Anti-Stress Injection of the Future? Immunization With Good Bacteria Made Rat Brains More Resilient to Stress in Study

Lots of potential implications for treating disorders or problems related to stress. Studies with rats are of course common and relevant because they share a surprising number of similarities to humans.

Immunization with beneficial bacteria can have long-lasting anti-inflammatory effects on the brain, making it more resilient to the physical and behavioral effects of stress, according to new research by University of Colorado Boulder scientists.

The findings, if replicated in clinical trials could ultimately lead to new probiotic-based immunizations to protect against posttraumatic stress disorder (PTSD) and anxiety or new treatments for depression, the authors say.

“We found that in rodents this particular bacterium, Mycobacterium vaccae, actually shifts the environment in the brain toward an anti-inflammatory state,” said lead author Matthew Frank, a senior research associate in the Department of Psychology and Neuroscience. “If you could do that in people, it could have broad implications for a number of neuroinflammatory diseases.”

Anxiety, PTSD and other stress-related mental disorders impact as many as one in four people in their lifetime. Mounting research suggests that stress-induced brain inflammation can boost risk of such disorders, in part by impacting mood-influencing neurotransmitters like norepinephrine or dopamine.

“There is a robust literature that shows if you induce an inflammatory immune response in people, they quickly show signs of depression and anxiety,” said Frank. “Just think about how you feel when you get the flu.”

Research also suggests that trauma, illness or surgery can sensitize certain regions of the brain, setting up a hair-trigger inflammatory response to subsequent stressors which can lead to mood disorders and cognitive decline.

“We found that Mycobacterium vaccae blocked those sensitizing effects of stress too, creating a lasting stress-resilient phenotype in the brain,” Frank said.

For the new study, published this week in the journal Brain, Behavior and Immunity, Frank and senior author Christopher Lowry, an associate professor in integrative physiology, set out to find out what exactly M. vaccae does in the brain.

Male rats injected with the bacterium three times, one week apart, had significantly higher levels of the anti-inflammatory protein interleukin-4 in the hippocampus — a brain region responsible for modulating cognitive function, anxiety and fear — eight days after the final injection.