Ethanol familiarity and naltrexone treatment affect ethanol responses in rats

In the present study, the effects of ethanol familiarity on the ability of naltrexone to alter ethanol palatability and consumption were examined. One group of rats was allowed continuous access to 10% vol/vol ethanol and water for 3 weeks. A second group received only water. At the end of this time, the groups were further subdivided and injected with either 3 mg/kg naltrexone or saline (total of four groups; n = 11-13 per group) before ethanol taste reactivity tests with 10% vol/vol ethanol and ethanol consumption tests. Results showed that naltrexone effectively decreased ingestive responding and increased aversive responding. Further, rats familiar with alcohol made more ingestive responses to 10% vol/vol ethanol. A significant interaction of drug treatment and familiarity was found in the data for aversive responses: naltrexone treatment produced more aversive responses in ethanol-familiar rats, whereas saline treatment resulted in fewer aversive responses in rats familiar with ethanol. Naltrexone treatment clearly reduced consumption of 10% vol/vol ethanol, although its effects were attenuated somewhat by ethanol familiarity. The present data indicate that both alcohol familiarity and naltrexone treatment affect ethanol reactivity and ethanol consumption in outbred rats. The interaction of naltrexone treatment and ethanol familiarity only for aversive reactivity and the lack of such an interaction for the consumption measures suggests that the mechanisms underlying ethanol reactivity and ethanol consumption may be dissociable at the neural level.