Ethanol-induced conditioned place aversion in rats: effect of interstimulus interval

The purpose of this study was to examine the effect of interstimulus interval (ISI) on ethanol-induced place aversion in rats. Six groups of rats initially received four pairings of a distinctive floor stimulus (CS+) with ethanol (1 g/kg, I.P.) and four pairings of a different floor stimulus (CS-) with saline. Groups -30, -15, -10, -5, 0, and 5 were injected 30, 15, 10, 5, or 0 min before, or 5 min after exposure to the 5 min CS, respectively. After testing for place aversion, all groups were exposed to an additional set of conditioning trials using a higher dose of ethanol (1.5 g/kg). During the first test, only groups 0 and -15 exhibited conditioned place aversion. However, during the second test, all groups showed conditioned aversion except group -30. The results suggest that ethanol's aversive effects dissipate by 30 min postinjection or that it is more difficult to associate those effects with short-duration external stimuli at long backward intervals. In contrast to recent findings with mice, the direction of ethanol-induced place conditioning was not altered in rats exposed to different ISIs.