Prolonged nonobstructive urinary retention induced by tibial nerve stimulation in cats.

Nonobstructive urinary retention (NOUR) is a medical condition without an effective drug treatment, but few basic science studies have focused on this condition. In α-chloralose-anesthetized cats, the bladder was cannulated via the dome and infused with saline to induce voiding that could occur without urethral outlet obstruction. A nerve cuff electrode was implanted for tibial nerve stimulation (TNS). The threshold (T) intensity for TNS to induce toe twitch was determined initially. Repeated (6 times) application of 30-min TNS (5 Hz, 0.2 ms, 4-6T) significantly (P < 0.05) increased bladder capacity to 180% of control and reduced the duration of the micturition contraction to 30% of control with a small decrease in contraction amplitude (80% of control), which resulted in urinary retention with a low-voiding efficiency of 30% and a large amount of residual volume equivalent to 130% of control bladder capacity. This NOUR condition persisted for >2 h after the end of repeated TNS. However, lower frequency TNS (1 Hz, 0.2 ms, 4T) applied during voiding partially reversed the NOUR by significantly (P < 0.05) increasing voiding efficiency to 60% and reducing residual volume to 70% of control bladder capacity without changing bladder capacity. These results revealed that tibial nerve afferent input can activate either an excitatory or an inhibitory central nervous system mechanism depending on afferent firing frequencies (1 vs. 5 Hz). This study established the first NOUR animal model that will be useful for basic science research aimed at developing new treatments for NOUR.

Frequency Dependent Tibial Neuromodulation of Bladder Underactivity and Overactivity in Cats.

OBJECTIVE: This study is aimed at determining if tibial nerve stimulation (TNS) can modulate both bladder underactivity and overactivity. METHODS: In α-chloralose anesthetized cats, tripolar cuff electrodes were implanted on both tibial nerves and TNS threshold (T) for inducing toe twitching was determined for each nerve. Normal bladder activity was elicited by slow intravesical infusion of saline; while bladder overactivity was induced by infusion of 0.25% acetic acid to irritate the bladder. Bladder underactivity was induced during saline infusion by repeated application (2-6 times) of 30-min TNS (5 Hz, 4-8T, 0.2 msec) to the left tibial nerve, while TNS (1 Hz, 4T, 0.2 msec) was applied to the right tibial nerve to reverse the bladder underactivity. RESULTS: Prolonged 5-Hz TNS induced bladder underactivity by significantly increasing bladder capacity to 173.8% ± 10.4% of control and reducing the contraction amplitude to 40.1% ± 15.3% of control, while 1 Hz TNS normalized the contraction amplitude and significantly reduced the bladder capacity to 130%-140% of control. TNS at 1 Hz in normal bladders did not change contraction amplitude and only slightly changed the capacity, but in both normal and underactive bladders significantly increased contraction duration. The effects of 1 Hz TNS did not persist following stimulation. Under isovolumetric conditions when the bladder was underactive, TNS (0.5-3 Hz; 1-4T) induced large amplitude and sustained bladder contractions. In overactive bladders, TNS during cystometry inhibited bladder overactivity at 5 Hz but not at 1 Hz. CONCLUSIONS: This study indicates that TNS at different frequencies might be used to treat bladder underactivity and overactivity.

Saphenous nerve stimulation normalizes bladder underactivity induced by tibial nerve stimulation in cats.

This study in α-chloralose-anesthetized cats aimed at investigating the bladder responses to saphenous nerve stimulation (SNS). A urethral catheter was used to infuse the bladder with saline and to record changes in bladder pressure. With the bladder fully distended, SNS at 1-Hz frequency and an intensity slightly below the threshold (T) for inducing an observable motor response of the hindlimb muscles induced large amplitude (40-150 cmH2O) bladder contractions. Application of SNS (1 Hz, 2-4T) during cystometrograms (CMGs), when the bladder was slowly (1-3 ml/min) infused with saline, significantly ( P < 0.05) increased the duration of the micturition contraction to >200% of the control without changing bladder capacity or contraction amplitude. Repeated application (1-8 times) of intense (4-8T intensity) 30-min tibial nerve stimulation (TNS) produced prolonged post-TNS inhibition that significantly ( P < 0.01) increased bladder capacity to 135.9 ± 7.6% and decreased the contraction amplitude to 44.1 ± 16.5% of the pre-TNS control level. During the period of post-TNS inhibition, SNS (1 Hz, 2-4T) applied during CMGs completely restored the bladder capacity and the contraction amplitude to the pre-TNS control level and almost doubled the duration of the micturition contraction. These results indicate that SNS at 1 Hz can facilitate the normal micturition reflex and normalize the reflex when it is suppressed during post-TNS inhibition. This study provides an opportunity to develop a novel neuromodulation therapy for underactive bladder using SNS.

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

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.