COEXISTENCE OF ENKEPHALIN-LIKE AND TYROSINE HYDROXYLASE-LIKE IMMUNOREACTIVITIES IN NERVE-FIBERS OF THE TEMPOROMANDIBULAR-JOINT CAPSULE OF THE GUINEA-PIG

Background: The innervation of joints has been suggested to play an im portant role for their normal function as well as for the pathogenesis of chronic arthritic conditions. It is therefore important to elucida te the functional anatomy of this innervation. Methods. The expression of methionine enkephalin-like immunoreactivity (ENK-LI) and tyrosine hydroxylase (TH)-LI as well as their possible colocalization were exam ined in the temporomandibular joint of the guinea pig. Results: Nerve fibers with ENK-LI were demonstrated in the synovium of the guinea pig temporomandibular joint capsule with the use of indirect immunofluore scence. The ENK+ fibers were found close to the surface of the synovia l membrane, deeper in the synovium, and at the walls of blood vessels. Coexistence of ENK- and TH-LI was observed frequently in the synovial nerve fibers. After removal of the superior cervical ganglion (SCG), the ENK-containing nerve fibers were reduced substantially in number o n the operated side or were completely absent if the cervical sympathe tic trunk was also excised. Conclusions: The findings indicate that th e majority of fibers with ENK-LI derive from the SCG. ENK may act as a neuromodulator on the catecholaminergic nerves and may also have an a nalgesic effect in the joint. (C) 1998 Wiley-Liss, Inc.