Fig. 1

Operant conditioning boxes and experimental timeline. Male and female adult Wistar rats were trained to self-administer 10% w/v alcohol using operant conditioning. Training began with 1 day of two-bottle choice in their home cages, followed by the first day of operant training for water (12 h session), a day of rest in the home cage, and two days of operant training for alcohol (2 h session on the first day and 1 h session on the second day). Operant testing was conducted twice each day, beginning at 2 h (early session) and 10 h (late session) in the dark cycle for a total of 117 days. Operant testing was conducted in normal sessions of minimal effort (30 m fixed ratio 1), normal sessions of increased effort (30 m fixed ratio 3) and compressed happy hour sessions of increased effort (15 m fixed ratio 3) which are summarized in the timeline. Operant boxes had two levers, one active and one inactive, as well as a food cup and water bottle that could be accessed ad libitum. Alcohol was delivered to a two-well acrylic drinking apparatus after every 1 press (FR1) or 3 presses (FR3). The cue light above the active lever is turned on for each alcohol delivery. w/v weight per volume, FR fixed ratio, h hour, m minutes. Created with BioRender.com