Topography and ultrastructure of sensory nerve endings in the glans penis of the rat

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Abstract
The aim of the present study was to describe the types and location of sensory nerve endings in the glans penis of the rat on the basis of light and electron microscopy. Free nerve endings are abundant throughout the glans and are derived from either thinly myelinated Aδ or unmyelinated C fibers. The free nerve endings derived from Aδ fibers often extend into the epidermis as far as the granular layer and exhibit buttonlike terminal thickenings. The distal urethra contains many free nerve endings from C fibers. Numerous lamellated corpuscles are present. Each corpuscle, innervated by one or two medium diameter myelinated nerve fibers, consists of 4–10 spiralling and intertwined inner cores enveloped by Schwann cell lamellae. The corpuscles are usually enclosed by a perineural capsule, although some located near the epidermis lack a capsule. Lamellated corpuscles in the superficial dermis are located adjacent to but not directly under a penile spine and change their orientation when the glans is erect. The dermal papillae of the penile spines are devoid of any neural structure. Lamellated corpuscles are also located within the trabeculae of the corpus spongiosum glandis and in the lamina propria of the urethra. Occasionally, unmyelinated nerve bundles are seen inside these corpuscles. Ruffini corpuscles are few in number and are located in the deep connective tissue near the os penis. They have an incomplete connective tissue capsule and the nerve terminals are anchored between collagen fiber bundles. No Merkel nerve endings, Meissner, or Vater-Pacini corpuscles were found in any of the sections. We conclude that the glans penis of the rat contains a sensory receptor complement that is generally similar to the human glans penis but is unlike the glabrous and hairy skin.