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

Abstract

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 reexamination 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.Urinary incontinence is clinical epidemiological health issues of older adults[1] Constipation is also common in adults older than 60 years [2]. Generally, constipation is considered for the peripheral enteric neurodegeneration [3,4]. Erectile dysfunction in men is also a sign of an underlying aging condition [5]. The sensation of the aging spinal cord could be changed in the singling circuitry in the dorsal horn of the lumbosacral segment [6]. The impact of aging on the cellular composition of the spinal cord reveals aging-associated changes in the numbers of neurons and non-neuronal cells [7].The sacral spinal cord innervates of the urogenital organs [8,9]. The relevant cell bodies of autonomic neurons distribute in the dorsal horn, intermediolateral nucleus (IML), dorsal commissural nucleus (DCN). In the dog [9, 10] and monkey [11], autonomic neurons also locate in the anterior horn. Many neuropeptides distribute in these neurons [12,13]. The NADPH diaphorase (N-d) is also important neuronal enzyme identical to nitric oxide synthase (NOS) distributed in the autonomic spinal cord[14-16], although some experiments may not completely reach the consistent conclusion [17][18][19][20]. Up to date, the N-d is also commonly used to investigate the neurodegenerative diseases[21-23]. Aging-related N-d alterations have been studied in the sacral spinal cord in the rat [18], dog[2...