Differences in Post-Traumatic Stress Disorder Symptoms among Post-9/11 Veterans with Blast- and Non-Blast Mild Traumatic Brain Injury

Sex Differences in Early/Unplanned Separation Among US Service Members With a History of Mild Traumatic Brain Injury

OBJECTIVE

To investigate the incidence of early/unplanned (E/U) separations following mild traumatic brain injury (mTBI) and assess whether sex impacts the hazard of separation.

SETTING

Military Health System (MHS).

PARTICIPANTS

Active duty service members (N = 75,730) with an initial mTBI diagnosis in military records between January 2011 and January 2018.

DESIGN

Retrospective cohort study of electronic health records in the MHS. Cause-specific Cox proportional hazards models were used with sex at birth as the primary predictor.

MAIN MEASURES

Early/unplanned (E/U) separation, defined as military separation attributed to disability, misconduct, poor performance, death, or other medical circumstances, within 2 years following the initial mTBI.

RESULTS

Incidence of E/U separation within 2 years following mTBI was 13.7% (11.0% in women and 14.2% in men). Disability and misconduct separations were most common. Female service members had lower adjusted hazards for any E/U separation (Hazard Ratio [HR] = 0.65; 95% Confidence Interval [CI]: 0.61,0.69), disability separation (HR = 0.71; 95% CI: 0.65, 0.78), misconduct separation (HR = 0.40; 95% CI: 0.36, 0.45), and poor performance separation (HR = 0.84; 95% CI: 0.72, 0.99), compared to males, but had higher adjusted hazards for separations due to other medical circumstances (HR = 1.24; 95% CI: 1.04, 1.48).

CONCLUSION

Male and female service members had different hazards of E/U separation following mTBI. Separating early may increase the risk of adverse health and socioeconomic outcomes, so additional research is needed on why these separations occur and why they may be impacting men and women differently.

Additive effects of mild head trauma, blast exposure, and aging within white matter tracts: A novel Diffusion Tensor Imaging analysis approach

Existing diffusion tensor imaging (DTI) studies of neurological injury following high-level blast exposure (hlBE) in military personnel have produced widely variable results. This is potentially due to prior studies often not considering the quantity and/or recency of hlBE, as well as co-morbidity with non-blast head trauma (nbHT). Herein, we compare commonly used DTI metrics: fractional anisotropy and mean, axial, and radial diffusivity, in Veterans with and without history of hlBE and/or nbHT. We use both the traditional method of dividing participants into 2 equally weighted groups and an alternative method wherein each participant is weighted by quantity and recency of hlBE and/or nbHT. While no differences were detected using the traditional method, the alternative method revealed diffuse and extensive changes in all DTI metrics. These effects were quantified within 43 anatomically defined white matter tracts, which identified the forceps minor, middle corpus callosum, acoustic and optic radiations, fornix, uncinate, inferior fronto-occipital and inferior longitudinal fasciculi, and cingulum, as the pathways most affected by hlBE and nbHT. Moreover, additive effects of aging were present in many of the same tracts suggesting that these neuroanatomical effects may compound with age.

Blast-related mild TBI: LIMBIC-CENC focused review with implications commentary

BACKGROUND

A significant factor for the high prevalence of traumatic brain injury (TBI) among U.S. service members is their exposure to explosive munitions leading to blast-related TBI. Our understanding of the specific clinical effects of mild TBI having a component of blast mechanism remains limited compared to pure blunt mechanisms.

OBJECTIVE

The purpose of this review is to provide a synopsis of clinical research findings on the long-term effects of blast-related mild TBI derived to date from the Long-Term Impact of Military-Relevant Brain Injury Consortium - Chronic Effects of Neurotrauma Consortium (LIMBIC-CENC).

METHODS

Publications on blast-related mild TBI from LIMBIC-CENC and the LIMBIC-CENC prospective longitudinal study (PLS) cohort were reviewed and their findings summarized. Findings from the broader literature on blast-related mild TBI that evaluate similar outcomes are additionally reviewed for a perspective on the state of the literature.

RESULTS

The most consistent and compelling evidence for long-term effects of blast-related TBI is for poorer psychological health, greater healthcare utilization and disability levels, neuroimaging impacts on brain structure and function, and greater headache impact on daily life. To date, evidence for chronic cognitive performance deficits from blast-related mild TBI is limited, but futher research including crucial longitudinal data is needed.

