Demonstration of sensory cutaneous nerve fibers in guinea-pig lip using endogenous oxidase histochemistry.

We developed a new histochemical method based on endogenous oxidase activity for the detection of cutaneous nerves in guinea-pig lips. After the application of a reaction mixture containing 0.14 mM 3,3'-diaminobenzidine(DAB) and 15 mM nickel ammonium sulfate in Tris-HCl buffer (pH 7.6), many blue-black sensory fibers were observed, i.e., dermal nerve fiber bundles, perifollicular plexuses, Merkel-cell endings, and Meissner-like nerve endings. The autonomic fibers of the skin were not stained. Electron microscopy revealed that the reaction product was mainly localized on mitochondrial cristae. The addition of 0.01 M sodium azide completely inhibited the reaction. This technique is simple and preferentially stains sensory nerves.