Organization and orchestration of male rat sexual behavior

Abstract

Sexual behavior is innately motivated and rewarding. The underlying neurobiological mechanisms of sexual motivation, copulation, and sexual reward have not been completely unraveled. This thesis gives insight in the structure, organization, and neurobiological orchestration of male rat sexual behavior. The research presented in this thesis demonstrates that a more extensive behavioral annotation allows for a more thorough analysis of the behavioral organization of copulation. By utilizing such analyses, we showed that the durations of inter-copulatory intervals are strongly correlated in individual male rats. This advanced understanding is valuable for the formulation of hypotheses about neurobiological underpinnings of sexual behavior. In addition, the more detailed behavioral analysis made it possible to conclude that the medial amygdala influences the latency to ejaculation through the processing of sensory feedback rather than impacting copulatory pace or efficiency, in a study in which we chemogenetically stimulated and silenced the medial amygdala. Neuronal circuitry involved in the orchestration of sexual behavior, including the medial amygdala and the medial preoptic area, is modified by gonadal hormones. It is reported in this thesis that gonadectomy and treatment with dihydrotestosterone affects dendritic spine plasticity in these mentioned brain regions, as well as in the nucleus accumbens, an important node in the mesolimbic reward system. Hormone-induced neuronal plasticity is hypothesized to permit the functional neuronal circuitry to orchestrate sexual behavior, and to be at the basis of long-term sexual reward learning. Together, these findings advance our understanding of the neuronal regulation of sexual behavior, and hopefully stimulate the field to employ more extensive behavioral assessments when studying sexual behavior in male rats.