CONCLUSION

Commentary is provided on: how LIMBIC-CENC findings assimilate with the broader literature; ongoing research gaps alongside future research needs and priorities; how the scientific community can utilize the LIMBIC-CENC database for independent or collaborative research; and how the evidence from the clinical research should be assimilated into clinical practice.

Executive function improvement in response to meta-cognitive training in chronic mTBI / PTSD

Objective

We tested Goal Management Training (GMT), which has been recommended as an executive training protocol that may improve the deficits in the complex tasks inherent in life role participation experienced by those with chronic mild traumatic brain injury and post-traumatic stress disease (mTBI/PTSD). We assessed, not only cognitive function, but also life role participation (quality of life).

Methods

We enrolled and treated 14 individuals and administered 10 GMT sessions in-person and provided the use of the Veterans Task Manager (VTM), a Smartphone App, which was designed to serve as a "practice-buddy" device to ensure translation of in-person learning to independent home and community practice of complex tasks. Pre-/post-treatment primary measure was the NIH Examiner, Unstructured Task. Secondary measures were as follows: Tower of London time to complete (cTOL), Community Reintegration of Service Members (CRIS) three subdomains [Extent of Participation; Limitations; Satisfaction of Life Role Participation (Satisfaction)]. We analyzed pre-post-treatment, t-test models to explore change, and generated descriptive statistics to inspect given individual patterns of change across measures.

Results

There was statistically significant improvement for the NIH EXAMINER Unstructured Task (p < .02; effect size = .67) and cTOL (p < .01; effect size = .52. There was a statistically significant improvement for two CRIS subdomains: Extent of Participation (p < .01; effect size = .75; Limitations (p < .05; effect size = .59). Individuals varied in their treatment response, across measures.

Conclusions and Clinical Significance

In Veterans with mTBI/PTSD in response to GMT and the VTM learning support buddy, there was significant improvement in executive cognition processes, sufficiently robust to produce significant improvement in community life role participation. The individual variations support need for precision neurorehabilitation. The positive results occurred in response to treatment advantages afforded by the content of the combined GMT and the employment of the VTM learning support buddy, with advantages including the following: manualized content of the GMT; incremental complex task difficulty; GMT structure and flexibility to incorporate individualized functional goals; and the VTM capability of ensuring translation of in-person instruction to home and community practice, solidifying newly learned executive cognitive processes. Study results support future study, including a potential randomized controlled trial, the manualized GMT and availability of the VTM to ensure future clinical deployment of treatment, as warranted.

Volumetric MRI Findings in Mild Traumatic Brain Injury (mTBI) and Neuropsychological Outcome

Region of interest (ROI) volumetric assessment has become a standard technique in quantitative neuroimaging. ROI volume is thought to represent a coarse proxy for making inferences about the structural integrity of a brain region when compared to normative values representative of a healthy sample, adjusted for age and various demographic factors. This review focuses on structural volumetric analyses that have been performed in the study of neuropathological effects from mild traumatic brain injury (mTBI) in relation to neuropsychological outcome. From a ROI perspective, the probable candidate structures that are most likely affected in mTBI represent the target regions covered in this review. These include the corpus callosum, cingulate, thalamus, pituitary-hypothalamic area, basal ganglia, amygdala, and hippocampus and associated structures including the fornix and mammillary bodies, as well as whole brain and cerebral cortex along with the cerebellum. Ventricular volumetrics are also reviewed as an indirect assessment of parenchymal change in response to injury. This review demonstrates the potential role and limitations of examining structural changes in the ROIs mentioned above in relation to neuropsychological outcome. There is also discussion and review of the role that post-traumatic stress disorder (PTSD) may play in structural outcome in mTBI. As emphasized in the conclusions, structural volumetric findings in mTBI are likely just a single facet of what should be a multimodality approach to image analysis in mTBI, with an emphasis on how the injury damages or disrupts neural network integrity. The review provides an historical context to quantitative neuroimaging in neuropsychology along with commentary about future directions for volumetric neuroimaging research in mTBI.

