Effect of photobiomodulation on connective tissue remodeling and regeneration of skeletal muscle in elderly rats.

The purpose of this study was to evaluate the effects of low-level laser therapy (LLLT) on morphological aspects, IL-6 and IL-1β expressions, as well as the distribution and organization of collagen in the tibialis anterior (TA) muscle of elderly rats submitted to cryoinjury. Histological photomicrographs were taken of TA muscles stained with HE and picrosirius red. Immunohistochemistry was used for the evaluation of IL-6 and IL-1β. Male Wistar rats, aged 20 months, were distributed into three groups: (1) control animals not injured or treated with LLLT (n = 5), (2) cryoinjury without LLLT treatment (n = 15), and (3) cryoinjury treated with infrared LLLT (n = 15). LLLT was applied to the TA 2 h after of the injury induction and consisted of daily applications until the sacrifice (1, 3, and 7 days). The following parameters were used: λ = 780 nm, power density 1 W/cm2, output power 40 mW, 10 s per point, 8 points, and 3.2 J of total energy. In the histomorphological analysis, the treated group exhibited a significant decrease in inflammatory infiltrate (p < 0.001) as well as an increase immature fibers and new blood vessels at 7 days compared to the untreated group (p < 0.05). Furthermore, treatment induced a better collagen distribution and organization at 7 days in comparison to the untreated group (p < 0.05). In conclusion, LLLT demonstrated a modulatory effect on the muscle repair process in elderly animals with regard to the collagen remodeling and morphological aspects of muscle tissue.