Revealing the Heavy Impacts of Repeated Low-Level Head Traumas
Soldiers training on heavy artillery and athletes in contact sports are routinely exposed to repetitive mild shockwaves and injuries. Unlike someone who has just dodged a missile explosion or been smacked by a linebacker, they may feel little immediate impact.
The cumulative effects of these low-level blasts can, however, cause neurological problems such as sleep disorders and attention deficits, noted Bryan Pfister, director of New Jersey Institute of Technology’s Center for Injury Biomechanics, Materials and Medicine.
He explained, “If you have a mild hit, the first hit, does that exposure put your brain in a vulnerable state, even if there is no detectable injury? Research on animals shows us that a mild shock wave doesn’t do much, but if the subject is hit again, then yes, we see neuroinflammation and measurable behavioral changes. With repetitive injuries, deficits developover time.”
Center researchers began studying these injuries five years ago to explore their impact on service members. Their goal is to understand the precise mechanisms driving persistent and chronic changes, which can then become targets for treatment.
In one approach, they’re focusing on damage to the blood-brain barrier, a tightly packed layer of capillaries around the brain that are the central nervous system’s first line of defense. Under normal conditions, they admit only the tiniest molecules, repelling pathogens and most foreign substances.
Earlier studies by NJIT researchers showed how cascading chemical effects from traumatic blasts can disrupt and destroy integral brain vasculature in the blood-brain barrier, promoting chronic inflammation.
Recent research reveals related effects from repeated low-level impacts. The brain becomes more permeable, admitting foreign molecules such as white blood cells from the peripheral system known as monocytes, which release cytokines to fight inflammation. The brain’s own immune cells, microglia, also mount an anti-inflammatory response.
“If this process is sustained, it can become pro-inflammatory and turn toxic, killing neurons,” said Tulika Das, a Ph.D. student in biomedical engineering at NJIT who studies these responses in transgenic mice. “We saw this cause not only neurodegeneration, but behavioral deficits such as anxiety and memory impairments.”
Her team is now trying to determine whether the invading immune cells or the brain’s own are driving the harmful cytokine cascades. They recently tested a polymer called Poloxamer 188 as a membrane resealing reagent to block the former.
“The mice seemed less anxious and memory-impaired,” she noted, “but we’re still trying to pin down the chemical pathways.”
Researchers at the center also seek to pinpoint the exposure levels that put the brain into a vulnerable state to help decide when someone returns to duty or a game, for example.
“Is it the number of times someone is hit, how hard, or the intervals between the hits that matter? There are many biomechanical parameters involved in head injury. How each parameter leads to injury remains to be determined,” Pfister said. “This is essential to setting exposure standards and to provide a threshold above which immediate treatments should be made.”
Das notes that brain researchers are concerned about the growing number of people around the world subject to these repetitive injuries.
“Blast-induced neurotrauma is a signature injury of soldiers exposed to explosive devices, but it may also be experienced by civilians in wartime,” said Das, citing just one little-studied group. “With increases in the use of weapons such as improvised explosives, they are at high risk."
