programmed events. No explicit cues were used at any time during the conditioning sessions. To facilitate acquisition of the lever-press response, rats were placed overnight (12–14 hours) in the operant chambers for two nights in a row and allowed to respond for ethanol on a continuous reinforcement schedule. After overnight training sessions, 30-minute daily training sessions were conducted, with the schedule requirement increasing to FR2 over the course of 2 weeks. Responses on the active and inactive levers, and ethanol port entries, were recorded. After stable responding developed, blood ethanol levels were measured (see below). These data indicated that rats achieved measurable levels of plasma ethanol following a single operant session (mean + SEM: 7.11 + 0.85 mM, range: 5.35–12.34 mM; equivalent to 32.71 + 3.91 mg%; range: 24.62–56.76 mg%; n = 14) and these values were predictive of the estimated g/kg (mean ± SEM: 0.6525 ± 0.066 g/kg, range: 0.4–1.04 g/kg, Pearson correlation, r = 0.944, P < 0.001). After 2 months of training, rats were divided into treatment and control virus groups by attempting to balance the groups for baseline operant responding. Surgery for virus infusion then commenced; after recovery, 30 minutes self-administration sessions occurred daily for 30
