Using an animal model of chronic stress, researchers at The Ohio State University have shown that the immune cells of the brain, called microglia, hold unique signatures of chronic stress that leave the animal more sensitive to future stressful experiences, evident by increased anxiety and immune responses. Eliminating microglia so that these "stress memories" could not be maintained did not prevent the increased anxiety in response to later stress but did prevent the hypersensitive immune response.
The study, published in Biological Psychiatry, indicates that eliminating the microglia can reverse some aspects of stress sensitization, which lasts for over 3 weeks after chronic stress ends. The increased anxiety behavior, which was not prevented by the elimination of the microglia, may have resulted from stress signatures maintained in neurons, which also persist for weeks after chronic stress.
"It is remarkable that memories of stress are not only stored in nerve cells, but also in the microglia, the immune cells of the brain. It is not the case that these immune cells can generate a representation of the stressful events. However, the microglia appear to be primed to produce a heightened immune response long after the stressful events that sensitized them have passed," said John Krystal, MD, Editor of Biological Psychiatry.