Nanowired Delivery of Cerebrolysin Together with Antibodies to Amyloid Beta Peptide, Phosphorylated Tau, and Tumor Necrosis Factor Alpha Induces Superior Neuroprotection in Alzheimer's Disease Brain Pathology Exacerbated by Sleep Deprivation

Sleep deprivation induces amyloid beta peptide and phosphorylated tau deposits in the brain and cerebrospinal fluid together with altered serotonin metabolism. Thus, it is likely that sleep deprivation is one of the predisposing factors in precipitating Alzheimer's disease (AD) brain pathology. Our previous studies indicate significant brain pathology following sleep deprivation or AD. Keeping these views in consideration in this review, nanodelivery of monoclonal antibodies to amyloid beta peptide (AβP), phosphorylated tau (p-tau), and tumor necrosis factor alpha (TNF-α) in sleep deprivation-induced AD is discussed based on our own investigations. Our results suggest that nanowired delivery of monoclonal antibodies to AβP with p-tau and TNF-α induces superior neuroprotection in AD caused by sleep deprivation, not reported earlier.

Close proximity to blast: No long-term or lasting effect on cognitive performance in service members with and without TBI during blast exposure

OBJECTIVE

Blast related characteristics may contribute to the diversity of findings on whether mild traumatic brain injury sustained during war zone deployment has lasting cognitive effects. This study aims to evaluate whether a history of blast exposure at close proximity, defined as exposure within 30 feet, has long-term or lasting influences on cognitive outcomes among current and former military personnel.

METHOD

One hundred participants were assigned to one of three groups based on a self-report history of blast exposure during combat deployments: 47 close blast, 14 non-close blast, and 39 comparison participants without blast exposure. Working memory, processing speed, verbal learning/memory, and cognitive flexibility were evaluated using standard neuropsychological tests. In addition, assessment of combat exposure and current post-concussive, posttraumatic stress, and depressive symptoms, and headache was performed via self-report measures. Variables that differed between groups were controlled as covariates.

RESULTS

No group differences survived Bonferroni correction for family-wise error rate; the close blast group did not differ from non-close blast and comparison groups on measures of working memory, processing speed, verbal learning/memory, or cognitive flexibility. Controlling for covariates did not alter these results.

CONCLUSION

No evidence emerged to suggest that a history of close blast exposure was associated with decreased cognitive performance when comparisons were made with the other groups. Limited characterization of blast contexts experienced, self-report of blast distance, and heterogeneity of injury severity within the groups are the main limitations of this study.

The association between blast exposure and transdiagnostic health symptoms on systemic inflammation

Chronic elevation of systemic inflammation is observed in a wide range of disorders including PTSD, depression, and traumatic brain injury. Although previous work has demonstrated a link between inflammation and various diagnoses separately, few studies have examined transdiagnostic symptoms and inflammation within the same model. The objective of this study was to examine relationships between psychiatric and health variables and systemic inflammation and to determine whether mild traumatic brain injury (mTBI) and/or exposure to blast munitions moderate these relationships. Confirmatory factor analysis in a large sample (N = 357) of post-9/11 Veterans demonstrated a good fit to a four-factor model reflecting traumatic stress, affective, somatic, and metabolic latent variables. Hierarchical regression models revealed that each of the latent variables were associated with higher levels of systemic inflammation. However, the strongest relationship with inflammation emerged among those who had both war-zone blast exposures and metabolic dysregulation, even after adjusting for mental health latent variables. Exploratory analyses showed that blast exposure was associated with metabolic dysregulation in a dose-response manner, with self-reported closer blast proximity associated with the greatest metabolic dysregulation. Together, these results provide a greater understanding of the types of symptoms most strongly associated with inflammation and underscore the importance of maintaining a healthy lifestyle to reduce the impact of obesity and other metabolic symptoms on future chronic disease in younger to middle-aged Veterans.

Relationship Between Headache Characteristics and a Remote History of TBI in Veterans: A 10-Year Retrospective Chart Review

BACKGROUND AND OBJECTIVES

The objective of this work was to examine the association between deployment-related traumatic brain injury (TBI) severity, frequency, and other injury characteristics with headache outcomes in veterans evaluated at a Veterans Administration (VA) polytrauma support clinic.

METHODS

We conducted a retrospective chart review of 594 comprehensive TBI evaluations between 2011 and 2021. Diagnostic criteria were based on the Department of Defense/VA Consensus-Based Classification of Closed TBI. Adjusted odds ratios (AORs) and 95% CIs were estimated for headache prevalence (logistic), headache severity (ordinal), and prevalence of migraine-like features (logistic) with multiple regression analysis. Regression models were adjusted for age, sex, race/ethnicity, time since injury, and mental health diagnoses.

