Central control of the cardiovascular and erection systems: possible mechanisms and interactions.

Sexual activity is accompanied by vascular changes mediated by parasympathetic and sympathetic outflow to the peripheral organs. The brain stem and spinal cord contain the neurons that innervate the cardiovascular system and the penis. Heart rate and blood pressure increase, suggesting a decrease of the cranial parasympathetic outflow and an increase of the activity of sympathetic efferent pathways. In contrast, penile erection occurs in response to increased activity of the sacral parasympathetic innervation and a decreased activity of sympathetic pathways. A modulation of the balance between sympathetic and parasympathetic activities may result from an adaptation of an intraspinal network that (1) would be the recipient of peripheral and supraspinal information; and (2) would coordinate the activity of the different efferent pathways. A variety of nuclei in the medulla, pons, and hypothalamus contain premotor neurons that exert an influence on brain stem and spinal autonomic motoneurons. These descending pathways release amines (noradrenaline, adrenaline, serotonin, dopamine) and peptides. A fine tuning of brain stem and spinal activity is made possible by the great variety of receptor subtypes through which these neuromediators act. More recently, the role of nitric oxide, synthesized and released by different cell populations, has been evaluated in the brain and spinal control of the cardiovascular system and penile erection. Depending on its central neural target, nitric oxide may either activate or inhibit the cardiovascular system. In contrast, its role on the central control of penile erection is only excitatory.