A discrete adjuvant-induced monoarthritis in the rat: effects of adjuvant dose.

Much evidence suggests an important role for the nervous system in the pathogenesis of peripheral inflammatory conditions such as arthritis. The classical adjuvant-induced arthritis model in the rat is a severe condition in which polyarthritis is accompanied by widespread systemic disease, complicating the interpretation of data. We have developed an adjuvant-induced arthritis of the tibio-tarsal joint in the rat, using a low dose of Freund's adjuvant administered locally. Initial inflammation is followed, after 14 days, by chronic monoarthritis which is maintained without generalised effects or loss of use of the limb until at least 30 days postinjection. A higher dose of adjuvant produces contralateral inflammation and arthritis, but only after 14 days, and without the complicating effects seen in classical adjuvant disease. Indirect measures of arthritis (joint circumference, inflammation score and nociceptive threshold) correlate closely with the histological state of the joint, supporting the use of these indices. This model can be easily exploited by alteration of adjuvant dose, to determine the roles of the nervous system in the pathogenesis, maintenance and symmetrical spread of inflammatory arthritis.