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 evaluate the contributions of the vagus to this detection of gastric volume, groups prepared with different selective vagotomies and equipped with pyloric cuffs and gastric catheters were tested. Liquid diet consumption 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. Consistent with earlier observations, sham animals with cuffs closed exhibited volume-dependent suppression of food intake to the infusions, and completely vagotomized animals did not inhibit feeding in response to 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 different 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 spared (nonsignificantly attenuated in comparison to shams) and the group with only the hepatic branch spared (significantly attenuated with respect to shams) both still exhibited significant dose-dependent suppression slopes (compared with completes), whereas the group with only celiac branches spared was not significantly different from completely vagotomized animals. In sum, the vagus nerve mediates the detection of the gastric volumes tested, and the different branches of the vagus make distinctive contributions to this afferent feedback.