Noradrenergic and peptidergic nerves in the synovial membrane of the Sprague-Dawley rat

This immunohistochemical study of nerves in the synovial tissue of Sprague-Dawley rats demonstrated the occurrence of 4 neuropeptides and 2 enzymes that are involved in the synthesis of catecholamines. Substance P and calcitonin gene-related peptide were colocalized in fibers that terminated as varicosal endings in the synoviocyte layer. Similarly, tyrosine hydroxylase and dopamine beta-hydroxylase, which reflect the presence of noradrenaline, were colocalized with neuropeptide Y. These fibers were predominantly found adjacent to and within blood vessel walls. Immunoreactivity to vasoactive intestinal polypeptide was seen in varicose nerve terminals in the synoviocyte layer. Many were localized in vessel walls. There is accumulating evidence of an involvement of substance P and noradrenaline in the pathogenesis of inflammatory joint disease and nociception. The role of these colocalized neuropeptides, namely, calcitonin gene-related peptide and neuropeptide Y, in the pathophysiology of such conditions warrants further analysis.