Arthritis induced in cat by sodium urate: a possible animal model for tonic pain

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Abstract
An attempt was made to determine whether cats rendered arthritic by the injection of monosodium urate (MSU) crystals (rod-shaped 40-130 .mu.m length) into 1 knee joint capsule can be used as an animal model for tonic (chronic) pain. A limp and a decrease in body weight supported by the injected hind leg''s paw occurred .apprx. 1 h after the MSU (20 mg) injection, reached a maximum at 2-3 h, and lasted for > 6 h before a gradual return to pre-injection levels. There were diminished by systemic administration and local (the dorsal part of the nucleus raphe dorsalis) application of morphine, this effect being blocked by naloxone. The limping and the paw pressure decrease are the reflexion of pain. The animal model of the MSU-induced arthritis is useful for the study of tonic pain.