Plasma proteins in normal neurons. Immunohistochemical studies on autopsy material and experimental animals.

Previous observations have shown that plasma proteins are taken up by damaged neurons after trauma, cold injury and anoxic lesions. The present study was undertaken to test whether such uptake also can occur in normal neurons. Normal human brains at different intervals after death as well as normal rat brains after perfusion and immersion fixation were studied. During the first 24 h after death, the human cases showed practically no immunostaining with anti-fibrinogen and vague and inconstant staining with anti-albumin in the cortex and hippocampus, while certain brain stem nuclei were stained with both antisera even at the shortest postmortem intervals. At longer intervals, increased immunostaining of the neurons in the cortex and hippocampus was also demonstrated. Generally, more cells were positive for albumin than for fibrinogen. Perfusion-fixed rat brains showed no immunostaining, whereas rat brains that were immersion-fixed 24 h after death showed positive staining, mainly located in the brain stem. It is concluded that the staining of normal neurons demonstrated with the present method is due to postmortem leakage of proteins. Since practically no uptake of fibrinogen occurs in the cortex or hippocampus during the first 24 h, a definite neuronal staining with anti-fibrinogen at these intervals probably indicates true neuronal damage. In the brain stem, on the other hand, this phenomenon can not be used to demonstrate neuronal damage even at the shortest postmortem intervals.