We show that the preference for a cue associated with ethanol spontaneously switches from negative (aversion) to positive (attraction) 12-15 hrs after conditioning. Opposing behavioral responses to an identical dose of a drug of abuse are surprisingly common. For example, acute exposure to nicotine in rats results in short-term conditioned place aversion that switches to longer-lasting conditioned place preference27. These opposing responses may be due to conflicting responses to the sensory and pharmacological effects of the drug. For example, infant rats exhibit aversive learning to ethanol’s orosensory effects, but show positive reinforcement to its post-ingestive effects28. We speculate that the initial aversive properties of ethanol in flies are not dependent on its intoxicating effects, but rather are a result of a negative physiological reaction or sensory response, similar to that observed in rats.
