Accumbal dopamine concentration during operant self-administration of a sucrose or a novel sucrose with ethanol...

The goal of the current study was to determine the effect of operant self-administration of (1) 10% sucrose and (2) a first-time solution of 10% sucrose with 5% or 10% ethanol, on dopamine concentration in the nucleus accumbens. We used an operant procedure that distinguished lever pressing (an appetitive behavior) from drinking to better assess the effect of fluid consumption on accumbal dopamine activity. Male Long-Evans rats were trained to bar press by using 10% sucrose reinforcement, and they were required to emit an escalating number of bar presses across daily sessions. Completion of the response requirement resulted in 20 min of access to the solution. Microdialysis samples were collected before, during, and after bar pressing and drinking, and content of ethanol and dopamine was determined. Dopamine concentration in the dialysate was slightly, but significantly, increased in both groups during lever pressing. However, after consumption began, dopamine concentration increased in the sucrose, but not in the sucrose with ethanol, group, followed by a return to baseline values. Ethanol consumption was low (0.27 +/- 0.02 g/kg) and corresponded to low dialysate ethanol concentrations, which appeared within 5 min of drinking. These results demonstrate that operant self-administration of sucrose increases accumbal dopamine concentration during consummatory phases of behavior, but that a similar increase is not apparent when a novel, perhaps aversive, solution (sucrose with ethanol) is presented. This difference may be due to the sensory-related stimulus properties of each solution. In addition, oral self-administration of ethanol at 0.27 +/- 0.02 g/kg over 20 min is not sufficient for stimulation of dopamine activity in the nucleus accumbens.