Prolonged Repetitive Head Trauma Induces a Singular Chronic Traumatic Encephalopathy-Like Pathology in White Matter Despite Transient Behavioral Abnormalities
Briggs DI, Agnoa-Pérez M, Kuhn DM. The American Journal of Pathology. 2016;ahead of print.
Take Home Message: Mild repetitive blows resulted in Alzheimer’s disease and chronic traumatic encephalopathy (CTE) like conditions in mice. Additionally, as number of head impacts increased balance coordination declined, and depressive symptoms progressed.
Multiple mild traumatic brain injuries have been suggested to have cumulative adverse effects such as chronic traumatic encephalopathy (CTE). These problems are not detectable during the time when athletes are actively exposed to repetitive head impacts, and animal studies that attempt to replicate a head impact have not focused on true repetitive impacts that would mimic those sustained by an athlete. Therefore, the researchers administered a randomized control trial implementing 30 head impacts using 2 different weights on 32 males, lightly anesthetized, unrestrained mice (16 mice received 75 gram impacts, 16 mice received 95 gram impacts) to stimulate the highly repetitive nature of a sport-related concussion. The head-impact mice received 1 impact per day for 5 days then the mice were given 2 days rest. This schedule was repeated for 6 weeks. Eight mice in the control group were anesthetized on the same schedule, but no head impacts were delivered. Researchers evaluated the mice on their level of consciousness (via reflex recovery, balance and coordination, locomotor activity, grip strength, depression like behavior, and cognitive performance). Lastly, researchers used brain tissue analyses to determine presence of neuropathological conditions (Alzheimer’s disease, CTE). As the number of head impacts increases, the time to recover consciousness diminished; however, balance and coordination, and cognition declined, and depressive symptoms progressed in the ensuing weeks. Brain tissue analysis revealed Alzheimer’s disease and CTE like conditions. No significant differences existed between controls and impact mice and locomotion and late stage test strength.
The researcher performed a novel and important study focusing on the cumulative effect of head impacts and the central nervous system’s response. It was interesting that the researchers found as the number of daily head impacts increased, the less time mice had to regain consciousness, which suggests that the brain attempts to adapt to head impact forces. This is alarming because researchers also found, cumulative effects of the head impacts were demonstrated within the brain tissue, where the brains looked like those suffering from Alzheimer’s disease and CTE. Researchers did find that mice receiving head impacts did display a decline in balance and cognition and developing depression like symptoms, compared to controls. Although, these were mild they still resulted in negative alterations in brain tissue. This study will lead to future progress on the frequency of head impacts and development of neuropathological conditions and identification of risk factors for the development of these chronic diseases. Medical professionals should be aware of the risks associated with repetitive head impacts, and that athletes with a potential head injury should be evaluated by a healthcare professional to determine severity and treatment approach.
Questions for Discussion: When you educate athletes about concussion, do you mention long-term problems like CTE? Do you think athletes would be more likely to report head impacts if they knew it could lead to a long-term disease like CTE?
Written by: Jane McDevitt, PhD
Reviewed by: Stephen Thomas
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