Sympathetic pathways and adrenergic innervation of the penis

Abstract

The sympathetic nervous system is important for penile function: it mediates detumescence and may contribute to the maintenance of the penis in a non-erect state. The sympathetic preganglionic neurons are found in the intermediolateral gray matter of the spinal cord. Postganglionic neurons are located to the sympathetic chain ganglia, the inferior mesenteric, hypogastric and pelvic ganglia, and possibly to ganglia near the target organ. Sympathetic ®bres can be found in the pelvic, cavernous, and pudendal nerves. Stimulation 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 in the pelvic plexus. In the penis, there is a rich sympathetic, adrenergic innervation of the corpus cavernosum (CC) and the vasculature, and in particular of the helicine arteries. Sympathetic, adrenergic nerves also contain neuropeptide Y. Parasympathetic cholinergic nerves, which mediate CC relaxation and erection, contain not only acetylcholine, but also vasoactive intestinal polypeptide, nitric oxide synthase, and probably other mediators andaor mediator-synthesizing enzymes. Activation of sympathetic adrenergic nerves causes release of noradrenaline, acting on a-adrenoceptors in the trabecular smooth muscle of the CC and in penile vessels. The role of interactions between different transmitters and mediators, released from nerves or generated locally, in the regulation of contraction and relaxation of CC and penile vessels, needs further study.

Sensory and Autonomic Neurons Project Both to the Smooth Retractor Penis and to the Striated Bulbospongiosus Muscles. Neurochemical Features of the Sympathetic Subset

“…Noradrenaline is excitatory in nature and causes contraction of smooth muscular cells (Owman and Stjernquist, 1988;Keast, 1999;Andersson, 2000;Andersson et al, 2000). As noradrenergic fibers are usually found in the muscular coat or around blood vessels of genital organs (Kaleczyc et al, 1993;Majewski et al, 1995;Czaja et al, 1996;Anderson and Stief, 1997), we think that the TH-or DbH-IR RDL neurons exert contemporaneously their influence on the smooth muscular cells and on the blood vessels of the smooth RPM and of the striated BSM.…”

Neuroanatomy and neurophysiology related to sexual dysfunction in male neurogenic patients with lesions to the spinal cord or peripheral nerves

“…It has been suggested that this supraspinal vasodilator pathway is a sympathetic cholinergic pathway, operating through cholinergic (NANC) neurons in the pelvic plexus. 23 Sympathetic fibres are found to take synapses in the pelvic plexus with NANC fibres, suggesting another mechanism for how patients with sacral lesions may have hypothetically psychogenic erections. Notwithstanding the fact that the sympathetic nervous system is considered to be the antierectile centre, this pathway may also facilitate erections after an injury to parasympathetic pathways.…”

The relaxation effect and mechanism of action of higenamine in the rat corpus cavernosum

“…The CC contracts in response to the activation of adrenergic a-receptors 18,19 and relaxes when adrenergic b-receptors are activated. 20,21 That is, activation of a-adrenoreceptors is involved in the flaccid state of the CC and suppression of penile erection. 22 In contrast, activating b-adrenoreceptors is involved in an erection.…”

“…23,24 In contrast, mixed b 1 -and b 2 -adrenoceptors mediate relaxation reactions in the horse CC. 21 Furthermore, atypical b-adrenoceptors and b 2 -adrenoceptors mediate the primary relaxation reaction in rabbits. 25 However, in our study, the b-adrenoceptor subtype of the CC that higenamine mediated the major relaxation reaction could not be assessed using the non-selective adrenergic b-antagonist propranolol.…”