Distribution of neuropeptide-containing nerve fibers in the synovium and adjacent bone of the rat knee joint

Abstract

Objective: The innervation of normal rat synovium and adjacent bone, especially the communicatory nerve fibers between them, were investigated.

Methods: Nerve fibers were visualized using immunohistochemistry. Antisera to substance P(SP) and antisera to calcitonin gene-related peptide (CGRP) were employed to identify sensory nerves, while antisera to neuropeptide Y (NPY) were used to identify sympathetic nerves.

Results: In the synovium, SP-positive nerve fibers were found in the lining cell layer, with some fibers branching toward the joint space. In the sublining layer of the synovium, SP-positive and CGRP-positive fibers were observed mainly near the blood vessels. NPY-positive fibers were predominantly seen as a network around the blood vessels in the sublining layer. A large number of SP-positive and CGRP-positive fibers were seen near the attachment of the meniscus to the synovium. Toluidine blue positive mast cells were detected in close proximity to all three types of fibers, especially near the blood vessels. In bones forming the knee joint, nerve fibers immunoreactive to SP, CGRP and NPY were present in the bone marrow and some of these fibers communicated with the synovium through the synovium-bone junction located in the bare area.

Conclusion: The role of nerves, especially the role of the communicatory nerves between the synovium and the bone marrow, should be considered in the pathophysiolosy of erosive arthritis.