Modulation by peripheral serotonin of the threshold for sexual reflexes in female rats

Using immunohistochemical techniques, a large number of serotonergic paracrine cells were identified in the urethral mucosa of the female rat. The functional significance of these cells was investigated. A model for the study of sexual climax in the anesthetized, acutely spinalized female rat was used. In this model, distension of the urethra with saline elicits a stereotyped coordinated genital response which closely resembles the neuromuscular concomitants of sexual climax. Addition of serotonin to the urethral perfusate (10(-4)-10(-7) M) caused a dose-dependent decrease in the mechanical threshold necessary to elicit the climax-like response. This effect was blocked by a specific 5-HT3 receptor antagonist. The physiological implications of these findings are discussed.