Chronic Neurobehavioral Sex Differences in a Murine Model of Repetitive Concussive Brain Injury

Abstract

Traumatic brain injury (TBI) resulting from repeated head trauma is frequently characterized by diffuse axonal injury and long-term motor, cognitive and neuropsychiatric symptoms. Given the delay, often decades, between repeated head traumas and the presentation of symptoms in TBI patients, animal models of repeated injuries should be studied longitudinally to properly assess the longer-term effects of multiple concussive injuries on functional outcomes. In this study, male and cycling female C57BL/6J mice underwent repeated (three) concussive brain injuries (rCBI) delivered via a Leica ImpactOne cortical impact device and were assessed chronically on motor (open field and rotarod), cognitive (y-maze and active place avoidance), and neuropsychiatric (marble-burying, elevated zero maze and tail suspension) tests. Motor deficits were significant on the rotarod on the day following the injuries, and slight impairment remained for up to 6 months. All mice that sustained rCBI had significant cognitive deficits on the active place avoidance test and showed greater agitation (less immobility) in the tail suspension test. Only injured male mice were significantly hyperactive in the open field, and had increased time spent in the open quadrants of the elevated zero maze. One year after the injuries, mice of both sexes exhibited persistent pathological changes by the presence of Prussian blue staining (indication of prior microbleeds), primarily in the cortex at the site of the injury, and increased GFAP staining in the perilesional cortex and axonal tracts (corpus callosum and optic tracts). These data demonstrate that a pathological phenotype with motor, cognitive, and neuropsychiatric symptoms can be observed in an animal model of rCBI for at least one year post-injury, providing a pre-clinical setting for the study of the link between multiple brain injuries and neurodegenerative disorders. Furthermore, this is the first study to include both sexes in a pre-clinical long-term rCBI model, and female mice are less impaired functionally than males.

Sex differences in cued fear responses and parvalbumin cell density in the hippocampus following repetitive concussive brain injuries in C57BL/6J mice

“…Open field (OF) testing was performed as previously described [10] in 40 cm x 40 cm OF arenas with a light level of approximately 5 lux and opaque walls 35 cm high (Stoelting Co., Wood Dale, IL). Each OF arena (8 available) was equipped with an overhead camera and connected to a computer with Any-Maze software (Stoelting) that tracked the mouse during a 20-min session.…”

“…The TST was performed on post-injury day 23 as previously described [10, 34]. Mice were suspended from laboratory shelves by their tails (approximately 1 cm from the tip of the tail) with standard laboratory tape approximately 25 cm long and 1.27 cm wide.…”

“…Animal models of rCBI have been developed that enable the study of functional deficits that evolve following multiple injuries [6–10], and pre-clinical traumatic brain injury (TBI) models also afford the opportunity to probe the neural mechanisms underlying behavioral dysfunction following injuries [11–15]. The fear conditioning (FC) behavioral paradigm, in which a rodent learns to associate a neutral context and auditory tone (conditioned stimuli; CS) with an aversive stimulus (unconditioned stimulus; US), has been employed in translational studies to model functional deficits following injury to study aspects of hippocampal- as well as amygdala-dependent memory [11, 15, 16].…”

Disruption of Midkine gene reduces traumatic brain injury through the modulation of neuroinflammation

“…After injury, we confirmed hemorrhage and brain edema in the circular window of the skull. Mice that present cessation of breathing or appendicular convulsions were included in this study as TBI models [33]. Finally, mice were left to recover in their cages with sufficient food and water.…”

Sex as a Biological Variable in Preclinical Modeling of Blast-Related Traumatic Brain Injury

“…There have been several recent reviews on sex differences following TBI in animal models (13,(27)(28)(29). However, the majority of translational TBI work employing both male and female animals has been performed with more severe and/or surgically invasive TBI models such as controlled cortical impact [CCI; e.g., (30)(31)(32)(33)(34)(35)], fluid percussion injury [FPI; e.g., (36,37)], or repetitive concussive brain injury [CBI; e.g., (38,39)]. Although blast injury models have been studied in male animals of many species (23,40), there is a near absence of female inclusion in blast models of neurotrauma.…”