Researchers have recently discovered that there is an enzyme in muscle that detoxifies a substance which tends to be high in the mentally ill. The substance Kynurenine is produced when an individual is exposed to stress. Exercise has long been considered as an antidepressant with stress reducing properties. This could perhaps be one explanation and a new way to target depression.
The researchers discovered that mice with higher levels of PGC-1a1 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 exact function of kynurenine is not known, but high levels of kynurenine can be measured in patients with mental illness. In this study, the researchers demonstrated that when normal mice were given kynurenine, they displayed depressive behaviour, while mice with increased levels of PGC-1a1 in muscle were not affected. In fact, these animals never show elevated kynurenine levels in their blood since the KAT enzymes in their well-trained muscles quickly convert it to kynurenic acid, resulting in a protective mechanism.
In comparison to medication I have received more benefits from exercise with respect to stress reduction. Many antidepressants can also reduce stress however they have side effects, one of which is sedation with a loss of motivation.