Repetitive mTBI Research Articles

Assessing Mild Traumatic Brain Injury-Associated Blood-Brain Barrier (BBB) Damage and Restoration Using Late-Phase Perfusion Analysis by 3D ASL MRI: Implications for Predicting Progressive Brain Injury in a Focused Review.

Mild traumatic brain injury (mTBI) is a common occurrence around the world, associated with a variety of blunt force and torsion injuries affecting all age groups. Most never reach medical attention, and the identification of acute injury and later clearance to return to usual activities is relegated to clinical evaluation-particularly in sports injuries. Advanced structural imaging is rarely performed due to the usual absence of associated acute anatomic/hemorrhagic changes. This review targets physiologic imaging techniques available to identify subtle blood-brain barrier dysfunction and white matter tract shear injury and their association with chronic traumatic encephalopathy. These techniques provide needed objective measures to assure recovery from injury in those patients with persistent cognitive/emotional symptoms and in the face of repetitive mTBI.

NHE1 Protein in Repetitive Mild TBI-Mediated Neuroinflammation and Neurological Function Impairment.

Mild traumatic brain injuries (mTBIs) are highly prevalent and can lead to chronic behavioral and cognitive deficits often associated with the development of neurodegenerative diseases. Oxidative stress and formation of reactive oxygen species (ROS) have been implicated in mTBI-mediated axonal injury and pathogenesis. However, the underlying mechanisms and contributing factors are not completely understood. In this study, we explore these pathogenic mechanisms utilizing a murine model of repetitive mTBI (r-mTBI) involving five closed-skull concussions in young adult C57BL/6J mice. We observed a significant elevation of Na+/H+ exchanger protein (NHE1) expression in GFAP+ reactive astrocytes, IBA1+ microglia, and OLIG2+ oligodendrocytes across various brain regions (including the cerebral cortex, corpus callosum, and hippocampus) after r-mTBI. This elevation was accompanied by astrogliosis, microgliosis, and the accumulation of amyloid precursor protein (APP). Mice subjected to r-mTBI displayed impaired motor learning and spatial memory. However, post-r-mTBI administration of a potent NHE1 inhibitor, HOE642, attenuated locomotor and cognitive functional deficits as well as pathological signatures of gliosis, oxidative stress, axonal damage, and white matter damage. These findings indicate NHE1 upregulation plays a role in r-mTBI-induced oxidative stress, axonal damage, and gliosis, suggesting NHE1 may be a promising therapeutic target to alleviate mTBI-induced injuries and restore neurological function.

Profiling the neuroimmune cascade in 3xTg-AD mice exposed to successive mild traumatic brain injuries

Repetitive mild traumatic brain injuries (rmTBI) sustained within a window of vulnerability can result in long term cognitive deficits, depression, and eventual neurodegeneration associated with tau pathology, amyloid beta (Aβ) plaques, gliosis, and neuronal and functional loss. However, a comprehensive study relating acute changes in immune signaling and glial reactivity to neuronal changes and pathological markers after single and repetitive mTBIs is currently lacking. In the current study, we addressed the question of how repeated injuries affect the brain neuroimmune response in the acute phase of injury (< 24 h) by exposing the 3xTg-AD mouse model of tau and Aβ pathology to successive (1x-5x) once-daily weight drop closed-head injuries and quantifying immune markers, pathological markers, and transcriptional profiles at 30 min, 4 h, and 24 h after each injury. We used young adult 2–4 month old 3xTg-AD mice to model the effects of rmTBI in the absence of significant tau and Aβ pathology. We identified pronounced sexual dimorphism in this model, with females eliciting more diverse changes after injury compared to males. Specifically, females showed: (1) a single injury caused a decrease in neuron-enriched genes inversely correlated with inflammatory protein expression and an increase in AD-related genes within 24 h, (2) each injury significantly increased a group of cortical cytokines (IL-1α, IL-1β, IL-2, IL-9, IL-13, IL-17, KC) and MAPK phospho-proteins (phospho-Atf2, phospho-Mek1), several of which co-labeled with neurons and correlated with phospho-tau, and (3) repetitive injury caused increased expression of genes associated with astrocyte reactivity and macrophage-associated immune function. Collectively our data suggest that neurons respond to a single injury within 24 h, while other cell types, including astrocytes, transition to inflammatory phenotypes within days of repetitive injury.

