A neuropathological study on axonal dystrophy in the gracile nucleus of an old Japanese monkey

: Ageing axonal dystrophy was studied electron microscopically in the gracile nucleus of a very old Japanese monkey (28 years of age) from the standpoint of comparative neuropathology. It was revealed that the Japanese monkey has characteristics different from albino rats concerning the ultrastructure of the dystrophic axonal spheroids. Spheroids in the former animal contained no traces of so-called layered loops of membrane nor coiled tubular rings etc. which have been interpreted in cases of albino rats and other animal species as morphological expression of secondary metamorphosis of primarily accumulated normal axoplasmic organelles at the presynaptic boutons. Instead, spheroids in the Japanese monkey contained dense homogeneous osmiophilic granules and screwnail-like filament crystalloids, which have not been found in other animal species including albino rats. These abnormal substructures were already present in the early stage of axonal dystrophy and tended to occupy a large volumetric proportion of gigantic spheroids. It was concluded that these substructures constitute essential components of formed spheroids in combination with smooth axoplasmic reticulum, and that they represent primary products of axonal dystrophy and not the secondary products of metamorphosis like coiled tubular rings or layered loops of membrane described above. The enormous accumulation of smooth axoplasmic reticulum in other animal species including albino rats is characterized by the formation of a dense tridimensional reticular network. In the Japanese monkey, this process is characterized by massive dense parallel aggregation of straightened tubules of apparently smooth axoplasmic reticular origin rather than by formation of tridimensional network.(ABSTRACT TRUNCATED AT 250 WORDS)