the initial days of training in which sessions lasted up to 2 h to permit acquisition of responding for the sweetened solution. Alcohol (ethanol, 10% w/v) then was added to the sweetened solution, and once mean responding stabilized (around 1 week; Fig. 1a), the glucose was removed from the solution, leaving only 0.125% saccharin and 10% w/v alcohol. Animals were kept at this stage until mean responding again stabilized (around 1 week; Fig. 1a), and saccharin concentrations were gradually reduced in ∼50% successive steps over 2-10 days, ultimately leaving an unsweetened 10% w/v alcohol solution. Animals then were maintained on 10% w/v alcohol for at least 3 weeks, and stable responders (±25% across three consecutive sessions and averaging >10 presses for alcohol) were evenly divided into two groups matched for baseline responding and exposed to intermittent alcohol vapors (alcohol dependent) or air (nondependent alcohol self-administering) as described below.
