The perineuronal glial reaction after axotomy.

The perineuronal glial reaction after axotomy of the facial nerve was examined in adult mice and rats and in newborn rabbits. The facial nerve was damaged in two ways: by crush lesions, which were followed by complete neuronal regeneration, and by transection (in mice) or evulsion (in rats and rabbits), which caused extensive nerve cell disintegration. After nerve lesions which caused irreversible damage the microglial cells encircled the degenerating neurons and ultimately phagocytosed them. After crush lesions there were great species variations in the glial reaction: the neurons of rats and rabbits showed considerable and reversible separation of the synaptic terminals by glial cells, while mice showed no significant synaptic separation. It is suggested that the main function of the microglial cells may be to serve as potential phagocytes for disintegrating neurons, and that the reversible glial changes around regenerating neurons possibly represent abortive glial reactions.