模型观察了大鼠全脑缺血２０ｍｉｎ再灌流８ｈ，ｃ－ｆｏｓ基因表达及再灌流７ｄ海马ＣＡ１区迟发性神经元损害。在缺血再灌流早期（８ｈ）海马ＣＡ１区极少ｃ－ｆｏｓ表达，而齿状回、海马ＣＡ３区、杏仁核大量ｃ－ｆｏｓ表达。缺血再灌流晚期（７ｄ）镀银染色显示海马ＣＡ１区神经元及其突触终末带呈黑色溃变相，而齿状回、海马ＣＡ３区、杏仁核呈金黄色正常相。相邻切片ＨＥ染色示缺血组海马ＣＡ１区核完整的锥体细胞数（５±２．６个／２００μｍ）与对照组（４０±２．９个／μｍ）比较差异有显著意义（Ｐ＜０．０１）。脑缺血诱导的ｃ－ｆｏｓ基因表达对于缺血易损海马ＣＡ１区迟发性神经元坏死可能起直接的调控作用。     

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)     

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.     

Environmental enrichment promotes neurogenesis and changes the extracellular concentrations of glutamate and GABA in the hippocampus of aged rats

The aim of the present study was to investigate the effects of environmental enrichment on the neurogenesis and the extracellular concentrations of glutamate and GABA in the hippocampus of freely moving young and aged rats. Male Wistar rats of 2 (young) and 25 (old) months of age were housed during 8 weeks in an enriched environment; control rats were kept in individual plastic cages during that same period of time. Rats were injected intraperitoneally with bromodeoxyuridine (BrdU; 40 mg/kg; 7 days) during the fourth week of the housing period to detect neurogenesis in the dentate gyrus (DG) of the hippocampus. Rats were sacrified 6 weeks after the last injection of BrdU. During the last week of housing, rats were tested in the water maze for the evaluation of spatial learning. After the housing period, rats were stereotaxically implanted with guide-cannulas to accommodate microdialysis probes in the CA3 area of the hippocampus and the extracellular concentrations of glutamate and GABA were determined. Aged rats showed a decrease in the number of BrdU positive cells in the dentate gyrus compared to young rats. However, neurogenesis in the dentate gyrus of both young and old rats was increased in animals housed in an enriched environment. Microdialysis experiments in the CA3 area of the hippocampus showed that enriched housing conditions increased basal extracellular concentrations of glutamate in aged rats. Perfusion of KCl 100 mM produced a higher increase of extracellular glutamate and GABA in aged rats but not in young rats housed in an enriched environment compared to control rats. These results suggest that enriched housing conditions change both neurogenesis in the dentate gyrus and glutamate and GABA levels in the CA3 area of the hippocampus of aged rats.     

The effect of MK-801 on extracellular neuroactive amino acids in hippocampus after closed head injury followed by hypoxia in rats

Increased neuronal vulnerability to ischemia or hypoxia has been demonstrated following traumatic brain injury but not explained. Animal data suggest that neuronal damage after traumatic brain injury is caused mainly by massive glutamate release that activates N-methyl- -aspartate (NMDA) receptors. Using rat models with controlled closed head injury (CHI) followed by hypoxia, we investigated extracellular concentrations of neuroactive amino acids in the hippocampus by in vivo microdialysis. CHI alone produced an immediate increase of glutamate and taurine; hypoxia alone did not alter amino acid concentrations. CHI followed by hypoxia produced a biphasic increase in extracellular glutamate and taurine, with an immediate peak after CHI and a prolonged plateau after hypoxia. Though changes in γ-aminobutylic acid (GABA) concentration is also prolonged by combined traumatic and hypoxic insults, it showed less alteration than glutamate. Pre-treatment with dizocilpine maleate (MK-801), a non-competitive NMDA antagonist, did not affect the immediate peak of glutamate after CHI but significantly diminished the prolonged plateau after hypoxia. These findings suggest that traumatic brain injury may increase hypoxic release of glutamate, contributing to increased vulnerability to hypoxia. Our data suggest that MK-801 may be beneficial in preventing secondary neuronal damages by hypoxia.     