Macroscopic changes in aquaporin-4 underlie blast traumatic brain injury-related impairment in glymphatic function.

Mild traumatic brain injury (mTBI) has emerged as a potential risk factor for the development of neurodegenerative conditions such as Alzheimer's disease and chronic traumatic encephalopathy. Blast mTBI, caused by exposure to a pressure wave from an explosion, is predominantly experienced by military personnel and has increased in prevalence and severity in recent decades. Yet the underlying pathology of blast mTBI is largely unknown. We examined the expression and localization of AQP4 in human post-mortem frontal cortex and observed distinct laminar differences in AQP4 expression following blast exposure. We also observed similar laminar changes in AQP4 expression and localization and delayed impairment of glymphatic function that emerged 28 days following blast injury in a mouse model of repetitive blast mTBI. In a cohort of veterans with blast mTBI, we observed that blast exposure was associated with an increased burden of frontal cortical MRI-visible perivascular spaces, a putative neuroimaging marker of glymphatic perivascular dysfunction. These findings suggest that changes in AQP4 and delayed glymphatic impairment following blast injury may render the post-traumatic brain vulnerable to post-concussive symptoms and chronic neurodegeneration.

Persistent MRI Findings Unique to Blast and Repetitive Mild TBI: Analysis of the CENC/LIMBIC Cohort Injury Characteristics.

MRI represents one of the clinical tools at the forefront of research efforts aimed at identifying diagnostic and prognostic biomarkers following traumatic brain injury (TBI). Both volumetric and diffusion MRI findings in mild TBI (mTBI) are mixed, making the findings difficult to interpret. As such, additional research is needed to continue to elucidate the relationship between the clinical features of mTBI and quantitative MRI measurements. Volumetric and diffusion imaging data in a sample of 976 veterans and service members from the Chronic Effects of Neurotrauma Consortium and now the Long-Term Impact of Military-Relevant Brain Injury Consortium observational study of the late effects of mTBI in combat with and without a history of mTBI were examined. A series of regression models with link functions appropriate for the model outcome were used to evaluate the relationships among imaging measures and clinical features of mTBI. Each model included acquisition site, participant sex, and age as covariates. Separate regression models were fit for each region of interest where said region was a predictor. After controlling for multiple comparisons, no significant main effect was noted for comparisons between veterans and service members with and without a history of mTBI. However, blast-related mTBI were associated with volumetric reductions of several subregions of the corpus callosum compared to non-blast-related mTBI. Several volumetric (i.e., hippocampal subfields, etc.) and diffusion (i.e., corona radiata, superior longitudinal fasciculus, etc.) MRI findings were noted to be associated with an increased number of repetitive mTBIs versus. In deployment-related mTBI, significant findings in this cohort were only observed when considering mTBI sub-groups (blast mechanism and total number/dose). Simply comparing healthy controls and those with a positive mTBI history is likely an oversimplification that may lead to non-significant findings, even in consortium analyses.

Long Noncoding RNA VLDLR-AS1 Levels in Serum Correlate with Combat-Related Chronic Mild Traumatic Brain Injury and Depression Symptoms in US Veterans.

More than 75% of traumatic brain injuries (TBIs) are mild (mTBI) and military service members often experience repeated combat-related mTBI. The chronic comorbidities concomitant with repetitive mTBI (rmTBI) include depression, post-traumatic stress disorder or neurological dysfunction. This study sought to determine a long noncoding RNA (lncRNA) expression signature in serum samples that correlated with rmTBI years after the incidences. Serum samples were obtained from Long-Term Impact of Military-Relevant Brain-Injury Consortium Chronic Effects of Neurotrauma Consortium (LIMBIC CENC) repository, from participants unexposed to TBI or who had rmTBI. Four lncRNAs were identified as consistently present in all samples, as detected via droplet digital PCR and packaged in exosomes enriched for CNS origin. The results, using qPCR, demonstrated that the lncRNA VLDLR-AS1 levels were significantly lower among individuals with rmTBI compared to those with no lifetime TBI. ROC analysis determined an AUC of 0.74 (95% CI: 0.6124 to 0.8741; p = 0.0012). The optimal cutoff for VLDLR-AS1 was ≤153.8 ng. A secondary analysis of clinical data from LIMBIC CENC was conducted to evaluate the psychological symptom burden, and the results show that lncRNAs VLDLR-AS1 and MALAT1 are correlated with symptoms of depression. In conclusion, lncRNA VLDLR-AS1 may serve as a blood biomarker for identifying chronic rmTBI and depression in patients.

