Ethanol as a reinforcer in the newborn's first suckling experience

Background: Recent evidence suggests that human infants prefer alcohol-flav ored milk when fed through a bottle. Animal models also indicate a surprisi ng predisposition for neonatal and infant rats to voluntarily and willingly ingest ethanol. These findings suggest high susceptibility to the reinforc ing properties of ethanol early in ontogeny. Methods: A surrogate nipple technique-a highly effective tool for investiga tion of the reinforcing properties of different fluids-was applied in the p resent study. Tests of ethanol reinforcement were accomplished in terms of two basic paradigms of Pavlovian conditioning. In one paradigm, the conditi oned stimulus (CS) was the surrogate nipple, and in the other, the CS was a novel odor. Results: Newborn rats showed sustained attachment to the nipple providing 5 % ethanol, and later reproduced this behavioral pattern toward the empty ni pple (CS alone). Ingestion of ethanol yielding appetitive reinforcement was accompanied by detectable blood alcohol concentrations, with most in the r ange of 20-30 mg/dl. The reinforcing efficacy of ethanol was also confirmed in the classical olfactory conditioning paradigm: following pairing with i ntraoral ethanol infusions, the odor (CS) alone elicited sustained attachme nt to an empty nipple. Females showed better olfactory conditioning with lo w concentrations of ethanol, whereas males were effectively more conditione d to high concentrations. Although there were no reinforcing consequences o f intraperitoneally injected ethanol [as an unconditioned stimulus (US)] wh en a neutral odor was the CS, when paired with ingestion of water from a ni pple, the injection of ethanol had a reinforcing effect. Conclusions: The present series of experiments revealed ethanol reinforceme nt in the newborn rat. Two varieties of Pavlovian conditioning established that ethanol can serve as an effective US, and hence reinforcer, in such a way as to increase the approach and responsiveness toward stimuli paired wi th that US, indicating appetitive reinforcement.