FUNCTIONAL CONDITIONS OF MICTURITION INDUCED BY SELECTIVE SACRAL ANTERIOR ROOT STIMULATION - EXPERIMENTAL RESULTS IN A CANINE ANIMAL-MODEL

Electrical stimulation of the sacral anterior roots using conventional rectangular current pulses results in a simultaneous contraction of t he urinary bladder and the striated urethral sphincter. Using a tripol ar nerve cuff electrode with quasitrapezoidal current pulses and appro priate stimulation parameters, hyperpolarization of the nerve-fiber ce ll membrane under the anode of the stimulating electrode can reversibl y arrest action potential propagation in large myelinated nerve fibers , innervating the striated urethral sphincter, while leaving action po tential propagation unaffected in small nonmyelinated nerve fibers inn ervating the urinary bladder smooth muscle (anodal arrest). Using this technique in 19 female mongrel dogs, we studied the effect of bladder filling, level of anesthesia, and sacral deafferentation on bladder p ressure, urethral pressure, and urinary flow. Effective micturition co uld be induced only after complete dorsal rhizotomy, abolishing reflex contraction of the striated urethral sphincter, when blocking quasi t rapezoidal current pulses were used for stimulation. Stimulation with rectangular current pulses directly induced a rise in distal urethral pressure, preventing micturition during stimulation.