Extended paced mating tests induces conditioned place preference without affecting sexual arousal

Abstract

One way to evaluate sexual arousal is by measuring approach behavior to sexual incentive stimuli. In our case we measure approach behavior to an originally non-preferred compartment which is associated with the physiological state induced by mating. This change of preference indicative of a positive affective (reward) state can be evaluated by conditioned place preference (CPP). We have shown that the CPP induced by paced mating is mediated by opioids. The administration of opioids also induces a reward state. The present study was designed to compare the rewarding properties of paced mating and a morphine injection. One group of females was allowed to pace the sexual interaction before being placed in the non-preferred compartment. In alternate sessions they received a morphine injection before being placed in the preferred compartment. In another group of females, the treatments were reversed. Only the females placed in the originally non-preferred compartment after paced mating changed their original preference, suggesting that paced mating induces a positive affective, reward, state of higher intensity than a morphine injection of 1mg/kg. In a second experiment we determined if females allowed to pace the sexual interaction for 1h would still developed CPP. No change in preference was observed in the females that mated for 1h without pacing the sexual interaction. On the other hand, females that received between 10 and 15 paced intromissions as well as females that paced the sexual interaction for 1h developed a clear CPP. The second experiment demonstrated that pacing is rewarding even in an extended mating session in which the females received around 25 intromissions and several ejaculations. These results further demonstrate the biological relevance associated with the ability of the female to space coital stimulation received during mating. This positive affective state will contribute to increase sexual arousal the next time a rat finds an appropriate mate.