Stimulation of three areas of the primary motor cortex interrupts micturition in dogs

To clarify the area of the motor cortex (M1) in dogs, which corresponds to the cortical area participating in voluntary interruption of micturition in humans, the cortical portions related to the external urethral sphincter were first clarified by recording of somato-sensory evoked potentials, and then systematic cortical stimulation was performed in anesthetized and paralyzed dogs. The hypogastric, pelvic and pudendal nerves innervating the lower urinary tract and rectum were severed to eliminate the secondary reflexes. Five foci were recognized in the cortical potentials evoked after stimulation of the pudendal nerve. These foci existed in the sacral (Sacral-S) and hind leg (Leg-S) areas of the somato-sensory cortex (S1), and in the sacral (Sacral-M), hind leg (Leg-M) and trunk (Abd-M) areas of the M1. Stimulation of the three M1 foci, but not the two S1 foci, provoked centrifugal firings of the pudendal urethral branch. The firings disappeared after cutting of the ipsilateral bulbar pyramis. When the M1 foci were stimulated during the micturition reflex, the reflex discharge of a pelvic vesical branch was interrupted concomitantly with firings of the urethral branch. The interruption was still induced after the pyramidotomy. Pulse train stimulation of these M1 foci reset the cycles (about 2 Hz) in the alternative rhythmic firings of the urethral and vesical branches, which are known to be formed in the pontine micturition center [31,32]. These results suggest that the pyramidal cells in the three M1 foci inhibit the pontine micturition center and concomitantly contract the external urethral sphincter through the pyramidal tract. The possible roles of these M1 foci were discussed.