Abstract
We have previously demonstrated that the intravenous administration of apomorphine induced increase in intragastric pressure via dopamine 2-like receptors situated in the area postrema. Since the microinjection of neurokinin-1 antagonist into the vicinity of the nucleus ambiguus (NA) diminished the increase in intragastric pressure, substance P responsive neurons in this area may mediate these gastric responses. To demonstrate this hypothesis, in the present study, we examined the response of neurons adjacent to the NA to the administration of apomorphine and the electrical stimulation of the efferent fibers from the nucleus tractus solitarii (NTS). Intravenous administration of apomorphine (0.1mg/kg) induced excitatory responses of neurons adjacent to the NA in anaesthetized rats. We further determined the effects of the electrical stimulation of the efferent fibers from the NTS and the bath-application of substance P on neurons adjacent to the NA by using whole-cell recording method in a slice preparation of 4-20 days old rats. Some of these neurons during pulse-train stimulation (50-Hz, 50-pulse, 10-sec interval) produced a "wind-up" response. These results suggest that gastric motor responses induced by the apomorphine administration are mediated by substance P responsive neurons adjacent to the NA. [Jpn J Physiol 54 Suppl:S194 (2004)]
