(Philadelphia, PA) - They may want to 'shake it off' and get back into the game, but a single head injury - even a mild one - can put athletes at risk for further traumatic brain injuries. According to researchers at the University of Pennsylvania School of Medicine, the brain has an increased vulnerability to severe, perhaps permanent, injury for at least 24 hours following a concussion.

Their results, published in the November issue of the Journal of Neurosurgery, have serious implications for victims of accidents and abuse, as well as amateur and professional athletes. The researchers believe their work provides a new model for looking at repetitive head injuries (RHI). The prospect that athletes may be returning to the field too soon after a head injury is alarming, say the researchers. Indeed, the research was funded by NFL Charities, the philanthropic arm of the National Football League.

"If you look at the guidelines for mild head injuries in athletes - from high school to the pros - you'll see that they are written with little hard scientific data," said Tracy K. McIntosh, PhD, the Robert A. Groff Professor in the Penn Department of Neurosurgery and Director of the Penn Head Injury Center. "Our findings represent the first real attempt to look at the science behind head injuries - and we were startled to see how permanent the damage can be."

According to the researchers, the effects of RHI may not be felt for months later. By studying the effects of brain trauma in mice, the researchers were clearly able to see how a second head injury exacerbates the effects of the first one when delivered within 24 hours.

Permanent cognitive damage, however, is not immediate. In fact, the effects of the trauma seemed transient, and mice returned to almost normal, doing well in a number of tests to monitor cognitive and motor skills.

"However, at about 56 days we began to see a measurable breakdown in motor skills and, subsequently, a breakdown in the cells of the brain," said McIntosh. "This correlates with what we know about the nature of repetitive head injuries in humans, and its role as a factor in neurodegenerative diseases."

There is already a growing body of data that suggests that those that suffer RHIs in sports may be at greater risk for neurodegenerative diseases later in life. In fact, the damage to the brain found in victims of Dementia Pugilistica, or "Punch Drunk Syndrome," closely resembles that of Alzheimer's patients.

Although they do not know the exact mechanism that leads to damage after repetitive head injuries, McIntosh and his colleagues are interested in one brain cell protein that has also been implicated in contributing to Alzheimer's. Accumulations of the beta-amyloid precursor protein (b-APP) was found in great quantities in the neurons of mice that received RHIs, accompanied by an increase in the amount of dead or dying neurons. They hypothesize that the damage from injury causes b-APPs to gradually accumulate in the cytoskeleton of neurons, which serves as the support structure for the cell as well as the roadway by which nutrients travel throughout the cell. This roadblock slowly chokes off the cell and eventually leads to its death.

"Clearly, we do not always recognize concussions for what they are: brain injuries," said McIntosh. "The damage is not always noticeable either. That is, you do not have to fracture your skull to injure your brain."

According to McIntosh, traumatic brain injury (TBI) is a 'silent epidemic' in our society. Each year, an estimated two million cases of TBI occur in the United States, with approximately 500,000 cases serious enough to require hospitalization. Most patients, however, do not seek professional medical help or are discharged immediately after examination. As yet, there is no medical treatment for TBI.

"The desire to get back into the game is admirable, but ultimately not worth the risk," said McIntosh.

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