Effects of combined exercise and progesterone treatments on cocaine seeking in male and female rats

Background: Individually, both treatment with progesterone and concurrent access to an exercise wheel reduce cocaine self-administration under long-access conditions and suppress cocaine-primed reinstatement in female rats. In the present study, wheel running and progesterone (alone and combined) were assessed for their effects on reinstatement of cocaine-seeking primed by yohimbine, cocaine, and cocaine-paired cues. Methods: Male and female rats were implanted with an intravenous catheter and allowed to self-administer cocaine (0.4 mg/kg/inf, iv) during 6-h sessions for 10 days. Subsequently, the groups of male and female rats were each divided into two groups that were given concurrent access to either a locked or unlocked running wheel under extinction conditions for 14 days. Next, all four groups were tested in a within-subjects design for reinstatement of cocaine-seeking precipitated by separate administration of cocaine-paired stimuli, yohimbine, or cocaine or the combination of yohimbine+cocaine-paired stimuli or cocaine+cocaine-paired stimuli. These priming conditions were tested in the presence of concurrent wheel access (W), pretreatment with progesterone (P), or both (W+P). Results: In agreement with previous results, females responded more for cocaine than males during maintenance. Additionally, concurrent wheel running attenuated extinction responses and cocaine-primed reinstatement in females but not in males. Across all priming conditions, W+P reduced reinstatement compared to control conditions, and for cocaine-primed reinstatement in male rats, the combined W+P treatment was more effective than W or P alone. Conclusion: Under certain conditions, combined behavioral (exercise) and pharmacological (progesterone) interventions were more successful at reducing cocaine-seeking behavior than either intervention alone.