Region-specific differences in the human myenteric plexus: an immunohistochemical study using donated elderly cadavers.

To identify site-dependent and individual differences in neuronal nitric oxide synthase (nNOS)-positive nerves of the myenteric plexus, we examined full-thickness walls of the stomach, pylorus, duodenum, ileum, colon, and rectum in 7 male and 8 female cadavers (mean ages, 80 and 87 years, respectively). The areas occupied by nNOS-positive nerve fibers in the myenteric plexus were fragmentary and overlapped with areas occupied by vasoactive intestinal polypeptide-positive fibers. The nNOS-positive fiber-containing areas per 1-mm length of intermuscular space tended to be larger at more anal sites, with positive areas four times greater in the rectum than in the stomach. Interindividual differences in rectal areas were extremely large, ranging from 0.017 mm(2) in one 80-year-old man to 0.067 mm(2) in another 80-year-old man. Similarly, the numbers of nNOS-positive ganglion cell bodies per 1-mm length in the rectum ranged from 4 to 28. These areas and numbers were weakly correlated (r = 0.62; p = 0.02). Interindividual differences in the rectum appeared not to depend on either age or gender. Anatomic studies using donated cadavers carried the advantage of obtaining any parts of intestine within an individual, in contrast to surgically removed specimens. We speculated excess control of evacuation with laxatives as one of causes of atrophy of the rectal myenteric plexus.