Influence of sex on reinstatement of cocaine-conditioned place preference

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To explore sex differences in reinstatement of conditioned place preference, we subjected intact male and female Long Evans rats to an extended conditioned place preference (CPP) paradigm, which included observations of acquisition, extinction, and reinstatement of a preference to cocaine-paired stimuli. In a series of experiments, separate groups of animals were given six 30-min pairings of one chamber with cocaine (3, 5, 10, 15, 20, 25 mg/kg) and six of the other with saline on alternate days. Overall, there were no sex differences in acquisition of cocaine CPP at any of the six doses tested ( p > 0.05). All animals established cocaine CPP at each of the six doses tested during the acquisition test, with the exception of the group of females conditioned with 5 mg/kg. Preferences for the cocaine-paired chamber were successfully extinguished for both males and females after an extinction-training period. CPP reinstatement was achieved by the groups of males and females given training and priming doses of 10, 15, 20, and 25 mg/kg ( p < 0.05). Overall, our reinstatement data demonstrate that reinstatement of cocaine CPP is greater for female versus male animals. Females showed a greater magnitude of reinstatement of cocaine CPP when trained and primed with 15 and 25 mg/kg as compared to males ( p < 0.05). Further, at the three highest doses tested (15, 20, and 25 mg/kg), females showed a greater magnitude of CPP in the reinstatement phase of CPP compared to that of the initial acquisition phase ( p < 0.05). The reinstatement data for the males show that the 20 mg/kg dose resulted in the highest levels of reinstatement preference for male rats. These results indicate that sex differences in reinstatement to conditioned behavior maybe due, in part, to females forming a stronger association for the salience of the drug and the environment in which it was administered.