Study on pathophysiology of cerebral hypoxia by means of the brain slice technique and the regional perfusion technique

研究一：采用细胞内记录的方法，在低氧高钾超融合介质条件下观察大鼠脑切片海马CAl神经元的活动。在缺氧（95%N_2-5%CO_2平衡）培养基中，大多数神经元出现小的超极化、缓慢渐进的去极化和快速去极化。电压依赖性K-^+通道阻滞剂（4-氨基吡啶、四乙基铵、钡、铯）和细胞内注射EGTA不能阻断缺氧引起的初始超极化。因此，缺氧诱导的超极化可能是由电压无关的K^+电导率的增加引起的，例如，atp敏感和/或na激活的K^+电导率。用高钾介质模拟了缓慢渐进退极化和快速退极化的过程。在Ca^<2+>阻滞剂存在的情况下，即使在60mM的K^+加载1.5min后，膜的活性仍部分保持不变。这些事实表明，细胞外K^+水平的缓慢增加导致缺氧时膜去极化缓慢，而Ca^<2+>的额外流入导致CAl神经元膜在长时间缺氧时发生不可逆的变化。对于突触传递，缺氧条件下ipsp消失，但epsp无变化。研究二：在不完全性脑缺血发生前一周用小针对小鼠进行轻微脑损伤。在戊巴比妥或氯胺酮麻醉下，双侧颈动脉夹持60 min，比较缺血损伤后1周内与单纯麻醉组和假手术组的存活人数。脑损伤组在戊巴比妥麻醉下脑缺血后的存活率明显高于其他两组。然而，在氯胺酮麻醉下，脑缺血对脑损伤小鼠存活率的提高并不显著。结果表明，脑损伤可能具有一定的抗脑缺血因子或保护机制，氯胺酮可拮抗脑损伤引起的抗脑缺血活性，巴比妥酸盐麻醉可增强其抗脑缺血活性。少

Study I: The activities of the hippocampal CAl neurons in rat brain slices were investigated by intracellular recording under hypoxic and high potassium conditions of superfuson media. By superfusion of the hypoxic (95%N_2-5%CO_2 equilibrated) medium, a small hyperpolarization, a slow and gradual depolarization and a rapid depolarization were spquentially oserved in a majority of the neurons. The initial hyperpolarization induced by hypoxia was not blocked by superfusion with voltage-dependent K-^+-channel blockers (4-aminopyridine, tetraethylammonium, barium, cesium) and by intracellural injection of EGTA. Therefore, The hypoxia-induced hyperpolarization may be brought about by the increase in voltage-independent K^+ conductivities, e.g., ATP-sensitive and/or Na-activated K^+ conductivities. The slow and gradual depolarization and the rapid depolarization were mimicked by superfusion with high pottasium media. In the presence of Ca^<2+> blockers, the membrane activities partially rema … More ined even after 1.5min of 60mM K^+ loading. These facts suggest that the extracellulae K^+ level increases slowly to cause slow membrane depolarization with hypoxia, and that the additional Ca^<2+> influx causes irreversible change in the membrane of CAl neurons during prolonged hypoxia. For synaptic transmissions, IPSPs disappeared without change in EPSPs under hypoxia.Study II: Minor brain injury was inflicted with a small needle one week before the production of incomplete brain ischemia in the mouse. A bilateral carotid clamp was applied for 60 min under pentobarbital or ketamine anesthesia, and the number of survivors in one week after the ischemic insult was compared with those in animals anesthetized only and a sham-oparated group. Survival rates following the brain ischemia induced during pentobarbital anesthesia were significantly higher in the brain injured group than in the other two groups. However, the improvement of the survival rates in mice with brain injury became insignificant when brain ischemia was imposed during ketamine anesthesia. The results suggest that the actions of certain factors or protective mechanisms against brain ischemia were developed by brain injury and that the brain injury-induced anti-ischemic activity is antagonized by ketamine and/or potentiated by barbiturate anesthesea. Less