Naltrexone treatment increases the aversiveness of alcohol for outbred rats

Acute naltrexone treatments (0.0, 0.5, 1., or 3.0 mg/kg body weight) were administered to separate groups of rats and alcohol taste reactivity and consumption were measured. Rats were given daily naltrexone injections and then tested for taste reactivity to 10% alcohol 30 and 60 min after injection. Each reactivity trial (total of 4) was 60 sec during which 1 ml of fluid was infused. The rats' orofacial and body movements were videotaped and scored later. In the final measure, rats were placed on a restricted fluid access schedule and given naltrexone treatments 10 min before being presented with the 10% alcohol solution in the home case (60-min drinking period). After 4 days of consumption tests under the drug condition, the rats were given 4 more daily tests without the drug. Results indicated that the two highest naltrexone doses significantly decreased ingestive responding and increased aversive responding, particularly at the 30-min test. Both the 1.0 and 3.0 mg/kg body weight doses also significantly decreased alcohol consumption as measured during the free access tests. Alcohol consumption returned to control levels immediately after the drug treatments were stopped. The data show that dosages of naltrexone 1.0 mg or higher significantly alter both alcohol taste reactivity (increased aversiveness and decreased palatability) and alcohol consumption (decreased intake) in outbred rats. These results are discussed in relation to naltrexone treatment as a means for decreasing alcohol use and abuse.