Under the Hood

Mice Exposed To Chronic Stress Have Worse Memory; Blame It On The Immune System?

Women in anguish
A new animal study reaffirms the disastrous effects chronic stress can have on memory and suggests the immune system may be to blame. Porsche Brosseau, CC BY 2.0

New research on mice further adds support to the link between chronic stress and memory impairment, as well as suggests a possible culprit for the connection — our very own immune system.

The study, published Tuesday in The Journal of Neuroscience, examined how well a group of mice performed on a memory task (finding the escape hole out of a maze) before and after they had been repeatedly exposed to a larger bully mouse. When compared to a control group of mice mercifully left alone, the bullied mice proved less able to remember the way out.

"The stressed mice didn't recall it,” said lead author Jonathan Godbout, associate professor of neuroscience at Ohio State University, in a statement. "The mice that weren't stressed, they really remembered it."

In humans, it’s widely established that acute bouts of stress can interfere with our ability to both form and retain short-term memories. When it comes to chronic, long-term, stress, however, the connection is less conclusive, with some research showing that certain people are more vulnerable to memory impairments than others. In either case, it’s theorized that the hippocampus, a region of the brain that plays a large part in memory and learning, is the primary source of the dysfunction, since it’s also been shown that experiencing stress causes it to undergo subtle changes.

When the current researchers looked at their overworked mice’s hippocampus, they found noticeable changes, namely inflammation caused by their owner’s immune system. Even more crucially, when they knocked out the mice’s ability to produce inflammation, their memory loss stopped as well.

While interfering with inflammation didn’t end the mice’s overall depression and reduced neural growth, the researchers believe the findings point to a direct relationship between the immune system and the specific side-effect of memory loss following chronic stress.

"Stress releases immune cells from the bone marrow and those cells can traffic to brain areas associated with neuronal activation in response to stress," fellow co-author Dr. John Sheridan,  associate director of Ohio State's Institute for Behavioral Medicine Research, explained. "They're being called to the brain, to the center of memory."

Should the results pan out and be verified by additional research, it may someday point the way to developing workarounds for people chronically exposed to stress, such as abuse survivors and soldiers, according to the researchers.  

"It's possible we could identify targets that we can treat pharmacologically or behaviorally," Godbout said.

That stress can have dramatic effects on our physical body should come as no surprise since earlier research has found it can affect everything from our libido to our appetite and even our cardiovascular system, raising the risk for heart attack and stroke.

Source: Godbout J, Sheridan J, et al. The Journal of Neuroscience . 2016.

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