Gastric relaxation induced by electrical and chemical stimulation of the area postrema in the rat.

Area postrema (AP) is considered to be an important neural center for emesis in carnivores. However, it is also known that AP mediates motor responses induced by apomorphine in rats which do not have an emetic reflex. To shed more light on the possible role of AP in the control of gastric motility in physiological or pathophysiological conditions, we observed the effects of electrical or chemical (apomorphine) stimulation of AP neurons on intragastric pressure (IGP) or intragastric volume (IGV) in rat. We found that electrical stimulation (ES) reduces IGP, and this is sensitive to hexamethonium or L-NAME, and apomorphine also reduces IGP and increases IGV. In slice preparations, apomorphine (10 micromol/l) increased the frequency of spontaneous single unit discharges of AP neurons recorded extracellularly. We also succeeded retrograde labeling of AP neurons by DiI applied into the gastric corpus, for the first time. These observations indicate that rat stomach receives efferent neural input from AP and the excitation of AP neurons relaxes the stomach in rat, suggesting some functional roles of AP neurons in the regulation of gastric motility.