Researchers say rats get more anxious as days grow longer.
Rats supposedly suffer their own version of seasonal gloom. It's brought on by brighter days, scientists say.
It's their version of SAD…seasonal affective disorder.
However, humans suffer from SAD during the wintertime. Because rats are a creature of the night, it is excess light rather than darkness that disturbs them.
Humans are diurnal, and rats are nocturnal.
Scientists say rats experience more anxiety and stress as the days grow longer. If they are only exposed to a few hours of light a day, they tend to do better.
In a series of experiments, the researchers exposed rats to 19 hours of light and just five hours of darkness a day for a week. Scientists found that the rodents' brain chemistry changed, increasing their stress and anxiety.
When the conditions were switched, the rats perked up and their mood improved. The rats became more willing to explore. They were less worried and stressed.
Their responses to light and dark were due to a 'switch' in the brain that toggled between producing two different kinds of nerve signaling chemical.
One was dopamine. This is boosted by darkness and served as a 'feel good' function. The rats had greater calmness and confidence.
The chemical linked to light, somatostatin, did the opposite. The animals became more fearful and edgy.
The research could actually help in the treatment of Parkinson's disease, which is caused by certain parts of the brain lacking dopamine.