Whether it be from movies such as The Best Years of Our Lives, Taxi Driver, The Deer Hunter, or others, or from personally knowing someone or even just watching the news, most Americans are at least somewhat familiar with Post Traumatic Stress Disorder (PTSD). While PTSD was first brought to the public’s attention by war veterans returning home from combat, it can effect anyone and can be triggered by things such as being a victim of a crime, car accident, natural disaster, etc… In 2009, the National Institute for Health estimated that around 7.7 million American adults suffer from PTSD. Due to the nature of combat, PTSD is more common in the military and in 2009 the Department of Veterans Affairs estimated that 31% of Vietnam Veterans, 10% of Desert Storm veterans, 11% of veterans of the war in Afghanistan, and 20% of Iraqi war veterans suffer from PTSD.
With so many Americans impacted by PTSD, it isn’t surprising that a lot of research has been done on the disease and while progress has been made, we still have a long way to go in order to understand what causes PTSD and how to treat and cure it. Fortunately researchers at Ohio State’s Institute for Behavioral Medicine Research and the Department of Neuroscience are on the case and have made important progress in understand what may trigger some PTSD behavior.
The OSU research team led by Professors Jonathan Godbout and John Sheridan has studied how mice react to longterm stress. The researchers started by placing a group of male mice in a cage and allowing them to develop a social hierarchy. Once this has been established, the researchers added an aggressive male mouse to the mix which would fight with and inflict a social defeat upon the mice in the group. The aggressive mouse would be removed and then re-added to the group many times over the course of a week, inflicting repeated social defeats on the other mice; these defeats caused an inflammatory immune response and anxiety in the mice. It is similar to a bully coming along and picking on you and your group of friends; the repeated social defeats at the hands of the bully would most likely cause you stress and anxiety.
After finishing their week of repeatedly stressing the mice, the OSU researchers examined them for the next several weeks looking for biological and behavioral signs of stress. The mice that had been stressed showed elevated levels of pro-inflammatory proteins in their blood and a build-up of monocytes in their brain compared to a control group of mice that had not been stressed; these chemicals had previously been linked to anxiety-like behavior and persisted for over a week, a rather long time for mice. These chemical markers in the stressed mice finally returned to normal levels after about 24 days.
After the chemical markers in the stressed mice had returned to normal, the mice were once again exposed to the aggressive mouse for a single, short period of time; a group of previously unstressed mice were also exposed to the same, short period stress. While the biological and behavioral markers of stress and anxiety were not changed in the group of previously unstressed mice from this single incident, the previously stressed mice however returned to the same state they had been after their week long exposure to chronic stress. It seems that because they have previously been ‘primed’ with stress, it took only a single incident to return the mice to that previous state. This could be compared to how your immune system works after being vaccinated; the vaccine primes the immune system to fight a disease and when you are exposed to that disease again, the immune system can respond quickly at full strength.
The Ohio State researchers found that a primed immune cell type that triggered the inflammatory reaction persisted in the spleen of the mice that had suffered from the repeated social defeats. The researchers then removed the spleen and found that the mice were no longer sensitive to the stressor of the aggressive mouse when it was reintroduced; instead of showing PTSD-like symptoms, the mice acted like the mice that had not previously been stressed. The fact that the PTSD-like symptoms in the mice were caused by a specific type of cell that seems to be stored in the spleen is a big breakthrough.
Work by other researchers who have been studying blood samples from human PTSD patients have found a connection with these patients had increased amounts of pro-inflammatory cytokines in their blood. This suggests that what the mice are experiencing potentially arises from the same causes as PTSD in humans.
Nobody is suggesting that we start to remove the spleens of humans that suffer from PTSD but these findings are a big breakthrough in our understanding of the role that the immune system plays in anxiety and PTSD.