A fine structural study of degenerative-regenerative pathology in the surgically deafferentated lateral vestibular nucleus of the rat.

An experiment was designed to examine the course of degeneration, phagocytosis, and regeneration in the central nervous system following surgical deafferentation. The anterior cerebellar vermis was ablated in young male rats. The animals were sacrificed by perfusion at postoperative times ranging from 24 hrs to 6 months. The lateral vestibular nuclei, to which the anterior cerebellar vermis projects, were processed for electron microscopy. Degenerating synaptic terminals, of the dark variety, were seen from 24 hrs to five days postoperatively. Phagocytosis of degenerating terminals occurred during this time. Degenerating axons persisted through 6 months survival, and phagocytosis of these degenerating axons were observed. Astrocyte scar formation began at 1 month postoperatively. The relative number of axosomatic synaptic terminals containing flattened vesicles ("F" terminals; presumed inhibitory in function) increased in operated animals. The highest F scores were found from 24 hrs to two weeks postoperatively, and then the F scores declined through six months. The significance of these sprouting activities is discussed in relation to the abortive sprouting phenomenon described by Ramon y Cajal.