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-The aim of the present study was to use a model of simulated human childbirth in rats to determine the damage to genitourinary structures and behavioral signs of urinary dysfunction induced by vaginal distension (VD) in female rats. In experiment 1, the length of the genitourinary tract and the nerves associated with it were measured immediately after simulated human delivery induced by VD or sham (SH) procedures. Electroneurograms of the dorsal nerve of the clitoris (DNC) were also recorded. In experiment 2, histological characteristics of the bladder and major pelvic ganglion of VD and SH rats were evaluated. In experiment 3, urinary parameters were determined in conscious animals during 6 h of dark and 6 h of light before and 3 days after VD or SH procedures. VD significantly increased distal vagina width (P Ͻ 0.001) and the length of the motor branch of the sacral plexus (P Ͻ 0.05), DNC (P Ͻ 0.05), and vesical nerves (P Ͻ 0.01) and decreased DNC frequency and amplitude of firing. VD occluded the pelvic urethra, inducing urinary retention, hematomas in the bladder, and thinness of the epithelial (P Ͻ 0.05) and detrusor (P Ͻ 0.01) layers of the bladder. Major pelvic ganglion parameters were not modified after VD. Rats dripped urine in unusual places to void, without the stereotyped behavior of micturition after VD. The neuroanatomic injuries after VD occur alongside behavioral signs of urinary incontinence as determined by a new behavioral tool for assessing micturition in conscious animals. external urethral sphincter; dorsal nerve of the clitoris; major pelvic ganglion; micturition MICTURITION consists of two phases: storage and urine expulsion. During storage, the detrusor is relaxed while the bladder neck and urethra are activated, preventing involuntary bladder emptying (11). Extrinsic elements such as the levator ani muscle also contribute to the maintenance of continence (3). When the bladder reaches its threshold volume, spinal and supraspinal reflexes are triggered to induce bladder contraction and urethral relaxation, and urine flows through the urethra (11). Damage to the lower urinary tract and/or its innervation can induce urinary dysfunction (3,29,41).Urinary dysfunction affects the health of many women (60). Stress urinary incontinence has been described as involuntary loss of urine during effort and is the most prevalent urinary disorder related to vaginal childbirth, which is known to injure the pudendal nerve and denervate the external urethral sphincter (EUS) (3, 15, 57).Maternal pelvic viscera and nerve damage results from the difficulty of human childbirth due the large fetal head and brain relative to the maternal pelvis size. Neonates at birth have heads that are close to the size of the maternal birth canal through which they must pass during the second stage of parturition (48). Births of fetuses over 4 kg or fetal malposition often prolong parturition (30), retaining the fetus in the pelvic cavity, the main anatomic resistance to fetal expulsion. Prolonged second stage of parturition...

Aims To analyze, in female rats, the anatomical and histological features of the urethra and its relationship with the vagina and clitoris, and its innervation. Methods Seventeen adult female Wistar rats were used. Gross anatomy and acetylcholinesterase (AchE) histochemistry were performed to describe the urethral features, adjacent structures, and innervation. The histomorphometric characteristics of the urethra were determined in transversal, longitudinal, or coronal sections stained with Masson's Trichrome. Results The female rat urethra is not a homogeneous tubular organ. The pre‐pelvic and pelvic regions are firmly attached to the vagina with belt‐like striated fibers forming a urethra‐vaginal complex. The bulbar regions have curved segments and a narrow lumen. The clitoral region is characterized by a urethra‐clitoral complex surrounded by a vascular plexus. The lumen area and thickness of the urethral layers significantly varied between regions (P < 0.05). Innervation of the urethra arrives from the major pelvic ganglion, the dorsal nerve of the clitoris (DNC), and the motor branch of the sacral plexus (MBSP). Conclusions Differential tissular composition of the urethra may underlie urinary continence and voiding dysfunction through different physiological mechanisms. The urethra‐vagina complex seems to be the main site controlling urinary continence through active muscular mechanisms, while the bulbar urethra provides passive mechanisms and the urethra‐clitoris complex seems to be crucial for distal urethral closure by means of a periurethral vascular network.

In male rats the perineal striated muscles are crucial to maintaining normal urinary continence, preventing retrograde ejaculation, and to expelling urine and seminal secretions. Bilateral neurectomy of the MBSP may not be appropriate for long term survival urinary studies because effects on urinary parameters can be contaminated and/or masked by impaired seminal fluid expulsion, as a consequence of impairment of striated urethral muscle function.

These results suggest that the pudendal nerve is an important neural pathway in the convergence and crosstalk of female urogenital neural circuits, and genital deafferentation may be a causal factor of coital urinary incontinence. Rats with bilateral transection of the dorsal nerve of the clitoris may serve as an animal model of coital incontinence.

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