Neural pathways of somatic and visceral reflexes of the external urethral sphincter in female rats

Abstract

The external urethral sphincter (EUS) plays a crucial role in maintaining urinary continence. The activity of the EUS is modulated by bladder and urethra sensory neurons. However, a complete understanding of the somatic or visceral sources that modulate the EUS is lacking. The aims of the present study were to characterize the response of the EUS to perineal skin, genital, rectal, and urethral mechanical stimulation, as well as to determine the peripheral neural pathways of the reflex. EUS reflex electromyographic activity (EMG), innervation of pelvic and perineal structures, and the anatomy of afferent and efferent nerves were determined in anesthetized female rats. The EUS responds to cutaneous as well as genital and rectal stimuli. However, the EUS EMG response is significantly larger when induced by genital stimulation. The dorsal nerve of the clitoris and the cavernous nerve both innervate the distal urethra and the distal vagina, as well as the clitoris and perigenital skin and are the main afferent pathways for the genito-sphincteric reflex. Efferent axons travel through the pudendal nerve and the lumbosacral trunk and converge in the motor branch of the lumbosacral plexus, which innervates the EUS. Because the nerves are located on the vaginal walls, they are susceptible to damage during childbirth. Physiology and anatomy of the different neural pathways that regulate EUS activity are important to consider when inducing nerve damage to create models of urinary incontinence.

Somatomotor and sensory urethral control of micturition in female rats

“…This plexus forms, among other nerves, the motor branch of the sacral plexus (MBSP), also known as the motor branch of the PD nerve (Fig. 1), which innervates the EUS and other perineal muscles (8,24,32,36,37). From the PD nerve also emerges the sensory branch of the PD nerve, which innervates the penis/clitoris (8, 32, 35).…”

Neuroanatomic and behavioral correlates of urinary dysfunction induced by vaginal distension in rats

“…However, in addition to the pudendal nerve, there are other somatic and autonomic nerves running over or adjacent to the vaginal wall that could also be stretched during childbirth (40). Nonetheless, injury to pelvic, perineal, or bladder nerves has not been investigated in the rat VD model of simulated delivery.…”

Coital Urinary Incontinence Induced by Impairment of the Dorsal Nerve of the Clitoris in Rats

“…DN also innervates distal urethra 4 and in anesthetized rats its transection increased voiding frequency 8, 9 . DN, and other peripheral nerves may be damaged during childbirth, aging and pelvic surgery, resulting in urogenital comorbidity 2,10,11 . In addition, DN may M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT be partial or totally removed with genital cancer 12 or female genital cutting 13 (a practice for cultural or religious reasons prevalent in certain countries).…”

“…In rats and humans, stimulation of genital structures or genital nerves has been shown to evoke EUS activity (genito-EUS-reflex) and inhibit or induce bladder contraction [4][5][6][7] . This suggests that during mating, in addition to the bladder-EUSreflex, activation of the genito-EUS-reflex may modulate urine expulsion and contribute to maintaining urinary continence during penile intromission.…”

“…This suggests that during mating, in addition to the bladder-EUSreflex, activation of the genito-EUS-reflex may modulate urine expulsion and contribute to maintaining urinary continence during penile intromission. These two guarding reflexes have been studied separately 3,4 and its unknown whether they work synergistically during mating.…”