Ipsilaterality of motor innervation of canine urethral sphincter

The functional activity of the sphincter muscle of the urethra is known to be controlled largely by the hypogastric and pudendal nerves. It remains unknown, however, whether innervation of the muscle by these peripheral nerves is ipsi- or bilateral. In an attempt to answer this question urethral closure pressure was determined simultaneously in the anterior, posterior, right and left portions of urethral wall in dogs. The pressure measurements were stereographed with the aid of a computer (stereo-UPP) and by this means the effect of unilateral section or electrical stimulation of hypogastric and pudendal nerves on the intraurethral pressure profile was analyzed. Unilateral section or electrical stimulation of the hypogastric nerve, distal to its division, produced a fall and a rise primarily in proximal intraurethral pressure, respectively, in all four directions. There was no significant difference in this response between the involved and uninvolved sides. Unilateral section of the pudendal nerve resulted in a fall primarily in distal intraurethral pressure in all four directions. No significant difference was present between the injured and noninjured sides. In contrast, electrical stimulation of the pudendal nerve distal to the point of its division caused a rise in intraurethral pressure in all four directions, with a significantly greater pressor response on the stimulated than on the nonstimulated side. These observations suggest decussating motor innervation of the urethra by the hypogastric nerves and also the possibility of the distal urethra being ipsilaterally innervated by the pudendal nerve.