[Distribution and localization of nitric oxide containing neural elements in the digestive tract]

Nitric oxide free radical is a presumed neurotransmitter of the gastrointestinal tract. It can play an important role in the relaxation of the smooth muscles. We used nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry and the localization and morphology of the NADPH-d positive neural elements of the different areas were compared in the cat. NADPH-d positive neurons could be found mainly in the myenteric plexus but some of them were located in the submucous plexus and in the inner circular muscle layer as well as around the blood vessels. The greatest number of the positive neuronal cell bodies could be seen in the myenteric plexuses of the sphincter regions. Stained nerve fibers were seen mainly in the inner circular muscle layer. These results suggest that the positive neurons of the sphincter regions can have an important role in the relaxation. NADPH-d positive neuronal elements of the submucous plexus were located around blood vessels and can regulate the blood flow and secretion of the glands or it is also possible that they belong to the sensory neurons.