Green Light Therapy For Chronic Pain
Many Americans suffer from chronic pain, such as migraines, headaches, arthritis and fibromyalgia – pain that often lasts long after an injury or illness has resolved. Standard pharmacological treatments often don’t provide relief or have serious side effects. Thankfully, some researchers are exploring non-drug alternatives to combatting pain.
One of the newest treatments available is green light therapy (phototherapy), which involves exposure to low-intensity green light that enters the body through the eye. Studies have demonstrated its beneficial effects on various disorders and could potentially serve as an effective means for managing pain for those who have difficulty using pharmacological treatments.
Researchers believe the pain-relieving properties of green light arise from the brain sending a molecule called PENK to neurons in the dorsal raphe nucleus (DRN) located in the brainstem. Eventually, these neurons activate our body’s own opioid system for natural pain relief.
But scientists were still uncertain as to how this occurred. To gain a better insight, they removed specific cells from mice that receive visual input through their eyes: rods and cones in the outer retina, as well as melanopsin-expressing intrinsically photosensitive retinal ganglion cell (ipRGC) receptors in the inner retina.
The researchers’ results demonstrated that when rods were removed, the pain-relieving effect diminished. However, even after both rods and cones had been taken out, mice still experienced some benefit from exposure to green light. Further investigation revealed that ipRGCs played a major role in these cells’ ability to reduce pain signals when exposed to green lighting.
After researchers eliminated ipRGCs from mice models, the pain-relieving effects of green light disappeared. This led them to hypothesize that this process started with rod and cone photoreceptors in the retina.
In a subsequent study, the researchers confirmed that green light-induced pain relief was due to rods and cones in the retina, but also noted an additional factor: dorsal raphe nucleus.
Early this year, a Duke team published research suggesting that green LED exposure can reduce pain levels in rats. After four days of exposure to green LEDs, researchers measured changes in pain levels.
Researchers then examined the effects of green light on three brain areas: rostral ventromedial medulla, lateral hypothalamus and dorsal raphe nucleus. They discovered that inactivating the rostral ventromedial medulla prevented antinociception, suggesting descending inhibition is responsible for some of these effects caused by green LEDs.
Furthermore, the study demonstrated that enkephalins, naturally produced by spinal cord neurons and involved in pain control, were activated when exposed to green LEDs. When naloxone, which reverses these effects when given to rats, reversed antinociception as well. These results suggest that green LEDs may improve pain perception by interacting with opioid neurons within the brain.