Social enhancement of cocaine intake: behavioral mechanisms and role of reinforcing stimulus

Abstract Rationale One of the leading prognosticators of whether an adolescent or young adult will use drugs is whether the person’s peers use drugs. Preclinical studies report that cocaine intake increases in the presence of a social partner that is also self-administering cocaine, but it is not known whether this effect extends across reinforcers. Objectives The purpose of this study was to examine the role of the reinforcing stimulus in the effects of social contact on cocaine self-administration. Methods Male and female Long-Evans rats were implanted with intravenous catheters and trained to self-administer cocaine or a semi-solid palatable food (i.e., vanilla icing) on a fixed ratio (FR1) schedule of reinforcement. All tests were conducted in custom-built operant conditioning chambers that allowed two rats to simultaneously self-administer either cocaine or food while maintaining complete visual, auditory, and olfactory contact with a social partner. Results In rats self-administering cocaine, cocaine intake was significantly greater when a partner was also self-administering cocaine relative to when a partner was self-administering food or when a partner was responding under extinction (i.e., no cocaine or food was available). In rats self-administering food, food intake was significantly inhibited when a partner was self-administering cocaine. Econometric analyses revealed that the behavioral mechanisms responsible for the influence of social contact differed across reinforcing stimuli. Conclusions These data indicate that social learning processes influencing drug use depend on the reinforcer maintaining the behavior of both the individual and the individual’s social partner.