Impact of Artificial Light on Circadian Rhythms

Overview of Artificial Light Exposure

Researchers at the Salk Institute in San Diego, USA, have explored how prolonged exposure to artificial light affects the eye’s response mechanisms. Daily, we encounter artificial light from various sources, including indoor lighting and screens on electronic devices such as phones, computers, and televisions. As technology advances, screen time continues to increase, particularly during the evening and into the night. Experts warn that late-night exposure to screen-generated light can disrupt our sleep patterns.

Circadian Rhythms and Their Significance

Our bodies operate on 24-hour internal clocks known as circadian rhythms, which regulate our alertness and sleepiness. Exposure to light significantly influences these rhythms. Artificial light at night can mislead our bodies into perceiving it as daytime, resulting in disturbed circadian rhythms, insomnia, and irregular sleep patterns.

Mechanism of Light Detection in the Eye

The Role of the Retina

Light detection occurs in a thin layer of tissue at the back of the eye called the retina. This structure contains various specialized light-sensitive cells. While many of these cells are responsible for capturing visible light to create images, there are also cells that respond to light without contributing to image formation.

Function of Melanopsin

Among these non-image-forming cells is a protein called melanopsin, which continuously responds to prolonged light exposure, such as daylight. Melanopsin plays a crucial role in regulating circadian rhythms, pupil dilation, and light-dependent behaviors in animals, such as inactivity in nocturnal rodents. Additionally, melanopsin suppresses melatonin, a hormone essential for sleep induction.

Research Findings on Melanopsin Response

Continuous Response Mechanism

In a recent study published in *Cell Reports*, researchers at the Salk Institute investigated how melanopsin maintains its response to artificial light in mice. They discovered that under artificial light stimulation, melanopsin interacts with another protein called arrestins. Typically, arrestins help terminate signals and may degrade melanopsin, thus ending its light response.

Gene Mutation Experiment

To study the light response in melanopsin-expressing retinal cells, researchers mutated the genes of the two arrestins that interact with melanopsin in mice. They measured the electrical activity in these cells, which would normally relay signals to the brain. The findings revealed that one arrestin is essential for ceasing the light response, while the absence of the other arrestin resulted in a delayed and diminished response, highlighting its role in sustaining the light response.

Implications for Circadian Rhythm Disorders

The study suggests that one arrestin halts the light response, while the other aids in signal regeneration. However, a limitation of this research was the inability to test the effects of removing both arrestins simultaneously, as such mice do not survive. Understanding this mechanism could lead to potential treatments for circadian rhythm disorders by targeting melanopsin or the regenerating arrestin with nighttime medications.

Conclusion

Relevance to Modern Habits

The researchers also discovered that melanopsin-expressing mouse retinal cells could maintain responses to repeated long pulses of artificial light, akin to the exposure we experience from frequently checking our phones at night. These habits may mislead our circadian rhythms into believing it is daytime, exacerbating sleep disruptions.

Written by Melissa H. Wong, MSc

Reference: Ludovic SM, Hatori M, Ruda K, Benegiamo G, Demas J, Panda S. Sustained melanopsin photoresponse is supported by specific roles of ß-arrestin 1 and 2 in deactivation and regeneration of photopigment. 2018. Cell Rep 25:2497-2509.