Study of mechanism of ischemic neuronal death.a molecular biological approach

我们发现脑缺血后神经元死亡有四种类型，即丘脑网状核的超早期缺血性神经元损伤、经典的能量衰竭所致的急性缺血性神经元死亡、被认为与细胞凋亡有关的迟发性神经元死亡、局灶性脑梗死后远隔区的缓慢进行性神经元死亡。本研究对脑缺血后神经元死亡类型的机制进行了如下研究：利用大鼠大脑中动脉（MCA）闭塞后的磁共振成像（MRI）技术，观察脑缺血后神经元死亡的远期变化。然后，我们发现，在远离原发性缺血性病变的区域，有两种类型的继发性变性与MR imaging.可能的诱导原癌基因c-myc和s-myc和抑癌基因p53的mRNA，这是已知的诱导细胞凋亡，和原癌基因bcl-2，抑制细胞凋亡，在大鼠局灶性缺血检查。c-myc基因表达迅速而显著地被诱导，并呈时间依赖性。这些结果提示c-myc基因的高表达可能参与了包括细胞凋亡在内的缺血性细胞事件，最近的研究表明鞘磷脂降解产生的神经酰胺在细胞凋亡中起第二信使的作用。测定了大鼠局灶性脑缺血时大脑皮质神经酰胺、鞘磷脂、神经节苷脂和神经节苷脂的含量。神经酰胺在缺血6小时开始增加。增加的神经酰胺中的氨基连接脂肪酸仅由非羟基脂肪酸组成，硬脂酸是最突出的。鞘磷脂，其氨基连接的脂肪酸主要是硬脂酸，以时间依赖性的方式减少。结果提示，脑缺血早期，神经酰胺在大脑皮层中通过鞘磷脂的分解而产生。

We found that there are four types of neuronal death following cerebral ischemia, such as ultra-early-type ischemic neuronal injury in the thalamic reticular nucleus, classical acute ischemic neuronal death due to energy failure, delayd neuronal death which is considered to be related to apoptosis, slowly progressive neuronal death in remote areas from focal cerebral infarction. Mechanisms of teses types of nuronal death after cerebral ischemia were studied as follows.We tried to detect the remote changes using MRI after MCA occlusion in the rat. Then, we found that, in areas remote from a primary ischemic lesion, there are two types of secondary degeneration with MR imaging.Possible induction of mRNAs for proto-oncogene c-myc and s-myc and oncosupressor gene p53, which are known to induce apoptosis, and protooncogene bcl-2, which inhibits apoptosis, was examined following focal ischemia in the rat. The c-myc gene expression was rapidly and markedly induced in a timedependent manner. The results indicate a possibility that high level expression of the c-myc gene may be involved in the ischemic cellular events including apoptosis.It is recently suggested that ceramide, generated by sphingomyelin degradation, plays a role as a second messenger in apoptosis. Level of ceremide, sphingomyelin, cerebroside and gangliosides were determined in rat cerebral cortex during focal ischemia. Ceramide began to increase at 6 hours of ischemia. Aminolinked fatty acids in increased ceramide were composed solely of non-hydroxy fatty acids, and stearic acid was the most prominent. Sphingomyelin, whose aminolinked fatty acids were mostly stearic acid, decreased in a time-dependent manner. The results suggested that ceramide was produced in the cerebral cortex by the breakdown of sphingomyelin during early ischemia.