The expression of tumor necrosis factor-alpha in the rat brain after fluid percussive injury

To investigate the role of tumor necrosis factor-alpha (TNF alpha) after traumatic head injury in rats, moderate brain injury of 1000 mmHg was generated by an original fluid percussion injury device. TNF alpha levels in cerebrospinal fluid (CSF) gradually increased during the first 1 h, rose to a maximal elevation at 3 h and 6 h and returned to basal values by 24 h. Horseradish peroxidase tracer experiments revealed that primary microvascular damage appeared as early as 15 min after impact, but rapidly recovered and 1 h after impact secondary microvascular damage occurred in the hippocampus and parasagittal cortex. By immunoelectron microscopy, TNF alpha reactions were detected in the lysosomes of microglia accumulated at the impact site of the cortex 30 min after impact, and 1 h after impact these reactions were mainly detected at the glial cells (such as microglia and astrocytes) in the hippocampus and parasagittal cortex. Therefore the delayed microvascular damage observed in sites remote from the impact may be induced by TNF alpha which is synthesized mainly by glial cells. The present study suggests that TNF alpha conveyed from the microglial cells is one co-factor contributing to the fluid percussive brain edema formation after moderate brain injury.