PROJECTIONS OF NITRIC-OXIDE SYNTHASE-CONTAINING AND PEPTIDE-CONTAINING NEURONS IN THE SMALL AND LARGE INTESTINES OF THE TOAD (BUFO-MARINUS)

The projections of galanin (GAL)- and vasoactive intestinal peptide (V IP)-immunoreactive (IR) and nitric oxide synthase (NOS)-containing neu rons in the small and large intestines of the amphibian Bufo marinus w ere investigated by their reactions to surgical interruption (myotomy) . In the small intestine, myotomy caused accumulation of GAL- and VIP- IR and of NADPH diaphorase reaction product (revealing NOS) in cut axo ns on the oral side of the operation site. On the anal side there was loss of GAL-IR axons from the circular muscle and myenteric plexus and long, anally directed processes could be traced from GAL-IR nerve cel l bodies. There was no significant loss of VIP-IR or NADPH diaphorase from nerve fibres in the myenteric plexus or circular muscle layer, al though anally-directed axons could be traced from nerve cell bodies on the anal side of the operation sites. In the large intestine, myotomy caused accumulation of VIP-IR and of NADPH diaphorase reaction produc t in cut axons on the oral side of the operation site. Anal to the cut , although there was no significant loss of these fibres from the musc le or myenteric plexus, anally directed axons could be traced from ner ve cell bodies. GAL-IR fibres in the large intestine are of two types: a few contain GAL-IR alone and are thought to arise from enteric neur ons; many contain both GAL- and SOM-IR and are thought to arise from n erve cell bodies in the hindgut. Myotomy caused an accumulation of GAL /SOM-IR material in fibres on the anal side of the cut and a substanti al decrease in the number of fibres on the oral side. There was no det ectable effect of myotomy on the GAL-IR fibres, although an abnormally high density of GAL-IR nerve cell bodies was found oral to the cut. T hese results indicate that VIP-IR and NOS-containing enteric neurons p roject in an oral to anal direction in the toad small and large intest ines. Some of the neurons have short anal projections to the circular muscle. GAL-IR enteric neurons have similar projections in the small i ntestine, but their projections could not be determined in the large i ntestine. GAL/SOM-IR axons in the large intestine project from anal to oral. Myotomy in the large intestine appears to induce an increased o r de novo expression of GAL-IR in enteric neurons oral to the cut.