Antinociceptive effects of color polarized light in animal with formalin test

Our recent results show the efficacy of pain suppression by exposure of antinociceptive acupuncture points (APs) to white polarized (P) light. But it is known that white light contains electromagnetic waves of different length (colors) and, possibly, not all of them produce a similar effect. There are no comparative data about analgesic affects of the different colors of P light now. The purpose of this study was to clear up a question if analgesic effects of low-intensive P light depend on the color of light/wavelength. Formalin-induced pain behavior (licking of the painful area) was tested in control mice and mice exposed to one of the color of P light (red, orange, yellow, green, blue, violet) on the painful area or AP E-36. Exposure of the painful area or AP E-36 to color P light evoked a statistically significant decrease of the licking time in mice to 31.5-64.1% and 36.1-54.4% respectively. The red light was the most effective for pain behavior depression, analgesia averaged 64.1% and 54.4% accordingly. The analgesic effects of red light in compare to three "cold" colors (blue, green, and violet) and white light was more pronounced in case of its application on the painful area than on AP E-36. In conclusion, the intensity of analgesic effects of P lights strongly depends on its color (wavelength).