Somatic innervation of the feline lower urinary tract

Electrical stimulation of pudendal nerve sensory pathways can evoke excitatory bladder reflexes. However, the precise peripheral innervation pattern of these somatic fibers remains unclear. In adult male cats, we investigated pudendal nerve innervation of the lower urinary tract (LUT) by employing anatomical (Sihler's stain) and electrophysiological (selective electrical nerve stimulation) techniques. The stained specimens revealed differential innervation of the proximal and distal urethrae by fibers derived from the sensory branch of the pudendal nerve. Cranial sensory branch fibers penetrated the prostate to terminate along the intraluminal surface of the urethra, whereas the dorsal nerve of the penis primarily innervated the glans penis. Further examination of the proximal urethra showed a separate pathway (deep perineal nerve) that inserted directly into the external urethral sphincter. These observations were confirmed electrophysiologically by the measured urethral sphincter activity evoked in response to selective nerve stimulation. Electrical activation of the sensory pathway evoked only reflex (latency=8.9+/-1.1 ms) contractions of the urethral muscle, whereas stimulation of the perineal pathway elicited direct (latency=1.3+/-0.1 ms) responses. Our findings identify specific pudendal nerve sensory pathways that can be used potentially to restore bladder function in persons with spinal cord injury and also treat LUT symptoms such as urinary retention.