Traumatic brain injury-induced peripheral damage: The dynamics of the inflammatory and autophagy pathway from acute to chronic stages.

Traumatic brain injury (TBI) is one of the major causes of death and disability worldwide, and brings a huge burden on the quality of life of patients with TBI and the country's healthcare system. Peripheral organs, especially the kidney, and liver, may be affected by the onset of molecular responses following brain tissue damage. While secondary injury responses post TBI has been well studied in the brain, the effect/consequences of these responses in the peripheral organs have not yet been fully elucidated. Thus, our study aimed to investigate the immunoreactivity of these responses, particularly via proinflammatory cytokines and autophagy markers in the kidney and liver post-acute and chronic TBI. Mild TBI (mTBI) and repetitive mTBI (r-mTBI) were induced in male and female 2-month-old Balb/c mice via the Marmarou weight-drop model. Liver and kidney tissues were sampled at 24 hours (acute) and 30 days (chronic) post TBI and subjected to histopathological and immunoreactivity analysis. Interleukin (IL)-6 levels were significantly increased in the male liver and kidney tissues in both TBI groups compared to the control group but were seen to be decreased in the female r-mTBI chronic liver and r-mTBI acute kidney. Tumor necrosis factor a (TNF-a) levels were found to increase only in the female r-mTBI chronic kidney tissue and mTBI chronic liver tissue. IL-1b levels were increased in the male and female r-mTBI liver tissues but decreased in the female mTBI kidney tissue. Inducible nitric oxide synthase (iNOS) levels were found to be significantly increased in the female mTBI acute and r-mTBI chronic kidney tissue and mTBI liver tissue, but decreased in the r-mTBI acute kidney and r-mTBI liver tissues. Beclin-1 levels were increased in male mTBI chronic and r-mTBI acute liver tissue but decreased in the r-mTBI chronic group. LC3A/B and P62/SQSTM1 levels were significantly increased in the female mTBI chronic and male r-mTBI chronic liver tissues but decreased in the male r-mTBI and female r-mTBI acute kidney tissues. Significant histopathological changes were also observed in the liver and kidney tissue which were dependent on the TBI severity, gender, and time post TBI. The results showed that TBI may elicit peripheral molecular responses, particularly in terms of alteration in the levels of inflammatory cytokines and autophagy markers, which were gender- and time-dependent. This suggests that TBI may have a significant role in the cellular damage of the kidney and liver in both the acute and chronic phases post TBI, thus ensuring that the effects of TBI may not be confined to the brain.

N-3 PUFA ameliorate functional outcomes following repetitive mTBI in the fat-1 mouse model.

Repeated mild traumatic brain injuries (mTBI) are a continuing healthcare concern worldwide, given its potential for enduring adverse neurodegenerative conditions. Past research suggests a potential protective effect of n-3 polyunsaturated fatty acids (PUFA) in experimental models of mTBI. The aim of this study was to investigate whether the neuroprotective benefits of n-3 PUFA persist following repetitive weight drop injury (WDI). Male fat-1 mice (n = 12), able to endogenously convert n-6 PUFA to n-3 PUFA, and their wild type (WT) counterparts (n = 12) were maintained on a 10% w/w safflower diet. At 9-10 weeks of age, both groups received one mild low-impact WDI on the closed cranium daily, for three consecutive days. Following each WDI, time to righting reflex and seeking behaviour were measured. Neurological recovery, cognitive, motor, and neurobehavioural outcomes were assessed using the Neurological Severity Score (NSS) over 7 days (168 h) post-last WDI. Brains were assessed for cerebral microhemorrhages by Prussian blue and cellular damage by glial fibrillary acidic protein (GFAP) staining. Fat-1 mice exhibited significantly faster righting reflex and seeking behaviour time, and lower mean NSS scores and at all post-WDI time points (p ≤ 0.05) compared to WT mice. Immunohistochemistry showed no significant difference in presence of cerebral microhemorrhage however, fat-1 mice had significantly lower GFAP staining in comparison to WT mice (p ≤ 0.05). n-3 PUFA is effective in restoring cognitive, motor, and behavioural function after repetitive WDI, which may be mediated through reduced cellular damage of the brain.

