No evidence that wheel-running exercise impacts cocaine conditioned place preference in male C57BL/6J mice

Wheel-running in rodents can mitigate addiction-related effects of drugs of abuse like cocaine. However, conditioned place preference (CPP) experiments have reported conflicting results, a situation warranting further studies. Our purpose was to test whether wheel-running exercise during adolescence could impact the formation and long-term retention of CPP to cocaine in mice. Male C57BL/6 J mice were individually housed either with (n = 32) or without (n = 32) a running wheel from the age of 35 days. Behavioral testing began 3 weeks after such housing, mice underwent a baseline session followed by 10 once-daily conditioning sessions receiving peritoneal injections of 10 mg/kg cocaine and saline on alternate days (n = 16), control mice receiving saline every day (n = 16). One and 21 days after the last conditioning session, they were tested for CPP. Both groups exhibited comparable well-marked cocaine-induced CPP in both post-conditioning tests resulting in a negligible interaction between housing and the pharmacological treatment (η²p < 0.01). These results, along with the discrepancy found in the literature, question the nature (and the robustness) of the effects that exercise induces on CPP to cocaine.