Mechanism of ischemic neuronal death

在此，我们对“缺血性神经元死亡机制”项目进行了三年的研究，取得的新发现进行了总结。延迟性神经元死亡，选择性发生在短暂性前脑缺血后2-3天的海马CAl区，对损伤期间的脑温度高度敏感，轻度低温（如降低4℃）几乎完全保护神经元免受损伤。损伤时完全消失的CAl神经元自发放电随着脑再灌注开始恢复，但放电频率明显不超过缺血前水平；这一事实与先前认为神经元延迟死亡是由于CAl神经元的缺血后过度兴奋性的观点不一致。沙鼠海马微透析结合酶循环方法的研究表明，前脑缺血诱导谷氨酸的快速和低温敏感性释放（缺血5分钟时15-20倍于缺血前水平），然后迅速恢复到缺血前范围。利用沙鼠海马切片，我们在荧光显微镜上开发了一种微荧光测定法——一种超灵敏的摄像机——一种图像分析仪装置。灌注低氧低血糖诱导全海马区域在损伤后20秒内产生区域性非选择性谷氨酸释放，随后在200秒内CAl区出现区域性选择性钙积累并伴有膜去极化。亚低温以剂量依赖性方式延长潜伏期。综上所述，缺血诱导的谷氨酸释放和随后的细胞内钙积累可能是缺血性神经元损伤早期最关键的过程。

We summarize herewith new findings obtained during the threeyear-research project "Mechanism of ischemic neuronal death".1. Delayed neuronal death, selectively occurred in hippocampal CAl area 2-3 days after transient forebrain ischemia, is highly sensitive to cerebral temperature during the insult, and mild hypothermia such as lowering by 4 C almost completely protected neurons from damage. Spontaneous firing of CAl neurons, which totally disappeared during the insult, began to recover along with reperfusion of brain, but the firing frequency decidedly did not exceed the preischemic level ; a fact which is not in accordance with, previous notion that delayed neuronal death is due to postischemic hyperexcitability of CAl neurons.2. Microdialysis studies in gerbil hippocampus coupled with an enzymatic cycling method revealed that forebrain ischemia induced a prompt and hypothermia-sensitive release of glutamate in a large scale (15-20 times preischemic level at 5 min ischemia) followed by a quick return to preischemic range.3. Using gerbil hippocampal slices, we developed a microfluorometry on a fluorescence microscope - a supersensitive video camera - an image analyzer setup. Introducing hypoxiahypoglycemia of perfusion medium induced regionally non-selective glutamate release from whole hippocampal area, within 20 sec of the insult, which followed by regionally selective calcium accumulation in CAl area accompanied by membrane depolarization within 200 sec. Mild hypothermia prolonged the latency in a dose-dependent manner. Taking -together, ischemia induced glutamate release followed by intracellular calcium accumulation is likely to be most crucial in early stage of ischemic neuronal damage.