Scientists Discover Evidence of Immune Cells in the Brain Regulating Anxiety

A recent study from the University of Utah, published on November 13, 2025, has revealed that anxiety in mice is regulated not by neurons but by two types of immune cells in the brain known as microglia. This groundbreaking research identifies these microglia as functioning like “accelerators” and “brakes” in modulating anxiety responses.

One subgroup of microglia was found to increase anxiety behaviors, while another subgroup was shown to decrease these behaviors, challenging the conventional understanding that neurons are the sole regulators of anxiety. The researchers conducted experiments involving the transplantation of specific microglia into mice lacking these cells. Mice that received only the anxiety-inducing microglia demonstrated increased anxiety, indicated by heightened grooming behaviors and a tendency to avoid open spaces. In contrast, mice with only the anxiety-reducing microglia exhibited no signs of anxiety. Notably, when both types of microglia were present, the anxiety-promoting effects were neutralized, suggesting a crucial balancing mechanism within the brain’s immune system.

These findings could significantly advance the understanding of the biological mechanisms underlying anxiety disorders and pave the way for novel treatments targeting specific immune cell populations in the brain. Modulating the activity of these microglia may enable the development of therapies aimed at restoring the natural balance of anxiety regulation, thus offering hope for those suffering from anxiety disorders.

The study, titled “Defective Hoxb8 microglia are causative for both chronic anxiety and pathological overgrooming in mice,” has been published in the journal Molecular Psychiatry and was supported by the National Institutes of Health and the Dauten Family Foundation.