Topography and distribution of sympathetic nerve fibers in the rat temporomandibular joint: immunocytochemistry and ultrastructure

The distribution and fine structure of nerve fibers containing neuropeptide Y (NPY), tyrosine hydroxylase (TH), and vasoactive intestinal polypeptide (VIP) in the temporomandibular joint were investigated by both the avidin-b iotin complex method and an indirect immunofluorescence technique. The inne rvation pattern of NPY- and TH-positive fibers differed from that of VIP-po sitive fibers. Specifically, the former was distributed in both the superfi cial and deep sublining layers, while the latter was mostly located in the deep sublining layer. NPY- and TH-immunoreactive fibers were largely confin ed to vascular elements; occasional fibers were observed in the synovial li ning layer close to the joint cavity. More nerves with NPY and TH immunorea ctivity were observed close to the upper joint compartment than near the lo wer compartment NPY and TH immunoreactivity was dramatically reduced in the TMJ of superior cervical ganglionectomized animals, indicating the sympath etic origin of these nerves. NPY immunoreactivity was found only in unmyeli nated axons, which were located in the adventitia and adventitia-medial bor der of arteries or arterioles. Occasionally, axons were near the joint cavi ty, in areas free of vascular structures. These observations show that abun dant sympathetic nerves supply the temporomandibular joint of the rat and p rovide a morphological basis for the involvement of differ ent neuropeptide s in vascular regulatory and modulatory functions in physiological and path ophysiological conditions.