Exploring addiction: How does a history of stress impact habit-like alcohol drinking in male and female rats?

Alcohol use disorder (AUD) is characterized by escalating alcohol consumption over time. As alcohol drinking progresses, it can shift from a goal-oriented behavior to a habitual behavior, with drinking continuing despite alcohol not producing rewarding effects. Stress increases the likelihood of developing AUD, particularly for women, yet its role in promoting habit-like alcohol seeking remains unclear. We studied footshock stress history effects on acquisition and expression of habit-like drinking. Once stress history was established, rats were trained to self-administer alcohol (10% v/v) first on a fixed ration-1 (FR1) schedule, with each lever press producing a reward. Then escalating to a random interval (RI) schedule to promote habit-like responding. This RI-schedule increased in difficulty, first at RI-30 for 3 sessions, then advancing to RI-60. Habit-like responding was tested in extinction following devaluation via free access to drink alcohol, or equivalent access to an alternative rewarding solution, 0.3% (w/v) sucrose. To study how stress history impacts acquisition of this behavior, we tested devaluation both early and late in RI-training. Our data show stress history rats resisted devaluation greater than controls, with greater alcohol-seeking during the nonreinforced session even though both groups consumed similar amounts of alcohol during devaluation. Female rats consumed more alcohol per unit body weight than male rats, consistent with previous research. Results of this experiment suggest that a history of stress impacts the formation of learning a habit-like cycle of alcohol drinking.