Sex differences in monoamines following amphetamine and social reward in adolescent rats

Interaction with social peers may increase rates of drug self-administration, but a recent study from our laboratory showed that social interaction may serve as a type of alternative reward that competes with drug taking in adolescent male rats. Based on those previous results, the current study examined sex differences in preference for social interaction compared with amphetamine (AMPH) in adolescent rats using the conditioned place preference (CPP) paradigm. Similar to previous results with males, females showed AMPH CPP regardless of whether they were individual- or pair-housed. In contrast to males, however, females failed to show social CPP, and they did not prefer a peer-associated compartment over an AMPH-associated compartment in a free-choice test. In separate experiments, dopamine (DA) and serotonin (5-HT) metabolite levels were measured in adolescent males and females that were exposed acutely to peer interaction, no peer interaction, AMPH, or saline. In amygdala, levels of the DA metabolite dihydroxyphenylacetic acid (DOPAC) were altered more in response to peer interaction in males than females; in contrast, there was a greater amygdala DOPAC response to AMPH in females. Furthermore, there were greater changes in the 5-HT metabolite hydroxyindoleacetic acid (5-HIAA) in females than in males following social interaction. These results indicate that the ability of peer interactions to reduce drug reward is greater in adolescent males than females, perhaps due to a greater ability of social cues to activate limbic reward mechanisms in males or a greater ability of AMPH cues to activate limbic reward mechanisms in females.