Hindbrain effects of PACAP on gastric motor function in the rat

Pituitary adenylate cyclase-activating polypeptide (PACAP)-like immunoreactive cell bodies and fibers are visualized in hindbrain nuclei that are involved in the regulation of autonomic function, yet little is known about the gastric and cardiovascular effects of this peptide in the dorsal vagal complex, nucleus raphe obscurus, and nucleus ambiguus. Therefore, multiple-barreled micropipettes were used to inject PACAP-38 (1-100 pmol) into each of these nuclei in alpha-chloralose anesthetized rats, while intragastric pressure, pyloric and greater curvature smooth muscle contractile activity, blood pressure, and heart rate were recorded. For comparison, the effect of L-glutamate (15 nmol) microinjected into the same sites on gastric motor activity was also assessed. L-Glutamate microinjected into each nucleus before PACAP-38 significantly increased intragastric pressure, both in terms of the peak increase and the total area of the response. Microinjections of PACAP-38 (10 and 100 pmol) into each of the nuclei significantly increased peak intragastric pressure, but the total area of the response was only significantly increased by the highest dose (100 pmol) in the case of the dorsal vagal complex and nucleus raphe obscurus. No consistent changes in heart rate and mean arterial blood pressure were noted after microinjection of PACAP-38 into each of the three nuclei. Bilateral vagotomy abolished the increase in intragastric pressure in response to microinjection of PACAP-38 into the dorsal vagal complex and nucleus raphe obscurus. We conclude that PACAP-38 in the dorsal vagal complex and nucleus raphe obscurus is involved in vagally mediated gastric motor excitation.