Increased ethanol consumption and locomotion develop upon ethanol deprivation in rats overexpressing the adenosine A(2A) receptor

Preclinical data indicate that ethanol produces behavioral effects that can be regulated by many neurotransmitters and neuromodulators like adenosine (A). The most important receptors with respect to the rewarding effects of ethanol seem to be the A(2A) receptors. This study used a transgenic strategy, specifically rats overexpressing the A(2A) receptor, to characterize the neurobiological mechanisms of ethanol consumption as measured by intermittent access to 20% ethanol in a two-bottle choice paradigm. In this model, no change in ethanol consumption was observed in transgenic animals compared to wild type controls during the acquisition/maintenance phase. Following alcohol deprivation, only transgenic rats overexpressing the A(2A) receptor exhibited escalation of ethanol consumption and drank more (by ca. 90%), but not significantly, ethanol than did the wild type rats. During ethanol withdrawal, the immobility time of rats overexpressing the A(2A) receptor in the forced swim test was lower than that of wild type rats. Moreover, transgenic rats withdrawn from ethanol, compared to the drug-naive transgenic animals, exhibited an increase above 70% in locomotion. The results indicated that the overexpression of A(2A) receptors may be a risk factor for the escalation of ethanol consumption despite the reduction in depression-like signs of ethanol withdrawal