Anxiety and post traumatic stress disorder (PTSD) can be linked to increased myelin in the brain, a new study has revealed.
The research linked anxiety behaviour in rats, as well as PTSD in military veterans, to increased myelin — a substance that expedites communication between neurons — in areas of the brain associated with emotions and memory.
The results, reported by scientists at the University of California, Berkeley, and UC San Francisco (UCSF), provide a possible explanation for why some people are resilient and others vulnerable to traumatic stress, as well as for the varied symptoms — such as avoidance behaviour, anxiety and fear — triggered by the memory of such stress.
If, as the researchers suspect, extreme trauma causes the increased myelination, the findings could lead to treatments — drugs or behavioural interventions — that prevent or reverse the myelin production and lessen the impact of extreme trauma.
“The combination of these studies in rats with our population of veterans with post traumatic stress disorders is, to me, really exciting,” said senior author Dr. Thomas Neylan, director of the Post Traumatic Stress Disorders Clinic and the Stress and Health Research Program at the San Francisco VA.
“At least it’s another mechanism to think about as we develop new treatments.
“If we see enduring ability to shape myelin content in an adult brain, maybe treatments will help reverse this. That’s where we want to go next with this.”
Researchers at the San Francisco Veterans Affairs Medical Center conducted brain MRI scans of 38 veterans — half with PTSD, half without — and found an increase in myelination in the grey matter of those with PTSD compared to that seen in the brains of those not suffering from PTSD.
The team at UC Berkeley discovered a similar increase in myelination in the grey matter of adult rats subjected to an acute stressful event.
While not all rats showed long-term effects from the stress — just as not all traumatised veterans develop PTSD — those that did had increased myelination in specific areas of the brain associated with particular symptoms of stress that was identical to what UCSF physicians found in veterans with PTSD.
Both veterans with PTSD and stressed rats that exhibited avoidance behaviour had increased myelination in the hippocampus, often thought of as the seat of memory.
Those exhibiting a fear response had increased myelination in the amygdala, which plays a key role in our response to strong emotions, such as fear or pleasure.
Those suffering from anxiety had increased myelination in the dentate gyrus, a region critical to learning and memory.
“We understand that there’s a lot of individual variation in humans, but with rats, they’re genetically identical, so you think when you expose them to stress you’re going to get the same response,” said senior author Dr Daniela Kaufer, UC Berkeley professor of integrative biology.
“But the response is extremely variable. They sort of fall into groups, such that some are really resilient, and some are vulnerable.
“And the ones that are vulnerable are vulnerable in different ways: Some show avoidance behaviour, and some show fear learning problems, and some show startle responses that are exaggerated.”
According to Dr Neylan, similar individuality is seen in people with PTSD. The new study suggests that the specific symptoms are related to which areas of the brain are being newly myelinated.
“There’s a lot of heterogeneity across different people with PTSD; it’s not one size fits all. Every PTSD patient generally has a mix of different symptoms,” said Dr Neylan, professor-in-residence in psychiatry at the UC San Francisco Weill Institute for Neurosciences.
“Some people are very avoidant. Some people are very hyper-reactive. The idea is that if you can show that these different symptom clusters have different neural circuitry, it might actually lead us closer to subtyping people in a way that we could be more targeted in our treatment.”
The new research builds on a project from 2014, when Dr Kaufer and her UC Berkeley colleagues discovered that rats subjected to acute stress produced more oligodendrocytes in the brain’s grey matter — specifically in the hippocampus.
She proposed that this led to increased myelination of axons, potentially interfering with the speed at which signals traveled between different areas of the grey matter of the brain, such as the hippocampus and the amygdala.
Dr Neylan was intrigued by the 2014 findings and contacted Dr Kaufer, and they have been collaborating ever since.
