Behavioral sensitization, opioid system and context

Abstract

A major difficulty in treating alcohol addiction is the high rate of relapse even after prolonged abstinence. Relapse can be triggered by many factors, including stress, re-exposure to the drug, conditioned stimuli and exposure to the context in which alcohol consumption occurred. The opioid receptor antagonist naltrexone has been found to attenuate the adquired behavioral sensitization to ethanol. The present study investigated the role of naltrexone as an attenuant in interaction with and specific context in the development of ethanol (2.5 g/kg/day; six sessions) induced locomotor sensitization in mice. We confirmed the development of behavioral sensitization to ethanol in two different groups; context and no-context. This was the first step before the preteatment with naltrexone after the 6 days with treatment of ethanol. Naltrexone (2 mg/kg) was given 30 min before saline or ethanol. Results of these experiments revealed that administration of a pretreatment (naltrexone) attenuate the induced locomotor sensitization in mice that were previously being administered ethanol in an specific context but no on those ones that where in non-specific context. The present data suggest that administration of naltrexone attenuated the expression of ethanol-induced sensitization, however, this effect was only found with animals tested in the same context where sensitization developed. These findings are in accordance with clinical reports claiming the efficacy of naltrexone in the treatment of alcohol relapse in humans, and indicate that the context may be an useful variable to investigate the biological mechanisms underlying alcohol relapse.