Low-level laser irradiation promotes the recovery of atrophied gastrocnemius skeletal muscle in rat

Running Title: Low-level laser irradiation in disuse muscle atrophyAbstract Low-level laser (LLL) irradiation promotes proliferation of muscle satellite cells, angiogenesis and expression of growth factors. Satellite cells, angiogenesis and growth factors play important roles in the regeneration of muscle. The objective of this study was to examine the effect of LLL irradiation on rat gastrocnemius muscle recovering from disuse muscle atrophy. Eight-week-old rats were subjected to hindlimb suspension for 2 weeks, after which they were released and recovered. During the recovery period, rats underwent daily LLL irradiation (Ga-Al-As; 830 nm; 60 mW; total, 180 sec) to the right gastrocnemius muscle through the skin. The untreated left gastrocnemius muscle served as the control. In conjunction with LLL irradiation, 5-bromo-2'-deoxyuridine (BrdU) was injected subcutaneously for labeling of nuclei of proliferating cells. After 2 weeks, myofiber diameters of irradiated muscle increased in comparison with those of untreated muscle, but did't recover back to normal levels. Additionally, in the superficial region of muscle, the number of capillaries and fibroblast growth factor levels in irradiated muscle exhibited meaningful elevation relative to those of untreated muscle. In the deep region of muscle, BrdU-positive nuclei of satellite cells and / or myofibers of irradiated muscle increased significantly relative to that of the untreated muscle. The results of this study suggested that LLL irradiation can promote recovery from disuse muscle atrophy in association with proliferation of satellite cells and angiogenesis.-3