Mouse emotions are, of course, opaque to us. We can’t ask mice if they are feeling cheerful or full of woe. Instead, researchers have delineated certain behaviors that indicate depression in mice. If animals lose weight, stop seeking out a sugar solution when it’s available — because, presumably, they no longer experience normal pleasures — or give up trying to escape from a cold-water maze and just freeze in place, they are categorized as depressed.
And in the new experiment, after five weeks of frequent but intermittent, low-level stress, such as being restrained or lightly shocked, mice displayed exactly those behaviors. They became depressed.
Previous research has shown that aerobic exercise increases the production of an enzyme called PGC-1alpha in muscles, both in mice and in people.
This study identified one particular effect of increased PGC-1alpha: it indirectly increased production of an enzyme that breaks down kynurenine. Kynurenine is a compound that is produced in the body during periods of high stress, and it has been shown to increase inflammation (and other adverse effects of stress) in the brain.
In rats with elevated PGC-1alpha (whether the result of exercise or through direct manipulation) kynurenine disappeared from the body quickly, before it could penetrate the blood-brain barrier.
They then showed that exercise had the same effects on kynurenine in humans who exercised regularly.
To quote the New York Times again –
The upshot of these results, in the simplest terms, is that “you reduce the risk of getting depression when you exercise,” said Maria Lindskog, a researcher in the department of neuroscience at the Karolinska Institute and a study co-author.
Whether the same biochemical processes likewise combat depression that already exists is less certain, said Jorge Ruas, a principal investigator at the Karolinska Institute and the study’s senior author. But he is hopeful. “We think that this mechanism would be efficient if activated after depression has begun,” he said. He and his colleagues hoped to test that possibility in mice soon.
In the meantime, if work and other pressures mount, it may be a good idea to go for a jog. It may just keep your kynurenine in check.