Anxiety affects about one out of every five people in the United States, making it one of the most common mental health problems.
Even though it is widespread, scientists still do not fully understand how anxiety begins inside the brain or which cells are responsible for controlling these feelings. New research from the University of Utah has now uncovered an unexpected answer.
Instead of neurons, which are known for sending electrical messages throughout the body, a different group of brain cells may act like hidden “switches” for anxiety. These cells are a kind of immune cell called microglia, and they may be working like the brain’s own accelerator and brake system for anxious behavior.
Microglia are usually known for their role in protecting the brain. They remove damaged cells, fight infections, and help maintain healthy brain tissue. But this new study shows that microglia do much more than scientists once thought.
The researchers discovered that one group of these cells increases anxiety, acting like an accelerator, while another group reduces anxiety, acting like a natural brake. This finding challenges long‑held beliefs about how anxiety works in the brain.
Earlier research had offered clues that microglia might be involved in anxious behavior, but the picture was unclear. Scientists believed all microglia behaved the same way. When they interfered with a specific type of microglia called Hoxb8 microglia, mice began to show anxious behaviors.
They groomed themselves too much and avoided open areas. But when all microglia were blocked at the same time, including both Hoxb8 and non‑Hoxb8 groups, the mice acted normally. This made no sense at first. If removing one type caused anxiety, removing all of them should make the problem worse. Instead, the behavior disappeared.
The research team realized that the two microglial groups must be opposing each other. One must push anxiety levels up while the other pushes them down. They decided to test this idea by studying each type of microglia separately.
To do this, they used mice that had no microglia at all and transplanted specific types into them. This unusual method allowed them to see exactly how each microglia group behaved.
When the researchers transplanted only non‑Hoxb8 microglia into the microglia‑free mice, the animals became anxious. They groomed themselves repeatedly and avoided open spaces.
The scientists described these cells as the anxiety “accelerator.” Without the Hoxb8 microglia present, nothing stopped these signals from becoming too strong.
But when the researchers transplanted only Hoxb8 microglia, the mice showed no signs of anxiety. These cells acted like a brake. They kept anxiety levels low and prevented the worrying behaviors seen when only the accelerator cells were present.
Even more interesting, when mice received both types of microglia at the same time, they also behaved normally. The brake cells balanced out the accelerator cells, creating the right level of anxiety for the situation.
As one researcher explained, the two groups work together to set healthy anxiety levels depending on what is happening around the animal.
This discovery may shape the future of anxiety treatment. Humans also have these two types of microglia, and they may work in a similar way. However, almost all current anxiety and depression medications target neurons, not microglia.
If microglia truly play a major role in anxiety, new treatments could be designed to strengthen the braking cells or reduce the activity of the accelerator cells. This could help people who struggle with severe or long‑term anxiety that does not improve with current medications.
The researchers caution that treatments based on this discovery are still far away. But in the future, doctors may be able to target very specific immune cells inside the brain to correct problems that lead to anxiety disorders.
This would be a completely new direction in mental health treatment and could offer hope to many people who live with anxiety every day.
Reviewing the findings, the study suggests that anxiety may not be caused only by neurons or chemical imbalances, as many people believe. Instead, part of the problem may come from the immune system inside the brain.
If the microglia responsible for reducing anxiety stop working correctly, or if the cells that increase anxiety become too active, a person may develop chronic anxiety.
This new idea could help explain why some people do not respond well to common treatments and may help guide scientists toward more effective therapies. More research is needed, especially in humans, but this study provides a strong starting point for understanding anxiety in a new way.
If you care about health, please read studies that scientists find a core feature of depression and this metal in the brain strongly linked to depression.
For more health information, please see recent studies about drug for mental health that may harm the brain, and results showing this therapy more effective than ketamine in treating severe depression.
The study is published in Molecular Psychiatry.
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