Progesterone does not affect cocaine-induced conditioned place preference or locomotor activity in male rats

Abstract

Introduction: The present study aimed to determine if, as occurs in female rats, progesterone attenuates cocaine-induced reward and psychomotor responses in male rats.

Methods: The role of progesterone in the acquisition and/or expression of cocaine-induced conditioned place preference (CPP) and locomotor responses of intact male rats was studied. For chronic progesterone treatment, rats received Silastic capsules with either progesterone (100%) or vehicle 1 week prior to conditioning. For acute progesterone treatment, rats received subcutaneous injections of progesterone (500 microg) or vehicle (sesame oil) 4 hours before intraperitoneal injections of saline or cocaine administration (20 mg/kg) on conditioning days (acquisition phase-formation of reward associations) or before testing (expression phase-recall of reward associations).

Results: Both progesterone-treatment paradigms produced equivalent progesterone serum levels. Progesterone administered chronically or acutely during the acquisition and expression phases of cocaine conditioning did not block cocaine-induced CPP. Nor did progesterone affect ambulatory or rearing behaviors after cocaine administration.

Conclusion: These results suggest that, unlike the findings with female rats (in which similar treatment paradigms inhibited the formation and recall of cocaine-induced CPP), progesterone plays a limited role in the cocaine-induced reward or psychomotor responses of male rats.