Urethral sphincteric responses to sacral root stimulation.

Deafferentation and stimulation of sacral nerves in patients with complete spinal cord lesions is a good model to study the parasympathetic influence on urethral behavior. During intradural sacral deafferentation from S2 to S4/S5 in preparation for implantation of the Finetech-Brindley anterior sacral root stimulator, sacral roots were stimulated with 3 and 30 Hz and 3 and 10 V and the bladder and urethral responses noted. Stimulation of the posterior roots at 3 Hz gives a urethral relaxation without bladder contraction. At this frequency, anterior sacral root stimulation has no effect on bladder nor urethral pressure. Stimulation of the anterior roots at 30 Hz produces simultaneous bladder contraction and urethral relaxation. These findings support the presence of an afferent parasympathetic inhibitory mechanism in the spinal micturition center in the human.