Selective gastric projections of nitric oxide synthase-containing vagal brainstem neurons

Nitric oxide has been proposed to act as an intercellular messenger in cent ral brainstem circuits controlling gastrointestinal motility. In particular , a subpopulation of preganglionic vagal neurons of the dorsal motor nucleu s of the vagus have been shown to be reduced nicotinamide adenine dinucleot ide phosphate(NADPH)-diaphorase positive; NADPH-diaphorase positive pregang lionic fibers are also known to make contact with enteric neurons in the st omach. No studies, however, have correlated the neurochemical phenotype of preganglionic vagal neurons to their stomach target. The purpose of this st udy was to identify the subpopulation of nitric oxide synthase positive vag al neurons projecting to the stomach. Fluorescent retrograde tracers were i njected in the fundus, corpus or antrum (Rhodamine beads) or painted on the anterior gastric branch of the vagus (DiI); five to 15 days later the brai nstem was processed for nitric oxide synthase immunoreactivity. Of the 532 DiI-labeled neurons from the vagal anterior gastric branch, 25 (4.7%, n=5 r ats) were co-localized with nitric oxide synthase immunoreactivity. Of the neurons labeled following injection of rhodamine beads in the antrum (N=231 neurons, n=5 rats) or corpus (N=166 neurons, n=4 rats) only three neurons showed nitric oxide synthase immunoreactivity (two in antrum and one in cor pus, respectively). Conversely, 26 of 222 neurons (12%, n=7 rats) labeled f ollowing injection of rhodamine in the fundus showed nitric oxide synthase immunoreactivity. These results provide evidence for a discrete phenotypic subpopulation of v agal motoneurons that project to the gastric fundus, and suggest that these neurons may be the ones involved in the receptive relaxation reflex. (C) 1 999 IBRO. Published by Elsevier Science Ltd.