GASTRIC VOLUME DETECTION AFTER SELECTIVE VAGOTOMIES IN RATS

Rats receiving intragastric infusions of 2.5, 5.0, 7.5, or 10.0 ml of normal saline while their pylori are reversibly occluded suppress meal size to the smallest infusion and display a dose-dependent reduction across volumes [Phillips, R. J., and T. L. Powley. Am. J. Physiol. 271 (Regulatory Integrative Comp. Physiol. 40): R766-R779, 1996]. To eval uate the contributions of the vagus to this detection of gastric volum e, groups prepared with different selective vagotomies and equipped wi th pyloric cuffs and gastric catheters were tested. Liquid diet consum ption during a 30-min feeding bout was measured after infusions of 5.0 and 10.0 ml of normal saline on cuff-open and cuff-closed trials. Con sistent with earlier observations, sham animals with cuffs closed exhi bited volume-dependent suppression of food intake to the infusions, an d completely vagotomized animals did not inhibit feeding in response t o the loads. In cuff-closed trials, the suppression function slopes of the selective vagotomy groups were intermediate to those of the shams and the completely vagotomized animals. Furthermore, for the differen t groups, the extent of suppression after vagotomy was proportional to the density of the afferent innervation respective branches supplied to the stomach. Specifically, the group with the gastric branches spar ed (nonsignificantly attenuated in comparison to shams) and the group with only the hepatic branch spared (significantly attenuated with res pect to shams) both still exhibited significant dose-dependent suppres sion slopes (compared with completes), whereas the group with only cel iac branches spared was not significantly different from completely va gotomized animals. In sum, the vagus nerve mediates the detection of t he gastric volumes tested, and the different branches of the vagus mak e distinctive contributions to this afferent feedback.