Neurotransmitters: central and peripheral mechanisms

Abstract

Re¯exive erection initiated by recruitment of penile afferents, involves both autonomic and somatic efferents. The re¯ex is mediated at the spinal cord level, modulated by supraspinal in¯uences, and may use several transmitters. Dopamine, acetylcholine, nitric oxide, and peptides, such as oxytocin and ACTHaa-MSH, seem to have a facilitatory role, whereas serotonin may be either facilitatory or inhibitory, and enkephalins are inhibitory. Peripherally, the balance between contractant and relaxant factors controls the degree of contraction of the smooth muscle of the corpora cavernosa, and determines the functional state of the penis. Noradrenaline contracts both corpus cavernosum and penile vessels via stimulation of a 1 -adrenoceptors. The role of endothelins in the control of penile smooth muscle tone is presently unclear. Neurogenic nitric oxide (NO) is considered the most important factor for relaxation of penile vessels and corpus cavernosum. The role of other mediators, released from nerves or endothelium has not been de®nitely established.

Oral Bisphenol A (BPA) given to rats at moderate doses is associated with erectile dysfunction, cavernosal lipofibrosis and alterations of global gene transcription

“…We believe that the use of the global miR transcriptional signatures in penile tissue and potentially in serum for investigating the pathophysiology of erectile dysfunction as well as its relationship with vascular disease where there is already substantial literature, may open up new investigative opportunities. Altogether, our results suggest that the ED reported in men after occupational exposure to BPA could be, as would be expected, due to a peripheral effect of this agent on the penile corpora cavernosa, although a central effect at the brain level cannot be discarded (38,39). …”

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.…”

Changes in nerve‐ and endothelium‐mediated contractile tone of the corpus cavernosum in a mouse model of pre‐mature ageing

“…It is generally considered that the production of NO by nitrergic nerves initiates corporal smooth muscle relaxation, whereas subsequent activation of eNOS by ACh and shear stress, and further production of NO by the endothelium, sustains the erectile response (Andersson, ). In contrast to other studies in rat and mice (Hedlund et al ., ; Mizusawa et al ., ), our results demonstrated the strong presence of eNOS in the endothelium lining the cavernous sinusoids and arteries of the SAMP8 and SAMR1 mice.…”

“…The first response to an erectile stimulus seems to be the increased release of both acetylcholine (ACh) and NO from parasympathetic nerves (Hedlund et al ., ). NO produced by neuronal NO synthase (nNOS), is the principal initiator of corporal smooth muscle relaxation, whereas both ACh and shear stress induce the activation of endothelial NOS (eNOS) and the further production of NO that sustains the erectile response (Andersson, ). Other relaxant factors are also considered to be important in erection, such as endothelium‐released vasodilator prostaglandins (PGs) (Minhas et al ., ; Lin et al ., ).…”