Suppression of bladder overactivity by activation of somatic afferent nerves in the foot

Abstract

Objective: To investigate the possibility of suppressing bladder overactivity by electrical activation of somatic afferent nerves in the foot.

Materials and methods: Cats with an intact spinal cord were studied under α-chloralose anaesthesia. Bladder pressure was recorded via a urethral catheter. Foot stimulation was applied via surface pad electrodes attached to the skin of the front or hind foot.

Results: Reflex micturition was inhibited by electrical stimulation of the hind foot at either low (5 Hz) or high (20 Hz) frequencies, but stimulation of the front foot was ineffective. The mean (sem) bladder capacity during a saline infusion cystometrogram (CMG) was significantly (P < 0.05) increased to 153.2 (18.2)% and 136.9 (14.3)% of the control bladder capacity by stimulation at frequencies of 5 Hz and 20 Hz, respectively. Intravesical infusion of 0.25% acetic acid (AA) induced bladder overactivity and reduced bladder capacity to 20.3 (8.9)% of the control capacity measured during saline infusion. Foot stimulation inhibited the AA-induced bladder overactivity recorded under isovolumetric conditions, and significantly (P < 0.05) increased bladder capacity during AA infusion. However, it only restored the small bladder capacity caused by AA irritation to 40-50% of the control bladder capacity measured during saline infusion. The effect of foot stimulation did not persist after termination of stimulation during repeated CMG tests.

Conclusions: This study shows the potential of noninvasive transcutaneous electrical stimulation of somatic nerves in the foot to inhibit reflex bladder activity and treat overactive bladder symptoms.

© 2010 THE AUTHORS. JOURNAL COMPILATION © 2010 BJU INTERNATIONAL.

Figures

Figure 1

Electrode placement for electrical stimulation of the cat hind foot.

Figure 2

Inhibition of isovolumetric bladder contractions by electrical stimulation applied to the hind foot via 3 different electrode configurations (A-C) as shown in Fig.1. Stimulation of the front foot was not effective in inhibiting the bladder (D). The thin lines under the pressure traces indicate zero pressure. Black bars under the pressure traces indicate the stimulation duration. Stimulation pulse width was 1 ms. T = threshold to induce toe twitching. Data were from 4 different cats.

Figure 3

Inhibition of isovolumetric bladder contractions by 5 Hz electrical stimulation of the foot. A. Complete inhibition was achieved at one half of the intensity threshold (T = 6 V) for inducing toe movement with electrodes 1-2. B. Complete inhibition was achieved at 2 times of the intensity threshold (T = 4 V) for inducing toe movement with electrodes 1-3. The thin lines under the pressure traces indicate zero pressure. Black bars under the pressure traces indicate the stimulation duration. Stimulation pulse width was 1 ms. Data in A and B were from the same animal.

Figure 4

Bladder capacity was increased by electrical stimulation of the foot at different frequencies (5 or 20 Hz). Stimulation intensity (12 V) was at 2 times of intensity threshold to induce toe movement. Stimulation pulse width was 1 ms. Electrodes 1-2 were used. The arrows indicate the start and stop of bladder infusion (2 ml/min). The black bars under the pressure traces indicate the stimulation duration.

Figure 5

Bladder capacity was significantly increased by electrical stimulation of the foot at different frequencies (5 or 20 Hz). Stimulation intensity (3-12 V) was at 1-2.5 times of intensity threshold to induce toe movement. Stimulation pulse width was 1 ms. Data were from total 5 cats. Electrodes 1-2 were used in 3 cats, and electrodes 1-3 were used in another 2 cats. * indicates statistical significance (P

Figure 6

Foot stimulation inhibited bladder overactivity induced by 0.25% acetic acid (AA). A. 0.25% AA irritated bladder, caused bladder overactivity, and reduced bladder capacity during CMG. The arrows indicate the start and stop of the infusion (2 ml/min). B. The overactive bladder contractions under isovolumetric condition at a smaller bladder volume as shown in A was inhibited by foot stimulation. The thin lines under the pressure traces indicate zero pressure. Black bars under the pressure traces indicate the stimulation duration. Stimulation pulse width was 0.2 ms. Electrodes 1-2 were used.

Figure 7

Reduction in bladder capacity induced by 0.25% acetic acid (AA) was partially reversed by foot stimulation at different frequencies (5 or 20 Hz). Stimulation intensity (10 V) was at 1.25 times of intensity threshold to induce toe movement. Stimulation pulse width was 1 ms. Electrodes 1-2 were used. The arrows indicate the start and stop of bladder infusion (2 ml/min). The black bars under the pressure traces indicate the stimulation duration.

Figure 8

Reduction in bladder capacity induced by 0.25% acetic acid (AA) was partially reversed by foot stimulation at different frequencies (5 or 20 Hz). Stimulation intensity (6-12 V) was at 1.25-3 times of intensity threshold to induce toe movement. Stimulation pulse width was 1 ms. Electrodes 1-2 were used in total 4 cats. * indicates statistical significance (P