Substitutability of cocaine and social interaction in male and female rats before and after intermittent access cocaine self-administration

Abstract Rational and objectives Previous studies have found that cocaine and social interaction act as substitutes in male rats, but it is unknown whether they are also substitutes in female rats. The two purposes of the present study were to compare male and female rats on the way cocaine and social reinforcement economically interact and to determine whether exposure to intermittent access (IntA) cocaine self-administration changes the interaction. Methods In a first phase, male (n = 16) and female (n = 17) rats were allowed to choose between cocaine and social reinforcement available at varying prices to determine how these reinforcers economically interact. Then, half of the rats of each sex received 12 sessions of IntA cocaine self-administration while the other half served as no-cocaine homecage controls. In a final phase, the way that cocaine and social reinforcement interacted was redetermined. Results Cocaine and social reinforcement were partial substitutes in male rats, replicating previous findings. In contrast, these reinforcers were not substitutes in females, but instead were independent economic goods. During IntA cocaine self-administration, female rats escalated their intake over sessions, but males did not. IntA cocaine exposure had no impact on reinforcer interactions. Conclusions The sex difference in the way that cocaine and social reinforcement interacted suggests that one or both of these reinforcers may serve different functions in male and female rats. The results of this study contribute to growing research on the way that the broader behavioral economic context contributes to choice between drug and non-drug alternatives.