Electrical Stimulation of the Spinal Dorsal Root Inhibits Reflex Bladder Contraction and External Urethra Sphincter Activity: Is This How Sacral Neuromodulation Works?

INTRODUCTION: Using a rat model, we aimed to confirm the inhibitory effect of dorsal spinal root (afferent) stimulation and test if bilateral stimulation is more effective than unilateral stimulation. External urethral sphincter (EUS) electromyography (EMG) is also assessed in conjunction with cystometrogram.

MATERIALS AND METHODS: Eighteen female Sprague-Dawley rats were tested following urethane anesthesia. Via urethral catheterization, the bladder was infused with normal saline to evoke rhythmic bladder reflex contractions (BRC). L6 spinal nerves were isolated and stimulated.

RESULTS: L6 stimulation was effective in inhibiting BRC. L6 bilateral dorsal root (DR) stimulation of 50% intensity was required to cause inhibition as compared to unilateral stimulation. In EUS EMG recordings, there was a strong association between EUS EMG activities and bladder contraction. When the bladder contraction was inhibited effectively by L6 DR stimulation, a considerable reduction was also found in the EUS EMG activities.

CONCLUSIONS: L6 DR stimulation abolished BRC in our rat model. Bilateral L6 DR stimulation produced a 50% reduction in stimulation intensity, providing a similar BRC block. Abolishing BRC also appeared to coincide with a reduction in EUS EMG, implicating that sacral neuromodulation might act centrally, at least rostrally at the T8-9 spinal level.