ABSTRACT:

We investigate the hypothesis that intrafascicular stimulation of the pudendal nerve (PN) can be used to selectively activate the detrusor bladder muscle and the external urethral sphincter (EUS). Nine anesthetized male canines were used in this study. Muscle activations were measured via bladder catheter pressure transducers and EUS electromyography (EMG) wires. The PNs were exposed via dissection of the ischioanal fossa and implanted with Utah Slanted Electrode Arrays (USEAs). USEAs consist of 100, 0.5–1.5 mm long microelectrodes that project out from a 4$,times,$4 mm substrate. Intrafascicular stimulation was delivered via individual USEA microelectrodes in order to map the ability of each electrode to selectively or nonselectively evoke detrusor and/or EUS contractions. We were able to selectively activate the detrusor using 33 Hz stimulation of PN axons with an average of $4.57 pm 3.82$ (${rm mean }pm {rm sd}$) USEA electrodes per animal tested. Electrically-evoked and distention-evoked bladder contractions had similar kinetics. Sustained bladder contractions were evoked via 60 s of intrafascicular stimulation. The EUS was activated using 33 Hz stimulation via an average of $26.14 pm 19.45$ electrodes per animal tested. High frequency ($> {2}~{rm kHz}$) stimulation delivered via EUS selective electrodes produced nonselective block of PN axons. Examples of how this selective axonal access could be used to restore continence and activate micturition were demonstrated in two animals. We report herein the first study demonstrating selective detrusor and EUS activation via microelectrodes implanted intrafascicularly in the-
PN. Such selective activation enables new therapeutic possibilities for controlling the muscles of micturition.