Development of a modified weight-drop apparatus for closed-skull, repetitive mild traumatic brain injuries in a mouse model
Repetitive mild traumatic brain injury (rmTBI) is a major contributor to long-term neurological dysfunction, yet many preclinical models lack precise control and quantification of biomechanical forces across impacts. We developed a reproducible, closed-skull mouse model of rmTBI using a custom-built weight-drop apparatus featuring a solenoid-based rebound arrest system, integrated high-speed videography, and accelerometry to track head kinematics during impact. Adult male and female mice received either a single impact or nine daily impacts. Linear and angular acceleration data were analyzed alongside behavioral and histological outcomes. Our apparatus delivered consistent impact and velocity forces with minimal inter-subject variability. Additionally, the animals exhibited consistent linear and angular acceleration when measured using high-speed video capture. Mice in the rmTBI model showed an increased return of righting reflex (RoRR) time, indicating cumulative effects of injury on return to consciousness. Behavioral testing revealed reduced performance of rmTBI-affected mice in an olfaction-mediated foraging task (buried food task), particularly at later timepoints, consistent with progressive olfactory impairment. Immunohistochemical analysis of Iba1 and CD68 in the brain demonstrated sex-dependent microglial activation, with males showing higher expression levels in single- and nine-impact models. Brain region-specific effects were most pronounced in the corpus callosum, neocortex, and olfactory tubercle. These findings underscore the importance of including sex as a biological variable in rmTBI research and support the utility of this model for probing injury thresholds, regional vulnerability, and potential therapeutic interventions in repetitive head trauma.