Presence of an unfamiliar peer reverses escalated cocaine intake in male rats: Involvement of the subthalamic nucleus.

The immediate social context critically modulates drug consumption. The presence of an unfamiliar conspecific, naive to the drug, at the time of consumption reduces cocaine self-administration in male rats during short-access sessions, as well as drug intake in human cocaine users. The subthalamic nucleus (STN), a brain structure involved in cocaine addiction and limbic processes, has been proposed to mediate such social influence on this limited level of drug intake. Whether this influence extends to escalated drug consumption remains an open question. In this study, we compared the effect of the presence of an unfamiliar peer, naive to cocaine, on cocaine self-administration in rats having been exposed to either short (2 h) or long-access sessions (6 h). We showed that the presence of the peer markedly reduced both limited and escalated cocaine intake in male rats. Preliminary tests in females revealed no effect of the peer's presence during short-access sessions; therefore, subsequent experiments were conducted in males only. Assessing the effect of STN photo-inhibition or high frequency (HF) stimulation in male rats, we demonstrated that it had no effect in the absence of the conspecific in short-access sessions, but STN photo-manipulation suppressed the influence of the peer's presence. Moreover, STN photo-inhibition and HF stimulation decreased drug consumption in long-access sessions, but no additive effect was observed when associated with the peer's presence, confirming an overriding effect of STN manipulation. Taken together, these results highlight the potential influence of socially oriented manipulations on cocaine intake and further position the STN as a critical mediator of the effect of social presence on addictive-like behaviors.