A new study of rat brains exposed to military-grade blasts indicates that troops subjected to explosive shockwaves may be at higher risk for developing Alzheimer's disease, including service members who show no symptoms of concussion or brain injury after a blast.
The Army Research Laboratory, U.S. Army Combat Capabilities Development Command, University of North Carolina at Pembroke and National Institutes of Health collaborated on the research, which showed that exposure to blasts alters the connections between neurons of the hippocampus at the molecular level.
The changes in the hippocampus, the part of the brain that helps form memories and guides social behavior, are similar to what is seen "deep in the brain" in patients with Alzheimer's disease, explained Frederick Gregory, an Army Research Lab neuroscientist.
"With these blast exposures, they might knock you down -- the blast wind -- but you may not come away with an injury. But even with that kind of exposure and no visible injuries, you go deeper into the brain, into these synapses, you start to see defects, which suggests you could have cognitive behavior issues," Gregory said in an interview with Military.com.
The finding may explain why service members returning from war zones without any detectable injuries have neurological symptoms such as depression, headaches, irritability and memory problems, added Ben Bahr, a biochemist at UNC-Pembroke.
"Studies linking blast exposures and traumatic brain injury, even mild TBI, to an increased risk of Alzheimer's disease are numerous," Bahr said in a release. "The mystery behind blast-induced neurological complications when traumatic damage is undetected may be rooted in distinct alterations to the tiny connections in the part of the brain particularly involved in memory encoding and social behavior, this region called the hippocampus."
According to the study, published last month in Brain Pathology, the changes were evident between neurons that weren't damaged.
Understanding the effects of blasts on molecular physiology and the potential long-term effects on brain health is important to help develop regimens or treatment to maintain healthy brains, according to Gregory.
"There are investment opportunities in lifelong programs that can contribute to brain health -- [programs that promote] being able to deal with stress, hypnotherapy, mindfulness, nutrition, all sorts of non-pharmaceutical approaches that research has shown has benefits for neurological disorders, TBI and maintaining brain health in general," he said.
According to the study, the researchers exposed living tissue slices of mouse hippocampi to controlled, military-grade blast waves. They then examined the neurons and the synapses in the samples and found that there were reductions in the connections -- a 60% to 80% decline in a synaptic protein needed for memory development -- and "sharply diminished" electrical activity.
Blast exposure does not mean that service members will develop Alzheimer's, but the disruption of communication between neurons may put them at increased risk and the findings could lead to improved diagnostics and treatment following blast exposure.
"Early detection of this measurable deterioration could improve diagnoses and treatment of recurring neuropsychiatric impediments, and reduce the risk of developing dementia and Alzheimer's disease later in life," Bahr said.
The research has limitations, including using slices of rat brains and not the whole animal.
"You can't see the whole animal response to the blast; you are looking at a surrogate for what happens to the brain. This is something that we could do -- move to an animal model at some point," Gregory said.
He added that more research on the topic is imperative
"My recommendation is not to panic, but to educate oneself as much as possible. Find out what DoD is doing, what scientists are doing in this area and advocate for more research funding. It's important to our warfighters and their longevity, leading healthy lives after military service," Gregory said.