The mechanism of diffuse axonal injury development

以辣根过氧化物酶为示踪剂，采用中线液压冲击致大鼠中度脑损伤模型，观察肿瘤坏死因子α在弥漫性轴索损伤(DAI)后的免疫定位及对轴膜通透性的影响。此外，我们还研究了β-淀粉样前体蛋白(β-APP)的积累，它最近被证明是与致命性脑损伤相关的轴突功能损害的可靠标志。脑组织中的肿瘤坏死因子-α水平在伤后1h逐渐升高，3h达最大值，6h逐渐下降，并持续至24小时。辣根过氧化物酶(HRP)示踪实验表明，初级轴突损伤早在撞击后15min就开始出现，但恢复较快，撞击后1h出现继发性轴突损伤。免疫电子显微镜显示，撞击后1h，β-APP在轴突内积聚，显示功能性轴突损伤。伤后30min，小胶质细胞溶酶体内可检测到肿瘤坏死因子-α反应，伤后1h，小胶质细胞、星形胶质细胞、少突胶质细胞等主要分布于穹隆体内和脑干内的胶质细胞。人们普遍认为，肿瘤坏死因子α可诱导原发脱髓鞘和少突胶质细胞凋亡。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神经胶质细胞合成的肿瘤坏死因子α引起的。提示神经胶质细胞分泌的肿瘤坏死因子α是液压脑损伤致弥漫性脑损伤形成的辅助因素之一。

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.