Elsevier

Physiology & Behavior

Volume 83, Issue 2, 15 November 2004, Pages 189-201
Physiology & Behavior

Neural control of erection

https://doi.org/10.1016/j.physbeh.2004.08.014Get rights and content

Abstract

Penile erection is a vascular event controlled by the autonomic nervous system. The spinal cord contains the autonomic preganglionic neurons that innervate the penile erectile tissue and the pudendal motoneurons that innervate the perineal striated muscles. Sympathetic pathways are anti-erectile, sacral parasympathetic pathways are pro-erectile, and contraction of the perineal striated muscles upon activity of the pudendal nerves improves penile rigidity. Spinal neurons controlling erection are activated by information from peripheral and supraspinal origin. Both peripheral and supraspinal information is capable of either eliciting erection or modulating or inhibiting an erection already present. Sensory information from the genitals is a potent activator of pro-erectile spinal neurons and elicits reflexive erections. Some pre-motor neurons of the medulla, pons and diencephalon project directly onto spinal sympathetic, parasympathetic and pudendal motoneurons. They receive in turn sensory information from the genitals. These spinal projecting pathways release a variety of neurotransmitters, including biogenic amines (serotonin, dopamine, noradrenaline, and adrenaline) and peptides that, through interactions with many receptor subtypes, exert complex effects on the spinal network that controls penile erection. Some supraspinal structures (e.g. the paraventricular nucleus and the medial preoptic area of the hypothalamus, the medial amygdala), whose roles in erection have been demonstrated in animal models, may not project directly onto spinal pro-erectile neurons. They are nevertheless prone to regulate penile erection in more integrated and coordinated responses of the body, as those occurring during sexual behavior. The application of basic and clinical research data to treatment options for erectile dysfunction has recently proved successful. Pro-erectile effects of phosphodiesterase type 5 inhibitors, acting in the penis, and of melanocortin agonists, acting in the brain, illustrate these recent developments.

Section snippets

Understanding penile erection: local mechanisms, peripheral neural pathways and peripheral pharmacology

Penile erection takes place when both dilation of the penile arteries and relaxation of the erectile tissue (corpus cavernosum and corpus spongiosum) occur [1]. Dilation of the penile arteries results in an increased blood flow to the penis, and erectile tissue relaxation results in an engorgement of the penis with blood. Because the erectile tissue is surrounded by the tunica albuginea, a tissue that does not distend easily, the increased blood flow to the penis increases not only the penile

The spinal network that controls erection

The spinal cord contains the three sets of motoneurons (thoracolumbar sympathetic, sacral parasympathetic and sacral pudendal) that are anatomically linked with the penis and functionally linked with erection. Recordings performed in humans and animals reveal that these spinal neural populations are closely linked; however, they are located neither in the same spinal segments (thoracolumbar and lumbosacral) nor in the same spinal areas (sacral parasympathetic nucleus and Onuf or DM and DL

Spinal pharmacology

Lumbosacral neurons, either sacral parasympathetic preganglionic ones, pudendal motoneurons or interneurons, bear a great variety of receptors and are surrounded by numerous fibers from local, peripheral and supraspinal origins that release many neurotransmitters. A rapid review of the literature suggests that a theoretical sacral parasympathetic preganglionic neuron bears the adrenergic alpha-1A-a, b, d and alpha-2A-a and b receptor subtypes, the dopaminergic D2 receptor subtype, the

Androgens and reflexive erections

In adult animals with a complete section of the spinal cord, castration strongly depresses reflexive erections [51]. In castrated rats that display few or no reflexive erections, testosterone [51], [113], [114] and dihydrotestosterone, but not estradiol [115], [116], delivered peripherally, restore reflexive erections. The implantation of testosterone directly into the lower spinal cord, or into the spinal canal, also reverses the deleterious effects of castration on reflexive erections [117].

Spinal lesions, reflexive erections and treatments for erectile dysfunction

Lesions of the spinal cord, such as those occurring during multiple sclerosis, spinal cord injury, tumor, syringomyelia, transverse myelitis, arachnoiditis, disk disease and myelodysplasia, can lead to erectile dysfunction [1]. As mentioned above, reflexive erections remain if the sacral reflex arch is spared. Although the basic mechanisms through which the spinal cord controls erection in physiological conditions are better understood today, this set of information has not yet provided any

The supraspinal control of penile erection

In humans and animals, penile erection occurs in several contexts, some of which have nothing to do with a sexually relevant context. Erections have been observed in utero in humans [131], and in rats during copulation, in response to genital stimulation, during sleep [132], in the presence of a receptive female with no possibility to engage in copulation (“noncontact erections” [133]), and in response to the injection of centrally acting drugs [134]. It is possible that several different areas

Central brain lesions in humans and penile erection

Among the neurologic disorders than can cause erectile dysfunction through alteration of central pathways are tumor, stroke, encephalitis, Parkinson's disease, dementias, the olivopontocerebellar degeneration (Shy-Drager syndrome) and epilepsy of the temporal lobe [1], [157]. In contrast, erections occur after lesions of the pyriform cortex and amygdaloid complex (the Kluver-Bucy syndrome [84]).

Perspectives for treating erectile dysfunction in humans through a central target

The link between dopaminergic pathways and central pro-erectile pathways has been indirectly evidenced in human patients suffering from the alteration of dopaminergic transmission. Some Parkinson's patients treated with apomorphine, L-DOPA or bromocriptine report the occurrence of erections and increased libido or an improved sexual interest [158], [159], [160], [161], [162], [163]. The effects of apomorphine in these patients must be evaluated on a basis different from other patients [164].

Androgens and the central control of penile erection

As castration depresses sexual behavior, it is not possible to record any erections during copulation in castrated male rats, although there are historical and clinical reports of castrated men keeping sexual activity and erections. In these men, it is possible that castration was performed when they were adults, a time after androgen-dependent systems have been organized during the neonatal period and activated during puberty. In rats, castration suppresses noncontact and apomorphine-induced

Provisory conclusions

What can we learn and what can we expect from the developments in basic and clinical research on the nervous control of penile erection? The last 20 years have seen tremendous advances in the understanding of the basic mechanisms of erection and in efficient treatments of erectile dysfunction. However, one should not forget that (i) the role of the various abdominal and pelvic nerves in the control of penile erection had been clearly stated at the end of the 19th century (see Ref. [15] as an

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