托吡酯对大鼠脑缺血时海马细胞外液兴奋性氨基酸释放的影响

目的　观察托吡酯对大鼠脑缺血时海马细胞外液兴奋性氨基酸释放的影响 ,探讨托吡酯在脑梗死治疗中应用的可能性。方法　建立大鼠脑缺血模型 ,给予托吡酯干预 ,应用微透析方法观察大鼠海马细胞外液中兴奋性氨基酸及抑制性氨基酸的变化。结果　脑缺血后兴奋性氨基酸和抑制性氨基酸的释放均增加 ,而给予托吡酯干预后 ,脑缺血后兴奋性氨基酸的释放明显减少 ,而抑制性氨基酸的释放明显增加。结论　托吡酯能有效地抑制脑缺血中兴奋性氨基酸的释放 ,能减轻兴奋性氨基酸的毒性作用。     

大鼠脑缺血再灌流后海马氨基酸水平变化与神经元损害的关系探讨

目的探讨脑缺血再灌流后海马氨基酸递质变化与神经元损害的关系。方法建立大鼠前脑缺血再灌流模型,测定海马ＣＡ１区和ＣＡ３／齿状回区游离氨基酸含量,观察阻断隔－海马通路对海马神经元损害和氨基酸水平的影响。结果（１）海马结构中仅ＣＡ１区神经元明显损害,但ＣＡ１区和ＣＡ３／齿状回区的Ｇｌｕ、Ａｓｐ和ＧＡＢＡ含量无差异。（２）阻断隔－海马通路可明显减轻海马神经元损害,但对海马氨基酸水平变化无影响。结论脑缺血再灌流后,氨基酸递质水平的异常变化不是海马ＣＡ１区神经元选择性易损的唯一决定因素,隔－海马通路末梢释放的神经递质也参与海马神经元损害过程。     

The disruption of spatial cognition and changes in brain amino acid, monoamine and acetylcholine in rats with transient cerebral ischemia

We investigated the disruption of spatial cognition due to transient forebrain ischemia using an 8-arm radial arm maze task in rats. Five or 10 min of ischemia did not affect the task acquisition. When rats established spatial cognition by daily training of the task, 10 min of ischemia significantly decreased the number of correct choices and increased the errors in the task when performed 24 h after reperfusion. These changes, however, returned to the normal level after about 4 days of daily training. Glutamic acid (Glu) and acetylcholine (ACh) release from the dorsal hippocampus (DH) was observed to transiently increase during ischemia. However, neither the content of noradrenaline (NA) nor the release of NA in the DH changed during ischemia. The NA and ACh release from the DH, however, gradually decreased during reperfusion, and the decrease became significant at 24 h after reperfusion. The NA content of the frontal cortex (FO and the DH increased 7 days after reperfusion. These results suggest that the disruption of spatial cognition induced by 10 min of ischemia may be attributed to a greater degree to the dysfunction of the hippocampal ACh and NA, and cortical NA systems, rather than to the development of neuronal cell death in these areas.     

老龄大鼠脑缺血再灌注血脑屏障损伤的变化及意义

目的研究老龄大鼠脑缺血再灌注（I／R）血脑屏障（BBB）损伤特点。方法采用大脑中动脉栓塞法复制局灶性脑缺血模型，随机分组，观察脑组织含水量、病理变化、免疫球蛋白（IgG）。结果随着再灌注时间的延长，BBB损伤逐渐加重，含水量增加和IgG漏出以I／R24h、3d显著；模型组含水量（I／R 12h～6d）较假手术组升高；青年模型（I／R12h～6d）和老龄模型（I／R 6h～6d）IgG漏出分别较青年和老龄脑缺血3h组增加；老龄模型组（I／R 12h～I／R6d）IgG的漏出高于同时间青年模型组。结论脑水肿和BBB损伤随着再灌注时间的延长而加重，IgG漏出老年较青年明显，血脑屏障的增龄变化可能是其机制之一。