Rheumatoid pain models in rodents and the application of dynamic weight-bearing test

Rheumatoid arthritis (RA) is an autoimmune systemic disease of unknown etiology, characterized by chronic inflammation and synovial infiltration of immune cells. Pain is one of the most dominant symptoms for patients with RA, which affects the health and quality of life. Animal models are helpful to study the pathogenesis of RA and related factors and mechanisms of RA-induced pain, which may aid in the development of new and better treatment strategies. Several animal models of RA have been validated to predict for efficacy in humans that include collagen type II-induced arthritis in rats and mice, adjuvant-induced arthritis in rats, and antigen induced arthritis in several species. However, the quantitative evaluation of pain in animal models is technically challenging. Until recent years, behavior methods are used to characterize acute and chronic pain stages by observing behavioral changes in preclinical arthritis models. Significant progress has been made in pain assessment with the development of nonreflexive tools, dynamic weight-bearing (DWB) apparatus was developed for the measurement of pain in rodents by capturing weight-bearing and surface distribution of the paws. In this article, we summarize several classical animal models of rheumatoid pain as well as discussion of the advantages and disadvantages of DWB test for spontaneous pain used in these models.