Afferent fibers of the pudendal nerve modulate sympathetic neurons controlling the bladder neck

Aims: Pudendal nerve stimulation is known to have a potential modulative effect on bladder function. However, even if its efficiency has been established for various neurogenic and non-neurogenic bladder dysfunctions, the underlying neuronal mechanism, and the involved pathways in humans remain unknown. In this prospective study we focused on the effects of pudendal nerve stimulation in complete spinal cord injured patients to identify neuromodulative processes that occur on spinal level. Methods: Twenty complete spinal male presenting with upper motor neuron lesion and neurogenic incontinence underwent pudendal nerve stimulation. Bladder, bladder neck (BN), and external urethral sphincter (EUS) pressures were continuously recorded with a three channel microtip pressure transducer catheter. Fifty six pudendal stimulations using biphasic rectangular impulses (0.2 ms, 10 Hz) with intensities up to 100 mA were applied to the dorsal penile nerve. In six patients, 18 stimulations were repeated after intravenous (i.v.) administration of 7 mg phentolamine. Results: Mean BN and EUS pressure increased during stimulation significantly (P < 0.001). The latencies to the EUS responses range between 27 and 41 ms and those to the BN responses between 188 and 412 ms. Phentolamine decreased initial BN pressure and reduced the pressure rise during stimulation significantly (P < 0.05). Conclusions: Pudendal nerve stimulation evoked somatic responses in the EUS and autonomic responses in the smooth muscle sphincter controlling the BN. Longer latencies of the BN responses and the sensitivity to the alpha-blocking agent phentolamine suggest that sympathetic alpha-adrenergic fibers are involved. Somatic afferent fibers of the pudendal nerve are supposed to project on sympathetic thoracolumbar neurons to the BN and modulate their function. This neuromodulative effect works exclusively at the spinal level and appears to be at least partly responsible for BN competence and at least continence. (C) 2003 Wiley-Liss, Inc.