Ingestive behavior in preweanling rats: emergence of postgastric controls.

Previous studies have indicated that the termination of intake in very young rat pups is controlled almost exclusively by the level of gastric fill; nutritive cues from diet have no effect on intake. In the present series of experiments, we investigated the ontogeny of postgastric nutritive controls of intake in rat pups ingesting independent of their dam. In 6-day-old pups, the level of gastric fill required to terminate ingestion was not affected by the presence or absence of post-gastric nutritive cues, but by 15 days of age a greater level of gastric fill was required to stop ingestion when postgastric cues were eliminated by a closed pyloric noose. This emergent post-gastric contribution to the inhibition of intake in 15-day-old pups does not depend on preexisting gastric fill signals, as sham-feeding pups (open gastric fistula) with nutrients in their intestines ingested less than pups without intestinal nutrients. These results provide evidence that postgastric controls of ingestive behavior mature during the postnatal period and just shortly before they are required at weaning.