Role of context in ethanol tolerance and subsequent hedonic effects

Two groups of male Sprague-Dawley rats received ethanol dose-effect tests for FR30, food-reinforced operant performance, in each of two environmental contexts, before and after a period of daily presession ethanol or saline injections. During the latter period, context alternated daily. The ethanol group received ethanol prior to sessions for one context and saline, prior to sessions for the other context. The saline group always received presession saline. The ethanol, but not the saline, group displayed robust tolerance to ethanol's rate-decreasing effects, with no difference between tests in each context. Both groups then received training and testing in an ethanol-conditioned place preference task. The saline group displayed significant avoidance of the compartment paired with ethanol. The ethanol group displayed no initial aversion for the ethanol compartment and, with extended conditioning, showed a significant increase in time spent in the ethanol compartment. We suggest that this tolerance represents context-independent, learning to compensate for ethanol-induced effects, and that this tolerance subsequently blocked the conditioned place aversion evident in nontolerant controls, thereby enhancing the estimates of ethanol's reward properties.