The role of bladder-to-urethral reflexes in urinary continence mechanisms in rats

Abstract

Urethral closure mechanisms during passive increments in intravesicular pressure (P(ves)) were investigated using microtip transducer catheters in urethane-anesthetized female rats. After a block of reflex bladder contractions by spinal cord transection at T8-T9, abruptly raising P(ves) to 20, 40, or 60 cmH(2)O for 2 min induced a bladder pressure-dependent contractile response in a restricted portion of the middle urethra (12.5-15 mm from the urethral orifice) that was abolished by cutting the pelvic nerves bilaterally. In pelvic nerve-intact rats, the bilateral transection of either the pudendal nerves, the nerves to the iliococcygeous/pubococcygeous muscles, or the hypogastric nerves significantly reduced (49-74%) the urethral reflex response induced by passive P(ves) increases, and combined transection of these three sets of nerves totally abolished the urethra-closing responses. In spinal cord-intact rats, similar urethral contractile responses were elicited during P(ves) elevation (20 or 40 cmH(2)O) and were also eliminated by bilateral pelvic nerve transection. After spinal cord and pelvic nerve transection, leak point pressures, defined as the pressure inducing fluid leakage from the urethral orifice during passive P(ves) elevation by either bladder pressure clamping in 2.5-cmH(2)O steps or direct compression of the bladder, were significantly lowered by 30-35% compared with sham-operated (spinal cord-transected and pelvic nerve-intact) rats. These results indicate that 1) passive elevation of P(ves) can elicit pelvic afferent nerve-mediated contractile reflexes in the restricted portion of the urethra mediated by activation of sympathetic and somatic nerves and 2) bladder-to-urethral reflexes induced by passive P(ves) elevation significantly contribute to the prevention of stress urinary incontinence.

Animal Models of Female Stress Urinary Incontinence

“…5,6,19 The rat is mounted on a vertical tilt table to best match the orientation of the human pelvis with respect to gravity. The spinal cord of the rat is transected at the T8-T9 level to eliminate spinobulbospinal pathways, while maintaining urethral closure mechanisms intact.…”

Role of vasopressin V1Areceptor in the urethral closure reflex in rats

“…We postulated that the mode of action for the AVP-induced increase in urethral resistance depends on the enhancement of the urethral closure reflex (spinal reflex potentiation) as the peptide drug was injected into the spinal cord. After transection of the pelvic nerve containing the bladder afferent nerve, the urethral closure reflex responses to bladder pressure increase disappear (10). AVP did not show any effect on the urethral resistance in the rats without the bladder afferent nerves.…”

“…Urethral closure reflex mediation. The urethral closure reflex is involved in urethral closure responses to increase and maintain urethral resistance (8,10). Hence, we investigated whether the AVP-induced increase in urethral resistance depends on the urethral closure reflex by the following two methods.…”

“…Urethral closure reflex responses were induced according to previously described methods with slight modification (10,12). Briefly, under isoflurane anesthesia, spinal cord transection and bladder catheter insertion were performed as described for the intravesical pressure clamp method.…”

Reflexes evoked by electrical stimulation of afferent axons in the pudendal nerve under empty and distended bladder conditions in urethane-anesthetized rats

“…On the other hand EUS reflex activity was not completely eliminated by crushing the pudendal nerves bilaterally (Fig. 6D, also see Kamo et al, 2004) indicating that the EUS or adjacent periurethral striated muscles that contribute to the EMG activity are innervated by other motor nerves, e.g., the muscular branch of the pelvic nerve to the illiococcygeus/pubococcygeus muscle (Kamo et al, 2004;Pacheco et al, 1989Pacheco et al, , 1997. These nerves could be involved in the pudendal-EUS reflex.…”