A study in Canada showed that exercise and stimulating environments protect the brain’s defensive barrier in mice exposed to chronic stress, preventing depression-like symptoms. 

Depression is one of the most prevalent mental disorders, affecting more than 300 million people worldwide, and chronic stress is a significant risk factor.  

Scientists at EARA member Université Laval demonstrated that when mice were exposed to chronic social stress, induced by encounters with a dominant male, their blood-brain barrier weakened.  

This barrier normally prevents harmful molecules circulating in the blood from entering the brain, but stress is known to cause the loss of claudin-5, a brain protein essential for maintaining the barrier’s integrity. 

When chronically stressed mice had access to an enriched environment with shelter, toys and nesting materials, or an exercise wheel in their cage, there was little to no decrease in claudin-5 levels. These mice also displayed fewer anxious and depressive behaviours compared with stressed mice lacking enrichment or the opportunity to exercise. 

The protective effects were linked to Fgf2, a protein that repairs the brain barrier. The levels of this protein actually increased in animals exposed to chronic stress, after their environment improved.

Afterwards, scientists also analysed human blood samples from 100 people with and without depression and found that Fgf2 levels also increased with the severity of depression in humans and were influenced by socioeconomic factors such as employment and education level. 

” We […] hope to inform governments about the biological impacts of difficult socioeconomic conditions  […] so that there will be more investment to improve living conditions for all and relieve pressure on the healthcare system,” said Caroline Ménard, senior author, from Université Laval, of the study published in Nature Communications.