Green light can reduce pain by affecting the brain

(ORDO NEWS) — Scientists have found that the color green triggers the release of a signaling molecule that activates opioid receptors in the brains of mice, leading to a significant reduction in pain.

While this study has yet to be tested in humans, the findings draw attention to previous studies showing that simply looking at the color green is enough to alleviate discomfort.

Recent studies have shown that green evokes positive emotions and reduces pain in people suffering from chronic migraine and fibromyalgia.

However, scientists still have not been able to explain how the contemplation of green light produces such a calming effect.

The authors of the study experimented with mice that were used to study the course of arthritis. Initial tests showed that exposure to green light reduced “pain responses,” indicating that the color did indeed help the rodents feel more at ease.

To find out which photoreceptors in the animal retina are responsible for this effect, the researchers first destroyed the receptor cells in mouse cones that capture colored light and found that this completely blocked the pain-relieving power of green light.

However, removing the rod receptors, which respond to black and white, only partially eliminated this analgesic effect.

Blocking a third type of receptor, called light-sensitive retinal ganglion cells (ipRGCs), did not reduce the effect of green light, leading scientists to conclude that the calming effects of green light are primarily mediated by cones.

The authors of the study then tried to identify the neural pathways that convert the signals sent by the cones to relieve pain.

Imaging experiments have shown that once green light has been detected by these cones, a stream of information is relayed to the ventral lateral geniculate nucleus (vLGN), which is located in a key brain structure called the thalamus.

The neurons in the vLGN then communicate with the spinal cord nucleus (DRN), which plays a central role in pain control.

Digging a little deeper, the researchers found that the interaction between vLGN and DRN was mediated by the PENK signaling protein.

Importantly, PENK is later converted to ENK, which binds to opioid receptors in the DRN.

So the researchers repeated their experiments in mice that did not have the ability to make these proteins, and found that green light provided absolutely no pain relief for these rodents.

Similarly, blocking opioid receptors in normal mice also abolished the analgesic effect of green.

Overall, the results suggest that green light relieves pain by stimulating cones, which then initiate a signaling pathway leading to activation of opioid receptors in the DRN.

Although it is unclear whether a similar mechanism underlies the analgesic effects of green light in humans. The authors of the study concluded that this signaling pathway could be used to reduce pain.

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