Standard operant chambers

Training and experiments took place using 8 standard operant chambers (Coulbourn Instruments) controlled by GraphicState 3.0 software and housed in sound-attenuating cabinets. Chambers were equipped with a house light, food magazine recessed into a side wall, and three nosepoke apertures located on the wall opposite the food magazine. A speaker for delivering auditory cues was located above the food magazine. A retractable lever was located to one side of the food magazine (left or right counterbalanced among subjects) with a white cue light above the lever. Subjects were initially trained to retrieve sucrose pellets (45 mg, Bio-Serv) from the food magazine over 2 daily sessions consisting of 50 pellets delivered on a variable interval schedule (mean = 60 s).

Strategy shifting took place in standard operant chambers (Coulbourn Instruments, Whitehall, PA) that were enclosed in sound-attenuating cubicles. The cubicles were equipped with fans that provided ventilation and masked extraneous noise. One wall of each operant chamber was equipped with a centrally located food trough outfitted on either side with retractable levers that were equidistant (87 mm) from the trough. White cue lights were located above each lever and a 2.9 kHz Sonalert speaker was located directly above the food trough. A white houselight was located near the chamber ceiling on the wall opposite the nosepoke ports. Graphic State software (v3.1; Coulbourn Instruments) was used for automated chamber control and data collection.

Adult MS rats (n=10) were trained to lever press for ethanol starting at P60–P70. The training described below takes approximately 4 weeks, followed by 21 days of testing. Standard operant chambers [Coulbourn Instruments, Inc., Lehigh Valley, PA] were enclosed in an isolated box. The operant apparatus contained two levers, two dipper manipulanda, triple cue lights over each lever, and a house light. The dipper cup size was 0.1 mL. The Coulbourn Graphic State “3” operant software was used to capture lever presses for the alcohol. Rats were trained to orally self-administer EtOH daily for 1h under a fixed ratio [FR] 1 schedule employing the sucrose fading technique (Harvey et al., 2002 (link)). After a period of stabilization on the FR1 schedule, the response requirement was then increased to an FR4 schedule, i.e., the rat had to press levers 4 times in order to receive the reward. For each schedule, responding was considered stable when responses were within ± 20% of the average responses for five consecutive days. Once responding was stabilized at FR4, the rats were allowed access every day over a 3-week period using a 5-day access and 2-day resting modifications of well-established procedures (June and Eiler, 2007 , Liu et al., 2011 (link)).