Effect of prior ethanol experience on dopamine overflow in accumbens of AA and ANA rats.

The purpose of this study was to investigate the effect of repeated ethanol administration on dopamine overflow in the nucleus accumbens of alcohol-preferring AA (Alko Alcohol) and alcohol-avoiding ANA (Alko Nonalcohol) rats. Dopamine is a possible mediator of the reinforcing effects of ethanol, but it has previously been shown that ethanol-naïve alcohol-preferring AA and alcohol-nonpreferring ANA rats do not differ in their dopaminergic reaction to an intraperitoneal ethanol injection (0.5-2.0 g/kg), as assessed by measuring extracellular dopamine in the nucleus accumbens with in vivo microdialysis. Here a group of AA rats drank 10% (v/v) ethanol voluntarily-continual access for 5-15 days, limited access for 3 weeks-while a yoked group of AA rats and a yoked group of ANA rats received the same amount intragastrically by intubation. The rats were implanted with guide cannulas on the fourth week of limited access. Dopamine overflow was monitored in the microdialysis perfusate after 1 g/kg i.p. ethanol. The AA and the ANA rats that received ethanol non-contingently showed the same dopaminergic response to this as naïve animals have before. The group that had ingested the ethanol voluntarily showed, however, a significantly smaller increase in dopamine after 1 g/kg ethanol i.p. This suggests that the active behavior associated with obtaining the contingent drug may have an important impact on the reactions of the dopamine system to the drug, producing different results than when the same drug is administered by other routes. The hypothesis that dopamine mediates ethanol reinforcement in AA rats is not supported by the results.