RESULTS

TBI severity groups were classified as sub concussive exposure (n = 189) and mild (n = 377), moderate (n = 28), and severe TBI (n = 0). Increased headache severity was reported in veterans with mild TBI (AOR 1.72 [95% CI 1.15, 2.57]) and moderate TBI (AOR 3.89 [1.64, 9.15]) compared to those with subconcussive exposure. A history of multiple mild TBIs was associated with more severe headache (AOR 2.47 [1.34, 4.59]) and migraine-like features (AOR 5.95 [2.55, 13.77]). No differences were observed between blast and nonblast injuries; however, greater headache severity was reported in veterans with both primary and tertiary blast effects (AOR 2.56 [1.47, 4.49]). Alteration of consciousness (AOC) and posttraumatic amnesia (PTA) >30 minutes were associated with more severe headache (AOR 3.37 [1.26, 9.17] and 5.40 [2.21, 13.42], respectively). The length of time between the onset of last TBI and the TBI evaluation was associated with headache severity (AOR 1.09 [1.02, 1.17]) and prevalence of migraine-like features (AOR 1.27 [1.15, 1.40]). Last, helmet use was associated with less severe headache (AOR 0.42 [0.23, 0.75]) and lower odds of migraine-like features (AOR 0.45 [0.21, 0.98]).

DISCUSSION

Our data support the notion of a dose-response relationship between TBI severity and headache outcomes. A history of multiple mild TBIs and longer duration of AOC and PTA are unique risk factors for poor headache outcomes in veterans. Furthermore, this study sheds light on the poor headache outcomes associated with subconcussive exposure. Past TBI characteristics should be considered when developing headache management plans for veterans.

Limbic Responses Following Shock Wave Exposure in Male and Female Mice

Blast traumatic brain injury (bTBI) presents a serious threat to military personnel and often results in psychiatric conditions related to limbic system dysfunction. In this study, the functional outcomes for anxiety- and depressive-like behaviors and neuronal activation were evaluated in male and female mice after exposure to an Advanced Blast Simulator (ABS) shock wave. Mice were placed in a ventrally exposed orientation inside of the ABS test section and received primary and tertiary shock wave insults of approximately 15 psi peak pressure. Evans blue staining indicated cases of blood-brain barrier breach in the superficial cerebral cortex four, but not 24 h after blast, but the severity was variable. Behavioral testing with the elevated plus maze (EPM) or elevated zero maze (EZM), sucrose preference test (SPT), and tail suspension test (TST) or forced swim test (FST) were conducted 8 days–3.5 weeks after shock wave exposure. There was a sex difference, but no injury effect, for distance travelled in the EZM where female mice travelled significantly farther than males. The SPT and FST did not indicate group differences; however, injured mice were less immobile than sham mice during the TST; possibly indicating more agitated behavior. In a separate cohort of animals, the expression of the immediate early gene, c-Fos, was detected 4 h after undergoing bTBI or sham procedures. No differences in c-Fos expression were found in the cerebral cortex, but female mice in general displayed enhanced c-Fos activation in the paraventricular nucleus of the thalamus (PVT) compared to male mice. In the amygdala, more c-Fos-positive cells were observed in injured animals compared to sham mice. The observed sex differences in the PVT and c-Fos activation in the amygdala may correlate with the reported hyperactivity of females post-injury. This study demonstrates, albeit with mild effects, behavioral and neuronal activation correlates in female rodents after blast injury that could be relevant to the incidence of increased post-traumatic stress disorder in women.

Investigation of the Relationship Between Frequency of Blast Exposure, mTBI History, and Post-traumatic Stress Symptoms

INTRODUCTION

Post-traumatic stress disorder (PTSD) and mild traumatic brain injury (mTBI) are common conditions among military personnel that frequently co-occur. This study investigated relationships between self-reported blast exposure, mTBI history, and current post-traumatic stress (PTS) symptoms in a population of active duty service members (n = 202) from the Intensive Outpatient Program at the National Intrepid Center of Excellence.

