Galanin is known to be associated with mental health. People born with genetically low levels of galanin face an uncommonly high risk of depression and anxiety disorders.
Multiple studies show that exercise increases production of the substance. In the rat experiments, some of which were conducted at Dr. Weinshenker’s lab, researchers found that exercise led to a surge in galanin production in the animals’ brains, particularly in a portion of the brain that is known to be involved in physiological stress reactions. Perhaps most interesting, they also found that the more galanin there, the greater the rats’ subsequent stress resilience.
For the new research, they gathered healthy adult male and female mice and gave some of them access to running wheels in their cages. Others remained inactive. Mice generally seem to enjoy running, and those with wheels skittered through multiple miles each day. After three weeks, the scientists checked for genetic markers of galanin in the mouse brains and found them to be much higher in the runners, with greater mileage correlating with more galanin.
Then the scientists stressed out all of the animals by lightly shocking their paws while the mice were restrained and could not dash away. This method does not physically harm the mice but does spook them, which the scientists confirmed by checking for stress hormones in the mice. They had soared.
The next day, the scientists placed runners and inactive animals in new situations designed to worry them again, including cages with both light, open sections and dark, enclosed areas. Mice are prey animals and their natural reaction is to run for the darkness and then, as they feel safe, explore the open spaces. The runners responded now like normal, healthy mice, cautiously moving toward the light. But the sedentary animals tended to cower in the shadows, still too overwhelmed by stress to explore. They lacked resilience.
Finally, the researchers confirmed that galanin played a pivotal role in the animals’ stress resilience by breeding mice with unusually high levels of the substance. Those rodents reacted like the runners to the stress of foot shocks, with full-body floods of stress hormones. But the next day, like the runners, they warily braved the well-lit portions of the light-and-dark cage, not recklessly but with suitable prudence.
The upshot of these experiments is that abundant galanin seems to be crucial for resilience, at least in rodents, says Rachel P. Tillage, a Ph.D. candidate in Dr. Weinshenker’s lab who led the new study. And exercise increases galanin, amplifying the animals’ ability to remain stalwart in the face of whatever obstacles life — and science — places before them.