Postpyloric stimuli are necessary for the normal control of meal size in real feeding and sham feeding rats

Abstract

When 0.8 M sucrose is sham fed, intake increases progressively on consecutive tests and then plateaus. Interspersing two real feeding tests between sham feeding tests prevents this increase in sham intake [J. D. Davis and G. P. Smith. Am. J. Physiol. 259 (Regulatory Integrative Comp. Physiol. 28): R1228-R1235, 1990]. This is consistent with an acquired control of ingestion based on an association between an oropharyngeal conditioned stimulus (CS) and a postingestional unconditioned stimulus (UCS). To determine if this postingestional UCS has a gastric or postgastric origin (or a combined one), we confined ingested 0.8 M sucrose to the stomach on real feeding and sham feeding tests by closing the pylorus with an inflatable Silastic cuff. Rats were tested on seven sham feeding tests separated by two real feeding tests and then on six consecutive sham feeding tests. In contrast to our previous results [Davis and Smith. Am. J. Physiol. 259 (Regulatory Integrative Comp. Physiol. 28): R1228-R1235, 1990], intake increased progressively on the real feeding and both types of sham feeding tests. We conclude that both gastric and postgastric stimuli act as a UCS for the acquired control of meal size.