Systemic vascular photobiomodulation accelerates the recovery of motor activity in rats following spinal cord injury

Abstract Objectives Spinal cord injury (SCI) causes the discontinuity of the spinal canal, leading to functional and sensorial losses in areas below the injury, which are often irreversible. Photobiomodulation (PBM) can enhance the neuromuscular repair process, especially in cases of peripheral nerve injuries. However, there is little knowledge regarding the effects of this therapeutic modality on recovery following a SCI, especially the noninvasive systemic form denominated vascular PBM (VPBM). To analyze the effects of VPBM in the immediate, acute and intermediate phases following a compression‐induced SCI on morphological aspects of neuromuscular tissue repair, functional recovery and the protein expression of brain‐derived neurotrophic factor (BDNF). Methods Wistar rats were divided into five groups: control, SCI, SCI + VPBM‐Im (immediate administration of VPBM), SCI + VPBM‐2h (VPBM administered 2 h after injury) and SCI + VPBM‐14d (VPBM administered 14 days after injury). VPBM was administered in the region of the caudal vein/artery with low‐level laser (AsGaAl, 780 nm, 80 J/cm², 40 mW for 80 s, totaling an energy of 3.2 J over a single point) for 14 consecutive days. During the analysis periods (1, 3, 7, 14, 21, 28 and 35 days after injury), functioning was evaluated using the Basso‐Beattie‐Bresnahan (BBB) index. At the end of each experimental period, blood samples were collected for the determination of the concentration of circulating BDNF using ELISA. Muscle tissue and nerve tissue samples were also extracted for morphological and histological analyses using H&E staining. Results SCI + VPBM‐Im and SCI + VPBM‐2 h led to the recovery of motor function beginning on the 7th day after injury ( p < 0.05), an increase in the cross‐sectional area (CSA) of the muscle fibers in the second week ( p < 0.05) and an increase in muscle fiber diameter beginning on Day 14 ( p < 0.05). Early irradiation had a greater effect on the reduction in the size of the cavity, with stabilization of the cavity found on Day 7 ( p < 0.05). Considering the circulating BDNF levels, no changes was found during the experimental periods. Conclusion The present results showed that VPBM was capable of modulating morphological and functional recovery following SCI, especially when administered early. The positive effects on functional recovery were demonstrated by the BBB index; the reestablishment of the structure of the muscle and nerve tissue was demonstrated by the preservation of CSA and diameter of muscle fiber and reduction in the area of the injury (cavity size) respectively. Thus, noninvasive VPBM may be an important component of treatment for spinal cord injuries.