Electron microscopic observations on nerve cell regeneration and degeneration after axon lesions. II. Changes in the glial cells.

Abstract

The glial reaction was examined in the facial nucleus of adult mice after crush lesions and complete section of the facial nerve. These lesions were followed by complete nerve cell regeneration and extensive nerve cell disintegration, respectively. After crush lesions the function reappeared on the tenth or eleventh day and there was no nerve cell loss. After nerve section about two thirds of the nerve cells disintegrated between the third and the ninth week. Both types of lesion induced reaction of astrocytes and of small perineuronal glial cells, which correspond to the microgliacytes demonstrated in light microscopy. The microglia had small dense nuclei, a diffusely dense cytoplasmic matrix, long narrow cisterns of agranular or granular endoplasmic reticulum, and free ribosomes which occurred both as single elements and in clusters of varying size. The possible nature of these cells is discussed. After nerve section the slender processes from the microglial cells extended along the surface of the nerve cells and dendrites, thus separating the boutons from their contacts. In late stages the microglial cells removed the neurons by phagocytosis. After crush lesions the microglial processes also extended to the surface of the neurons and dendrites but they covered only short segments of the surface. Convincing separation of boutons was not observed after lesions which produced regeneration. The functional significance of the glial reaction is discussed.