Olfactory influences on the ingestive behavior of infant rats.

Twenty-four-hour deprived infant rats from 1 to 12 days of age were exposed to the odor of milk, either by itself or accompanied by oral infusions of water, sucrose, quinine, or milk (Experiment 1). Pups from 3 to 9 days of age became behaviorally active, and mouthed and probed in response to the odor of milk, even in the absence of oral infusions. Six- and 9-day-old pups also increased their intake of various test solutions in the presence of milk odor. This responsiveness to milk odor was not seen in 1-day-old pups, and waned by 12 days of age. Other stimulus odors that were presented in the same context (Experiment 2) failed to elicit such intense behavioral activation, indicating that there was some degree of specificity in the responsiveness to milk odor. Finally, 2 manipulations that influence pups' ingestion of milk, deprivation and ambient temperature, were found to influence pups' responses to milk odor (Experiment 3).