Social preference and drug self-administration: a preclinical model of social choice within peer groups.

Background: selection models of substance use propose that individuals choose or self-select into peer groups based on shared substance use histories. Few experimental studies have examined the role of selection in substance use, possibly because few preclinical models allow subjects to choose or select individuals based on a shared self-administration history.

Methods: In the present study, we used custom-built, three-compartment, operant conditioning chambers that permitted multiple rats to self-administer cocaine simultaneously in the same session. Rats assigned to the center compartment had access to two response levers, each in close physical proximity to one of its partners. In one group, a rat with access to cocaine was assigned to the center compartment and flanked by one rat with access to cocaine and one rat without access. In a second group, a rat without access to cocaine was assigned to the center compartment and flanked by one rat with access to cocaine and one rat without access.

Results: In the first group, rats with access to cocaine emitted more responses on the lever in close proximity to the other rat with access to cocaine; in the second group, rats without access to cocaine emitted more responses on the lever in close proximity to the other rat without access. These preferences were not apparent immediately but developed gradually over the course of several days of testing.

Conclusion: These data suggest that rats prefer to be in close physical proximity to another rat with a shared behavioral history during periods of drug self-administration.