Parameters for abolishing conditioned place preference for cocaine from running and environmental enrichment in male C57BL/6J mice

Rationale Evidence suggests that 4 weeks of voluntary wheel running abolishes conditioned place preference (CPP) for cocaine in male C57BL/6J mice. Objectives To determine the duration and timing of exposure to running wheels necessary to reduce CPP, and the extent to which the running per se influences CPP as compared to environmental enrichment without running. Methods A total of 239 males were conditioned for 4 days twice daily with cocaine (10 mg/kg) and then split into 7 intervention groups prior to 4 days of CPP testing. Experiment 1 consisted of two groups housed as follows: short sedentary group (SS; n = 20) in normal cages for 1 week; the short running group (SR; n = 20) with running wheels for 1 week. Experiment 2 consisted of five groups housed as follows; short 1 week of running followed by a 3 week sedentary period (SRS; n = 20); a 3 week sedentary period followed by 1 week of running (SSR; n = 20); long sedentary group (LS; n = 66) in normal cages for 4 weeks; long running group (LR; n = 66) with running wheels for 4 weeks; and long environmental enrichment group (EE; n = 27) with toys for 4 weeks. Results Levels of running were similar in all running groups. Both running and environmental enrichment reduced CPP relative to sedentary groups. Conclusions Results suggest that the abolishment of cocaine CPP from running is robust and occurs with as low as 1 week of intervention but may be related to enrichment component of running rather than physical activity.