Lumbosacral spinal segmental contributions to tibial and pudendal neuromodulation of bladder overactivity in cats.

Aims: To determine the spinal segmental afferent contributions to tibial and pudendal inhibition of bladder overactivity.

Methods: Intravesical infusion of 0.5% acetic acid was used to irritate the bladder and induce bladder overactivity in anesthetized cats. Tibial or pudendal nerve stimulation was used to suppress the bladder overactivity and increase bladder capacity during cystometry. L5-S3 dorsal roots ipsilateral to the stimulation were exposed by a laminectomy and transected sequentially during the experiments to determine the role of individual dorsal roots in tibial or pudendal neuromodulation.

Results: Transection of L5 dorsal root had no effect. Transection of L6 dorsal root in four cats produced an average 18% reduction in tibial inhibition, which is not a significant change when averaged in the group of 10 cats. Transection of L7 dorsal root completely removed the tibial inhibition without changing reflex bladder activity or pudendal inhibition. Transection of S1 dorsal root reduced the pudendal inhibition, after which transection of S2 dorsal root completely removed the pudendal inhibition. Transection of S3 dorsal root had no effect. The control bladder capacity was increased only by transection of S2 dorsal root.

Conclusions: This study in cats revealed that tibial and pudendal neuromodulation of reflex bladder overactivity depends on activation of primary afferent pathways that project into different spinal segments. This difference may be related to the recent observation in cats that the two types of neuromodulation have different mechanisms of action.