Neural control of erection

Activation of sacral parasympathetic pathways elicits penile erection through the release of vasorelaxant neurotransmitters that increase blood flow to the penis and relax the penile erectile tissue. Sympathetic pathways are antierectile. The pudendal pathway, responsible for the contraction of the perineal striated muscles, enhances an already present erection. All pathways originate in the spinal cord, but at various levels and areas. The convergence of information from peripheral and supra-spinal origins onto spinal neurones is very likely activating more specifically the spinal pro-erectile network. Peripheral information is the afferent limb of reflexive erections, impinges onto spinal interneurones and is able to activate or regulate the activity of sympathetic, parasympathetic and somatic nuclei. Supra-spinal information impinges onto either the same or a different spinal network. Premotor neurones located in supra-spinal structures, that project directly onto spinal sympathetic, parasympathetic or pudendal motoneurones, are present in the medulla, pons and diencephalon. Several of these premotor neurones may in turn be activated by sensory information from the genitals. Descending pathways release a variety of aminergic and peptidergic neurotransmitters in the vicinity of spinal neurones, thereby exerting complex effects on the spinal pro-erectile network. Brainstem and hypothalamic nuclei (among the latter, the paraventricular nucleus and the medial preoptic area) may not reach directly the spinal pro-erectile network. They are prone to regulate penile erection in more integrated and coordinated responses of the body, as those occurring during sexual behaviour. The pro-erectile central and spinal effects of neuropeptides such as oxytocin, melanocortins and endorphins have only recently been analyzed. Such compounds may represent therapeutic strategies to treat erectile dysfunction through a central site of action.