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), for example. But now, scientists have been able to look at these effects down to the level of brain neurons.
In a new study in mice, neurons in the suprachiasmatic nucleus (SCN) – the brain’s 24-hour timekeeper located within the hypothalamus – were observed coordinating with each other to adapt to different wavelengths of light. day, with changes in individual cells as well as the network as a whole.
Both the mixture and the expression of key neurotransmitters were altered in response to the amount of light each day.
We already know that changes in the SCN can affect the functioning of the paraventricular nucleus (PVN), the brain region also within 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 novel molecular adaptations of the SCN-PVN network in response to day length in the regulation of hypothalamic function and daily behavior,” says neuroscientist Alessandra Porcu of the University of California, San Diego.
In both mice and humans, the SCN is part of the brain’s timing mechanisms, responsible for circadian physical, mental, and behavioral rhythms that follow a 24-hour pattern. The SCN is controlled by special photosensitive cells in the retina, transmitting information about available light and the length of each day.
What’s not clear—and what this study provides great insight into—is how the small group of 20,000 neurons in the SCN reacts in response to incoming data about day length. Knowing more about this can be helpful in treating health problems like SAD, as well as other conditions where light is used as a treatment option.
The researchers were able to identify changes in the neurotransmitters neuromedin S (NMS) and vasoactive intestinal polypeptide (VIP) in the mice, which could then be manipulated to alter network activity in the PVN.
In other words, we are getting closer to being able to manage our response to more or less daylight.
“The most impressive new finding in this study is that we discovered how to artificially manipulate the activity of specific SCN neurons and successfully induce dopamine expression within the hypothalamic PVN network,” says neuroscientist Davide Dulcis of the University of California San Diego.
This research is still at an early stage – although there are strong similarities between the mouse brain and the human brain, which makes mice suitable test subjects, it remains to be seen whether human neurons work in exactly the same way.
But building on previous research, the findings have the potential to give us new ways to treat nerve disorders using light therapy. The team suggests that the mechanism they have discovered may also affect our ‘memory’ of how much daylight to expect as the seasons change.
The study is an example of how scientists are able to dig deeper, at the level of molecular mechanisms, using discoveries that have already been made. One of the next steps will be to see if the same mechanisms are at work in the human brain.
“The multi-synaptic switching of neurotransmitters that we showed in this study may provide the anatomical/functional link that mediates seasonal changes in mood and the effects of light therapy,” says Porcu.
The research was published in Advances in science.