EFFECTS OF CCK-8 ON INGESTIVE BEHAVIORS OF SUCKLING AND WEANLING RATS

The present series of experiments was designed to determine the dose-r esponse characteristics of the cholecystokinin suppression effect on r at pups ingesting through suckling and adult modes. Pups at 10-22 days of age were deprived of their dam and food for 6 hr. At test time, th e subjects received intraperitoneal injections or intravenous infusion s of CCK-8 at 2, 4, 8, or 16 mu g/kg in saline, or the saline vehicle alone. The pups were permitted to ingest for 30 min immediately after the injection or during the infusion. Ingestion included taking milk f rom the dam by suckling or feeding from the substrate. Regardless of t he route of administration, CCK-8 elicited a low level of suppression across all doses and all ages when pups ingested within the natural su ckling situation. In marked contrast, pups ingesting from the substrat e in the adult mode suppressed their intake of bovine light cream or c how pellets in a dose-related manner following injections of the pepti de. The blockade of the CCK dose-related suppression effect during suc kling indicates that a different set of mechanisms governs intake of m ilk from the mother. The results may be related to the level of arousa l required to sustain motivated behaviors while pups engage in the dif ferent modes of ingestion. (C) 1994 John Wiley and Sons, Inc.