Neural mechanisms of impaired micturition reflex in rats with acute partial bladder outlet obstruction

To determine the contribution of neural elements to micturition, we evaluat ed, in intact rats, the cystometrogram, pelvic afferent nervous activity, p elvic efferent nervous activity and external urethral sphincter-electromyog ram activity in the normal and acute partial bladder outlet obstruction sta tes. In the normal state, in response to saline filling, mechanoreceptor-de pendent pelvic afferent nervous activity gradually activated and finally tr iggered a voiding reflex, including four phases of detrusor contractions. P hase 1 was characterized by an initial rising intravesical pressure, Phase 2 was characterized by a series of high-frequency oscillations in intravesi cal pressure, Phase 3 contraction was characterized by a rebound intravesic al pressure and Phase 4 contraction was characterized by a rapid fall in in travesical pressure. In the acute partial bladder outlet obstruction state, Phase 1 contraction rose and high-frequency oscillations fell in Phase 2. This voiding dysfunction is ascribed to the bursting extraurethral sphincte r activity being converted to tonic extraurethral sphincter activity. In summary, the suppressed high-frequency oscillations in Phase 2 of the de trusor muscle contraction could be detrimental to efficient voidings in the acute partial bladder outlet obstructed rat. (C) 2000 IBRO. Published by E lsevier Science Ltd.