Nerves in inflammatory synovium: immunohistochemical observations on the adjuvant arthritis rat model

Previous evidence has been presented that neurogenic input may influence adjuvant induced arthritis (AA) in rats. We now present evidence of alterations in synovial nerves in AA. Nerves were studied in well perfused and fixed rats, using immunohistochemistry with the sensitive avidin-biotin peroxidase complex (ABC) method and heterologous antisera to cytoskeletal protein gene product 9.5 (PGP) and the neuropeptides substance P and calcitonin gene related peptide (CGRP). The innervation of synovium was compared in normal rats and rats with AA. Observations concordant with what has been reported for neuropeptide nerves in the synovium of patients with rheumatoid arthritis (RA) are presented. It has been suggested that neural peptide substances are reduced in nerves of synovium from patients with RA. In the AA rat a specific reduction of lining zone and sublining nerves in the synovium was noted. The AA rat model is very suitable for studying the involvement of synovial nerves in arthritis, permitting optimal preservation of immunoreactive neural epitopes.