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F.C Barcelona women's soccer team play against RCD Espanyol on April 18, 2010 in Barcelona, Spain. Photo: Christian Bertrand

Past studies have shown that female athletes have a higher rate of concussion than their male counterparts in the same sport, and a new study from the University of Pennsylvania may point to the culprit—axons in the brain.

According to laboratory tests using rat and human neuronal cells, researchers found that female axons (the long, slender part of the neuron that carries messages from one cell to another) were smaller than male axons, and were more likely to break when applying the same amount of force expected from a simulated traumatic brain injury (TBI). It is this “breaking” that researchers believe is associated with concussion symptoms, such as dizziness, loss of consciousness and nausea—although research on concussions in general is not conclusive.

“When axons function normally, they let sodium pass through the membrane, and it creates a spark that can be transferred as ‘electricity’ down the axon,” lead researcher Douglas Smith, M.D., said. “In concussion, you can have immediate loss of that ability to transfer that ‘electricity.’ That’s why the characteristic behavioral changes occur.”

Smith, the director of the Penn Center for Brain Injury and Repair, believes the abnormal flow of sodium eventually causes a buildup that becomes high enough to release protein-breaking enzymes in the brain, which then degrade the axonal structure.

The researchers’ in vitro findings showed that 24 hours after trauma, female axons had significantly more swellings and a greater loss of calcium signaling function than male axons.

The research team is planning further in vivo studies to support their findings. One possible route is to explore blood biomarkers to see if concussed females have more axon proteins, which rise in the blood after a TBI. Another possibility is to neurologically investigate white matter changes in female and male athletes playing the same sport. Interestingly, both of these approaches are already underway—and seen as important milestones—in the continued research of chronic traumatic enencephalopathy (CTE).

More importantly, Smith and his team said the findings could point toward potential treatment options for concussed patients, including microtubule-stabilizing drugs that would help reduce degradation and breakdown after a brain injury.

“We have a couple avenues to look at to help this ion imbalance, to get the lights back on, to get the network to better function after injury, and at the same time prevent the microtubule from falling apart,” Smith said.

This is not the first study to link an increase of injury with gender. Previous studies over decades have shown that women are almost 10 times more likely to injure their ACL than men, due to testosterone levels in the body. And a study earlier this year suggested estrogen is to blame for a women’s “weak” connective tissue, and thus increased chance of developing osteoarthritis.

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