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Night Light and Depression: Research Advance for Nighttime-Light-Induced Depressive Behaviors in Mice

Updated: 2020-06-09 (cas.cn)

Do you have the habit of bringing cellphone up in bed? Well, think it over -- for it can be related to depression if excessive.

Researchers at University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS) recently found the light-at-night induced depressive-like behaviors in mice, without disturbing the circadian rhythm. The study, led by USTC Prof. XUE Tian, was published in Nature Neuroscience on June 1.

Light matters in all lives on earth. Besides generating vision of our eyes, light modulates various physiological functions, including mood. Excessive light exposure at night has been reportedly associated with depressive symptoms.

Researchers first demonstrated this in their experiments. They simulated the abnormal illumination of the modern world, two hours per night, for three weeks. "This way it induces the depressive-like behaviors without disturbing its daily rhythm", said AN Kai, first author of this study.

Of course that the habits of mice differ from humans', but their behaviors are still governed by change of illumination and circadian rhythm. When light at night increased, the research uncovered, that although the mice's circadian rhythm remained almost unchanged, they gradually performed some abnormal behaviors. When faced with their favorite sugary water, for example, their interests decreased.

Researchers then revealed that the depressive effect was mediated by a neural pathway, and importantly they showed that one node of the pathway was gated by the circadian rhythm, being more excitable at night than at day, which indicates that the pathway preferentially conducts light signals at night, thereby mediating depressive-like behaviors.

"Our findings provide clues for how to impede the negative mood induced by abnormal light environment, helping in explaining the clinical observations with the potential neural pathway mechanism", Prof. XUE said.

Authors remind, however, that whether the research can be applied to human requires further proof. But what can be certain is, considering the prevalent nighttime devices usage in modern world, we should at least be careful.