Electron microscopic observations in the trigeminal mesencephalic nucleus following neurotomy of the third division of the trigeminal nerve.

The trigeminal mesencephalic nucleus was studied with an electron microscope after neurotomy of the third division of the trigeminal nerve in rats. Neuronal ultrastructures were characterized by the changes of the cell organelles 17hrs after neurotomy. Especially numerous polysomes appeared in the perinuclear area and then migrated into the peripheral area. Concomitantly, the central area of the cytoplasm was filled with bundles of synthesized neurofilaments. Ten days after neurotomy, the Nissl pattern shifted to dispersing free ribosomes and granular endoplasmic reticulum. Necrotic neurons and degenerating processes of the affected neurons revealed dense matrix and often lamellated dense bodies. These neurons packed with fibrous or tubular substances showed loss of the Nissl substances after 40 and 95 days. In the neuropil, astrocyte end feet accumulated more glycogen particles than usual. The vascular walls showed remarkable changes after 17hrs. Pericytes were activated as phagocytes, which have dense cytoplasmic matrix and large masses of lysosomal dense bodies and phagocytotic vesicles. Slight changes were observed in the vascular walls and perikarya of the neurons of the contralateral mesencephalic nucleus as well.