Sports Medicine Research: In the Lab & In the Field: A Mild Traumatic Brain Injury May Be Just the Beginning (Sports Med Res)

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Wednesday, January 17, 2018

A Mild Traumatic Brain Injury May Be Just the Beginning

Lifelong behavioral and neuropathological consequences of repetitive mild traumatic brain injury

Mouzon BC, Bachmeier C, Ojo JO, Acker CM, Ferguson S, Paris D, Ait-Ghezala G, Crynen G, Davies P, Mullan M, Stewart W, Crawford F. 2017. Annals of Clinical and Translational Neurology: ahead of print.

Take Home Message: Mice help demonstrate that a mid traumatic brain injury may be an initiating event for chronic cognitive impairments, white matter degeneration, and neuroinflammation.

Long-term behavioral and cognitive impairments following repetitive mild traumatic brain injury (mTBI) are a health concern. Despite evidence that concussions are associated with late neurodegenerative pathologies, there are limited models exploring the persistent and evolving consequences of these repeated mTBIs. Therefore, the authors completed behavioral and neuropathological assessments at 24 months after either single mTBI (7 mice), repeated mTBI (7 mice; 5 impacts 48 hours in between), single sham (8 mice), or repeated sham (7 mice) using a closehead mTBI rodent model. The authors defined a mTBI as having a short period of posttraumatic signs/symptoms, no skull fracture, and no major hemorrhages. Sham mice were exposed to same procedures (e.g., anesthesia) but without the head impact. Three mice from each group were assigned to biochemical analysis, and the remaining mice were processed for histological examination. Behavior and histological analysis started 2 years after the last hit/anesthesia. The researchers used common tests to study motor function, cognition, and anxiety (see links for specific tests). The authors found that single and repeated mTBI mice had impaired cognition (traveling 38 or 45% farther to find a target box) compared to their respective sham counterparts. The authors also identified that the repeated mTBI mice had more anxiety compared with their sham counter parts. However, the authors found no differences between groups in motor function. Structurally, the authors found that both the single and repeated impact mice had a reduction in white matter integrity and thickness compared to their sham counterparts. The authors also identified an increase in neuroinflammation in both single and repeated impact mice compared to their respective sham controls; however, there was no injury effect on tau phosphorylation.

The authors evaluated the behavioral and neuropathological consequences of a single and repetitive brain injury over the life span of 14 mice, and found that both result in long-term problems at varying levels. Repetitive mTBI mice displayed poorer scores on cognition (the maze exams) as well as displayed worsening degeneration on the histological analysis compared to single mTBI mice. The repetitive mTBI mice demonstrated increased risk seeking, which is a sign of anxiety following trauma. Though, none of the mice demonstrated long-term motor deficits this may suggest that similar to humans motor control deficits are typically seen acutely and return to normal fairly quickly. The authors also found notable white matter thinning and neuroinflammation within the single and repetitive mTBI mice; however, there was no abnormal tau phosphorylation, which suggest no sign of chronic traumatic encephalopathy. Overall, the authors concluded that even one mTBI can result in harmful consequences later in life. Currently, medical professionals should be aware of this complex injury and recognize mTBIs as potential chronic health condition. In addition, medical professionals should consider rehabilitation services and treatments, and seek therapeutic activities that could be used over the life span of an athlete to promote healthy brain function.

Questions for Discussion: Should we be following up with our athletes after they return to play? If so, what do you think the protocol should look like? Are there long-term rehabilitation exercise we could be using to help our athletes following a concussion?

Written by: Jane McDevitt, PhD
Reviewed by: Jeff Driban

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