Exploring the Potential of Exosomal Biomarkers in Mild Traumatic Brain Injury and Post-Concussion Syndrome: A Systematic Review.

Alongside their long-term effects, post-concussion syndrome (PCS) and mild traumatic brain injuries (mTBI) are significant public health concerns. Currently, there is a lack of reliable biomarkers for diagnosing and monitoring mTBI and PCS. Exosomes are small extracellular vesicles secreted by cells that have recently emerged as a potential source of biomarkers for mTBI and PCS due to their ability to cross the blood-brain barrier and reflect the pathophysiology of brain injury. In this study, we aimed to investigate the role of salivary exosomal biomarkers in mTBI and PCS. A systematic review using the PRISMA guidelines was conducted, and studies were selected based on their relevance to the topic. The analyzed studies have shown that exosomal tau, phosphorylated tau (p-tau), amyloid beta (Aβ), and microRNAs (miRNAs) are potential biomarkers for mTBI and PCS. Specifically, elevated levels of exosomal tau and p-tau have been associated with mTBI and PCS as well as repetitive mTBI. Dysregulated exosomal miRNAs have also been observed in individuals with mTBI and PCS. Additionally, exosomal Prion cellular protein (PRPc), coagulation factor XIII (XIIIa), synaptogyrin-3, IL-6, and aquaporins have been identified as promising biomarkers for mTBI and PCS. Salivary exosomal biomarkers have the potential to serve as non-invasive and easily accessible diagnostic and prognostic tools for mTBI and PCS. Further studies are needed to validate these biomarkers and develop standardized protocols for their use in clinical settings. Salivary exosomal biomarkers can improve the diagnosis, monitoring, and treatment of mTBI and PCS, leading to improved patient outcomes.

Axonal injury mediated by neuronal p75NTR/TRAF6/JNK pathway contributes to cognitive impairment after repetitive mTBI

Repetitive mild traumatic brain injury (rmTBI) is one of the leading causes of cognitive disorders. The impairment of axonal integrity induced by rmTBI is speculated to underlie the progression of cognitive dysfunction. However, few studies have uncovered the cellular mechanism regulating axonal impairment. In this study, we showed that after rmTBI, the activation of neuronal p75NTR signaling contributes to abnormal axonal morphology and impaired axonal transport, which further leads to cognitive dysfunction in mice. By neuron-specific knockdown of p75NTR or treatment with p75NTR inhibitor LM11A-31, we observed better recovery of axonal integrity and cognitive function after brain trauma. Further analysis revealed that p75NTR relies on its adaptor protein TRAF6 to activate downstream signaling via TAK1 and JNK. Overall, our results provide novel insight into the role of neuronal p75NTR in axonal injury and suggest that p75NTR may be a promising target for cognitive function recovery after rmTBI.

A - 156 History of Mild Traumatic Brain Injury Is Not Associated with worse Neuropsychological Functioning in Amnestic Mild Cognitive Impairment.

The mechanisms for traumatic brain injury (TBI) being a risk factor for Alzheimer's disease is unclear, and whether mild TBI (mTBI) may relate to decreased neural circuit functioning in the prodromal phase is unknown. This study examined whether a history of mTBI was associated with lower functioning of neural circuits, measured with neuropsychological tasks, in amnestic Mild Cognitive Impairment (aMCI). Twenty older adults (MAge = 71years; 70% Male; 90% White) with aMCI were recruited to complete a detailed TBI interview and were classified based on the presence (mTBI+ n = 13) or absence (mTBI- n = 7) of past mTBI. Most mTBI+ participants (n = 11) had multiple mTBIs, and on average were 32years from last injury. A comprehensive neuropsychological assessment was administered, and composite T-scores were calculated for the domains of attention, executive functioning, memory, and language. One-tailed T-tests were conducted to compare the means between groups. No statistically significant differences (p's = 0.06-0.09) were found between the groups in memory (mTBI+ M = 38.11; mTBI- M = 33.19), executive function (mTBI+ M = 48.79; mTBI- M = 43.09), language (mTBI+ M = 48.12; mTBI- M = 43.09), or attention (mTBI+ M = 40.54; mTBI- M = 35.57). Nonetheless, medium effect sizes were seen for the mTBI+ group performing better than the mTBI- group on all composite scores (Cohen's d = 0.45-0.66). A history of mTBI was not associated with poorer neuropsychological performance in aMCI, often a prodromal stage of Alzheimer's disease. While concerns about later-in-life effects from multiple mTBIs is prevalent, repetitive mTBI may not be related to lower neural circuit functioning in aMCI, though further evaluation with larger samples is needed.

