AbstractThe present series of experiments was designed to determine the dose—response characteristics of the cholecystokinin suppression effect on rat 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, the subjects received intraperitoneal injections or intravenous infusions of CCK‐8 at 2, 4, 8, or 16 μg/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 from the dam by suckling or feeding from the substrate. Regardless of the route of administration, CCK‐8 elicited a low level of suppression across all doses and all ages when pups ingested within the natural suckling situation. In marked contrast, pups ingesting from the substrate in the adult mode suppressed their intake of bovine light cream or chow pellets in a dose‐related manner following injections of the peptide. The blockade of the CCK dose‐related suppression effect during suckling indicates that a different set of mechanisms governs intake of milk from the mother. The results may be related to the level of arousal required to sustain motivated behaviors while pups engage in the different modes of ingestion.© 1994 John Wi