The neurogenic contribution to synovial leucocyte infiltration and other outcome measures in a guinea pig model of arthritis.

A neurogenic contribution to joint inflammation has been demonstrated in rat adjuvant arthritis, however as inflammatory mechanisms vary between species it is unclear whether these observations can be applied more generally. The aim of this study was to assess the neurogenic contribution to cellular infiltration and other outcome measures in a guinea pig model of arthritis. Compared to arthritic controls, animals pre-treated with capsaicin at doses sufficient to reduce sensory activity exhibited a significant attenuation of both mechanical and thermal hyperalgesia. Measures of inflammation, including swelling and radiological scores were also improved. Furthermore, capsaicin selectively reduced synovial T cell infiltration whereas no difference was seen with respect to synovial macrophages. These observations confirm a neurogenic component in guinea pig arthritis and indicate a selective sensory influence on T cell activity within the chronically inflamed joint. As T cells are strongly implicated in the pathogenesis of rheumatic disease, such an influence may serve to explain some of the clinical features observed in these disorders.