A - 146 Subjective and Objective Cognitive Functioning in Women Survivors of Intimate Partner Violence with Repetitive Mild Traumatic Brain Injuries.

This study examined subjective and objective cognitive functioning among women survivors of intimate partner violence (IPV) with a history of repetitive mild traumatic brain injury (mTBI), hypothesizing they would have elevated subjective cognitive complaints and lower objective cognitive test performances compared to national norms. Women were recruited from a domestic violence shelter (N = 16; M = 39.8 ± 7.9years-old) and completed the Neurological Quality-of-Life Cognitive Function questionnaire (Neuro-QoL-CF), Rey Auditory Verbal Learning Test (RAVLT), NIH Toolbox Cognition Battery (NIHTB-CB), and Delis-Kaplan Executive Function System (D-KEFS) Trail Making and Verbal Fluency tests. One-sample t-tests compared mean scores against national norms for the Neuro-QoL-CF, RAVLT trials 1-5 and delayed recall, NIHTB-CB Crystallized-Fluid difference score, and D-KEFS composite index score. Nearly all women (81.3%) reported elevated subjective cognitive concerns on the Neuro-QoL-CF, significantly greater than the national average, t = 10.50, p < 0.001, d = 2.62. RAVLT learning, t = 5.41, p < 0.001, d = -1.35, and delayed recall, t = 4.54, p < 0.001, d = -1.28, were significantly lower than the national average. NIHTB-CB difference scores were significantly higher than the national average, t = 5.23, p < 0.001, d = 1.14, indicating worse fluid cognition than anticipated compared to estimated premorbid functioning. Mean D-KEFS composite scores were comparable to national norms, t = 0.73, p = 0.474, d = 0.18. Women survivors of IPV with repetitive mTBI history had greater subjective cognitive concerns and lower cognitive test performances compared to national norms, indicating cognitive health needs in this population. These findings may be attributable to repetitive mTBI or other neurobehavioral variables that may affect this population, including concurrent physical conditions (e.g., headache), mental illness, chronic pain, substance use, or a combination thereof.

Whole-Blood Metabolomics of a Rat Model of Repetitive Concussion.

Mild traumatic brain injury (mTBI) and repetitive mTBI (RmTBI) are silent epidemics, and so far, there is no objective diagnosis. The severity of the injury is solely based on the Glasgow Coma Score (GCS) scale. Most patients suffer from one or more behavioral abnormalities, such as headache, amnesia, cognitive decline, disturbed sleep pattern, anxiety, depression, and vision abnormalities. Additionally, most neuroimaging modalities are insensitive to capture structural and functional alterations in the brain, leading to inefficient patient management. Metabolomics is one of the established omics technologies to identify metabolic alterations, mostly in biofluids. NMR-based metabolomics provides quantitative metabolic information with non-destructive and minimal sample preparation. We employed whole-blood NMR analysis to identify metabolic markers using a high-field NMR spectrometer (800MHz). Our approach involves chemical-free sample pretreatment and minimal sample preparation to obtain a robust whole-blood metabolic profile from a rat model of concussion. A single head injury was given to the mTBI group, and three head injuries to the RmTBI group. We found significant alterations in blood metabolites in both mTBI and RmTBI groups compared with the control, such as alanine, branched amino acid (BAA), adenosine diphosphate/adenosine try phosphate (ADP/ATP), creatine, glucose, pyruvate, and glycerphosphocholine (GPC). Choline was significantly altered only in the mTBI group and formate in the RmTBI group compared with the control. These metabolites corroborate previous findings in clinical and preclinical cohorts. Comprehensive whole-blood metabolomics can provide a robust metabolic marker for more accurate diagnosis and treatment intervention for a disease population.

Propranolol treatment during repetitive mild traumatic brain injuries induces transcriptomic changes in the bone marrow of mice.

