Fine structural changes in the trigeminal motor nucleus following neurotomy of the third division of the trigeminal nerve.

Abstract

The fine structural changes during retrograde degeneration were studied in the trigeminal motor nucleus from 17hrs to 95 days following neurotomy of the 3rd division of the trigeminal nerve in the rat.The typical Nissl bodies composed of a parallel array of long granular endoplasmic reticulum presented derangement and fragmentation. Concomitantly an accumulation of polysomes became eminent in the perinuclear area adjacent to the nuclear indentation and the peripheral portion of the perikaryon. In the neuron with advanced degeneration, dilatation of cisterns of the granular endoplasmic reticulum and gradual change of polysomes to single free ribosomes were demonstrated. However, the motor neurons concerned gave few necrotic images, suggesting the recovery from the affection. Concernig the highly dark and shrunken neurons frequently observed in the affected side of the motor nucleus some possibilities were discussed.The lamellar cisterns of the Golgi apparatus were replaced by well-developed Golgi vesicles, coated vesicles and dense bodies. Neurofilaments and neurotubules moderately increased in number and irregularly dispersed without forming unique bundles. The mitochodria often showed indistinct cristae and a decrease in electron density of the matrix.In the neuropil some axon terminals supposed to be axon collaterals from the trigeminal mesencephalic neurons showed moderate abnormalities characterized by the high density of the axoplasm, glycogen accumulation and the occasional appearance of neurofilaments. Directly after neurotomy the microglial cells markedly proliferated as satellites, which migrated around the neurons separating synaptic endings from the synaptic area with finger-like processes. The necrotic neuron was completely enclosed and digested within a hypertrophied microglial cytoplasm. Astrocytal processes around the nerve cells and vascular walls accumulated glycogen particles shortly after operation. An astrocytal perikaryon showed hypertrophy with gliofilamentous proliferation but an increase in the number of astrocytes was obscure.