Neurophysiology and pharmacology of female genital sexual response.

Vaginal sexual arousal is a vasocongestive and neuromuscular event controlled by facilitatory parasympathetic and inhibitory sympathetic inputs. Autonomic preganglionic parasympathetic and inhibitory sympathetic fibers to the vagina and clitoris originate in the spinal cord in the sacral parasympathetic nucleus at the sacral level and in the dorsal gray commissure and the intermediolateral cell column at the thoracolumbar level, respectively. Parasympathetic fibers are conveyed by the pelvic nerve, and sympathetic fibers are conveyed by the hypogastric nerve and the paravertebral sympathetic chain. The activity of these spinal nuclei is controlled by descending projections from the brain and sensory afferens (conveyed in the pudendal, hypogastric, pelvic, and vagus nerves) from the genitalia. A key but unresolved issue concerns the neurotransmitters involved in the control of genital sexual arousal. At the peripheral level, acetylcholine plays a minor role in the regulation of vaginal blood flow, however, recent data suggests that it may be involved in the control of vaginal smooth muscle contractions. Vasoactive intestinal peptide and nitric oxide may be responsible for the increase in vaginal blood flow during sexual arousal, whereas noradrenaline is likely inhibitory. Within the central nervous system, serotoninergic projections from the brain to the spinal cord likely inhibit the induction of genital arousal by peripheral informations (spinal reflex). Although some neurotransmitters regulating the display of sexual behavior have been identified (for example, dopamine), their involvement in the control of genital sexual arousal has not been invested. Anatomical and electrophysiological data point to a contribution of the paraventricular nucleus of he hypothalamus and the median preoptic area, respectively, as key elements in the control of genital arousal. The recent development of models allowing the assessment of vaginal sexual arousal in anesthetized female rats should assist in deciphering the neurochemical pathways controlling vaginal sexual arousal and the development of suitable pharmacological treatment for female sexual dysfunctions.