Mechanism for the Development of Irreversible Damages in Cerebral Ischemia.

为阐明缺血性不可逆损伤的病理生理机制，本研究采用沙土鼠脑缺血模型，采用高效液相色谱法、近红外分光光度法和磁共振成像技术，分析脑缺血后生化和生理指标的时序性变化，并与免疫组化结果进行比较.我们建立了同时评估10至50微克干重脑组织中能量代谢物区域水平变化和免疫组织化学变化的方法。局部ATP水平的降低可能是免疫组化损伤发生的先决条件.磁共振弥散加权成像显示组织水的弥散系数迅速降低，提示能量衰竭导致细胞骨架和细胞损伤，离子泵衰竭.近红外光谱分析结果表明，ATP含量的降低可能先于细胞色素氧化酶的完全还原.微管蛋白和MAPIA的易损性比较表明，微管蛋白的损伤似乎比MAPIA的损伤更接近不可逆性损伤.在迟发性神经元死亡区域检测到N-乙酰天冬氨酸水平的区域性降低，表明其是脑中神经元损失和不可逆损伤的敏感标志物.在培养星形胶质细胞的缺氧/复氧模型中，观察到与沙土鼠脑缺血模型相似的能量状态紊乱和应激蛋白的诱导.在后脑区域，存在对缺血的选择性脆弱性，如前脑缺血的情况。从这些结果来看，脑缺血的不可逆损伤可能是细胞色素氧化酶完全还原、ATP耗竭、离子泵失效和细胞骨架蛋白降解的结果。

To elucidate the pathophysiological mechanism for ischemic irreversible damage, we analyzed the sequential changes of biochemical and physiological parameters by use of HPLC,near infra-red spectro-photometry and magnetic resonance imaging, and compared them with the immunohistochemical changes in the gerbil model of cerebral ischemia.1. We established the method for the simultaneous assessment of changes in regional levels of energy metabolites and immunohistochemical changes in brain tissues of 10 to 50 microgram dry weight. The decrease of regional ATP level seemed prerequisite for the development of immunohistochemical damages.2. The diffusion-weighted magnetic resonance imaging showed prompt decrease of diffusion coefficient of tissue water, indicating ion pump failure as the results of energy failure caused cytoskeletal and cell damage.3. The results by near-infrared spectroscopy indicated complete reduction of cytochrome oxidase seemed preceded for the decrease of ATP.4. The comparison of vulnerability between tubulin and MAPIA indicated damages of tubulin seemed more closely related to irreversible damage than those of MAPIA in ischemia.5. The regional decrease in N-acetyl aspartate levels was detected in the area of delayd neuronal death, indicating the sensitive marker for the neuronal loss and irreversible damages in the brain.6. In hypoxia/reoxygenation model using cultured astrocytes, similar derangement of energy states and induction of stress proteins were observed as in the gerbil model of cerebral ischemia.7. In hindbrain regions, selective vulnerability to the ischemia existed as in the case of forebrain ischemia. From these results, irreversible damages in cerebral ischemia could be the result of complete reduction of cytochrome oxidase, ATP depletion, ion pump failure, and degradation of cytoskeletal proteins.