Anyone who’s exercised regularly knows it makes you feel better physically and emotionally. Who cares why? It works. The sense of accomplishment alone is enough to put a spring in your step.
What if exercise heads off some terrifying clinical conditions such as stress-induced depression via another mechanism, such as the muscle putting out a substance that affects mood? Or what if it purges muscles of a substance that is known to collect there under stressful conditions, and is ultimately harmful to the brain?
In neurobiological terms, depression is still somewhat unexplained. But a recent study published in Science Daily adds a piece to the puzzle.
The study, which was conducted by researchers at Karolinska Institutet in Sweden, used mice submitted to a mildly stressful atmosphere over a period of five weeks. After enduring flashing lights, noises, and subtle changes in circadian rhythms (it sounds like they were not technically “tortured”), the normal mice began to show signs of depression, whereas another test group of mice that had been genetically modified to have “fit” muscles remained unaffected. The Institutet reports:
Our initial research hypothesis was that trained muscle would produce a substance with beneficial effects on the brain. We actually found the opposite: 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," says Jorge Ruas, principal investigator at the Department of Physiology and Pharmacology, Karolinska Institutet.
The researchers also found that these modified mice had higher levels of particular enzymes called KAT. These particular enzymes convert a stress-induced substance called kynurenine in to kynurenic acid which is not able to pass from the blood to the brain. Science Daily goes onto explain that,
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.”
The implications of this discovery are numerous. In particular it could very well spur a new way of treating depression.
How physical exercise protects the brain from stress-induced depression via Science Daily