WT and KO mice (n = 8) were food restricted to reduce body weights to 90% of free-feeding weight, and trained to press a lever for 10% sucrose in mouse operant chambers (Med Associates, Georgia, VT, USA) constructed of clear Perspex (18×18×15 cm), and contained in sound and light attenuating cubicles. Each operant chamber possessed a single house light located on the wall opposite the levers. The front wall was fitted with a liquid dipper, located between 2 ultrasensitive mouse levers. Following an initial 15 hour training session, which included the dark phase, the response requirement to obtain 10% sucrose reinforcer was increased over consecutive days (range 2–7) from FR1 to FR2 to FR4 in daily one hour sessions. Motivation to consume ethanol was investigated using the sucrose fading technique [28]: over the following sessions the sucrose concentration was decreased and the ethanol concentration was increased as follows; 10% sucrose +3% ethanol; 10% sucrose +5% ethanol, 7% sucrose +5% ethanol, 10% sucrose +10% ethanol. The mice remained at each stage until reaching a criterion of at least 30 reinforcers per session on 3 consecutive days.
