happy rats

Rats are happier when they've been habituated to the "positive stress" of exercise*: a lesson for laggards and misanthropes (and devotees of Schopenhauer and Nietzsche).

New research has undermined the simplistic view of serotonin as the “happy” brain chemical... rats taught to feel helpless and anxious, by being exposed to a laboratory stressor, showed increased serotonin activity in their brains. But rats that had run for several weeks before being stressed showed less serotonin activity and were less anxious and helpless despite the stress.

Anxiety in rodents and people has been linked with excessive oxidative stress, which can lead to cell death, including in the brain. Moderate exercise, though, appears to dampen the effects of oxidative stress... rats that had exercised were relatively nonchalant under stress. They didn’t run for dark corners and hide, like the unexercised rats. They insouciantly explored.

*This goes for moderate walker-rats, too, not just gym rats. The best exploring is pedestrian.