Swedish Study: Exercise protects brain from depression

Endorphins came first, those home-grown opioids or pain-killers called “runner’s high.” Then came the endocabbinoids, the pleasure-inducing molecules released during hard exercise that turn exercise nuts into gym rats.

Now, decades after scientists first speculated on the effects of physical activity on the brain, Swedish researchers have discovered a new reason for lacing up those sneakers:

Exercise not only feels good, it protects the brain from depression.

In mouse studies at the Karolinska Institutet, neuroscientists showed that changes in skeletal muscles, incurred through exercise helped rid the body of a stress-induced amino acid called kynurenine that has been associated with mental illness.

“Our initial research hypothesis was that trained muscle would produce a substance with beneficial effects on the brain,” Jorge Ruas, principal investigator at Karolinska Institutet’s Department of Physiology and Pharmacology, told the media last week. “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 liver.”

Well-trained muscles mean increased levels of a protein known as PGC-1(alpha)1. The Swedish scientists developed a genetically modified mouse strain with high levels of PGC-1(alpha)1 in their muscles and exposed them (as well as normal mice) to a highly stressful environment of noises and flashing lights. After five weeks, the normal mice showed evidence of depressed behavior, including lethargy and disinterest in food, but the genetically modified mice did not.

The reason, the scientists believe, was that the modified mice also had higher-than-normal levels of an enzyme called KAT, which, under stress, converts kynurenine into kynurenic acid, which cannot cross the blood-brain barrier. In effect, KAT in these muscled-up mice detoxed their brain of stress-related neurochemicals.

“It’s possible that this work opens up a new pharmacological principle in the treatment of depression, where attempts could be made to influence skeletal muscle function instead of targeting the brain directly,” Ruas said.

“Skeletal muscle (when activated) can protect the brain from insults and related mental illness.”

By Amy Ellis Nutt