Fig. 1.

Representative recordings of simultaneous measurement of intravesical pressure (IVP) and external urethral sphincter (EUS)-electromyogram (EMG) activity in a spinal intact unanesthetized rat. Traces B, C, and D depict sections of trace A on expanded time scales. Traces B, C, and D are the expanded portion of traces A, B, and C, respectively, indicated by rectangular boxes. The EUS-EMG exhibits tonic activity before the onset of voiding and bursting activity during voiding (A, B, and C). The EUS bursting is characterized by clusters of high-frequency spikes (active periods: APs) separated by low tonic activity (silent periods: SPs) (C and D). The bursting produces rhythmic contractions and relaxations of the EUS and is thought to generate a urethral pumping action during voiding, which is seen as pressure oscillations on the continuous cystometry (CMG) tracing (D).