Reduced locomotor activity correlates with increased severity of arthritis in a mouse model of antibody-induced arthritis.

INTRODUCTION Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by synovial hyperplasia and progressive cartilage and bone destruction that leads to a substantial loss of general functions and/or a decline in physical activities such as walking speed in humans. The K/BxN serum transfer arthritis in mice shares many immunological and pathological features with human RA. Very few studies are available in mice that investigate the changes in physical activity in relation to arthritis development. In this study we investigate the effect of arthritis on the locomotor activity of mice during K/BxN sera transfer arthritis. METHODS Arthritis was induced in Balb/c mice by injecting intraperitoneally with 200ul of K/BxN sera; Balb/c mice injected with phosphate buffered saline (PBS) served as control. Progress of arthritis was estimated by daily measurements of joint thickness. Each mouse's locomotor activity (travel distance and travel time) was assessed every day for duration of 20 minute period using the SmartCage™ platform. Data were analyzed using the SmartCage™ analysis software (CageScore™). RESULTS Arthritic Balb/c mice showed a reduction in distance covered and travel speed when compared to arthritis-free, control Balb/c mice. Maximum decline in locomotor activity was observed during the peak period of the disease and correlated to the increase in joint thickness in the arthritic mice. CONCLUSION This report demonstrates that measuring locomotor activity of mice during progression of K/BxN sera-induced arthritis using the SmartCage™ platform offers a quantitative method to assess physical activity in mice during arthritis.