MATERIALS AND METHODS

Participants were divided into four mTBI groups (0, 1, 2, and 3+) and four blast exposure groups (0-10, 11-100, 101-1,000, and 1,000+). Self-reported lifetime mTBI and blast history were obtained via the Ohio State University TBI Identification Method. PTSS severity was obtained via the PTSD Checklist-Civilian version (PCL-C). Several secondary measures of depression, anxiety, chronic mTBI symptoms, and sleep were also assessed.

RESULTS

The total PCL-C scores differed significantly between mTBI groups, with significant differences detected between the 0/1 mTBI groups and the 3+ mTBI groups. Similar group differences were noted across the three PCL-C subgroup scores (avoidance, re-experiencing, and hyperarousal); however, when comparing the proportion of group participants meeting DSM-IV criteria for each symptom cluster, significant differences between mTBI groups were only noted for avoidance (P = .002). No group differences were noted in PTS symptom severity or distribution between blast groups.

CONCLUSIONS

This study demonstrates an association between lifetime mTBI history and PTS symptom severity and distribution but failed to identify the significant group in self-reported symptoms between the blast exposure groups. Results suggest that additional research is needed to understand the neurobiological mechanism behind these associations and the need for the development of precise assessment tools that are able to more accurately quantify significant lifetime sub-concussive and blast exposures experienced by service members in training and combat operations.

Early Stage Longitudinal Subcortical Volumetric Changes following Mild Traumatic Brain Injury

Objective: To investigate early brain volumetric changes from acute to 6 months following mild traumatic brain injury (mTBI) in deep gray matter regions and their association with patient 6-month outcome.Methods: Fifty-six patients with mTBI underwent MRI and behavioral evaluation at acute (<10 days) and approximately 1 and 6 months post injury. Regional volume changes were investigated in key gray matter regions: thalamus, hippocampus, putamen, caudate, pallidum, and amygdala, and compared with volumes from 34 healthy control subjects. In patients with mTBI, we further assessed associations between longitudinal regional volume changes with patient outcome measures at 6 months including post-concussive symptoms, cognitive performance, and overall satisfaction with life.Results: Reduction in thalamic and hippocampal volumes was observed at 1 month among patients with mTBI. Such volume reduction persisted in the thalamus until 6 months. Changes in thalamic volumes also correlated with multiple symptom and functional outcome measures in patients at 6 months.Conclusion: Our results indicate that the thalamus may be differentially affected among patients with mTBI, resulting in both structural and functional deficits with subsequent post-concussive sequelae and may serve as a biomarker for the assessment of efficacy of novel therapeutic interventions.

The effects of posttraumatic stress disorder symptoms on educational functioning in student veterans

Posttraumatic stress disorder (PTSD) occurs at high rates among student veterans and is known to negatively impact educational functioning; however, the unique effects of PTSD are less clear, given that PTSD is highly comorbid with many other conditions that could potentially affect educational functioning. The present study had two objectives: (a) to determine the impact of PTSD symptom severity on educational functioning after accounting for demographic variables, traumatic brain injury, and commonly co-occurring mental health conditions; and (b) to identify which symptom clusters of PTSD have the greatest impact on educational functioning. Educational functioning and other commonly occurring mental health conditions were assessed cross-sectionally among 90 student veterans. Traumatic brain injury and major depressive disorder (MDD) were initially associated with impaired educational functioning; however, after adding PTSD into the final model, only PTSD (β = .44, p < .001) and MDD (β = .31, p = .001) remained associated with educational impairment. Follow-up analyses indicated that the reexperiencing symptom cluster was most strongly associated with impaired educational functioning (β = .28, p = .031). Overall, these results suggest that PTSD symptoms-especially reexperiencing symptoms-may be a driving force behind impaired educational impairment, even after accounting for other commonly co-occurring mental health conditions. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Military TBI—What civilian primary care providers should know

In June 2019, the Department of Veterans Affairs (VA) launched the VA Mission Act, which expanded veterans’ health-care access to the private sector. Since civilian primary care providers may see more veterans in their practice, it will be important to understand the unique experiences, comorbidities, and culture of this population in order to provide optimal care. Military service members (SMs) are at an increased risk for traumatic brain injury (TBI), and comorbidities, such as post traumatic stress disorder (PTSD), increasing the likelihood of prolonged symptoms. Military training and repetitive low-level blast exposure may cause symptoms similar to TBI or increase long-term negative effects in SMs. Military culture often has a strong influence in this population. Those who serve in the military identify with military values and have a strong team mentality, which places emphasis on the mission above all else, not accepting defeat, and not ever leaving a fellow SM behind. These values can impact the way a SM/veteran seeks care and/or communicates with his or her health-care provider. Taking a detailed history to understand how these factors apply, as well as screening for mental health comorbidities, are recommended. Understanding the military cultural influences can assist in promoting a stronger therapeutic alliance and encourage more open communication. Ultimately, it is the trusting and respectful relationship between the SM/veteran and the provider that will determine the most effective treatment and result in the most effective resolution of TBI and comorbid symptoms.

