Optimization of the Duration and Dose of Photobiomodulation Therapy (660 nm Laser) for Spinal Cord Injury in Rats

<b><i>Objective:</i></b> Spinal cord injury (SCI) causes motor deficits, urinary incontinence, and neuropathic pain. This study was designed to optimize a photobiomodulation therapy (PBMT) protocol using a continuous wave (CW) 660 nm laser in rats with SCI. Specifically, the number of days of irradiation and the daily dose of PBMT were investigated. <b><i>Methods:</i></b> The study was performed in two steps. In the first step, a comparison between the effects of PBMT (45 sec) daily for 2 and 4 weeks on pain and movement [Basso, Beattie, and Brenham (BBB) score] was made. In the second step, a comparison between different durations of irradiation (27, 45, 90, and 117 sec) was performed. PBMT used a 100 mW laser delivered to 9 points on and around the lesion site. Oxidative stress, fibroblast invasion, and time to achieve spontaneous urination were also assessed. <b><i>Results:</i></b> The improvement in movement and pain stopped with discontinuation of radiation at week 2 and fibroblast invasion resumed. No improvement was seen in movement and pain in the group receiving PBMT for 27 sec compared with the groups receiving higher doses of laser radiation. Animals receiving 117 sec of photobiomodulation showed a higher BBB score even in the first 3 days. <b><i>Conclusions:</i></b> The number of days is an important factor for improving mobility; however, the daily dose of radiation is more important for pain relief.