Bladder cooling reflex and external urethral sphincter activity in the anesthetized and awake guinea pig

A spinal bladder cooling reflex, triggered by cold receptors of transient receptor potential melastatin type in the bladder wall, has been identified in several mammals, including man. This reflex and its influence on the external urethral sphincter were further characterized in the urethane anesthetized and awake guinea pigs. A total of 214 bladder infusions were performed in the 12 animals. Compared to controls, cold fluid induced a significant decrease in the threshold volume for reflex bladder contractions (median 82%, p < 0.01). Menthol induced a further decrease (median 50%), signifying a bladder cooling reflex. Detrusor-sphincter activities were dyssynergic during voidings triggered by cold or menthol infusions but were coordinated during control infusions. The bladder cooling reflex was suppressed and the sphincter activity synergic following cold infusions in the awake state. Thus, the bladder cooling reflex is under the active descending inhibitory control in intact, awake animals.