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

Abstract

-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...

Anatomical organization and somatic axonal components of the lumbosacral nerves in female rabbits

“…The appropriate visceral function require of spinal and supraspinal reflexes, and damage to the organs and/or their innervation causes excretory dysfunctions, such as urinary and fecal incontinence. 6,12 The present study describes the organization and the somatic composition of the peripheral innervation of pelvic and perineal organs in female rabbits. This animal has recently been started to be used for the study of the neurophysiology of micturition, as well as for use as an animal model of multiparity-induced damage of the pelvic musculature.…”

“…The pelvic and perineal regions are the anatomical substrate of excretory, reproductive, and sexual functions. The appropriate visceral function require of spinal and supraspinal reflexes, and damage to the organs and/or their innervation causes excretory dysfunctions, such as urinary and fecal incontinence …”

“…FIGURE 5 Sensory field and electroneurographic (ENG) activity of sacral nerves in the female rabbit. The colored areas indicate the skin innervated by the nerves described in Table 1 (6,14,16,18) and depicted in Numerous unmyelinated fibers have been described in the sensory and motor branch of the PDN of male and female rats. 21 PDN cutaneous innervation is the afferent arm of visceral and motor reflexes, for example, mechanical stimulation of the perigenital skin induces micturition in neonatal rats and in spinal cord injured adult animals.…”

“…These nerves may be damaged during pelvic surgeries and parturition, compromising pelvic functions. For instance, peripheral nerve injury related to childbirth has been shown by using vaginal distension models in rats, the main laboratory animal used in genitourinary studies . Unfortunately, the effect of the vaginal distension on the perineal muscles, such as ischiocavernosus and bulbospongiosus, cannot be analyzed because in contrast to women, rats have vestigial perineal muscles …”

“…For instance, peripheral nerve injury related to childbirth has been shown by using vaginal distension models in rats, the main laboratory animal used in genitourinary studies. 6 Unfortunately, the effect of the vaginal distension on the perineal muscles, such as ischiocavernosus and bulbospongiosus, cannot be analyzed because in contrast to women, rats have vestigial perineal muscles. 7 Female rabbits have been started to be used to investigate the contribution of pelvic and perineal muscles on the control of micturition, as well as in the understanding of the impact of multiparity on the pelvic musculature.…”