Adenosine is an important mediator of ethanol intoxication. In vitro, ethanol stimulates adenosine signaling by inhibiting the type 1 equilibrative nucleoside transporter (ENT1), whereas chronic ethanol exposure downregulates ENT1. It is not known, however, whether ENT1 is important for ethanol intoxication or consumption in vivo. Here we report that ENT1-null mice show reduced hypnotic and ataxic responses to ethanol and greater consumption of alcohol as compared with their wild-type littermates. These features are associated with a decrease in adenosine tone, as measured indirectly as a reduction in A(1) receptor-mediated inhibition of glutamate excitatory postsynaptic currents (EPSCs) in the nucleus accumbens, leading to increased phosphorylation of CRE-binding protein (CREB) in the striatum. Treatment with an A(1) receptor agonist decreases EPSC amplitude and reduces ethanol consumption in ENT1-null mice. Our results indicate that ENT1 has a physiological role in ethanol-mediated behaviors and suggest that decreased A(1) adenosine receptor function promotes alcohol consumption.

Dopamine in the nucleus accumbens modulates both motivational and addictive behaviors. Dopamine D1 and D2 receptors are generally considered to exert opposite effects at the cellular level, but many behavioral studies find an apparent cooperative effect of D1 and D2 receptors in the nucleus accumbens. Here, we show that a dopamine-induced enhancement of spike firing in nucleus accumbens neurons in brain slices required both D1 and D2 receptors. One intracellular mechanism that might underlie cooperativity of D1 and D2 receptors is activation of specific subtypes of adenylyl cyclases by G-protein betagamma subunits (Gbetagamma) released from the Gi/o-linked D2 receptor in combination with Galpha(s)-like subunits from the D1 receptor. In this regard, dopaminergic enhancement of spike firing was prevented by inhibitors of protein kinase A or Gbetagamma. Furthermore, intracellular perfusion with Gbetagamma enabled D1 receptor activation but not D2 receptor activation to enhance spike firing. Finally, our data suggest that these pathways may increase spike firing by inhibition of a slow A-type potassium current. These results provide evidence for a novel cellular mechanism through which cooperative action of D1 and D2 receptors in the nucleus accumbens could mediate dopamine-dependent behaviors.