No abstract

Arthritis was induced in 9-week-old female Dark Agouti rats by injecting type II collagen. Serum levels of the derivatives of reactive oxygen metabolites (dROMs), which are oxidative stress markers, and C-reactive protein (CRP) in arthritic rats that were exposed to a pressure of 1.25 atmospheres absolute and an oxygen concentration of 36% for 3 weeks (arthritis + HBO group) were compared to those of control rats (control group) and arthritic rats that were not exposed to hyperbaric oxygen (arthritis group). The body weights of the arthritis and arthritis + HBO groups were lower than that of the control group, whereas no difference in the body weight was observed between the arthritis and arthritis + HBO groups. The serum levels of dROMs and CRP in the arthritis group were higher than those in the control and arthritis + HBO groups. No difference in the serum level of CRP was observed between the control and arthritis + HBO groups. These results indicate that the conditions of hyperbaric oxygen exposure used in this study are effective for reducing the levels of reactive oxygen species, which are overproduced during arthritis.

The effects of hyperbaric exposure with high oxygen concentration on the physical activity of developing male rats were investigated. Five-week-old male rats were exposed to an atmospheric pressure of 1.25 with an oxygen concentration of 36.0% for 12 h (7.00–19.00 h) and exercised voluntarily for 12 h (19.00–7.00 h) daily for 8 weeks. The voluntary running activities were compared with those in age-matched rats without hyperbaric exposure. In addition, the properties of the soleus and plantaris muscle fibers and their spinal motoneurons were examined. The voluntary running activities of rats with or without hyperbaric exposure increased during development. However, the mean voluntary running activities were higher in rats with hyperbaric exposure (7,104 m/day) than in those without hyperbaric exposure (4,932 m/day). The oxidative capacities of the soleus and plantaris muscle fibers and their spinal motoneurons increased following hyperbaric exposure. It is suggested that adaptations of neuromuscular units to hyperbaric exposure with high oxygen concentration enhance the metabolism, and thus, the function of neuromuscular units is promoted.

Femur bone densities and tibialis anterior muscle properties of type II collagen-induced arthritic mice were determined. Furthermore, voluntary running activities of arthritic mice were compared with those of controls. Arthritis was induced by an intradermal injection of type II collagen in the adjuvant. Body and muscle weights were lower in arthritic mice than in controls. Cortical and trabecular bone densities and muscle fiber crosssectional areas were decreased by arthritis. After classifying the arthritic severity into slight, intermediate, and severe levels based on the degree of knuckle swelling, cortical and trabecular bone densities, fiber cross-sectional areas, and fiber succinate dehydrogenase activities were lowest when arthritis was most severe. Furthermore, arthritic mice, especially those with intermediate and severe levels, showed lower voluntary running activities. These findings indicate that lower bone density and muscle atrophy of type II collagen-induced arthritic mice are related to arthritic severity and decreased motor activity.Key words : bone density, cross-sectional area, motor activity, mouse, muscle fiber, succinate dehydrogenase activity, type II collagen-induced arthritis.Degeneration in the musculoskeletal system, including muscle atrophy and bone osteoporosis, is widely accepted as being induced by aging [1][2][3][4][5], hind-limb suspension [6][7][8], or exposure to microgravity [9][10][11][12]. These changes are considered to result from decreased motor activity.Previous studies observed that animal models [13-16] and patients [17] with arthritis showed decreased spontaneous motor activities because of severe chronic pain in the joints. Type II collagen-induced arthritis is a model of polyarthritis induced in susceptible rodents by immunization with type II collagen [18,19]. Muscle atrophy and decreased bone density occur in type II collageninduced arthritic rodents because these animals may have lower motor activities as a result of their distal joint pain. Therefore this study investigated cortical and trabecular bone densities of the femur and fiber cross-sectional areas and succinate dehydrogenase (SDH) activities of the tibialis anterior muscle in type II collagen-induced arthritic mice. Furthermore, voluntary running activities of arthritic mice were compared with those of controls. METHODSAll experimental procedures and animal care were conducted in accordance with the Guide for the Care and Use of Laboratory Animals prepared by the Physiological Society of Japan. This study was also approved by the Institutional Animal Care and Use Committee of Kyoto University.Antigens and immunizations. Sixty-day-old DBA/1J male mice were randomly divided into control ( n = 5) and arthritic ( n = 13) groups. All mice were individually housed in cages of the same size. The mice in the arthritic group were immunized from 60 to 81 days after birth. Type II collagen was solubilized from fetal bovine articular cartilage by limited proteolysis with pepsin [20]. Type II collagen was...