Opposing effects of vasoactive intestinal polypeptide on gastric motor function in the dorsal vagal complex and the nucleus raphe obscurus of the rat.

Vasoactive intestinal polypeptide (VIP)-like immunoreactive cell bodies and fibers and VIP binding sites exist in the brainstem nuclei that regulate autonomic function. Therefore, we investigated the effects of microinjection of VIP in the dorsal vagal complex (DVC), nucleus raphe obscurus (nROb) and nucleus ambiguus of alpha-chloralose-anesthetized rats while recording intragastric pressure, pyloric and greater curvature smooth muscle contractile activity, blood pressure and heart rate. Microinjection of VIP into the DVC increased intragastric pressure (1-100 pmol) and pyloric smooth muscle contractile activity (100 pmol), as well as arterial blood pressure (1-100 pmol). Whereas VIP microinjected into the nROb (10-100 pmol) decreased intragastric pressure and inhibited pyloric smooth muscle contractile activity. Mean arterial blood pressure increased in response to VIP in the nROb at the highest dose of 100 pmol only. No changes in gastric motor and cardiovascular function were noted after microinjection of VIP (1-100 pmol) into the region of the nucleus ambiguus. The gastric motor effects of VIP in the DVC (10 pmol) and nROb (50 pmol) were completely abolished by bilateral cervical vagotomy. These data show that VIP may produce opposite vagally mediated gastric motor responses upon its microinjection into the DVC and nROb.