Chronic Dynamic Behavioral Changes and Upregulation of Glutamatergic Signaling Proteins Following Traumatic Brain Injury in Female Sprague Dawley Rats

STUDY PURPOSE: The purpose of this study was to assess changes in anxiety- and depression-like behavior at 1 week, 4 weeks, 8 weeks, and 12 weeks post-injury in female Sprague Dawley rats using a closed-head controlled impact model of traumatic brain injury and relate behavioral changes to the estrous cycle phase on the date of injury. Alterations in glutamatergic protein expression in the frontal cortex and hippocampus were measured at 12 weeks post-injury. DATA COLLECTED: Closed-head controlled impact was used to model mild traumatic brain injury in 12-week old female Sprague Dawley rats (n=24 animals total). Animals were randomly divided into sham (n=11) and injury (n=13) groups, where the injury group received a single impact at a velocity of 6 m/s, depth of 3 mm, and dwell time of 300 ms while anesthetized under isoflurane anesthesia. Animals had their heads shaved and a rat skull template was used to mark the site of impact over the right parietal cortex prior to impact. The sham group underwent the same procedures but did not receive an impact. Righting response times were recorded following impact (or removal from anesthesia for sham animals). Body weights were recorded every 4 weeks, beginning on the date of impact testing and continuing through 12 weeks. Estrous cycle phase was determined for each animal daily through vaginal cytology beginning 14 days before the date of injury and ending on the date of injury. The open field test was conducted at 1 week post-injury to assess anxiety-like or risk-taking behaviors. The splash test and the three-chamber sociability and social novelty tests were carried out at 4, 8, and 12 weeks post-injury to assess changes in self-care and social behaviors, respectively. Behavioral outcomes of sham and injury groups were compared to one another and across time points, if applicable. Additionally, animals were stratified according to their estrous phase on the date of injury and behavioral metrics for all assessments were analyzed to evaluate the association between estrous phase and injury outcomes. Simple Western was used to assess protein expressional changes in N-methyl-D-aspartate receptor subunits GluN1, GluN2A, and GluN2B, in addition to glutamate transporters GLAST and GLT-1, in the frontal cortex and hippocampus at 12 weeks post-injury. Statistical analyses including one-way ANOVA, repeated measures two-way ANOVA and unpaired t-tests were used to examine differences between groups. DATA USAGE NOTES: