Membrane potential changes in sphincter motoneurons during micturition in the decerebrate cat.

Intracellular recordings from external urethral sphincter (EUS) and external anal sphincter (EAS) motoneurons were obtained during micturition in the decerebrate cat. The neural circuitry mediating micturition was activated by distension of the bladder or by electrical stimulation of the pontine micturition center (PMC). During micturition, the membrane potential of EUS motoneurons hyperpolarized 3-9 mV, during which time the motoneuron somatic membrane conductance increased. The membrane hyperpolarization could be reversed with passive diffusion or active ejection of chloride from the intracellular microelectrode into the motoneuron. In contrast, the membrane potential of EAS motoneurons either depolarized slightly or showed no change during micturition. We have shown that the neural circuitry mediating micturition can influence the EUS and EAS independently. In addition, stimulation of the PMC provides a valuable tool for identifying spinal neurons mediating the postsynaptic inhibition of EUS motoneurons during micturition.