Comparison of Clinical Outcomes 1 and 5 Years Post-Injury Following Combat Concussion

OBJECTIVE

To compare 1-year and 5-year clinical outcomes in 2 groups of combat-deployed service members without brain injury to those of 2 groups with combat-related concussion to better understand long-term clinical outcome trajectories.

METHODS

This prospective, observational, longitudinal multicohort study examined 4 combat-deployed groups: controls without head injury with or without blast exposure and patients with combat concussion arising from blast or blunt trauma. One-year and 5-year clinical evaluations included identical batteries for neurobehavioral, psychiatric, and cognitive outcomes. A total of 347 participants completed both time points of evaluation. Cross-sectional and longitudinal comparisons were assessed. Overall group effect was modeled as a 4-category variable with rank regression adjusting for demographic factors using a 2-sided significance threshold of 0.05, with post hoc Tukey p values calculated for the pairwise comparisons.

RESULTS

Significant group differences in both combat concussion groups were identified cross-sectionally at 5-year follow-up compared to controls in neurobehavioral (Neurobehavioral Rating Scale-Revised [NRS]; Cohen d, -1.10 to -1.40, confidence intervals [CIs] [-0.82, -1.32] to [-0.97, -1.83] by group) and psychiatric domains (Clinician-Administered PTSD Scale for DSM-IV [CAPS]; Cohen d, -0.91 to -1.19, CIs [-0.63, -1.19] to [-0.76, -1.62] by group) symptoms with minimal differences in cognitive performance. Both combat concussion groups also showed clinically significant decline from 1- to 5-year evaluation (66%-76% neurobehavioral NRS; 41%-54% psychiatric CAPS by group). Both control groups fared better but a subset also had clinically significant decline (37%-50% neurobehavioral NRS; 9%-25% psychiatric CAPS by group).

CONCLUSIONS

There was an evolution, not resolution, of symptoms from 1- to 5-year evaluation, challenging the assumption that chronic stages of concussive injury are relatively stable. Even some of the combat-deployed controls worsened. The evidence supports new considerations for chronic trajectories of concussion outcome in combat-deployed service members.

Chronic elevation of plasma vascular endothelial growth factor-A (VEGF-A) is associated with a history of blast exposure

Mounting evidence points to the significance of neurovascular-related dysfunction in veterans with blast-related mTBI, which is also associated with reduced [18F]-fluorodeoxyglucose (FDG) uptake. The goal of this study was to determine whether plasma VEGF-A is altered in veterans with blast-related mTBI and address whether VEGF-A levels correlate with FDG uptake in the cerebellum, a brain region that is vulnerable to blast-related injury 72 veterans with blast-related mTBI (mTBI) and 24 deployed control (DC) veterans with no lifetime history of TBI were studied. Plasma VEGF-A was significantly elevated in mTBIs compared to DCs. Plasma VEGF-A levels in mTBIs were significantly negatively correlated with FDG uptake in cerebellum. In addition, performance on a Stroop color/word interference task was inversely correlated with plasma VEGF-A levels in blast mTBI veterans. Finally, we observed aberrant perivascular VEGF-A immunoreactivity in postmortem cerebellar tissue and not cortical or hippocampal tissues from blast mTBI veterans. These findings add to the limited number of plasma proteins that are chronically elevated in veterans with a history of blast exposure associated with mTBI. It is likely the elevated VEGF-A levels are from peripheral sources. Nonetheless, increasing plasma VEGF-A concentrations correlated with chronically decreased cerebellar glucose metabolism and poorer performance on tasks involving cognitive inhibition and set shifting. These results strengthen an emerging view that cognitive complaints and functional brain deficits caused by blast exposure are associated with chronic blood-brain barrier injury and prolonged recovery in affected regions.

