Sympathetic pathways and adrenergic innervation of the penis

Department of Pathology, University of Lund, Lund University Hospital, Lund, Sweden;The sympathetic nervous system is important for penile function: it mediates detumescence andmay contribute to the maintenance of the penis in a non-erect state. The sympathetic preganglionicneurons are found in the intermediolateral gray matter of the spinal cord. Postganglionic neuronsare located to the sympathetic chain ganglia, the inferior mesenteric, hypogastric and pelvicganglia, and possibly to ganglia near the target organ. Sympathetic fibres can be found in thepelvic, cavernous, and pudendal nerves. Stimulation of the sympathetic pathways to the penismay, however, also produce erection. It has been suggested that the suprasacral vasodilatorpathway is a sympathetic cholinergic pathway, operating through cholinergic neurons in thepelvic plexus. In the penis, there is a rich sympathetic, adrenergic innervation of the corpuscavernosum (CC) and the vasculature, and in particular of the helicine arteries. Sympathetic,adrenergic nerves also contain neuropeptide Y. Parasympathetic cholinergic nerves, whichmediate CC relaxation and erection, contain not only acetylcholine, but also vasoactive intestinalpolypeptide, nitric oxide synthase, and probably other mediators and=or mediator-synthesizingenzymes. Activation of sympathetic adrenergic nerves causes release of noradrenaline, acting ona-adrenoceptors in the trabecular smooth muscle of the CC and in penile vessels. The role ofinteractions between different transmitters and mediators, released from nerves or generatedlocally, in the regulation of contraction and relaxation of CC and penile vessels, needs furtherstudy. International Journal of Impotence Research (2000) 12, Suppl 1, S5–S12Keywords: noradrenaline; sympathetic nerves; penile erection; penile detumescence; alphaadrenoceptors