Glial endocytosis of protein in the traumatized brain

The effect of trauma on the clearance of exogenous protein from the extracellular space of the brain was examined in monkeys and rats. Manual contusion of the monkey temporal lobe or air puff contusion of the rat parietal cortex resulted in intense glial uptake of the protein marker, horseradish peroxidase (HRP). There was no evidence of punctate or diffuse material in neurons at or distant from the trauma site. Cellular uptake was evident as early as 4 hr post trauma and reached maximal expression 24 hr post injury. By 72 hr post trauma few labeled cells could be seen. The extent of the glial uptake of protein was suggested by the decrease in extracellular marker in the vicinity of the labeled cells and by calculation of the fraction of glia so labeled. Sites of labeled glia were highly localized, corresponding to regions of stress. The corpus callosum was most clearly labeled in the rat experiments. The data suggest that in cases of traumatic injury to the brain, glia may be selectively stimulated to pronounced uptake of protein marker and thus may represent a potential means of clearing the extracellular space of extravasated serum protein.