Mechanism of Neuronal Cell Death following Cerebral Ischemia

海马CA1区神经元在短暂缺血后死亡。这里的神经元损伤几乎完全是突触后损伤。用精细结构形态测量法研究剩余突触前终末的长期变化。终末长期维持3个月以上，终末数量逐渐减少。CA1区萎缩与剩余突触前终末消失一致。短暂缺血本身对海马神经元并不致命，即使缺血损伤对完整状态下的神经元是致命的，它也赋予进一步缺血的耐受性。在获得缺血耐受的神经元中，应激蛋白hsp70被强烈表达。我们用放射自显影技术研究了耐受诱导神经元中蛋白质合成的变化。缺血后，Ca1蛋白合成受到严重抑制，且无法恢复。另一方面，在耐受诱导的动物中，即使缺血达到致死水平，蛋白质合成也能迅速恢复。采用原位杂交法研究hsp70 mRNA的变化。即使神经元即将死亡，该信息也总是在CA1神经元中表达。诱导耐受后，mRNA表达后hsp70蛋白强烈表达。另一种应激诱导蛋白，泛素，已知在缺血后CA1神经元中消失。然而，当我们使用另一种主要识别泛素缀合形式的抗泛素抗体时，情况并非如此。免疫印迹和免疫沉淀研究表明，缺血后CA1神经元中独特素的总量不减少，但泛素的游离形式减少。游离泛素的消失在缺血性神经元死亡中的作用尚不清楚。

Neurons in the hippocampal CA1 sector die following brief period of ischemia. The neuronal injury here is almost purely postsynaptic. The long term change in remaining presynaptic terminals was studied by fine structural morphometry. The terminals were chronically maintained for longer than 3 months and gradually decreased in number. The CA1 region fell in atrophy in accordance with disappearance of residual presynaptic terminals. Brief ischemia, which in itself is not lethal to hippocampal neurons, confer tolerance to further ischemia even if the ischemic insult is lethal to neurons in intact condition. In neurons which have acquired ischemic tolerance, a stress protein, hsp70, is strongly expressed. We studied the change in protein synthesis in tolerance-induced neurons by autoradiography. Following ischemia, protein synthesis is severely inhibited in Ca1 and never recovers. On the other hand, in tolerance-induced animals, the recovery of protein synthesis was rapid even if ischemia was of lethal level. The change in mRNA for hsp70 was studied by in situ hybridization method. The message was always expressed in CA1 neurons even if the neurons were going to die. Following tolerance induction, mRNA expression was followed by intense expression of hsp70 protein. Another stress-inducible protein, ubiquitin, was known to disappear in CA1 neurons following ischemia. However, this was not the case when we used another type of anti-ubiquitin antibody which recognize mainly conjugated form of ubiquitin. Immunoblot and immunoprecipitation study revealed that uniqutin does not decrease in total amount but free form of ubiquitin is depleted from the CA1 neurons following ischemia. The role of the disappearance of free ubiquitin in ischemic neuronal death is still unknown.