Resilience of females to acute blood-brain barrier damage and anxiety behavior following mild blast traumatic brain injury

Abstract

Low-level blast exposure can result in neurological impairment for military personnel. Currently, there is a lack of experimental data using sex as a biological variable in neurovascular outcomes following blast exposure. To model mild blast traumatic brain injury (mbTBI), male and female rats were exposed to a single 11psi static peak overpressure blast wave using the McMillan blast device and cohorts were then euthanized at 6h, 24h, 7d, and 14d post-blast followed by isolation of the amygdala. After mbTBI, animals experience immediate bradycardia, although no changes in oxygen saturation levels or acute weight loss. Male mbTBI animals displayed significantly higher levels of anxiety-like behavior (open field and elevated plus maze) compared to male sham groups; however, there was no anxiety phenotype in female mbTBI animals. Blast-induced neurovascular damage was explored by measuring expression of tight junction (TJ) proteins (zonula occludens-1 (ZO-1), occludin and claudin-5), glial fibrillary acidic protein (GFAP) and astrocyte end-feet coverage around the blood-brain barrier (BBB). Western blot analysis demonstrates that TJ protein levels were significantly decreased at 6h and 24h post-mbTBI in male rats, but not in female rats, compared to sham. Female animals have decreased GFAP at 6h post-mbTBI while male animals display decreased GFAP expression at 24h post-mbTBI. By 7d post-mbTBI, there were no significant differences in TJ or GFAP levels between groups in either sex. At 24h post-mbTBI, vascular integrity and astrocytic end-feet coverage around the BBB was significantly decreased in males following mbTBI. These results demonstrate that loss of GFAP expression may be due to astrocytic damage at the BBB. Our findings also demonstrate sex differences in acute vascular and behavioral outcomes after single mbTBI. Female animals display a lack of BBB pathology after mbTBI corresponding to improved acute neuropsychological outcomes as compared to male animals.

Timing matters: Sex differences in acute and chronic outcomes following repetitive blast mild traumatic brain injury

“…In line with these results, models of single moderate to severe impact TBI have demonstrated disparate inflammatory outcomes in male vs. female mice acutely following injury (Bromberg et al, 2020; Doran et al, 2019; Krukowski, 2021; Krukowski et al, 2020; Späni et al, 2018; Villapol et al, 2017). Likewise, a recent study using a single mild blast exposure with body shielding reported worse acute and sub-acute neuroinflammatory and BBB outcomes in male vs. female rats (Hubbard et al, 2022). The discrepancy between this study and our current results of similar BBB disruption in male vs. female blast mice is likely due to the repetitive nature of our blast model, suggesting that while female rodents are protected from acute single TBI effects, repetitive blast exposure is sufficient to result in cytokine changes and BBB disruption in females as well as males.…”

“…In relation to potential sex differences in adverse behavioral outcomes following blast exposure, only three studies thus far have been reported (Hubbard et al, 2022; McNamara et al, 2022; Russell, Handa, et al, 2018). Hubbard et al (2022) found increased anxiety-like behavior in male but not female rats in the open field (at 2 days post) and elevated plus maze (at 14 days post) following single blast mTBI with body shielding. Conversely, McNamara et al (2022) found no injury effects in either female or male mice on the elevated plus and zero mazes when tested at 2-4 weeks post single blast exposure.…”

“…Indeed, few preclinical studies have included both male and female animals and the few that have, have exclusively focused on impact TBI, a single TBI exposure, and/or only examined acute timepoints. While a handful of reports have characterized potential sex differences following a single blast exposure (Hubbard et al, 2022; Kawa et al, 2020; McNamara et al, 2022; Russell, Handa, et al, 2018; Russell, Richardson, et al, 2018), very little is known about the effects of repetitive blast exposure in male vs. female rodents.…”