Physiological Response and Tissue Damage Following Different Depths of Impact in a Rodent Model of Mild Traumatic Brain Injury

Mild traumatic brain injury (mTBI) is a serious public health concern that can result in significant neurological and behavioral deficit. mTBI results from impact to the head and can be repetitive in nature, especially in sports and domestic violence cases. Our laboratory studies the effects of repetitive mTBI on risky choice behavior in rodents using a closed-head controlled cortical impact (CH-CCI) model of injury and a well-established probabilistic discounting task that assesses risk-based decision-making behavior. We have recently found that females, but not males, display transient increases in risky choice behavior following three CH-CI’s delivered at 5.5m/s velocity and 2.5 mm impact depth. These findings suggest that our injury parameters may produce marginally threshold influences on behavioral outcomes that do not allow observation of the extent of repetitive mTBI-induced effects and have prompted us to explore expansion of our model to include greater depths of injury. In the present work we subjected rats to a series of three fixed velocity impacts at depths of 2.5mm, 3.0mm, or 3.5mm. The goal was to compare physical manifestations of injury in male and female rats following different depths of injury. The survival rate, righting reflex time, skull injury observations, animal weights, and histological markers of tissue damage were evaluated post-injury. Our hypothesis was that these indices of injury would be more prominent as injury depth increased