Exercise and depression

UPDATE: Here's another article, in slightly simpler terms:

“If you consistently exercise and your muscle is conditioned and adapted to physical exercise, then you acquire the ability to express this class of enzymes that have the ability to detoxify something that accumulates during stress and that will be harmful for you,” …

Everyone knows that exercise is a sress and depression reliever.

The question is, how?

A little bit technical NY Times health and fitness article.

… precisely how exercise, a physical activity, can lessen someone’s risk for depression, a mood state, has been mysterious.

So for the new study, which was published last week in Cell, researchers at the Karolinska Institute in Stockholm delved into the brains and behavior of mice in an intricate and novel fashion.

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.

The scientists could then have tested whether exercise blunts the risk of developing depression after stress by having mice run first. But, frankly, from earlier research, they knew it would. They wanted to parse how.