De novo aging-related NADPH diaphorase positive megaloneurites in the sacral spinal cord of aged dogs

We investigated aging-related changes in nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) in the spinal cord of aged dogs. At all levels of the spinal cord examined, NADPH-d activities were observed in neurons and fibers in the superficial dorsal horn (DH), dorsal gray commissure (DGC) and around the central canal (CC). A significant number of NADPH-d positive macro-diameter fibers, termed megaloneurites, were discovered in the sacral spinal cord (S1-S3) segments of aged dogs. The distribution of megaloneurites was characterized from the dorsal root entry zone (DREZ) into the superficial dorsal horn, along the lateral collateral pathway (LCP) to the region of sacral parasympathetic nucleus (SPN), DGC and around the CC, but not in the cervical, thoracic and lumbar segments. Double staining of NADPH-d histochemistry and immunofluorescence showed that NADPH-d positive megaloneurites co-localized with vasoactive intestinal peptide (VIP) immunoreactivity. We believed that megaloneurites may in part represent visceral afferent projections to the SPN and/or DGC. The NADPH-d megaloneurites in the aged sacral spinal cord indicated some anomalous changes in the neurites, which might account for a disturbance in the aging pathway of the autonomic and sensory nerve in the pelvic visceral organs.