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

Approaches to furthering our understanding of the bioeffects, behavioral changes, and treatment options following exposure to blast are a worldwide priority. Of particular need is a more concerted effort to employ animal models to determine possible sex differences, which have been reported in the clinical literature. In this review, clinical and preclinical reports concerning blast injury effects are summarized in relation to sex as a biological variable (SABV). The review outlines approaches that explore the pertinent role of sex chromosomes and gonadal steroids for delineating sex as a biological independent variable. Next, underlying biological factors that need exploration for blast effects in light of SABV are outlined, including pituitary, autonomic, vascular, and inflammation factors that all have evidence as having important SABV relevance. A major second consideration for the study of SABV and preclinical blast effects is the notable lack of consistent model design—a wide range of devices have been employed with questionable relevance to real-life scenarios—as well as poor standardization for reporting of blast parameters. Hence, the review also provides current views regarding optimal design of shock tubes for approaching the problem of primary blast effects and sex differences and outlines a plan for the regularization of reporting. Standardization and clear description of blast parameters will provide greater comparability across models, as well as unify consensus for important sex difference bioeffects.

Alterations in Plasma microRNA and Protein Levels in War Veterans with Chronic Mild Traumatic Brain Injury

Blast-related mild traumatic brain injury (mTBI) is considered the "signature" injury of the wars in Iraq and Afghanistan. Identifying biomarkers that could aid in diagnosis and assessment of chronic mTBI are urgently needed, as little progress has been made toward identifying blood-based biomarkers of repetitive mTBI in the chronic state. Addressing this knowledge gap is especially important in the population of military veterans who are receiving assessment and care often years after their last exposure. Circulating microRNAs (miRNAs), especially those encapsulated in extracellular vesicles (EVs), have gained interest as a source of biomarkers for neurological conditions. To identify biomarkers for chronic mTBI, we used next generation sequencing (NGS) to analyze miRNAs in plasma and plasma-derived EVs from 27 Iraq and Afghanistan war veterans with blast-related chronic mTBI, 11 deployed veteran non-TBI controls, and 31 civilian controls. We identified 32 miRNAs in plasma and 45 miRNAs in EVs that significantly changed in the chronic mTBI cohort compared with control groups. These miRNAs were predominantly associated with pathways involved in neuronal function, vascular remodeling, blood-brain barrier integrity, and neuroinflammation. In addition, the plasma proteome was analyzed and showed that the concentrations of C-reactive protein (CRP) and membrane metalloendopeptidase (MME) were elevated in chronic mTBI samples. These plasma miRNAs and proteins could potentially be used as biomarkers and provide insights into the molecular processes associated with the long-term health outcomes associated with blast-related chronic mTBI.

Blast Preconditioning Protects Retinal Ganglion Cells and Reveals Targets for Prevention of Neurodegeneration Following Blast-Mediated Traumatic Brian Injury

Purpose

The purpose of this study was to examine the effect of multiple blast exposures and blast preconditioning on the structure and function of retinal ganglion cells (RGCs), to identify molecular pathways that contribute to RGC loss, and to evaluate the role of kynurenine-3-monooxygenase (KMO) inhibition on RGC structure and function.

Methods

Mice were subjected to sham blast injury, one single blast injury, or three blast injuries separated by either 1 hour or 1 week, using a blast intensity of 20 PSI. To examine the effect of blast preconditioning, mice were subjected to sham blast injury, one single 20-PSI injury, or three blast injuries separated by 1 week (5 PSI, 5 PSI, 20 PSI and 5 PSI, 5 PSI, 5 PSI). RGC structure was analyzed by optical coherence tomography (OCT) and function was analyzed by the pattern electroretinogram (PERG). BRN3A-positive cells were quantified to determine RGC density. RNA-seq analysis was used to identify transcriptional changes between groups.

Results

Analysis of mice with multiple blast exposures of 20 PSI revealed no significant differences compared to one 20-pounds per square inch (PSI) exposure using OCT, PERG, or BRN3A cell counts. Analysis of mice exposed to two preconditioning 5-PSI blasts prior to one 20-PSI blast showed preservation of RGC structure and function. RNA-seq analysis of the retina identified multiple transcriptomic changes between conditions. Pharmacologic inhibition of KMO preserved RGC responses compared to vehicle-treated mice.

Conclusions

Preconditioning protects RGC from blast injury. Protective effects appear to involve changes in KMO activity, whose inhibition is also protective.