Conditioned preferences and aversions in infant rats mediated through ethanol inhalation

Little is known about the acute motivational effects of inhaled ethanol during early postnatal development. We analyzed the motivational properties of ethanol inhalation in infant rats by using two distinct schedules of ethanol vapor delivery. Ethanol was presented in a continuous conditioning trial or in separate, distributed trials. Maximum blood ethanol concentrations (BECs) induced by these schedules were 55 and 15 mg%, respectively (Experiment 1). In Experiment 2, subjects were given daily pairings (postnatal days [PD] 14 and 15) between a tactile conditioned stimulus (CS, sandpaper) and the postabsorptive effects of ethanol inhalation. A tactile preference test (PD16) revealed a significant aversion for the CS in pups given continuous exposure to ethanol vapor. In Experiment 3, an ethanol pre-exposure phase (PD13) preceded tactile-ethanol pairings. During conditioning, pups were given distributed pairings between the tactile CS and ethanol or uncontaminated air. At test, ethanol-pre-exposed animals spent significantly more time on the ethanol-related CS than on an alternative texture. These results indicate that inhaled ethanol exerts differential hedonic effects in infant rats as a function of schedules of exposure that yield different levels of intoxication. Continuous experience with ethanol vapor induces aversive learning. Yet, pre-exposure to ethanol vapor allowed expression of ethanol-induced appetitive learning in pups given distributed vapor ethanol exposure.