What if you could cure (or at the very least, significantly reduce symptoms of) your anxiety with an injection? Sadly, this isn't a possibility now but scientists may be one step closer to developing an immunization for inflammation-induced mood disorders such as anxiety, depression, and post-traumatic stress disorder (PTSD) after a trial in rats proved successful.
The study, published in the journal Brain, Behavior, and Immunity, builds on previous research that examined the effects of a soil-based bacterium called Mycobacterium vaccae on mice placed in close proximity to large and aggressive male mice. It turned out the inoculated mice displayed fewer signs of anxiety and were less likely to experience inflammation in the bowel and other tissues than the uninoculated mice.
This time, researchers from the University of Colorado (CU) at Boulder wanted to find out how exactly M. vaccae affects the brain. To do so, they injected male rats with a preparation of the bacterium a total of three times one week apart. The result – noticeably more chill rats.
The team measured proteins in the brain and found that eight days after treatment, inoculated rats showed substantially higher levels of an anti-inflammatory protein called interleukin-4 in the brain region associated with mood control, anxiety, and fear (the hippocampus). Then, when put in a stressful situation, the rats showed lower levels of HMGB1, a stress-induced protein responsible for sensitizing the brain to inflammation, and higher levels of CD200R1, a receptor that helps keep the brain's immune cells in an anti-inflammatory state.
"We found that in rodents this particular bacterium, Mycobacterium vaccae, actually shifts the environment in the brain toward an anti-inflammatory state," lead author Matthew Frank, a senior research associate in the Department of Psychology and Neuroscience at CU Boulder, said in a statement.
“If you could do that in people, it could have broad implications for a number of neuroinflammatory diseases."
Stress-related mood disorders, like anxiety, PTSD, and depression, will hit one in four people at some point in their lifetime and there is strong evidence to suggest that they are at least partly caused by inflammation.
"There is a robust literature that shows if you induce an inflammatory immune response in people, they quickly show signs of depression and anxiety," Frank added.
"Just think about how you feel when you get the flu."
While M. vaccae injections are yet to be trialed in humans, Frank and his team hope a similar treatment could in the not-so-distant future be administered to people with a high risk of developing inflammation-induced conditions, such as soldiers and emergency room workers.