Differences in Compulsive-Like Ethanol Consumption in Adolescent-Trained and Adult-Trained Rats Exposed to Acute Isolation Stressors

The Pavlovian Conditioned Approach (PCA) procedure is an experimental procedure used with animals to induce compulsive-like behaviors directed towards an object conditioned stimulus (CS) paired with a sucrose pellet unconditioned stimulus (US) presented in a nearby food tray (sign tracking). When the object CS is an alcohol-containing bottle, the rats demonstrate compulsive-like interactions with the bottle object (e.g., approach, contact, and licking) that also results in alcohol consumption (drinking) in most rats. Compulsive alcohol drinking in a sign-tracking procedure is a result of the combined effects of schedule-induced compulsive-like behavior and the intake of alcohol (Tomie & Sharma, 2013). The first goal of the present study was to investigate possible age differences in the acquisition of sign tracking of an alcohol bottle CS in Sprague-Dawley rats trained directly in their enriched home environment. If adolescent-trained rats are more susceptible to the compulsive-inducing effects of the sign-tracking procedure or to the pharmacological effects of alcohol, then adolescents should show more sign tracking than the adults. However, the results showed faster acquisition and greater asymptotic sign tracking of an alcohol bottle in the adult-trained rats. The second goal of the study was to investigate the effects of an acute stressor on asymptotic sign-tracking performance in both groups once the adolescent rats reached an adult age. I tested the possibility that rats exposed to acute stress conditions in adulthood are more likely to show stress-induced increases in compulsive-like behavior if the compulsive behavior was learned during adolescence rather than during adulthood. All rats were subjected to acute isolation stress by placing them in restrictive home cages (i.e., isolated from their home environment). Results showed that overall, the rats who were trained in the PCA procedure during adolescence did not display increased compulsive-like behaviors in adulthood during acute stress conditions compared to rats who were initially trained in adulthood; the adolescent-trained rats exhibited less sign tracking than the adult-trained rats. Stress-induced changes in compulsive-like behaviors were seen in adult-trained rats; the adult-trained rats exhibited increased sign tracking. Age differences in goal-directed behaviors, goal tracking, were also seen. Overall, the results demonstrate that compulsive-like alcohol consumption is readily evoked by the sign tracking procedure in adolescent and adult rats even when trained in an enriched home environment, providing an opportunity to examine the effects of age and environmental factors on the acquisition and modulation of compulsive-like behavior