main difference between the nondependent and dependent conditions is the exposure to intermittent alcohol vapors in the dependent groups and higher intake of alcohol during self-administration sessions. After several weeks of intermittent vapor exposure, dependent animals show mild physical dependence (Richardson et al., 2008) and robust motivational dependence, characterized by increased willingness to work for alcohol (Walker and Koob, 2007) and excessive, binge-like drinking patterns (O'Dell et al., 2004; Richardson et al., 2008). Thus, the total amount of alcohol exposure differed greatly between the dependent and nondependent groups. Dependent rats self-administered alcohol in 30 min sessions and received 14 hours of vapor daily. As such, the dependent groups maintained blood alcohol levels 150 mg% for approximately 14.5 hours per day versus the nondependent groups, which self-administered alcohol to maintain blood alcohol levels not exceeding 50 mg% for 30 min per day (Richardson et al., 2008). Food and water were available ad libitum. Rats were subjected to alcohol self-administration and were 21-25 weeks old when intracardially perfused. All procedures were performed during the dark phase of the light/dark cycle. Experimental procedures were conducted in strict adherence to the National Institutes of Health Guide for the Care and Use of Laboratory Animals
