A single exposure to voluntary ethanol self-administration produces adaptations in ethanol consumption and accumbal dopamine signaling

In well-trained animals, accumbal dopamine release is stimulated during operant ethanol self-administration, but the time course of development of this dopaminergic response, particularly during the acquisition of ethanol drinking behavior, remains unknown. To examine this, we trained male Long-Evans rats to self-administer 10% ethanol plus 10% sucrose, using a protocol in which the concentration of ethanol was kept constant throughout the study. The animals were required to press the lever four times to gain continuous access to the drinking solution for 20 minutes, and microdialysis was performed on either the first or second day of 10% ethanol plus 10% sucrose self-administration or 10% sucrose as controls. Ethanol and dopamine were both analyzed in the dialysates. All groups (day 1 and 2 ethanol and their corresponding sucrose controls) showed an increase in accumbal dopamine during the transfer from the home cage into the operant chamber. Our main finding was an increase in dopamine in the nucleus accumbens core-shell border during the first 5 minutes of consumption on the second day but not on the first day of ethanol self-administration. Our results suggest that a single exposure to a 10% ethanol plus 10% sucrose drinking solution may be sufficient to learn the association between ethanol cues and its reinforcing properties. Furthermore, we speculate that the dopamine response during ethanol consumption likely reflects the reward-prediction role of the mesolimbic dopamine system.