Mild thermal stimulation of the buttock skin increases urinary voiding efficiency in anesthetized rats

In the present study, we examined the effects of mild thermal stimulation of the skin on voiding efficiency using urethane-anesthetized rats with reduced voiding efficiency. Spontaneous urination was induced by infusing saline. For each voiding, the voiding efficiency was calculated from the voided volume and the bladder capacity measured. A Peltier thermode was attached to the buttock skin to apply stimulation: cooling between to 25 °C and 35 °C, every 20 s throughout the saline infusion. The voiding efficiency was 29 ± 9 % (mean ± SD) before stimulation and increased significantly by 10-15 % during stimulation. During thermal stimulation, the maximum vesical pressure during micturition was unchanged, but the urethral relaxation duration was significantly prolonged. Applying local anesthesia to the stimulated skin area abolished the changes in voiding efficiency in response to thermal stimulation. These results suggest that the excitation of cutaneous thermoreceptive afferents modulates urethral function during urination, thereby improving voiding efficiency.