Synergistic interaction between nicotine and social rewards in adolescent male rats

Smoking typically begins during adolescence and is largely reinforced by social cues. During adolescence in rats, sensitivity to both social cues and drugs of abuse is enhanced. We have previously demonstrated in adolescent male rats that a low dose of cocaine interacts with social reward to produce an enhanced conditioned place preference (CPP) relative to either reward given alone. The present study further examined the nature of drug-social reward interactions using nicotine. Dose-effect functions for nicotine-CPP were established using two different routes of administration (vehicle, 0.1, 0.3, and 0.6 mg/kg, SC and vehicle, 0.01, 0.03, and 0.06 mg/kg, IV). The effects of nicotine on social reward-CPP and social play behavior were next examined using parameters presumed to be sub-threshold for establishing social reward- and nicotine-CPP. Dose-dependent nicotine-CPP was observed using both routes of administration. Two pairings of the initially non-preferred side of the apparatus with either SC nicotine or another adolescent rat failed to produce CPP when examined alone, but together produced a robust CPP despite nicotine reducing social play. This interaction effect was not observed with the IV nicotine. A final experiment demonstrated that the enhancement of CPP with the combination of rewards was not due to additive effects of weak, sub-threshold conditioning. These findings suggest that nicotine and social rewards interact synergistically in adolescent rats resulting in a greater, perhaps qualitatively different, reward than either reward given alone. Understanding drug-social reward interactions may provide new directions for development of preventions and interventions of adolescent smoking.