Inhibitory controls of ingestion in 6-day-old rat pups.

The ability of gastric preloads of milk, water, and isotonic saline to inhibit ingestion was studied in deprived 6-day-old rat pups being fed through oral cannulas. Preloads were delivered through gastric cannulas or by gavage, and both the volume of the load and the interval between the preload and testing were varied in order to assess the relative contributions of pre- and post-absorptive cues from the loads. Pups' willingness to initiate ingestion in short (10 min) tests (appetite) was unaffected by the degree of gastric filling produced by a load but was depressed by post-absorptive changes in hydrational state. On the other hand, pups terminated ingestion in long (30 min) tests (satiety) in response to gastric filling. Cessation of intake in long tests was only slightly influenced by post-absorptive factors. These results reveal two distinct phases of ingestion in infant rats and show that each is controlled in a different manner.