Opioidergic, serotonergic, and dopaminergic manipulations and rats' intake of a sweetened alcoholic beverage.

Groups of rats were maintained on a daily regimen of 22 h of water deprivation followed by a 2-h opportunity to take either water or a sweetened ethanol solution (ES). In one experiment, it was shown that previous morphine (M) dependence had no effect on initial daily intakes of fluids. After stable ES intakes were achieved, a variety of pharmacological manipulations were assessed for their effects on intake of the ES. Nalmefene, an opioid antagonist, dose-relatedly decreased intakes of ES, and was effective across days of injections. Fluoxetine (FX), a serotonergic reuptake inhibitor, also reduced ES intakes dose relatedly, and across days of injections, but the reduction was not as great as that seen with opioid antagonists. A small dose of M increased ES intakes when given in combination with an ineffective dose of FX, just as it does by itself. However, M had no effect on ES intakes in combination with an effective dose of FX. Pimozide (PIM), a dopaminergic antagonist, dose-relatedly decreased intakes of ES and water, and responding for positively reinforcing intracranial stimulation (ICS). When given in combination, M blunted PIM's reduction of ES intake, but had no effect on PIM's ability to decrease either intake of water or responding for ICS. Amphetamine did not reliably affect rats' intakes of ES across a range of doses. The data, in addition to previous work, lead to the idea that endogenous opioid systems are more salient, with respect to intake of alcoholic beverages, than the other tested neurotransmitter systems. Furthermore, the collective data suggest that a long-lasting opioid antagonist may be an effective pharmacological adjunct to other treatments for alcohol abuse and alcoholism.