Ethanol-induced conditioned place aversion in mice

Previous studies have shown that ethanol produces conditioned place prefere nce (CPP) in mice when injections are given immediately before exposure to the conditioned stimulus (CS). Paradoxically, however, injection of ethanol immediately after the CS produces conditioned place aversion (CPA). Four e xperiments were conducted to characterize the parametric boundaries of CPA produced by post-CS ethanol exposure. Experiment 1 showed that CPA is posit ively related to ethanol dose, with significant CPA at 2 and 4 g/kg, but no t at 1 g/kg. Experiment 2 revealed an inverse relationship between CPA and trial duration, i.e. significant CPA occurred when the trial duration was 5 , 15 or 30 min, but not when it was 60 or 90 min. Experiment 3 indicated th at ethanol pre-exposure (eight daily injections) significantly reduced subs equent development of CPA. Finally, experiment 4 showed that repeated expos ure to the CS alone (six 30 min exposures to each CS) after CS-ethanol pair ings produced complete extinction of CPA. The same extinction procedure als o completely eliminated CPP induced by pre-CS injections of ethanol. Overal l, these studies demonstrate that CPA induced by post-CS ethanol injection is influenced by many of the same variables that affect CPP produced by pre -CS ethanol injection in mice. However, these findings do not resolve the i ssue of whether the 'before-versus-after' effect in ethanol place condition ing is better explained by assuming ethanol produces only rewarding effects or by assuming that ethanol produces both rewarding and aversive effects. (C) 2000 Lippincott Williams & Wilkins.