Nerve fibers in the urethral mucosa of canine penis are immunoreactive for both substance P and calcitonin gene-related peptide.

The urethral mucosa in the canine penis was immunostained by use of antibodies against substance P and calcitonin gene-related peptide. Numerous nerve fibers immunoreactive for both peptides were found to invade the epithelium from the tunica propria; here they ran various courses with occasional branchings and conspicuous varicosities. Some looped to return into the tunica propria, while others ended on the epithelial surface. These findings confirm and extend our knowledge on the sensory innervation of the urethra which has previously been based on silver impregnation techniques.