We already know that light and dark influence our circadian rhythm, but exactly how it impacts our sleep-wake cycle is less clear. Now, new research seems to have found part of the answer.
Why does the light wake us up?
A team of researchers from l California Institute of Technology in Pasadena (EE. UU.) Set out to examine the effect of light on sleep. Taking into account that they had previously identified the photoreceptors in the eye that are required for the direct effect of light in wakefulness and sleep, the experts wanted to go a step further and see how the brain uses this visual information for sleep.
To do this, they chose to analyze the zebrafish, which has a sleep / wake pattern similar to that of humans and whose body is transparent, allowing researchers to take images of their neurons in a non-invasive way.
Several specimens of zebrafish were genetically modified to express a certain protein, called Prokinethicin 2 (PROK2), in excess. This overexpression of the protein made the fish more likely to fall asleep during the day and wake up at night, compared to unmodified zebrafish.
Interestingly, this did not appear to depend on the fish’s regular circadian rhythm, but rather the effect was exclusively influenced by whether the lights were on or off around it.
The results of the experiments indicate that Prok2 can inhibit the awakening effect that light normally has, as well as the sleep-inducing effect of darkness.
In this light-triggered sleep effect, the researchers also found that high levels of PROK2 also increased levels of galanin, a neuropeptide found in the anterior hypothalamus of the brain (which plays a key role in sleep regulation).
Will it have this same effect on humans? Future research hopes to answer this question. But if this were the case, we could count on new drugs in the future to control both sleep and waking.
“The results of our study suggest that Prok2 levels play a critical role in establishing the correct balance between sleep and wakefulness during the day and at night. Although diurnal animals such as zebrafish spend most of their time asleep at night and awake during the day, they also take naps during the day and occasionally wake up at night, similar to many humans “, clarifies David Prober, leader of the work.
Reference: Light-Dependent Regulation of Sleep and Wake States by Prokineticin 2 in Zebrafish. Neuron. June 2017. http://dx.doi.org/10.1016/j.neuron.2017.06.001
