Sacral neuromodulation blocks pudendal inhibition of reflex bladder activity in cats: insight into the efficacy of sacral neuromodulation in Fowler’s syndrome

Abstract

This study tested the hypothesis that sacral neuromodulation, i.e., electrical stimulation of afferent axons in sacral spinal root, can block pudendal afferent inhibition of the micturition reflex. In α-chloralose-anesthetized cats, pudendal nerve stimulation (PNS) at 3-5 Hz was used to inhibit bladder reflex activity while the sacral S1 or S2 dorsal root was stimulated at 15-30 Hz to mimic sacral neuromodulation and to block the bladder inhibition induced by PNS. The intensity threshold (T) for PNS or S1/S2 dorsal root stimulation (DRS) to induce muscle twitch of anal sphincter or toe was determined. PNS at 1.5-2T intensity inhibited the micturition reflex by significantly ( P < 0.01) increasing bladder capacity to 150-170% of control capacity. S1 DRS alone at 1-1.5T intensity did not inhibit bladder activity but completely blocked PNS inhibition and restored bladder capacity to control level. At higher intensity (1.5-2T), S1 DRS alone inhibited the micturition reflex and significantly increased bladder capacity to 135.8 ± 6.6% of control capacity. However, the same higher intensity S1 DRS applied simultaneously with PNS, suppressed PNS inhibition and significantly ( P < 0.01) reduced bladder capacity to 126.8 ± 9.7% of control capacity. S2 DRS at both low (1T) and high (1.5-2T) intensity failed to significantly reduce PNS inhibition. PNS and S1 DRS did not change the amplitude and duration of micturition reflex contractions, but S2 DRS at 1.5-2T intensity doubled the duration of the contractions and increased bladder capacity. These results are important for understanding the mechanisms underlying sacral neuromodulation of nonobstructive urinary retention in Fowler's syndrome.

Bladder underactivity after prolonged stimulation of somatic afferent axons in the tibial nerve in cats

“…25 Sacral neuromodulation is a very effective treatment to relieve the NOUR condition in Fowler's syndrome patients. 9 Our recent study in cats 14 confirmed that sacral neuromodulation can reverse the bladder inhibition produced by electrical stimulation of the pudendal nerve. The current study raises the possibility that other populations of somatic afferents such as tibial afferents may also contribute to NOUR.…”

“…The animals were anesthetized with isoflurane (2‐5% in oxygen) during surgery and then switched to α‐chloralose anesthesia (initial 65 mg/kg i.v. and supplemented as needed) during data collection . The left cephalic vein was catheterized for administration of anesthetics and fluid.…”

“…and supplemented as needed) during data collection. 14 The left cephalic vein was catheterized for administration of anesthetics and fluid. A tracheotomy was performed and a tube was inserted to keep the airway patent.…”

Sacral Neuromodulation for Lower Urinary Tract and Bowel Dysfunction in Animal Models: A Systematic Review With Focus on Stimulation Parameter Selection

“…Bladder pressure continued to rise steeply after the SNM onset and reduced rapidly to a lower level for the remaining 60 sec SNM until a void occurred (17). The effect of different frequencies on bladder capacity in healthy and acetic acid (a.a.) induced overactive bladder (OAB) animals was investigated (6,7,11,18,19). SNM at 5 Hz increased bladder capacity (defined as inhibition of isovolumetric bladder contractions) in healthy and a.a. induced OAB in cats, whereas SNM at 15 and 30 Hz did not change bladder capacity (18,19).…”

Neuromodulation in Urology: Current Trends and Future Applications

“…Basic science evidence suggests that by blocking the inhibitory effect that abnormal afferent activity from the external urethral and anal sphincters has on micturition, restoration of the ability of the patient to void occurs. This stimulation is through blockade of the pudendal nerve's stimulatory effect of the micturition reflex [99].…”