Daylight does something to the brain, and new research may explain this mystery

(ORDO NEWS) — We know that seasonal changes in the amount of daylight we get can have a significant impact on us – such as seasonal affective disorder (SAD). But now scientists have been able to study this influence down to the level of neurons in the brain.

In a new study in mice, neurons in the suprachiasmatic nucleus (SCN) – the brain’s 24-hour clock located in the hypothalamus – were seen to coordinate with each other to adapt to different daylight hours, with changes occurring both in individual cells, and in the network as a whole.

Both the blend and the expression of key neurotransmitters varied with the amount of light each day.

We already know that changes in the SCN can affect the functioning of the paraventricular nucleus (PVN), a brain region located in the hypothalamus that helps manage stress, metabolism, the immune system, biological growth, and more.

Now researchers have a molecular link between daylight and our behavior.

“We discovered new molecular adaptations of the SCN-PVN network in response to day length in regulating hypothalamic function and daily behavior,” says neuroscientist Alessandra Porcu of the University of California, San Diego.

In both mice and humans, SCN is part of the brain’s timing mechanisms responsible for physical, mental, and behavioral circadian rhythms that follow a 24-hour pattern. The SCN is controlled by special light-sensitive cells in the retina that relay information about the amount of light available and the length of each day.

What is not clear – and what this study provides insight into – is how a small group of 20,000 or so neurons in the SCN react in response to incoming data on the length of the day. Knowing this can be helpful in treating problems such as SAD, as well as other conditions that use light as a treatment.

The researchers were able to identify changes in the neurotransmitters neuromedin S (NMS) and vasoactive intestinal polypeptide (VIP) in mice, which could then be manipulated to change network activity in the PVN.

In other words, we are getting closer to being able to control our response to more or less daylight.

“The most exciting new result of this study is that we have discovered how to artificially manipulate the activity of specific SCN neurons and successfully induce dopamine expression in the hypothalamic PVN network,” says neuroscientist Davide Dultzis of the University of California, San Diego.

This research is still in its early stages – while there are strong similarities between mouse brains and human brains, making mice suitable test subjects, it remains to be seen if human neurons function the same way.

But based on previous research, the findings could potentially give us new ways to treat neural disorders with light therapy. The team suggests that the mechanism they discovered may also affect our “memory” of how much daylight to expect as the seasons change.

This study is an example of how scientists can dig deeper, down to the level of molecular mechanisms, using the discoveries already made. One of the next steps will be to test whether the same mechanisms operate in the human brain.

“The multisynaptic neurotransmitter switching that we demonstrated in this study could be an anatomical/functional link that mediates seasonal mood changes and the effect of light therapy,” says Porcu.

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