Ontogenetic differences in the expression of olfactory-conditioned aversions resulting from a state of acute alcohol intoxication in the rat.

Three experiments examined the effects of acute alcohol intoxication on olfactory conditioning in infant (16 days old) and adult rats (60-65 days old). In both age groups, alcohol administration (2 g/kg, IG) prior to conditioning procedures failed to affect subsequent expression of methyl-conditioned aversions in a two-way odor locational test. Nevertheless, whenever this same alcohol dose was administered prior to testing procedures, the expression of the olfactory conditioning was substantially impaired in infants but unaffected in adults. The factorial design allowed rejection of the possibility that ontogenetic differences in alcohol-induced state-dependent retention might explain this developmental difference (Experiment 1). A subsequent experiment (Exp. 2a) revealed major age related differences in terms of peak blood alcohol levels (BALs) that resulted from the 2 g/kg alcohol dose previously employed. As revealed by gas chromatography, infants exhibited significantly higher BALs than adults at time of conditioning and/or testing. Therefore in Experiment 2b, the alcohol dose administered in adults was increased until BALs were comparable to those attained in infants given 2 g/kg. This was accomplished with a 2.5 g/kg alcohol dose, employed in Experiment 2c to evaluate responsiveness of adults in conditioning circumstances identical to those of Experiment 1. Yet even with this dose the adults' expression of the conditioned olfactory aversion was unaffected by the alcohol at the time of testing. Experiment 3 analyzed the effects of alcohol intoxication on infantile and adult motor responses elicited by methyl and a novel odor (lemon), which might conceivably have affected performance in the two-way odor locational tests used to assess olfactory conditioning. The results failed to support the possibility that the previously observed ontogenetic differences in the expression of olfactory-conditioned aversions were due to alcohol's effect on sensorimotor responsiveness. In accordance with prior studies, the present results seem to indicate age-related sensitivity to alcohol's effects on cognitive processes.