There are 1.5 million new mild traumatic brain injuries (mTBI) annually in the US, with many of the injured experiencing long-term consequences lasting months after the injury. Although the post injury mechanisms are not well understood, current knowledge indicates peripheral immune system activation as a causal link between mTBI and long-term side effects. Through a variety of mechanisms, peripheral innate immune cells are recruited to the CNS after TBI to repair and heal the injured tissue; however, the recruitment and activation of these cells leads to further inflammation. Emerging evidence suggests sympathetic nervous system (SNS) activity plays a substantial role in the recruitment of immune cells post injury. We sought to identify the peripheral innate immune response after repeated TBIs in addition to repurposing the nonselective beta blocker propranolol as a novel mTBI therapy to limit SNS activity and mTBI pathophysiology in the mouse. Mice underwent repetitive mTBI or sham injury followed by i.p. saline or propranolol. Isolated mRNA derived from femur bone marrow of mice was assayed for changes in gene expression at one day, one week, and four weeks using Nanostring nCounter® stem cell characterization panel. Differential gene expression analysis for bone marrow uncovered significant changes in many genes following drug alone, mTBI alone and drug combined with mTBI. Our data displays changes in mRNA at various timepoints, most pronounced in the mTBI propranolol group, suggesting a single dose propranolol injection as a viable future mTBI therapy in the acute setting.

Long-term resting EEG correlates of repetitive mild traumatic brain injury and loss of consciousness: alterations in alpha-beta power.

Long-term changes to EEG spectra after mild traumatic brain injury (mTBI, i.e., concussion) have been reported; however, the role of injury characteristics in long-term EEG changes is unclear. It is also unclear how any chronic EEG changes may underlie either subjective or objective cognitive difficulties, which might help explain the variability in recovery after mTBI. This study included resting-state high-density electroencephalography (EEG) and mTBI injury data from 340 service members and veterans collected on average 11 years after injury as well as measures of objective and subjective cognitive functioning. The average absolute power within standard bands was computed across 11 spatial regions of the scalp. To determine how variation in brain function was accounted for by injury characteristics and aspects of cognition, we used regression analyses to investigate how EEG power was predicted by mTBI history characteristics [number, number with post-traumatic amnesia and witnessed loss of consciousness (PTA + LOC), context of injury (combat or non-combat), potentially concussive blast exposures], subjective complaints (TBIQOL General Cognitive and Executive Function Concerns), and cognitive performance (NIH Toolbox Fluid Intelligence and premorbid IQ). Post-traumatic amnesia (PTA) and loss of consciousness (LOC), poorer cognitive performance, and combat experience were associated with reduced power in beta frequencies. Executive function complaints, lower premorbid IQ, poorer cognitive performance, and higher psychological distress symptoms were associated with greater power of delta frequencies. Multiple regression confirmed the relationship between PTA + LOC, poor cognitive performance, cognitive complaints, and reduced power in beta frequencies and revealed that repetitive mTBI was associated with a higher power in alpha and beta frequencies. By contrast, neither dichotomous classification of the presence and absence of mTBI history nor blast exposures showed a relationship with EEG power variables. Long-term alterations in resting EEG spectra measures of brain function do not appear to reflect any lasting effect of a history of mTBI or blast exposures. However, power in higher frequencies reflects both injury characteristics and subjective and objective cognitive difficulties, while power in lower frequencies is related to cognitive functions and psychological distress associated with poor long-term outcomes after mTBI.

Repeated closed-head mild traumatic brain injury-induced inflammation is associated with nociceptive sensitization.

