Mice are stressed by longer days

(Longer days) - Longer days make mice suffer from winter blue symptoms, as opposed to humans.

Most of us are familiar with winter psychological disorders, a sign of depression known as "seasonal affective disorder", or abbreviated in English as SAD. When winter comes in . In the winter, shorter days make us more restricted to natural light exposure and make us sleep more than usual, irritable and restless. the mouse is the opposite.

Biologists at UC San Diego found that rats experienced more anxiety and depression when the day became longer. More importantly, they discovered that mouse brain cells accept a new chemical code when enduring major changes in day and night cycles, triggering a switch that allows completely different neurotransmitters. to stimulate the same area of ​​the brain.

Their surprising discovery is detailed in the April 26 issue of Science. Research results show that the brains of adult mammals are more susceptible than those thought by neuroscientists.

Because the rat brain is very similar to the human brain, this finding also provides a better insight into the behavioral changes in our brains related to light reception. This study opens up a new way to treat brain disorders like Parkinson's, caused by the death of dopamine-producing cells in the brain.

Neuroscientists found that mice exposed to light for 5 hours / day and darkness for 19 hours a day for a week had more neurons producing dopamine. Dopamine is a neurotransmitter that helps mice with less stress and anxiety when evaluated by standard behavioral tests. Meanwhile, mice exposed to light for 19 hours / day and darkness for 5 hours / day, continuously for a week, have many neurons synthesizing somatostatin neurotransmitters, making them increasingly More stress and anxiety.

'We live in the daytime and mice are nocturnal,' said Nicholas Spitzer, a biology professor at UC San Diego University and director of the Brain and Conscious Research Institute. 'So for rats, longer days make them stressful, while longer nights cause stress for humans.'

Because rats seek food at night, while humans and some other creatures hunt and seek food during the day, such differences in brain chemicals and behavior are available. meaning. Evolutionary opportunities may have supported humanity, we are creatures who have been very active in storing food during the long days of summer and saving energy during the shorter days of the season. east.

'Light makes us wake up and if we feel depressed, we often go for a walk outside,' says Davide Dulcis, a scientific researcher at Spitzer's lab, the lead author of this study. said. 'In the spring, I feel more motivated to do things that I enjoy for longer days. But for mice, that is the opposite. Because rats are night-hunting species, during the night they are less stressed, darkness is good for them because they can spend a lot of time eating or foraging. "

But how the human brain has changed when we evolved millions of years ago from tiny rodents to being living things in the daytime, to adapt to the changing behavior that?

'We think there has been a change somewhere in the brain , ' Spitzer said. 'Sometimes during evolution from mice to humans, there has been an evolutionary adjustment of brain circuits to allow neurotransmitters to switch in the opposite direction in response, with the same. an exposure to a balance of light and darkness ".

A study published earlier this month in the American Journal of Preventive Medicine found a number of correlations with the light-dark cycle in mice and stress in humans, at least when it comes to People search the Internet for information about mental health issues in the winter compared to the summer. Using Google search data from 2006 to 2010, a research team led by John Ayers of San Diego State University found that searches for mental health information on Google in general increased by 14. % in the winter in the US and 11% in winter in Australia.

"Now that we know that the length of the day can alter neurotransmitters and lead to behavioral changes, there may be a connection here," Spitzer said.

In mouse experiments of neuroscientists at UC San Diego, they found that the transition between two neurotransmitters dopamine and somatostatin, or somatostatin, back then converted to dopamine is not due to the growth of new neurons, but it is possible that the same neurons can produce different neurotransmitters.

The mice exposed to the darker 19-hour hour in a week had a higher number of dopamine neurons in the brain and behavioral tests showed less anxiety. These mice are also ready for swimming, another laboratory test showed they were less stressed.

'Because rats are nocturnal, they want to explore all night and dopamine is an important part for mice and humans to be confident and reduce anxiety'.

Until now, researchers still do not know exactly how these neurotransmitters work. They also did not know the ratio between light and darkness or increased stress caused the above transformation in brain chemistry.'Is this rate 50 - 50? Or 80% is due to light compared to the dark and the remaining 20% ​​is due to stress? We still don't know, ' Spitzer added. 'If we only stress the mice and not change the lighting time, would that lead to changes in the characteristics of the transmitters? We don't know, but it's all possible experiments . '

But when the researchers learned more about this mechanism of activation, they said a promising path for human application, could use dopamine neurotransmitter transitions to brain regions. also received dopamine of Parkinson's patients.

"We can switch to another similar way to place dopamine at the site where it is needed with fewer side effects than other drugs."

This research is funded by grants from Ellison Medical Foundation, other researchers also involved in the study, including Pouya Jamshidi and Stefan Leutgen of UC San Diego University.