STUDY OF AXONAL DYSTROPHY. II. DYSTROPHY AND ATROPHY OF THE PRESYNAPTIC BOUTONS: A DUAL PATHOLOGY

Abstract

A qualitative study was carried out on the nature of a dual pathology affecting presynaptic boutons in the posterior tract nuclei of aging rats. Based on the morphology of dystrophic boutons in early stages, the initial and essential characteristic of the dystrophic process is apparently an abnormal increase of normal axonal components within the presynaptic boutons and various abnormal substructures of spheroids reported in the literature are probably the result of their secondary metamorphosis. The dystrophic process within the posterior tract nuclei is a selective one, involving presynaptic boutons and preterminal axons of the posterior tract fibers. Comparison of the frequency of early dystrophic boutons and of fully mature spheroids indicates that a small percentage of boutons deriving from posterior tract fibers become dystrophic and of these dystrophic boutons only a small percentage again continue to develop into large spheroids, throughout the life of the animal. In search of a morphological counterpart for the age-related decrease of volume ratio of presynaptic boutons to the neuropil, some dubious atrophic changes were found in presynaptic boutons, which could have been easily missed from observation if studied qualitatively alone. Accordingly, no less numerous boutons other than dystrophic ones are supposed to atrophy independently and disappear silently during the same period. The dystrophic and the atrophic changes involve different boutons (of different or the same terminal axons) within the same gray matter. This dual pathology of boutons needs further elucidation of its neurocytopathological and neurobiological background.