Lumbar vertebrae from nonarthritic control and vehicle-treated adjuvant-induced arthritis and collagen-induced arthritis rats. Representative photomicrographs of lumbar vertebrae from nonarthritic control and vehicle (Veh) (PBS)-treated adjuvant-induced arthritis (AIA) and collagen-induced arthritis (CIA) rats. The trabeculae beneath the physeal plate (pale vertical column at the left margin) were attenuated in arthritic animals but the bone marrow composition and density - including the population of subphyseal osteoclasts (brown cells, cathepsin K-positive) - were equivalent among nonarthritic and arthritic animals. Stain: immunohistochemistry for cathepsin K with H & E counterstain. Magnification: ×100.