Poster P10 - Investigating the Relationship Between Engineering Parameters of Laboratory Head Impacts and Resulting Biological Brain Responses

Introduction: Closed-head concussions, also referred as mild traumatic brain injuries (mTBI), are a common type of injury that can occur from falls, sports, and motor vehicle accidents. These injuries can cause both short-term and long-term damage to the brain and may trigger other biological disorders. The main cause of mTBIs is direct or inertia loading to the head, which results in rotational head kinematics. This is believed to be the major contributor to the lasting effects of mTBIs. This understanding is based on animal studies and computational simulations. One of the main challenges in this field is to understand the relationship between engineering parameters such as linear and rotational head kinematics and the various biological brain responses that follow the impact. To better understand this relationship, we developed a closed-head, large-rotation neurotrauma impact model in the lab. We measured head kinematics through high-speed video and observed the delayed post-impact complex brain responses through function evaluations and pathological measurements. The goal of this research is to understand the correlations between regional brain biomechanical responses and various biological reactions. Eventually, we aim to develop region- and function-specific tolerances for sports related safety gear development.

Materials and

Methods: Laboratory Head Impacts and Kinematics
Injured mice were paired with sham mice of the same sex, litter, and similar weight. Injured mice were subjected to a triple impact protocol over 48 hours using a controlled cortical impact (CCI) impactor at the bregma suture. Both cohorts were anesthetized with ketamine/xylazine. Impacts were conducted using an elevated tear-away platform, allowing the specimen to free-fall 14 cm onto a cushion. Data was obtained using two high-speed cameras to record the impact from two angles and later analyzed using open-source tracking software.
Preliminary Brain Response Observations
Touchscreen Protocol: 32 male C57/Bl6 mice (hit and sham cohorts divided equally) were trained on a touchscreen-based continuous performance task. Attention-based probes were done at 6 weeks and 6 months post-injury with four varying attentional demands.
Morris Water Maze Protocol: 32 male mice (same male mice from the touchscreen testing ) underwent Morris Water Maze testing at 9 weeks post-injury, following traditional protocols.
Pathology Protocol (silver staining): Samples were collected for both male and female mice, in two locations, Corpus Callosum, and optic-tract at one-week post-injury and analyzed using FD NeuroSilverTM Kit II. A total of 13 hTauApp VChtKD underwent silver staining, with 5 shams (3 male and 2 female), and 8 injured (6 male and 2 female).
Pathology Protocol (total Tau): Samples were collected for both male and female mice from Prefrontal Cortex, 6 months post-injury. A total of 3 APOE4 (2 male and 1 female) and 5 APOE3 (5 male) mice underwent Western Blots testing.

Results, Conclusions, and Discussions:

Results:
Head Kinematics
A total of 33 mice were injured, out of which 29 were male and 3 were female with average peak angular velocity of 300  79 rad/s and linear velocity of 3.33  0.73 m/s for male mice and 219  31 rad/s and 2.78  0.16 m/s for female mice, respectfully. All the impacts were clean, meaning that all mice broke through the plastic without any hindrance and fell directly downwards with no additional head rotation.
Preliminary Results of Brain Responses
Touchscreen: At 6 weeks and 6 months post-injury, similar trends were found with little correlation between a higher angular velocity with the overall testing, showing a higher hit rate and false alarm with the mice who endured higher linear and angular velocity.
Morris Water Maze: Mice with higher linear and angular velocities spent less time in the non-target quadrants, and more time in the target quadrants, compared to those with lower velocities. Potentially shows better spatial awareness or memory in mice with higher velocities.
Pathology (Staining): Negative correlations were found when comparing both linear and angular velocity and silver staining, for both sexes and locations. Meaning results showed that the higher linear and angular velocities showed less staining, however, larger R2 values were found when comparing angular velocities with 0.6963 (corpus callosum) and 0.2194 (optic-tract).
Pathology (total Tau): Negative correlations were found when comparing both linear and angular velocity with the amount of total tau for males with the R2 of 0.0966. Meaning mice with higher linear and angular velocity had less tau present.

Discussion & Conclusion
The relationship between the biomechanics of an impact and the resulting brain responses needs to be studied and better understood. The current preliminary study has revealed interesting and counterintuitive results that go against traditional beliefs, such as less staining present in the brain for those mice who experienced higher linear and angular velocities upon impact. Further investigation is warranted to better understand regional brain biomechanical responses, such as strains, and various biological consequences.

Acknowledgements (Optional): This project is partially supported by the US Department of Defense under congress-directed medical research program (CDMRP), Peer-Reviewed Alzheimer’s Research Program (PRARP) by award# W81XWH-20-1-0323.