| Research Abstract |
The conditioned place preference (CPP) paradigm has been used for evaluating sexual-incentive motivation, as well as reinforcing property of drugs. Martinez & Paredes (2001) demonstrated a clear CPP associated only with paced mating in female rats. On the other hand, Meerts, Christensen & Clark (2005) reported that female rats showed a place preference for the compartment associated with mating, whether mating was paced or non-paced.
In this study, we addressed this controversial aspect of mating-induced CPP in female rats. In addition, several studies revealed the relationship between sexual behavior and drug abuse, suggesting that the reinforcing properties in sexual behavior and drugs lie on a common neural basis. In the present study, we examined the influence of an opioid receptor antagonist, naloxone, on accomplishment of CPP associated with mating in the female rat.
Male and female Long-Evans rats (8 weeks old at start) were used. All females were ovariectomized and given mating e
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xperiences after injections of 5 μg estradiol benzoate (EB) and 500 μg progesterone (P). After that, subjects were divided into 4 groups (in each group, n=8) according to 2x2 experimental design, mating conditions (paced or non-paced) and drug treatments (4 mg /kg naloxone or saline). Each female received injections of EB and P before mating. On the 1st, 3rd, and 5th conditioning sessions, all subjects were injected saline and transferred directly from their home cage to preferred compartment for 30 min without copulation. On the 2nd, 4th and 6th conditioning sessions, subjects were injected intraperitoneally with either saline or naloxone. One min after injection, the subjects were allowed to mate with stud males in either paced or non-paced condition. Immediately after receiving 15 intromissions, the females were placed in the non-preferred compartment for 30 min. In consistent with the findings by Meerts, et. Al. (2005), females showed a place preference for the compartment associated with mating, whether mating was paced or non-paced. Opiate antagonist, naloxone, blocked the CPP induced only by paced mating.
These results suggest that different reward mechanisms for sexual interaction may be involved in paced and non-paced mating. Less
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