Distribution and morphological features of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) activity in intrinsic neurons of the Oddi sphincter of the cat.

To clarify the role of nitric oxide (NO) in the sphincter of Oddi, we histochemically investigated the distribution of nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d), a marker for NO synthase, in the cat. NADPH-diaphorase activity was localized in two neuronal subtypes: large neurons with many dendrites and smaller with one process. Most of the nerve cell bodies (99%) in the wall of the sphincter of Oddi showed strong activity for this enzyme. The nerve fibers with NADPH-d activity were observed in all layers, chiefly in the muscle layers. These results suggest that NO may play a very important role in the neuronal regulation of sphincter of Oddi.