Sham feeding in intact and chronic decerebrate rats.

In the traditional sham-feeding paradigm, the amount of sugar solution consumed by the rat is influenced by its concentration and the open or closed condition of the gastric fistula. The present experiments examine: 1) whether sham intake effects obtained under the "intraoral intake" paradigm, developed to explore controls of ingestion in otherwise aphagic preparations such as the decerebrate, are similar to those of previous studies in which intact rats obtained the fluid stimulus by spout licking; and 2) whether chronic decerebrate and intact rats show a similar elevation of their sucrose intake when ingesting with an open (sham intake) vs. closed gastric fistula. Experiment 1 showed that sham intraoral intake exceeded intake in the closed condition only for sucrose concentrations greater than 0.1 M. After it was established that the results obtained with the intraoral paradigm were consistent with those reported in the literature, the new paradigm was applied to the chronic decerebrate rat in experiment 2 to determine whether forebrain structures are necessary for sham-feeding effects. The effect of sucrose concentration and fistula condition on the behavior of chronic decerebrates was similar to that of intact rats. Like intact rats, decerebrate rats consumed more sucrose in the open condition but only for concentrations exceeding 0.1 M. This concentration-dependent sham sucrose intake of chronic decerebrate rats provides compelling evidence that the integration of sucrose's taste and postingestive effects that modulates ingestive behavior can be accomplished by the caudal brain stem.