Investigating the Behavioral and Histopathological Changes in a Rat Model of Repetitive Subconcussion

A subconcussive impact (SCI) is defined as a bump, jolt, or blow that does not result in any apparent symptoms. Many athletes who participate in contact sports suffer from long-lasting effects of neurodegeneration after many years of continued exposure to such SCIs. Since the existing preclinical models do not adequately replicate the delivery of repetitive subconcussive head impacts that are representative of head injuries in a sport, the goal of this research was to develop a model of repetitive subconcussive impacts (rSCIs) based on comparisons with sham rats and rats that received a single or rSCIs using behavioral and histological outcomes. Thirty adult male rats were randomly divided into three groups in which they were treated either with a sham procedure, a single SCI or rSCI. The SCIs were administered using the Marmarou impact acceleration model by dropping a 50-gram weight from a height of 50 cm onto a steel helmet affixed on the rat’s head and delivering 0.25 J of energy with each impact. Surface righting was found to be significantly increased in the rSCI group compared to the sham and single SCI animals. Although no group differences in learned behaviors were observed, the rSCI group showed significantly greater variance in learning. Histological analysis demonstrated a significant presence of beta-amyloid precursor protein–reactive profiles in the rSCI group compared with the sham and SCI groups. This research establishes a foundational subconcussive animal model that is noninjurious in singularity but produces changes in righting reflex and axonal injury with repeated exposures.