Exposure to green LED could provide an inexpensive, non-pharmacological approach to managing chronic pain, by altering the levels of endogenous substances that potentially inhibit pain and decrease inflammation of the nervous system. In a study at the University of Arizona, rats with experimental neuropathic pain that were bathed in 525-nm wavelength green LED showed more tolerance for thermal and tactile stimulus than rats that were not bathed in green LED. In the case of both groups, no side effects from the light therapy were observed, nor was motor or visual performance impaired. The beneficial effects of the therapy lasted for four days after the rats’ exposure to the green LED was terminated. No tolerance to the therapy was noted. To receive the green LED exposure, one group of rats was placed in clear plastic containers that were affixed with green LED strips, allowing them to be bathed in green light. Another group of rats was exposed to room light and fitted with contact lenses that allowed the green spectrum wavelength to pass through. Both groups benefited from the green LED exposure (suggesting that the visual system may play a role in antinociception). Naloxone reversed the pain blocking, suggesting involvement of central opioid circuits. Rostral ventromedial medulla inactivation prevented expression of light-induced pain blocking, suggesting the engagement of descending inhibition. Green LED exposure also reversed thermal and mechanical hyperalgesia in rats with spinal nerve ligation. Pharmacological and proteomic profiling of dorsal root ganglion neurons from green LED-exposed rats identified changes in calcium channel activity. A third group of rats was fitted with opaque contact lenses, which blocked the green light from entering their visual system. Despite LED exposure, the opaque lenses prevented this group from benefiting from its exposure to the green LED. “While the pain-relieving qualities of green LED are clear, exactly how it works remains a puzzle,” said professor Rajesh Khanna. “Early studies show that green light is increasing the levels of circulating endogenous opioids, which may explain the pain-relieving effects. Whether this will be observed in humans is not yet known and needs further work.” The researchers are now conducting a clinical trial using green LED therapy in people with fibromyalgia. Such therapy could easily be used worldwide. “. . . While the results of the green LED are still preliminary, it holds significant promise to manage some types of chronic pain,” said professor Mohab Ibrahim. Professors Mohab Ibrahim and Rajesh Khanna discuss the experiment and results in this video. The research was published in the journal Pain (doi: 10.1097/j.pain.0000000000000767). UA researchers find promise in light therapy to treat pain. Courtesy of University of Arizona.