Organization of nitric oxide-producing nerves in the rat pyloric sphincter.

The architecture of nitric oxide (NO)-producing nerves in the rat pylorus was studied in relation to the muscular structure. The musculature of the rat pylorus was observed to be composed of two discrete muscle loops (proximal and distal sphincters). Connective tissue septa containing neural elements divided the thick musculature of the distal sphincter into many bundles. The myenteric nerve plexus of the stomach with a subpopulation of NO-producing nerves was continuous with that of the duodenum. Nitrinergic nerve fibers which originated from the antral myenteric plexus ran through the connective tissue septa in the pyloric musculature and were densely distributed on the submucosal surface of the distal sphincter. The innermost portion of the distal sphincter consisted of smooth muscle cells showing many cytoplasmic processes and abundant nitrinergic nerve terminals. This particular architecture of the nitrinergic nerves in the sphincter would seem to account for the coordinate motor function of the rat pyloric sphincter.