The esophageal distension-gastric relaxation response or "receptive relaxation reflex" [RRR] is an autonomic mechanism which normally increases gastric volume and reduces intragastric pressure to assure that swallowed food is efficiently transported to and retained by the stomach. There is a large body of descriptive literature which supports the existence of the RRR in a number of species including rats and humans. This reflex is mediated largely, is not exclusively by a vagal afferent-CNS-vagal efferent pathway. Failure of this reflex mechanism has been held responsible for a number of serious swallowing and reflux disorders. This circuitry, which produces gastric relaxation, may also play a critical role in the perception of nausea and the production of emesis. Our preliminary results suggest that the central RR circuitry of esophageal vagal afferent connections with the nucleus of the solitary tract, pars centralis (NSTc] which, in turn, projects throughout the entire dorsal motor nucleus of the vagus [DMN]. DMN efferents which control the motility and compliance functions of the stomach are separable into two distinct vagal pathway. The other DMN projection to the stomach probably activates a non-adrenergic non-cholinergic [NANC] enteric circuit. Based on our preliminary physiological data we formulate the following hypotheses: the NSTc neurons activated by esophageal afferent input operate on these two separate DMN pathways to the stomach such that the muscarinic ["excitatory"] pathway is inhibited while the NANC ["inhibitory"] pathway is activated. The combination of effects produces a profound relaxation. Furthermore, we predict that a previously identified corticotrophin releasing hormone [CRH]- ergic CNS mechanism activated by psychological stress produces gastric stasis by activating RR circuit elements in the dorsal vagal complex. These predictions will be tested by a combination of in vivo and in vitro neurophysiological and immunocytochemical protocols.