Reuters Health - Damage to the filter that protects the brain from toxins may partly explain why explosions have been leaving soldiers with lasting brain injuries, researchers say.

In a study of U.S. veterans after hazardous tours in Iraq and Afghanistan, the researchers found that the higher the exposure to blasts, the lower the activity in a brain region called the cerebellum.

The cerebellum is important for motor skills and also for emotions. Problems with irritability, mood and impulsivity are very common in veterans who suffer the kinds of mild traumatic brain injury that a blast can inflict, said study coauthor Dr. Elaine Peskind.

Peskind and colleagues also found, in experiments with mice, that the cerebellum in particular was affected by microscopic damage in the protective blood-brain barrier after blasts.

"The brain is a very special environment that requires protection and all types of things get into your bloodstream," said Peskind's coauthor David Cook, also of the VA Puget Sound Health Care System. When that blood-brain barrier is broken, the brain may be briefly exposed to those toxins.

As reported in Science Translational Medicine, the researchers had data on 41 blast-exposed veterans. Positron emission tomography (PET) scans of their brains showed that activity in the cerebellum was generally poorer as the number of blasts they'd been exposed to increased.

Going a step further, the researchers exposed lab mice to blasts and found a link between the blasts and damage to the blood-brain barrier, with the greatest loss of neurons occurring in the cerebellum.

"This pattern of brain cell loss in the cerebellum exactly matched what had been reported earlier in the brains of retired former boxers," said Cook.

This finding suggests early damage to the blood-brain barrier may be an important factor in long-term brain changes, the authors believe.

Dr. Maiken Nedergaard, an expert on neurology at the University of Rochester Medical Center in New York who wasn't involved with the study, told Reuters Health the findings suggest that "with blast injury, the cerebellum is particularly more sensitive."

Cook and Peskind told Reuters Health that blast effects are not limited to the cerebellum and that damage to the blood-brain barrier is likely just one of the ways that blasts cause lasting effects on the brain.

Their paper notes that brain problems after explosions can also take the form of neurodegenerative disorders like Alzheimer's or Parkinson's disease, or so-called chronic traumatic encephalopathy, which can also develop after years of playing contact sports.

The new study "helps us close the gaps just a little bit," Peskind said.

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