810 NM Light Treatment of Acute Spinal Cord Injury Alters the Immune Response and Improves Axonal Regeneration and Functional Recovery

摘要

Spinal cord injury (SCI) results in substantial and often permanent impairment of function due to the lack of regeneration of damaged axons. Despite vigorous research, no cure for SCI has been found. Light therapy (LT), through the absorption of light by target tissue, improves healing in a number of injury models. However, no study to date has assessed the ability of LT to facilitate the regeneration of specific spinal cord tracts. Our hypothesis was that transcutaneous application of 810 nm light promotes axonal regeneration and functional reinnervation following transection of the corticospinal tract (CST) by changing the extracellular milieu of the spinal cord. Three studies were implemented to investigate this hypothesis. First, anterograde and retrograde tract tracing techniques were used to investigate axonal regrowth after SCI and LT. LT (810 nm) was applied at the site of acute injury to the CST of adult rats. Anterograde tract tracing demonstrated that LT improved axonal regrowth after injury, with significant increases in axon number (199 +/- 12) and distance of regrowth (8.7 +/- 0.8 mm) as compared to controls (p<0.01). Double label retrograde tract tracing revealed that transected axons regrew and reinnervated motor neurons in the lumbar spinal cord in the light treated group only (p<0.05). Functional analyses revealed that this regeneration was coupled with significant improvement in 2 tests of CST performance, angle of rotation and ladder beam cross time (p<0.05). Second, to explore the effect of LT on the spinal cord cellular environment, we investigated the inflammatory response after SCI, using quantitative immunohistochemistry techniques.