Central neural regulation of penile erection

Penile erection is caused by a change of the activity of efferent autonomic pathways to the erectile tissues and of somatic pathways to the perineal s triated muscles. The spinal cord contains the cell bodies of autonomic and somatic motoneurons that innervate the peripheral targets. The sympathetic outflow is mainly antierectile, the sacral parasympathetic outflow is proer ectile, and the pudendal outflow, through contraction of the perineal stria ted muscles, enhances an erection already present. The shift from flaccidit y to erection suggests relations among these neuronal populations in respon se to a variety of informations. Spinal neurons controlling erection are ac tivated by information from peripheral and supraspinal origin. Both periphe ral and supraspinal information is capable of eliciting erection, or modula ting or inhibiting an erection already present. One can hypothesize a spina l network consisting of primary afferents from the genitals, spinal interne urons and sympathetic, parasympathetic and somatic nuclei. This system is c apable of integrating information from the periphery and eliciting reflexiv e erections. The same spinal network, eventually including different popula tions of spinal interneurons, would be the recipient of supraspinal informa tion. Premotor neurons that project directly onto spinal sympathetic, paras ympathetic or somatic motoneurons, are present in the medulla, pens and die ncephalon. Several of these premotor neurons may in rum be activated by sen sory information from the genitals. Aminergic and peptidergic descending pa thways in the vicinity of spinal neurons, exert complex effects on the spin al network that control penile erection. This is caused by the potential in teraction of a great variety of receptors and receptor subtypes present in the spinal cord, Brainstem and hypothalamic nuclei (among the latter, the p araventricular nucleus and the medial preoptic area) may not necessarily re ach spinal neurons directly. However they are prone to regulate penile erec tion in more integrated and coordinated responses of the body, such as thos e occurring during sexual behavior. Finally, the central and spinal role of regulatory peptides (oxytocin, melanocortins, endorphins) has only recentl y been elucidated. (C) 2000 Elsevier Science Ltd. All rights reserved.