Long-term stress can have lots of effects on the body—it can cause chronic muscle tension, heart problems, and fertility issues in both men and women. Now researchers have performed a new study in mice that they believe reveals another effect of chronic stress on the brain: Inflammation, which can lead to memory loss and depression. The researchers published their study today in the Journal of Neuroscience.
In the study, the researchers stressed out several mice by periodically putting a much more aggressive mouse into their cage. After six days of exposure, the stressed mice could no longer recall the location of a hole to escape a maze, which they remembered easily before the stressful period began. “The stressed mice didn’t recall it. The mice that weren’t stressed, they really remembered it,” said Jonathan Godbout, a neuroscience professor at Ohio State University and one of the study authors in a press release. For four weeks after the trauma, the mice continued to cower in corners, the mouse equivalent of social avoidance, a major symptom of depression.
The researchers suspected that the stress was affecting the mice’s hippocampi, a part of the brain key to memory and spatial navigation. They found cells from mice’s immune system, called macrophages, in the hippocampus, and the macrophages were preventing the growth of more brain cells.
The stress, it seemed, was causing the mice’s immune systems to attack their own brains, causing inflammation. The researchers dosed the mice a drug known to reduce inflammation to see how they would respond. Though their social avoidance and brain cell deficit persisted, the mice had fewer macrophages in their brains and their memories returned to normal, indicating to the researchers that inflammation was behind the neurological effects of chronic stress.
This isn’t the first study to point out the connection between chronic stress and memory loss, or between inflammation and depression. But it provides a new, promising link between all four. That could help doctors prescribe more immune-focused treatments for conditions like anxiety and depression, some of which are being tested now, as the New Scientist reports.