Even a single blast injury like those experienced by soldiers or some crowd members at the Boston Marathon can create subtle chemical changes in the brain, a new animal study led by the University of Pittsburgh shows.
In the study, funded by the Defense Advanced Research Projects Agency, researchers examined the brains of rats that had been exposed to a blast wave in the laboratory.
The rats did not show much obvious physical damage to their brains in the first 24 hours, lead investigator Patrick Kochanek said, but there were biomarkers that mimicked those seen in Alzheimer's disease and other brain disorders.
The scientists found three types of changes, Dr. Kochanek said. There were signs of damage in the white matter "cabling" at the base of the brain, where the spinal cord enters, and in the cerebellum, which controls movement and shapes some emotional responses.
A test of the genes expressed in the brain after the blast showed a pattern that was a close match for the genes that are active in Alzheimer's disease, he said, and there also were elevated levels of inflammatory proteins and signs of oxidative stress.
"When you trigger inflammation, which evolution developed so we could fight infection," he said, "you also cause a little damage, and in the brain this neuro-inflammatory fallout isn't tolerated very well, so it is probably more pathological than helpful in the brain environment."
It is impossible to say in such a limited experiment exactly what this means for humans exposed to the pressure waves that come from explosions, Dr. Kochanek said, "but it suggests a very interesting possibility that even a really low level exposure triggers a pattern that, if you get this over and over, you are at high risk for developing neurodegenerative diseases."
One real-world corollary? Previous research already has shown that munitions experts who do explosives training often develop memory problems later in life, he said.
In the experiment, the researchers made sure the rats' heads were secured during the blast. If they had been allowed to move freely, the wrenching of the head from the blast might have caused even more damage, he said.
"Despite the lack of a lot of obvious neuronal death, there is a lot of molecular madness going on in the brain after a blast exposure. Even these subtle injuries resulted in significant alterations of brain chemistry."
Mark Roth: firstname.lastname@example.org or 412-263-1130.