London: It is known that physical exercise has many beneficial effects on health and researchers have now found how exercise shields the brain from stress-induced depression.
Exercise training induces changes in skeletal muscle that can purge the blood of a substance that accumulates during stress, and is harmful to the brain, the study on mice showed.
"Skeletal muscle appears to have a detoxification effect that, when activated, can protect the brain from insults and related mental illness," said principal investigator Jorge Ruas from Karolinska Institutet in Sweden.
It was known that the protein PGC-1I1 (pronounced PGC-1alpha1) increases in skeletal muscle with exercise, and mediates the beneficial muscle conditioning in connection with physical activity.
In this study researchers used a genetically modified mouse with high levels of PGC-1I1 in skeletal muscle that shows many characteristics of well-trained muscles (even without exercising).
After five weeks of mild stress, normal mice had developed depressive behaviour, whereas the genetically modified mice (with well-trained muscle characteristics) had no depressive symptoms.
"Well-trained muscle produces an enzyme that purges the body of harmful substances. So in this context the muscle's function is reminiscent of that of the kidney or the liver," Ruas explained.
The researchers discovered that mice with higher levels of PGC-1I1 in muscle also had higher levels of enzymes called KAT.
KATs convert a substance formed during stress (kynurenine) into kynurenic acid, a substance that is not able to pass from the blood to the brain.
The study is forthcoming in the journal Cell.