The mechanism of diffuse axonal injury development

我们试图通过中线液体冲击大鼠模型（产生中度脑损伤lOOOmmHg）显示弥漫性轴索损伤（DAI）后TNF - a的免疫定位，并以山葵过氧化物酶为示踪剂显示TNF - α对轴膜通透性的影响。除此之外，我们还研究了β -淀粉样蛋白前体蛋白（β -APP）的积累，该蛋白最近被证明是与致命性头部损伤相关的轴突功能损伤的可靠标志。包括胼胝体在内的冲击皮质部位脑组织TNF α水平在前1h逐渐升高，在3h达到最高，在6h逐渐下降，至24h进一步下降。辣根过氧化物酶（HRP）示踪实验显示，早在撞击后15min就出现了原发性轴突损伤，但很快恢复，撞击后1h胼胝体和脑干发生继发性轴突损伤。在免疫电镜下，β -APP在撞击后1小时在轴突内积累，显示轴突功能性损伤。撞击后3min小胶质细胞溶酶体中检测到TNF α反应，撞击后1h主要在胼胝体和脑干的胶质细胞（如小胶质细胞、星形胶质细胞和少突胶质细胞）中检测到TNF α反应。TNF α诱导原发性脱髓鞘和少突胶质细胞凋亡已被广泛接受。因此，在这些部位观察到的迟发性轴突损伤可能是由主要由胶质细胞合成的TNF - a诱导的。本研究提示，神经胶质细胞传递的TNF α是导致液体性脑损伤DAI形成的辅助因子之一。

We approach to show the immunolocalization of TNF a after diffuse axonal injury (DAI) by midline fluid percussion rat model (moderate brain injury of lOOOmmHg was generated) and the effects of TNF alpha on the axolemmal permeability using horseradish peroxidase as a tracer. Add to this, we investigate the accumulation of beta -amyloid precursor protein (beta -APP), which has recently been shown to be reliable marker for the functional damage of axons associated with fatal head injury. TNF alpha levels of brain tissues, which was impact cortex site including the corpus callosum, gradually increased during the first 1h, rose to a maximal elevation at 3h and gradually decresed at 6h and more decreased to 24h. Horseradish peroxidase (HRP) tracer experiments revealed that primary axonal damage appeared as early as 15min after impact, but rapidly recovered and 1h after impact secondary axonal damage occurred in the corpus callosum nd the brain stem. By theimmunoelectron microscopy, beta -APP accumulated in the axon at 1h after impact and this revealed functional axonal damage. TNF alpha reactions were detected in the lysosomes of microglia at the 3Omin after impact, and 1h after impact these reactions were mainly detected at the glial cells (such as microglia, astrocytes and oligodendrocytes) in the corpus callosum and the brain stem. It is widely accepted that TNF alpha induces primary demyelination and oligodendrocyte apoptosis. Therefore the delayed axonal damage observed in these sites may be induced by TNF a which is synthesized mainly by glial cells. The present study suggests that TNF alpha conveyed from the glial cells is one cofactor contributing to the DAI formation by the fluid percussive brain injury.