Projections of nitric oxide synthase and vasoactive intestinal polypeptide-reactive submucosal neurons in the human colon

Background: The submucosal plexus is important in the control of secretomot or and motor function of the intestine. Our aim was to describe the project ions of submucosal neurons to the mucosa within the submucosal plexus and t o the circular muscle of human colon and to determine whether submucosal ne urons that projected to different layers were located at different levels o f the submucosa. Methods: A retrogradely transported fluorescent dye was applied to the muco sa, submucosa or circular muscle layer of human colon which was then mainta ined in organo typic culture for 5 days. The submucosa was then dissected i nto two preparations, one containing the inner layer of the submucosal plex us and the other containing both the intermediate and outer layers. The dis sected preparations were labelled with antibodies to nitric oxide synthase (NOS) or vasoactive intestinal peptide (VIP). Results: Submucosal neurons projected to the mucosa, submucosa and circular muscle layers for mean distances of 3.7, 3.0 and 4.3 mm, respectively. Nin ety-seven per cent of submucosal neurons labelled from the circular muscle were located in the outer or the intermediate layers, while 51% of those pr ojecting to the mucosa were in inner layer and 49% in the intermediate/oute r layers of the submucosal plexus. Eleven per cent of submucosal neurons pr ojecting to the circular muscle were immunoreactive for NOS and 12% were im munoreactive for VIP. Forty-five per cent of those projecting within the su bmucosa were immunoreactive for VIP and 38% of those projecting to the muco sa were immunoreactive for VIP. Conclusions: Submucosal neurons in the human colon innervate the mucosa, ci rcular muscle and submucosa and different functional classes of neurons are located in different layers of the submucosal plexus. (C) 1999 Blackwell S cience Asia Pry Ltd.