The effects of bilateral bipolar sacral neurostimulation on urinary bladder activity during filling before and after irritation in a rat model.

ABSTRACT

AIMS: To design an optimal rat model for studying sacral neurostimulation (SNS), and examine the effect of SNS on myogenic non-voiding contractions (NVC) during filling before and after intraluminal irritation. METHODS: Bilateral paired bipolar SNS was performed in 10 female urethane anesthetized Sprague-Dawley rats at the L6-S1 trunks at 10 Hz, 0.1 msec pulse duration and 0.15-0.80 mA (below motor threshold). Transvesical cystometry was performed before and during SNS under conditions of control (saline, N = 10) and irritation [0.25% acetic acid (AA), N = 5]. RESULTS: Functional bladder capacity (FBC) and NVC count were significantly increased during SNS under both control and irritation conditions (P < 0.01 for all). In six instances (four in control, two in irritation), micturition reflexes were completely inhibited by SNS resulting in overflow incontinence. Filling compliance, NVC period and NVC maximum amplitude were not affected by SNS (P > 0.05 for all). Non-parametric two-way analysis of variance for repeated measures revealed increased FBC and NVC count during SNS under both control and irritation conditions (P = 0.004 for both, N = 5 rats). Linear regression analysis of NVC count versus FBC revealed a slope significantly different than zero, independent of control or irritation conditions (slope 33.10 ± 2.43, R(2) = 0.81, P < 0.001). CONCLUSIONS: This model achieved reliable, reversible and robust increases in bladder capacity up to overflow incontinence at stimulations below somatic motor threshold. SNS dramatically increased FBC and reversed AA-induced changes without affecting the character of normal NVC associated with bladder filling. Increased number of NVC is simply a consequence of increased fill time.