Reflex neuromodulation of bladder function elicited by posterior tibial nerve stimulation in anesthetized rats

Although posterior tibial nerve stimulation (PTNS) has been shown in both clinical and animal studies to elicit bladder-inhibitory reflexes, our understanding of the role of posterior tibial nerve (PTN) afferents that elicit these responses is significantly limited. To this end, we investigated the effects of frequency-dependant PTNS in urethane-anesthetized rats undergoing repeated urodynamic fills. Nerve stimulation trials (10 min) resulted in statistically significant inhibition of the urinary bladder, both during and after nerve stimulation (P < 0.05). PTNS applied at 5 Hz resulted in both acute and prolonged changes that corresponded to 38.0% and 34.1% reductions in the bladder contraction frequency, respectively. In contrast, PTNS applied at 10 Hz could only elicit an acute decrease (22.9%) in bladder activity. Subsequent electrical activation of individual PTN branches (lateral or medial plantar nerves) confirmed that these bladder reflexes are mediated by specific subsets of the PTN trunk. Both acute and prolonged inhibition of the bladder were achieved by electrical stimulation of the lateral plantar (10 and 20 Hz) and medial plantar (5 and 10 Hz) nerves. Finally, we report a bladder-excitatory reflex that is elicited by electrical activation of either the PTN trunk or lateral plantar nerve at 50 Hz. This study shows that multiple bladder reflexes are tuned to specific subsets of nerve afferents and stimulation frequencies, each of which provide novel insights into the physiological effects of PTNS.