Gracile Axonal Dystrophy in an Old (28 Years) Japanese Monkey: Species‐Specificity of Ultrastructural Features and Particular Pattern of Proliferation of Smooth Endoplasmic Reticulum

This report deals with the study of aging gracile axonal dystrophy in an old (28 years), but healthy Japanese monkey. Light and electron microscopy was used throughout. The animal was systemically perfused, under deep anesthesia, with a mixture of glutaraldehyde and paraformaldehyde. For light microscopy, epoxy resin-embedded tissue of the gracile nucleus was cut into one μm sections, and for electron microscopy (accelerating voltage 300 KV), into 0.2 μm sections. The fine structure of over 20 different spheroids was investigated. Several ultrastructural features not previously observed and/or documented in lower mammals were found in the spheroids of the monky studied. These features are: 1) a unique pattern of smooth endoplasmic reticulum proliferation, characterized by dense parallel alignment of non-branching tubules; 2) the accumulation of dense homogeneous osmiophilic substance; 3) presence of screw-like paracrystalline needles, and 4) absence of such characteristic secondary structures as layered loops of membranes and coiled tubular rings. The dense homogeneous osmiophilic substance and the screw-like paracrystalline needles were previously described or claimed to be present in aging axonal dystrophy of humans. The author addresses and emphasizes the value and importance of a comparative approach in neuropathology and concludes that the study of the brains of other primates is indispensable for the elucidation of human axonal dystrophy, brain aging in humans, and human brain diseases in general.