Effects of pudendal nerve injury in the female rat

To test a neurogenic hypothesis for external urethral sphincter (EUS) dysfunction associated with urinary incontinence, the proximal pudendal nerve was crushed in anesthetized retired breeder female rats (n = 5) and compared with a sham lesion group (n = 4). Outcome measures included concentric needle electromyograms (EMGs) from the target EUS, voiding patterns during a 2-hour dark period, and micturition data over a 24-hour period. Fast Blue (FB) was introduced to the crush site at the time of injury and Diamidino Yellow (DY) to the EUS at the time the rats were killed (3 months post-operative), when histological analysis of the nerve and urethra was also performed. EMG records indicated the EUS motor units undergo typical denervation changes followed by regeneration and recovery. Voiding patterns from the crush group show a significant increase of small urine marks in the front third of the cage. At 1-2 weeks post-op, the frequency of voids was significantly increased in the crush group compared to pre-op and late post-op time periods. The mean volume voided in the light phase at the early post-op time was significantly increased in the sham group. Light and electron microscopic patterns seen in nerve and muscle suggest the regenerating motor units maintain a structural integrity. Motoneurons in the lower lumbar cord were labeled with either DY (14. 5 +/- 6.8), FB (31.7 +/- 23.7), or both (35.0 +/- 17.5) tracers, indicating approximately 54% of the crushed pudendal neurons regenerated to the EUS. In conclusion, several measures suggest this reversible crush lesion induces mild urinary incontinence. This animal model is promising for further development of hypotheses regarding neural injury, the pathogenesis of incontinence, and strategies aimed at prevention and treatment. Neurourol. Urodynam. 19:53-69, 2000.