Electron microscopy of degeneration in the lateral olfactory tract and plexiform layer of the prepyriform cortex of the rat.

Abstract

The synaptic organization of the plexiform layer of the prepyriform cortex in the rat has been studied with the electron microscope both in the normal and after ipsilateral olfactory bulb removal. Survival times ranged from six hours to three months. In normal preparations synaptic contacts occur mainly on dendritic branches, spines or lateral projections. Gray's Type I contacts are most frequent and Type II contacts usually contain flattened vesicles after formalin fixation. Degeneration of the presynaptic bags begins within 24 hours after the lesion and some degenerated bags are still seen after three months survival. During this time degenerated bags are apparently removed by astroglia but the spine tips appear to be unaffected by the phagocytosis. Glia or other processes may come to occupy the denervated sites. The evidence for possible reestablishment of new contacts is considered. The severed axons show a characteristic mode of degeneration and at three months some appear to be phagocytosed by oligodendroglia which also contain lamellated inclusion bodies.