Bladder and urethral pressures evoked by microstimulation of the sacral spinal cord in cats

Experiments were conducted to measure the bladder and urethral pressures evoked by intraspinal microstimulation of the sacral segments (S1-S2) in neurologically intact, chloralose anesthetized adult male cats. The bladder pressure was measured with a superpubic catheter and the urethral pressure was measured simultaneously at the level of the urethral sphincter and at the level of the penis using a two-element micromanometer. Intraspinal stimuli (typically 1 s, 20 Hz, 100 microA, 100 microseconds) were applied with activated iridium microwire electrodes in ipsilateral segments and intersegmental boundaries with a 250 micrometer mediolateral resolution and a 200 micrometer dorsoventral resolution. Increases in bladder pressures were generated by microstimulation in the intermediolateral region, in the lateral and ventrolateral ventral horn, and around the central canal. Simultaneous increases in urethral pressure were evoked by microstimulation in the ventrolateral ventral horn, but not at the other locations. Small reductions in urethral pressure (<10 cm H(2)O) were evoked at locations in the intermediate laminae and around the central canal. The magnitude of these pressure reductions was weakly dependent on the stimulus parameters. Stimulation around the central canal produced bladder contractions with either no change or a reduction in urethral pressure and voiding of small amounts of fluid. These results demonstrate that regions are present in the spinal intact anesthetized cat where microstimulation generates selective contraction of the bladder without increases in urethral pressure and that regions are present where microstimulation generates small reductions in urethral pressure.