| Popis: |
Sexual behaviour encompasses a variety of sensory stimuli that makes sex rewarding in both humans and rats alike. Despite what we know about the clitoris’ contribution to sexual pleasure in human females there is still a lack of research focusing on the function of the clitoris and its role in learning, sexual development, and sexual expression. The rat is a good animal model for the study of sexual function and dysfunction and can be used to add to our understanding of clitoral stimulation and function. Accordingly, the five chapters encompassing this thesis were designed to expand our comprehension of the role that the clitoris plays in female sexual behaviour and reward in the rat. Chapter 1 showed that the clitoris is important for interpreting genital signals that differentiate stimulation received from males during copulation. It also showed that sexual experience buffers female rat pacing behaviour from the disruptive effects of lidocaine administration to the clitoris. Chapter 2 showed that manual external clitoral stimulation (CLS) is rewarding as assessed by the development of robust conditioned place preference, and activates immediate early gene c-fos expression selectively in the medial preoptic area (mPOA) and medial amygdala (MeA). Chapter 3 showed that manual external CLS could be paired with a neutral olfactory stimulus in sexually naïve rats and induced a copulatory partner preference for a male bearing the odour cue during the female’s first sexual experience with males. Moreover, if CLS was applied to sexually naïve rats in the presence of a scented but inaccessible male, those females solicited more an unscented male during their first sexual experience with males. Thus, the ability of CLS to be a positive reinforcer is context-dependent. Chapter 4 examined the sexual reward state induced by paced mating or CLS and its dependence on ovarian hormones. The conditioned place preference (CPP) induced by CLS developed regardless of the hormonal state of the female, whereas paced-mating induced CPP required hormonal priming. This shows that the reward state induced by CPP is independent of ovarian hormones, whereas the sexual behaviors that entice males to mount and intromit (thus bringing the clitoris into contact with the male’s penis and perineum at the female’s preferred rate) are not. Finally, Chapter 5 showed that prior copulatory experience with males eliminated the ability of CLS alone to induce CPP, suggesting either that experience with full internal and external CLS provided by a male conspecific has a greater reward magnitude and/or that copulatory experience renders subsequent external CLS alone ineffective as an unconditioned stimulus due to sensory preconditioning. Taken together, these data show that external CLS is a powerful reinforcer to a sexually naïve female rat. Although its hedonic value is not dependent on ovarian hormones, the sexual behaviors required to receive it are, and copulatory experience appears to reduce or eliminate its hedonic value. |
