In a new mouse study, the mice prone to PTSD had more stress-hormone (glucocorticoid) receptors in the hippocampus, a memory area of the brain. They also had more of a protein called HCN1. Those lasting changes explain why PTSD is not just bad memories you can easily get past. They also explain why it is so hard to cure. PTSD is a common mental health problem. It causes too much fear, broken sleep, aggression, memory problems, avoiding people, and more in people who are prone to it.
It is no secret that some people are more prone to it. Two people can go through the same kind of trauma, and only one may get PTSD. Some people bounce back from trauma well, while others are very sensitive. So there must be chemical differences between people who are prone to PTSD and people who are resilient. PTSD must also cause brain changes that are hard to reverse. That is why it is hard to cure.
In a new study, researchers found brain changes that make some more prone to PTSD. They studied a group of mice exposed to stress. In some mice, a surge of stress hormone caused short-term excitement in the memory area. That set off a fight-or-flight response. But in other mice with the same genes, this did not happen. Instead, researchers saw reduced excitability in the key brain area, the dorsal hippocampus. These were the mice that later developed PTSD-like symptoms. The researchers published their findings in the journal Molecular Psychiatry.
Earlier studies suggest this low activity in the dorsal hippocampus is typical of PTSD patients. Studies have also tied it to stress-hormone (glucocorticosteroid) receptors. People prone to PTSD have more of these receptors in this part of the brain. To mimic real-life stress, researchers put aggressive mice in with the mice being studied. The mice prone to PTSD avoided the aggressors, much like people with PTSD avoid social contact.
People with chronic migraine disorder may be more prone to PTSD. It is important to find and treat PTSD in patients with chronic migraine disorder to improve their quality of life. Good post traumatic stress disorder treatment may include cognitive behavioral therapy, exposure therapy, and drugs such as antidepressants and antipsychotics. The researchers found that the brains of mice prone to PTSD had too many stress-hormone receptors in the CA1 area of the dorsal hippocampus. Constant stimulation of these receptors seems to raise levels of the protein HCN1. HCN1 shapes how nerve cells connect in the hippocampus.
HCN1 protein was the main focus of the study. Interestingly, even a single stress episode was enough to raise HCN1 levels. It also raised a protein called TRIP8b in the prone mice. So the study not only shed light on how PTSD works. It also confirmed that in prone mice, one stressful episode is enough to cause PTSD-like brain changes. These changes also last a long time. They could still be seen months after the stress. The prone mice not only avoided social contact. They also had worse spatial memory (memory for where things are). People with PTSD also have worse spatial memory, so they tend to forget things like where they left their car keys.
So the researchers concluded that different HCN1 levels in this part of the hippocampus were the main cause of PTSD and social avoidance. They could still see changes in HCN1 after three months. Mice usually live 2-3 years, so that is a long time in their life. The dorsal hippocampus is known to play a role in memory and learning. But researchers say more studies are needed to learn what makes some mice prone to stress and others resilient. Still, this study is a step forward. In the future, we may see drugs that target these molecules to treat the condition.
Frequently asked questions
Why do some people get PTSD after trauma and others don’t?
Biology, not willpower. In this study, mice with the same genes went through the same stress. Yet only some developed PTSD-like behavior. Those mice showed lower activity in the dorsal hippocampus, a memory area. They also had more stress-hormone (glucocorticoid) receptors there and more of a protein called HCN1. The resilient mice did not show those changes.
Can a single traumatic event cause PTSD?
In prone animals, yes. A single stressful episode was enough to raise HCN1 and a related protein, TRIP8b. It set off PTSD-like brain changes. Those mice then avoided social contact when aggressive mice were added, much as people with PTSD pull away from others. They also had worse spatial memory.
What are the signs of PTSD?
PTSD causes too much fear, broken sleep, aggression, memory problems and avoiding people. Spatial memory suffers too. In daily life, that shows up as forgetting where you left your car keys. The mice in this study showed the same pattern. They avoided aggressors and got lost on spatial memory tasks.
Can PTSD go away on its own?
This study explains why it often does not. PTSD is not just bad memories that fade with time. The brain changes in prone mice were still there three months after the stress. That is a long stretch in an animal that lives two to three years. Treatment helps: cognitive behavioral therapy, exposure therapy, and drugs such as antidepressants and antipsychotics.
Dr. Gurpreet Singh Padda, MD, MBA, MHP
