Prolonged Modulation of the Micturition Reflex by Electrical Stimulation

Abstract: Intravesical electrical stimulation (IVES) has been used in treatment of patients with urinary bladder dysfunctions for more than four decades. While some investigators have reported excellent results others have observed less convincing effects or outright failures. The discrepancies may reflect differences in patient selection or stimulation procedure. A better theoretical understanding of the IVES working mechanism might help to improve the success rate of the treatment. The aims of the present study were to provide such information.Experiments were performed on adult female cats and rats under /alpha/-chloralose anesthesia. IVES was delivered by a catheter electrode in the bladder. At proper intensity and frequency, IVES evoked reflex detrusor contractions that were abolished by bilateral rhizotomy of sacral dorsal roots. Stimulation parameters and response characteristics revealed that bladder mechanoreceptor A/delta/ afferents were activated by the IVES, the same afferents that drive the normal micturition reflex.Five minutes of continues IVES at 20 Hz induced a prolonged, significant decrease in the micturition threshold volume of anesthetized rats. Similarly, selective bladder A/delta/ afferent stimulation induced a long-lasting enhancement of micturition reflex discharges in cats. A comparable prolonged inhibitory effect on the micturition reflex was demonstrated after ano-genital afferent stimulation. Both modulatory effects occurred without changes in response sensitivity of stimulated afferents. The IVES induced modulation was prevented by transient exposure of the bladder to a local anesthetic and by systemic administration of a glutamate NMDA receptor antagonist.In conclusion, IVES induces a prolonged modulation of the micturition reflex by an LTP like enhancement of excitatory synaptic transmission in the central micturition reflex pathway. The findings provide an experimental explanation for the neuronal mechanisms underlying the curative effect of IVES in patients with bladder evacuation problems.