Variations in the perineuronal glial changes after different types of nerve lesion: light and electron microscopic investigations on the facial nucleus of the rat.

The perineuronal glial changes were studied by light and electron microscopy after avulsion or a crush lesion of the facial nerve in rats. The changes consisted of proliferation of microglia, ensheathment of neurons by thin astrocytic processes, and separation of the synaptic boutons from the neuronal surface. Quantitative estimates of the glial proliferation were made with the light microscope. In spite of marked differences in the acute nerve cell reaction, 4 days after the two types of lesion the glial and synaptic changes did not differ significantly. Ultimately, all changes were reversible after crush lesions, while neuronophagia occurred after nerve avulsion. It is concluded that the acute synaptic and glial reactions were not influenced by the type of nerve lesion or the severity of the nerve cell reaction, but the latter stages differed depending upon whether the neurons recovered or disintegrated.