DISTRIBUTION, ORIGIN AND PROJECTIONS OF NITRIC-OXIDE SYNTHASE-CONTAINING NEURONS IN GUT AND PANCREAS

Nitric oxide has been put forward as an important inhibitory neurotran smitter in the gut. Nitric oxide synthase-containing neurons were visu alized by immunocytochemistry using antibodies against neuronal nitric oxide synthase or by beta-nicotinamide adenine dinucleotide phosphate diaphorase staining in whole mounts and cryostat sections from the ga strointestinal tract and pancreas of several mammals (mouse, rat, hams ter, guinea-pig, cat and man). Nitric oxide synthase-containing neuron al cell bodies were numerous in the myenteric but fewer in the submuco us ganglia all along the gut of all species. Varicose nerve terminals formed extensive networks in the circular smooth muscle and the myente ric ganglia. Nitric oxide synthase-containing nerve terminals were fre quently found around the Brunner glands in the duodenum; scattered ner ve terminals were also found in the gastric and colonic mucosa and aro und blood vessels in the submucosa all along the gut. In the rat small and large intestine nitric oxide synthase-containing submucous neuron s terminated within the mucosa/submucosa and nitric oxide synthase-con taining myenteric neurons issued short descending projections, approxi mately 3 mm, to the smooth muscle and other myenteric ganglia. In the pancreas of all species nitric oxide synthase-containing nerve cell bo dies were regularly seen in intrapancreatic ganglia. Positive nerve fi bers were mainly found within nerve trunks in interlobular spaces and as delicate fibers within the islets. Double staining for nitric oxide synthase and neuropeptides in intestine and pancreas of rat, guinea-p ig and man revealed that only occasionally the nitric oxide synthase-c ontaining nerve cell bodies stored in addition vasoactive intestinal p eptide and neuropeptide Y, or enkephalin. However, nitric oxide syntha se-containing nerve terminals, particularly those in the circular musc le of the gut, frequently contained vasoactive intestinal peptide/neur opeptide Y (rat and man) or vasoactive intestinal peptide/enkephalin ( guinea-pig). In intrapancreatic ganglia few nitric oxide synthase cont aining nerve cell bodies were also vasoactive intestinal peptide-immun oreactive. Coexistence of nitric oxide synthase and vasoactive intesti nal peptide in nerve terminals could here be detected around blood ves sels and interlobular ducts. The distribution of nitric oxide synthase indicates a major role of nitric oxide in the regulation of gut motil ity; a role in the regulation of blood flow and secretion in both gut and pancreas is also likely.