Nat Neurosci . . . Light affects emotions: Xue Tian/Zhao Huan's team reports on the "light-emotional" neural loop of circadian rhythm gating.

Light is the basis of life. Life on earth evolves under the alternating light conditions of day and night, and develops a series of neurophysiological functions of light perception and light regulation, except image Besides, it also includes a series of physiological functions called "non image forming vision", such as light regulation of biological clock, sleep, photophobia, pupil light reflex, melatonin expression, etc.in the thousands of years of human evolution, there is really a rich night light, which is only a hundred years after the industrial revolution, and evolution is far from enough to make human adapt to the changes of artificial light environment.a series of public health evidences show that long-term exposure to abnormal night light can lead to depressive mood and cognitive impairment, but we know little about the underlying neural mechanism.recently, the research on the neural loop of light regulating emotion has become a hot spot. A study on cell in 2018 (Fernandez et. al., cell, 2018) showed that long-term fragmented light dark stimulation may induce negative emotions through the projection from retina to the perihabenular nucleus (PHB).however, it is still unknown whether the disturbance of light or rhythm affects emotion, and the complete light controlled emotional neural circuit has not been described.more importantly, the light of the day often positively regulates human emotions (Huang et. al., neuron, 2019). The principle behind the effect of the opposite light of day and night on emotion has always been an unsolved mystery.aiming at these scientific problems, on June 1, 2020, Professor Xue Tian of University of science and technology of China and Zhao Huan team of Hefei University published an online publication entitled "a circular rhythm gate subcortical pathway for nighttime light induced depressive like behaviors in Nature Neuroscience "Mie" for the first time describes the structure and function of the neural circuit that mediates the depression like phenotype induced by abnormal light at night; proves that it is the abnormal light at night rather than the disorder of rhythm or sleep that causes depression like behavior, and finds that the excitability of the circuit is modulated by circadian rhythm gating, which is the first interpretation of the opposite emotional effect of light in day and night Internal mechanism.the research group built a light at night (LAN) model to simulate the abnormal light patterns in the current society.for three weeks, blue light irradiation for 2 hours from 9:00 to 11:00 every night can make mice show depression like behavior without disturbing rhythm or sleep.non imaging visual function is considered to be mediated by a class of photoreceptor cells in the retina, which are different from the cone rod cells.through the use of rod cells, cone cells and iprgc deficient transgenic animals, the research group found that iprgc played a full and necessary role in the process of LAN induced depression.in order to further reveal the central structure that mediates the action of LAN, the research group found that iprgcs projected to PHB. After PHB was damaged, the emotion related behavior of mice was no longer affected by LAN.at the same time, using photogenetic activation of iprgc to project PHB, can also induce depression like performance in mice.these results fully verify that PHB is an important loop node that mediates the role of LAN.further loop studies showed that the dorsal part of PHB (dphb) projected to the nucleus Accumben (NAC), while the ventral part (vphb) projected to the medial prefrontal cortex (mPFC).NAC is closely related to reward, while mPFC is closely related to emotion and advanced cognition.the study group inhibited the input of PHB to mPFC and NAC respectively through AAV virus tool. The results showed that only the inhibition of dphb NAC projection could affect the effect of LAN. for three weeks at the same time, the projection of dphb NAC was directly activated at a specific time of night, which did not depend on the night light to induce depression like performance. These evidences reveal the core role of dphb NAC projection in LAN induced negative emotions. finally, in order to further explore the mechanism of different regulation of light on emotion in different periods of time (day / night). using single cell patch clamp and in vivo optical fiber recording, the researchers found that dphb neurons projecting to NAC were more excitable and more likely to release action potentials at night than during the day, while vphb neurons projecting to mPFC had no similar phenomenon. these results indicate that dphb neurons projecting to NAC, as a valve controlled by circadian rhythm, only open at night, allowing nocturnal light signals to regulate NAC, which is closely related to reward, through dphb, thus inducing negative emotions. further study suggested that this neural circuit of iprgcs dphb NAC might avoid the animals from being exposed to light during the alternation of day and night under normal physiological conditions, thus avoiding natural enemies. if this loop also exists in human beings, it may be hijacked by artificial light environment at night, thus inducing negative emotions. this study is the first time to elaborate the loop basis and rhythm gating mechanism of nocturnal light induced negative emotions. These findings can, to a certain extent, suggest the mechanism of negative emotions such as depression caused by night light interference (the use of electronic devices such as city lighting or mobile phones and computers), which is of great significance for people to correctly understand the potential hazards of nighttime excessive lighting and explore prevention and control measures 。 human beings have created a lot of brand-new living environment changes in the course of industrialization for more than 100 years. Whether our body can effectively adapt to it is a field worthy of in-depth study. friends who are reading this article, it's time to put down your mobile phone at night! Original link: plate maker: sy