|Budget Amount *help
¥1,900,000 (Direct Cost : ¥1,900,000)
Fiscal Year 1995 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1994 : ¥1,400,000 (Direct Cost : ¥1,400,000)
The bladder shows a large micturition contraction-relaxation rhythm under volume clamp. The present study examined the neural mechanisms determining the upper limit of the pressure or triggering the relaxation, by clamping an intravesical pressure of chloralose anesthetized cats. 1.The bladder kept fairly constant volume at low pressure-clamp, or gradually expanded at higher pressure-clamp. The efferent nerve of the pelvic bladder branch kept firing vigorously even while the bladder expanded gradually. Expansion of the bladder appeared to be related, at least partly, to the structure of smooth muscle fibers. 2.Inflow-outflow rhythm of the bladder with a high frequency (up to 30/min) was observed even after dissecting all bladder nerves. The efferent activities of the pelvic showed a rhythmic firing at lower pressure stimulation. At higher pressure stimulation, however, the efferent nerve showed no distinguishable rhythmic activities. It appeared that the inflow-outflow rhythm is originally generated myogenically and/or by the peripheral circuit between the bladder and the postganglionic neurones, and that there is no central mechanism generating this flow rhythm. 3.Inflow to the bladder increased as the clamped pressure was raised up to 1000 mmH_2O.The firing frequency of the efferent nerve also increased dependent on the clamped pressure, but it reached a plateau above a certain pressure (P-plateau). The value of P-plateau almost equaled the maximal pressure of micturition contraction, suggesting that the upper bound of micturition contraction is determined by the saturating level of the micturition center. 4.Dramatic decrease of the efferent activity concurrent with intermittent large inflows were observed at low pressure as well as high pressure-clamp, suggesting the existence of an inhibitory neural mechanism in the central nervous system. This appeared to be closely related to the relaxation mechanism occurring after micturition contraction.