Sex differences in sensory and motor branches of the pudendal nerve of the rat.

The morphology of the pudendal nerve was quantified in adult male and female rats. The sensory branch of the pudendal nerve was about three times as large in cross section in males as in females, and the motor branch was about five times as large. Electron microscopy was used to determine the ultrastructural bases of these gross size differences. Differences that were found included greater packing density of both myelinated and unmyelinated axons in females, larger myelinated and unmyelinated axons in males, larger myelin sheaths of sensory axons in males, more numerous myelinated axons in both branches of males, and more numerous unmyelinated axons in the sensory branch of males. There was also some indication that myelinated sensory axons were more likely to branch in the dorsal clitoral nerve of females than in the homologous nerve of males. Morphological differences in the structure of pudendal axons, their associated Schwann cells, and the extracellular matrix as well as differences in sensory and motor axonal number all have potential implications for the sexual differentiation of the central nervous system and behavior.