Ontogeny of glucose inhibition of independent ingestion in preweanling rats.

Rat pups that have been maternally and nutritionally deprived will vigorously ingest diet infused directly into the mouth. The development of nutritive controls in this form of ingestion was examined by administering nutritive and non-nutritive gastric preloads to 6- and 15-day-old pups. In 6 day-old pups, nutritive gastric preloads (0.6 M glucose in distilled H2O or saline) and vehicle preloads were followed by similar intakes; only the change in hydrational state caused by distilled H2O loads appeared to affect intake. By 15 days of age, intake following nutritive preloads was less than intake following non-nutritive preloads. Also, at 15 days, stomach volume at the termination of intake was less following nutritive preloads. In a separate experiment with 6-day-old pups, gastric preloads of an alternative energy source, the ketone beta-hydroxybutyrate, also failed to inhibit intake when given at a dose that did not cause excessive gastric distension. These results indicate that a nutritive control of intake termination in rats is not present at 6 days of age but develops by 15 days of age.