INNERVATION OF NONMYSTACIAL VIBRISSAE IN THE ADULT-RAT

Vibrissal follicle-sinus complexes (F-SCs) in the mystacial pad of rod ents are heavily innervated by different types of sensory nerve ending s. One site in mystacial F-SCs, the inner conical body (ICB), is uniqu ely well innervated only in those species, such as the rat, that rhyth mically whisk their mystacial vibrissae. In this study, we examined th e innervation of rat nonmystacial F-SCs, which are not whisked. Suprao rbital, posteroorbital, lateral cervical, median cervical, submental, and carpal forelimb F-SCs were cut on a cryostat and were either prepa red for anti-human protein gene product (PGP 9.5) immunofluorescence o r stained using the Winkelmann silver technique. Much of the innervati on of the nonmystacial F-SCs is similar to that of mystacial F-SCs. Ah are innervated by a large deep vibrissal nerve (DVN) and several smal ler superficial vibrissal nerves (SVNs). As in the mystacial pad, the SVNs show a distribution of Merkel and free nerve endings qualitativel y similar to the rete ridge collar of all the nonmystacial F-SCs as we ll as provide circumferentially oriented endings to the ICBs to all bu t median-cervical and carpal F-SCs. Not only was the ICB innervation r elatively sparse in median-cervical and carpal F-SCs, but a large port ion of the carpal ICB innervation also ascended from the DVNs, which m ake only a small ICB contribution in other locations. Similar to mysta cial pad F-SCs, the DVNs provided Merkel and lanceolate endings to the level of the ring sinus as well as reticular and irregular lanceolate -like endings to the level of the cavernous sinus. However, all but th e posteroorbital F-SCs have relatively few lanceolate endings. Carpal F-SCs also have relatively few ring-sinus Merkel endings, which are di ffusely distributed, are limited to the superficial portion of the out er root sheath. They also lack reticular and irregular lanceolate-like endings in the cavernous sinus. However, carpal F-SCs have a unique s et of corpuscular endings in the ICB, ring sinus, and cavernous sinus that are rarely seen in other F-SCs. PGP 9.5 immunofluorescence also r evealed two sets of fine-caliber profiles at the level of the ICB and ring sinus that were not previously seen in mystacial F-SCs. Although there was no correlation between ICB innervation and whisking, the reg ional variations in F-SC innervation suggest that functional differenc es may exist between vibrissae at different locations in the body. (C) 1995 Wiley-Liss, Inc.