Adolescent but not adult Sprague-Dawley rats display goal-directed responding after reward devaluation

Alcohol drinking is typically initiated in adolescence, with use sometimes escalating to problematic levels. Escalation of drinking is often associated with a shift in drinking motives, with goal-directed initial use later transitioning to more habitual behavior. This study assessed whether adolescents are more sensitive than adults to habit formation when indexed via insensitivity to reward devaluation in an operant task for food reward. Adolescent and adult Sprague-Dawley rats were trained on either a random ratio (RR) or random interval (RI) schedule before undergoing devaluation. Adolescent animals on both schedules increased the number of lever presses across all training days. In contrast, adults in the RR group increased the number of lever presses across days whereas RI adults remained relatively stable. In response to pellet devaluation, only adolescents exhibited reduced responding, suggestive of goal-directed behavior, whereas no age differences were evident following control (home cage chow) devaluation. Contrary to our hypothesis, adolescents (but not adults) displayed goal-directed responding indexed via sensitivity to reward devaluation. These findings suggest that adolescents are not necessarily more likely to develop habits than adults, and hence other factors may contribute to the greater propensity of adolescents to engage in and escalate alcohol use.