Neural control of electrical gastric activity in response to inflation of the antrum in the rabbit.

The respective roles of the extrinsic innervation (vagal and splanchnic) and of the myenteric plexus in the control of gastric motility were investigated in rabbits by quantifying the effect of cutting the extrinsic nerves on the electrical response of the antrum and pylorus to inflation of the antrum. In intact animals the frequency of bursts during distension was significantly increased above the frequency during the 30 min preceding inflations. The interval from the end of step inflation to the first burst recorded after inflation was significantly longer than the mean interval between bursts in the 30 min preceding inflation, whereas no such difference was observed following ramp inflation. Both atropine and hexamethonium abolished the responses to distension. The basal rhythm of bursts recorded on the antrum and pylorus was markedly reduced during the first 3 days after vagotomy: the mean values of the frequency in response to distension were significantly less than those in intact animals, whereas the first interval after inflation was significantly increased. Thereafter no such differences were encountered. The only change after section of the splanchnic nerves was a significant reduction in the first interval after inflation, resulting in rapid restoration of the initial rhythm at the end of inflation. In vagotomized animals with cut splanchnic nerves, the basal electrical activity of the antrum was not affected but the responses to step inflations were much greater; the frequency of bursts during distension and the first interval after inflation were both significantly increased. Section of the vagal afferent fibres changed neither the frequency of the basal rhythm nor the responses to distension. These results indicate that the tonic excitatory effect mediated by vagal efferents on the basal rhythm of the antrum is of central origin and independent of visceral inputs. Local mechanisms within the peripheral plexus of neurones could be responsible for the enhanced responses to step inflations, which would normally be adjusted by the central mechanisms through the extrinsic innervation. Possible effects of changes in the sensitivity of the post-ganglionic neurones are discussed.