Presence of a social peer enhances acquisition of remifentanil self-administration in male rats

Background: Social peers influence human drug use at every stage of addiction. Using a dual-compartment apparatus that allows for limited social contact, recent work has shown that cocaine self-administration is enhanced when two rats are trained to self-administer at the same time compared to rats trained alone or trained in the presence of a saline self-administration control peer. The current study measured social influence on self-administration of the short-acting opioid remifentanil using a dual-compartment operant conditioning chamber. Methods: Adult male rats were placed in one of five groups: (1) REMI-REMI group, in which both rats self-administered remifentanil; (2) REMI-SAL group, in which rats self-administered remifentanil in the presence of a peer that self-administered saline; (3) SAL-REMI group, in which rats self-administered saline in the presence of a peer that self-administered remifentanil; and (4) REMI ALONE and (5) SAL ALONE groups, in which rats administered their respective drugs alone (no peer). Self-administration was measured using a 2-lever procedure during acquisition, maintenance, increasing fixed-ratio, and dose-response phases. Results: The presence of a social peer enhanced drug intake during acquisition, regardless of the drug exposure of their peer. Additionally, active lever position significantly affected remifentanil intake during acquisition and maintenance, with the greatest influence occurring when the active lever was close to the peer. Conclusion: The presence of a social peer in the drug-taking context potentiates remifentanil self-administration, regardless of the peer's drug access. Future studies utilizing the dual-compartment apparatus will help elucidate the neural mechanisms underlying social influence on opioid abuse.