Spacing spheroids, curl-up and coiled neuritic plexus of the sacral spinal cord of aged dog: Hypothesis based on continued NADPH diaphorase histological observations

NADPH diaphorase (N-d) neurons distribute in spinal cord and function for visceral sensation and autonomic regulation. N-d positive neurons innervate pelvic organs. In previous investigation, we report that aging-related N-d body (ANB) in the lumbosacral spinal cord in aged rat and megaloneurite in the sacral spinal cord in aged dog. This article was a continued data report of aging-related N-d alterations in aged dog. N-d positivity in aged spinal cord has revealed a certain of morphological profiles in the spinal cord of several species. However, we still found some denoted N-d neurodegenerative changes that we failed to notice in our previous studies when re-examination of the sacral spinal cord of aged dog. In the horizontal section, spacing spheroids in the superficial laminae of the dorsal horn, curl-up and coiled neurites in the intermediate zone were detected in the sacral spinal cord. The ANB and vacuolar neurite were also detected. Vacuolar degeneration also occurred in the dorsal ganglia at the sacral segment. The curl-up and coiled neurites did not occur in the lumbothoracic segment, but the ANB and vacuolar neurite were scatteringly detected in in the lumbothoracic segment of aged dog. The results suggested that the N-d sensory inputs interrupted and disconnected with integration of autonomic centers and output circuits of regulating urogenital organs during the aging. These specialized profiles were speculated that the N-d neurite deterioration of visceral sensory circuit implicated dysfunction of pelvic organs in the aging. Megaloneurite and fiber dilation may make backward reasoning to N-d fiber architecture under normal condition.