A procedure for studying the organization of peripheral nerves with horseradish peroxidase demonstrated on the facial and hypoglossal nerves in the rat.

The intraaxonal transport of horseradish peroxidase, applied to the proximal stump of different transected hypoglossal and facial nerve branches, was used to label fibers in the hypoglossal main trunk and in the intratemporal portion of the facial nerve in the rat. By using tetramethylbenzidine as a substrate, numerous heavily labeled fibers are obtained. In longitudinal sections the arrangement of fibers can be studied for long distances. From these sections, sites of specific interest can be further examined in transverse-like reconstructions of the nerve. Thus, the procedure described offers a convenient way of analyzing the intrinsic organization of peripheral nerves.