OBJECTIVETo study the neurophysiologic of detrusor overactivity (DO) due to partial bladder outflow obstruction (PBOO).

METHODSTwenty four female Wistar rats with DO caused by PBOO were studied simultaneously with ten sham-operated rats. An electrophysiological multi-channel simultaneous recording system was used to record pelvic afferent fiber potentials as well as the pudendal nerve motor branch potentials, external urethral sphincter electromyogram (EUS EMG) and abdominal muscle EMG during filling cystometry. To test the effect of the unstable contraction in DO rats after the decentralization of the central nervous system, DO rats were studied the changes of the unstable contraction after transection of the spinal cord (T(8) level), pelvic nerve, the sympathetic trunk, and the pudendal nerve.

RESULTSThe incidence of DO was 62.5% in filling cystometry. During filling cystometry, there are two type of DO contraction according to the changes of pelvic afferent fiber signals, the relevant nerves and muscles responses: the small pressure of the unstable contraction (S-DO) and the big pressure of the unstable contraction (B-DO). For the B-DO, there were significant changes in the recordings of pelvic afferent fiber, the motor branch of the pudendal nerve, EUS EMG, and abdominal muscle EMG. While all these differences have not been recorded during S-DO. Both the filling-voiding cycle and the unstable contraction of B-DO were eliminated and the base line of bladder pressure increased after T(8) spinal cord transection. While the S-DO was not affected by such transection. When bladder relevant nerves were transected by the sequence of the pelvic nerve, the sympathetic trunk, and the pudendal nerve, the filling-voiding cycle was eliminated. The base line of bladder pressure increased significantly. No B-DO was recorded, but the S-DO still existed.

CONCLUSIONThere are some bladder-genic factors take part in the DO contractions induced by PBOO.