Reflex bladder activation via pudendal nerve and intraurethral stimulation depends on stimulation pattern and location

Bursting stimulation of proximal urethral afferents improves bladder pressures and voiding

Reflex bladder excitation has been evoked via pudendal nerve, pudendal nerve branch and intraurethral stimulation; however, afferent-evoked bladder emptying has been less efficient than direct activation of the bladder via sacral root stimulation. A stimulation method that improves activation of the urethra-bladder excitatory reflex with minimal sphincter recruitment may lead to improved bladder emptying. Fine wire electrodes were placed in the wall of the urethra in five cats. Placement of electrodes near the proximal urethra evoked bladder contractions with minimal sphincter activation. On these electrodes, lower frequency burst-patterned stimuli evoked greater bladder voiding efficiencies (71.2 +/- 27.8%) than other stimulus patterns on the same electrodes (50.4 +/- 41.5%, p > 0.05) or any stimulus pattern on electrodes that elicited urethral closure (16.5 +/- 12.7%, p < 0.05). Fine wire electrodes specifically targeted afferent fibers in the urethra, indicating the feasibility of clinical evaluations using the same method. This work may improve the translation of next generation neuroprostheses for bladder control.

Intraurethral stimulation for reflex bladder activation depends on stimulation pattern and location

AIMS

Reflex bladder excitation has been demonstrated by stimulation of the pudendal nerve and several of its distal branches. However, excitation parameters have not been consistent and the relationship to anatomical locations within the urethra has not been fully investigated. An improved understanding of the lower urinary tract neurophysiology will improve human studies and neuroprosthetic device development.

METHODS

Intraurethral stimulation was performed in nine cats at near isovolumetric bladder volumes before and/or after spinalization. Bladder excitability profiles were obtained for lower (2 Hz) and higher (33 Hz) frequency stimuli along the urethra between the bladder neck and external meatus.

RESULTS

Higher frequency stimuli were excitable at all urethral locations prior to spinalization but only excitable in the middle and distal urethra after spinalization. Lower frequency stimuli were excitable at proximal and middle locations before spinalization but not excitable at any location after spinalization. In most evaluations, bursting pulse stimulation patterns evoked greater bladder pressures than the dominant continuous frequency (2 or 33 Hz).

CONCLUSIONS

These data indicate the potential presence of two distinct pathways for reflex bladder activation within the urethra: a supra-T10 circuit initiated in the proximal and mid urethra that responds to lower and higher frequency stimuli, and a sacral circuit initiated in the mid and distal urethra that responds to higher frequency stimuli. This work suggests potential anatomical targets and stimulus patterns for clinical evaluations of peripheral nerve-based neuroprostheses for bladder control.