Control of the unstable urinary bladder by graded thermoelectric cooling of the spinal cord

To evaluate local lumbosacral spinal-cord cooling (a novel technique for neuromodulating urinary bladder reflexes) for its feasibility in possible clinical use, by determining the efficacy and the optimum temperature for suppressing reflex urinary incontinence in two rat models of neurogenic urinary bladder instability.

Overactivity of the detrusor muscle was induced by inflammation of the urinary bladder in a group of rats. A second group of rats was examined 6 weeks after complete midthoracic spinal cord transection, when all animals had developed neurogenic bladder hyper-reflexia. The intravesical pressure, urethral pressure and electromyographic (EMG) activity of the external urethral sphincter (EUS) were recorded simultaneously during repetitive local cooling and re-warming of the dorsal L6/S1 spinal cord segments, using a thermoelectric cooling device.

Spinal cord cooling at L6/S1 had no influence on the recorded values at >26 degrees C, but markedly suppressed detrusor contraction frequency at 21- 25 degrees C. Cooling to <20 degrees C completely and reversibly eliminated inflammation-induced bladder contractions in rats with an intact neural axis and significantly reduced the contraction amplitudes (mean reduction 61%) and duration of contractions in spinally transected rats. Cooling simultaneously increased tonic EUS EMG activity and urethral perfusion pressure in both experimental groups, indicating closure of the urethral outlet. Cooling of adjacent spinal cord segments had no influence on bladder and urethral functions.

Cooling the dorsal spinal cord at the origin of the parasympathetic innervation of the bladder can be used to reversibly suppress bladder instability with simultaneous closure of the urethral outlet. Therefore, local spinal cord cooling, e.g. as an implantable thermoelectric device, may offer a suitable method to treat detrusor overactivity and restore continence.