Functional and neuroanatomical effects of vaginal distention and pudendal nerve crush in the female rat

Purpose: We tested the hypothesis that neuroanatomical degeneration near the external urethral sphincter (EUS) would parallel urinary dysfunction after vaginal distention or bilateral pudendal nerve crush in female rats. Materials and Methods: A total of 28 female rats underwent bilateral pudendal nerve crush or vaginal distention, or were unoperated controls. Two days later a catheter was implanted into the bladder dome and 2 days after that (4 days after injury) urethral leak point pressure testing was performed with the rat under urethane anesthesia. The pudendal nerve and urethra were then dissected and prepared for light and electron microscopy. Results: Leak point pressure was significantly decreased 4 days after pudendal nerve crush and vaginal distention (29.3 +/- 3.4 and 31.0 +/- 2.5 cm H2O, respectively) compared with controls (44.3 +/- 3.4 cm H2O). The percentage of nerve fascicles with degeneration near the EUS was significantly greater in the nerve crush (13.1% +/- 1.7%) and vaginal distention (7.2% +/- 2.2%) groups than in the control group (0% +/- 0%). There were fewer nerve fascicles near the EUS in the ventral half of the urethral cross section than in the dorsal half in all 3 groups and the percent of fascicles with degeneration was greater in the ventral half than in the dorsal half in the 2 injury groups. Conclusions: These results suggest that the pudendal nerve is particularly vulnerable to injury during vaginal distention in this animal model. The 2 injury models may be useful for investigating the pathophysiology of stress urinary incontinence.