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Environmental enrichment, administered after establishment of cocaine self-administration, reduces lever pressing in extinction and during a cocaine context renewal test

The objective of this study was to test the hypothesis that environmental enrichment (EE) administered to rats previously trained to self-administer cocaine would reduce responding in extinction and in a cocaine-context renewal test. Long−Evans male rats were trained to press an active lever reinforced by cocaine (1.0 mg/kg/injection) under a fixed-ratio 1 schedule of reinforcement (inactive lever presses produced no consequences). After stable responding was established, all rats were given a 10-day break from the operant chambers followed by random assignment to EE (larger cages equipped with visual and auditory stimuli) or control (standard housing) group conditions in which they lived for the remainder of the experiment. Ten days after this move, rats were exposed to 10 extinction-responding sessions in a context different from the one in which self-administration occurred, followed by a context-renewal session occurring in the original self-administration context. The EE group responded significantly less in both the extinction and context-renewal sessions compared with the control group. These results suggest that EE reduces the ability of cocaine-associated stimuli to control cocaine-related responding.