Ontogeny of hyperphagia in the Zucker (fa/fa) rat

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Abstract
The ontogeny of hyperphagic behavior in the Zucker fatty ( fa/fa) rat was examined. Wild-type, +/fa, andfa/fapups aged postnatal day 5(P5),P9,P12,P15, andP18 were evaluated using a test that measured ingestive behavior independent of the dam. The independent ingestive test consisted of giving pups access to a test solution [half-and-half (cream and milk)] on a tissue on the floor of a test chamber for 20 min. The latency to ingest and the intake (weight gain and percent weight gain) were measured and normalized to +/fa littermates. Pups were tested once to eliminate any effects of test experience.fa/faPups ingested significantly more than lean pups (+/+ and +/fa) onP12,P15, andP18, but not onP5 orP9. The latencies offa/fapups did not differ significantly from the latencies of +/+ pups except on P18, when the latencies offa/fapups were significantly shorter. The latencies of +/fa pups were significantly longer than the latencies offa/faor +/+ pups on P5 andP12. These results demonstrate that hyperphagia infa/farats emerges between P9 andP12 under the test conditions used.