Nitric oxide synthase-containing neurons in the myenteric plexus of the rat gastrointestinal tract: distribution and regional density

Nitrergic(NO) neurons play crucial inhibitory roles in the control of gut m otility. Variations in the density of these neurons within the gastrointest inal tract (GI) may provide useful functional information, but, most survey s available have employed limited and/or highly localized samples. It remai ns unclear to what extent (a) NO neurons are concentrated disproportionatel y in particular GI regions, or (b) variations in NO cell number merely refl ect changes in overall myenteric neuron density. This experiment surveyed t he distributions of neuronal nitric oxide synthase-positive (NOS+) and othe r myenteric neurons in the GI tract, using immunohistochemical and Cuprolin ic blue counterstaining techniques. Adjustable sampling grids superimposed on wholemounts were used to investigate the topographic patterns in the sto mach (90 sampling sites; 45 per side) and proximal duodenum (63 loci). We p resent four major findings: First, variations were detected in the number o f NOS+ neurons in specific regions of the stomach (e.g., corpus>antrum cong ruent to forestomach) and along both longitudinal (oral>anal) and circumfer ential (mesenteric>antimesenteric) axes in the duodenum. Second, the variat ions in NOS+ neuronal counts within each organ covaried with the total numb er of myenteric neurons at different locations (stomach, r=0.77; duodenum, r=0.59), suggesting that local myenteric plexus density is a factor determi ning NOS+ cell concentrations. Third, in contrast to such a principle of co variation within each organ, NOS+ neurons constituted a consistently smalle r proportion of gastric (20%) than of duodenal (28%) myenteric plexus neuro ns, suggesting that a second principle controls the characteristic percenta ges of the myenteric plexus that express NOS in different organs. Fourth, t he regional samples were used to extrapolate the overall number of NOS+ and total myenteric cells in the rat stomach (43,000; 217,000) and first 3.5 c m of the small intestine (29,000; 103,000). These results, taken together, also suggest that the surveying protocol used is capable of detecting subtl e differences in cellular distributions, thus providing a practical strateg y for investigating patterns of chemical phenotypes within the GI tract.