The distribution of NPY-containing nerves and the catecholamine contents of canine enteric nerve plexuses.

Our previous study demonstrated that PYY was a major neuropeptide in the canine enteric nervous system, the present study defines the locations of NPY-containing enteric neurons. NPY-positive nerve cell bodies and fibers were numerous in gastric and pyloric myenteric plexuses as were positive nerve fibers in antral and pyloric muscle layers, pyloric sphincter muscle layers, and surrounding blood vessels. In contrast to findings for PYY, there were considerably fewer NPY-positive nerve cell bodies and fibers in the canine ileum and colon. Noradrenaline was the predominant catecholamine in all plexuses, the rank order of its contents being: deep muscular > submucous > myenteric plexus. The dopamine/noradrenaline ratio was constant in all plexuses; adrenaline was present in minor amounts. PYY is the more abundant neuropeptide in ileum and colon, and NPY has a greater presence in the gastric antrum, pylorus, and surrounding blood vessels. PYY and NPY may play different functional roles in the GI tract.