Anyone who’s spent any amount of time around someone with a stressful job knows the impact that it can have on a person’s life. We’ve evolved to have a very specific physical response to stress, which back in the day used to be elicited mainly by large predators threatening to eat us. Adrenaline levels spike, hearts race, and the immune system is put into overdrive, among other physiological responses.
In short, we weren’t built to be under constant stress; it’s not very good for our health. And besides physical health, it’s also detrimental to our mental health. There are plenty of anecdotes out there about how being under constant stress can change a personality, or even lead to psychological disorders.
Now, researchers from the Ohio State University have a small clue as to how that happens. It seems as though certain immunological cells called monocytes get recruited to the brain where they cause inflammation.
In the study, researchers put a bunch of mice together and let them setup their social structure. You know, leaders, nerds, workers, etc. Then they introduced a hugely aggressive alpha mouse to the group, which completely upset the group dynamics and stressed the mice right the hell out.
Then the researchers did this a whole bunch of times so that the mice were under a lot of stress a lot of times during an extended period of time. The result, unsurprisingly, was that afterward the mice exhibited signs of anxiety disorder. They hesitated longer than their peers going into open spaces and, given the choice, clung to the darkness like a prom date with a giant zit.
Naturally, the scientists then opened up the mice’s brains to try to figure out why the anxiety set in. What they found was an overabundance of monocytes in the regions of the brain associated with fear and anxiety, with mice that were stressed out the most showing the highest levels. What’s more, these monocytes do not originate in the brain – they’re produced and called up out of our bone marrow.
What this indicates is a whole-body response to stress that can cause psychological issues, which is a pretty novel idea for the field. In general, researchers usually look for changes to the brain that originate in the brain as a result of emotional experiences. A difference in the secretion of neurotransmitters, a rewiring of neural networks… those sorts of changes. The thought that stress signals coming from the brain are affecting the rest of the body in a way that forms a feedback loop and comes back to further affect the brain is a new one.
While it is known that the monocytes cause inflammation, exactly how they’re affecting the brain to cause anxiety disorders remains unclear. But you can be sure they’re working on it.
“Our data alter the idea of the neurobiology of mood disorders,” said Eric Wohleb, first author of the study and a predoctoral fellow in Ohio State’s Neuroscience Graduate Studies Program. “These findings indicate that a bidirectional system rather than traditional neurotransmitter pathways may regulate some forms of anxiety responses. We’re saying something outside the central nervous system – something from the immune system – is having a profound effect on behavior.”
The paper, “β-Adrenergic Receptor Antagonism Prevents Anxiety-Like Behavior and Microglial Reactivity Induced by Repeated Social Defeat,” by Wohleb, along with John Sheridan, senior author of the study, professor of oral biology and associate director of Ohio State’s Institute for Behavioral Medicine Research; Jonathan Godbout, a senior co-author of the paper and an associate professor of neuroscience; and Nicole Powell of the Division of Oral Biology.