Sympathetic pathways and adrenergic innervation of the penis

The sympathetic nervous system is important for penile function: it mediate s detumescence and may contribute to the maintenance of the penis in a non- erect state. The sympathetic preganglionic neurons are found in the interme diolateral gray matter of the spinal cord. Postganglionic neurons are locat ed to the sympathetic chain ganglia, the inferior mesenteric, hypogastric a nd pelvic ganglia, and possibly to ganglia near the target organ. Sympathet ic fibres can be found in the pelvic, cavernous, and pudendal nerves. Stimu lation of the sympathetic pathways to the penis may, however, also produce erection. It has been suggested that the suprasacral vasodilator pathway is a sympathetic cholinergic pathway, operating through cholinergic neurons i n the pelvic plexus. In the penis, there is a rich sympathetic, adrenergic innervation of the corpus cavernosum (CC) and the vasculature, and in parti cular of the helicine arteries. Sympathetic, adrenergic nerves also contain neuropeptide Y. Parasympathetic cholinergic nerves, which mediate CC relax ation and erection, contain not only acetylcholine, but also vasoactive int estinal polypeptide, nitric oxide synthase, and probably other mediators an d/or mediator-synthesizing enzymes. Activation of sympathetic adrenergic ne rves causes release of noradrenaline, acting on ol-adrenoceptors in the tra becular smooth muscle of the CC and in penile vessels. The role of interact ions between different transmitters and mediators, released from nerves or generated locally, in the regulation of contraction and relaxation of CC an d penile vessels, needs further study.