Individuals who have experienced mild traumatic brain injuries (mTBIs) suffer from several comorbidities, including chronic pain. Despite extensive studies investigating the underlying mechanisms of mTBI-associated chronic pain, the role of inflammation in long-term pain after mTBIs is not fully elucidated. Given the shifting dynamics of inflammation, it is important to understand the spatial-longitudinal changes in inflammatory processes following mTBIs and their effects on TBI-related pain. We utilized a recently developed transgenic caspase-1 luciferase reporter mouse model to monitor caspase-1 activation through a thinned skull window in the in vivo setting following three closed-head mTBI events. Organotypic coronal brain slice cultures and acutely dissociated dorsal root ganglion (DRG) cells provided tissue-relevant context of inflammation signal. Mechanical allodynia was assessed by mechanical withdrawal threshold to von Frey and thermal hyperalgesia withdrawal latency to radiant heat. Mouse grimace scale (MGS) was used to detect spontaneous or non-evoked pain. In some experiments, mice were prophylactically treated with MCC950, a potent small molecule inhibitor of NLRP3 inflammasome assembly to inhibit injury-induced inflammatory signaling. Bioluminescence spatiotemporal dynamics were quantified in the head and hind paws, and caspase-1 activation was confirmed by immunoblot. Immunofluorescence staining was used to monitor the progression of astrogliosis and microglial activation in ex vivo brain tissue following repetitive closed-head mTBIs. Mice with repetitive closed-head mTBIs exhibited significant increases of the bioluminescence signals within the brain and paws in vivo for at least one week after each injury. Consistently, immunoblotting and immunofluorescence experiments confirmed that mTBIs led to caspase-1 activation, astrogliosis, and microgliosis. Persistent changes in MGS and hind paw withdrawal thresholds, indicative of pain states, were observed post-injury in the same mTBI animals in vivo. We also observed enhanced inflammatory responses in ex vivo brain slice preparations and DRG for at least 3days following mTBIs. In vivo treatment with MCC950 significantly reduced caspase-1 activation-associated bioluminescent signals in vivo and decreased stimulus-evoked and non-stimulus evoked nociception. Our findings suggest that the inflammatory states in the brain and peripheral nervous system following repeated mTBIs are coincidental with the development of nociceptive sensitization, and that these events can be significantly reduced by inhibition of NLRP3 inflammasome activation.

Acute effects of single and repeated mild traumatic brain injury on levels of neurometabolites, lipids, and mitochondrial function in male rats.

Mild traumatic brain injuries (mTBIs) are the most common form of acquired brain injury. Symptoms of mTBI are thought to be associated with a neuropathological cascade, potentially involving the dysregulation of neurometabolites, lipids, and mitochondrial bioenergetics. Such alterations may play a role in the period of enhanced vulnerability that occurs after mTBI, such that a second mTBI will exacerbate neuropathology. However, it is unclear whether mTBI-induced alterations in neurometabolites and lipids that are involved in energy metabolism and other important cellular functions are exacerbated by repeat mTBI, and if such alterations are associated with mitochondrial dysfunction. In this experiment, using a well-established awake-closed head injury (ACHI) paradigm to model mTBI, male rats were subjected to a single injury, or five injuries delivered 1 day apart, and injuries were confirmed with a beam-walk task and a video observation protocol. Abundance of several neurometabolites was evaluated 24 h post-final injury in the ipsilateral and contralateral hippocampus using in vivo proton magnetic resonance spectroscopy (1H-MRS), and mitochondrial bioenergetics were evaluated 30 h post-final injury, or at 24 h in place of 1H-MRS, in the rostral half of the ipsilateral hippocampus. Lipidomic evaluations were conducted in the ipsilateral hippocampus and cortex. We found that behavioral deficits in the beam task persisted 1- and 4 h after the final injury in rats that received repetitive mTBIs, and this was paralleled by an increase and decrease in hippocampal glutamine and glucose, respectively, whereas a single mTBI had no effect on sensorimotor and metabolic measurements. No group differences were observed in lipid levels and mitochondrial bioenergetics in the hippocampus, although some lipids were altered in the cortex after repeated mTBI. The decrease in performance in sensorimotor tests and the presence of more neurometabolic and lipidomic abnormalities, after repeated but not singular mTBI, indicates that multiple concussions in short succession can have cumulative effects. Further preclinical research efforts are required to understand the underlying mechanisms that drive these alterations to establish biomarkers and inform treatment strategies to improve patient outcomes.

Repetitive mild traumatic brain injury induces hippocampal neural immune signaling linked to astrocyte reactivity

AbstractBackgroundRepeated mild traumatic brain injuries (mTBIs) sustained within a “window of vulnerability” can lead to a cumulative severity of outcomes such as memory impairment, depression, and long‐term development of amyloid beta (Aβ) pathology and neurofibrillary tangles. We previously reported that acute increases in neural immune signaling within the MAPK pathway and expression of pro‐inflammatory cytokines were associated with low cerebral blood flow (CBF) and worse long‐term spatial learning and memory in a weight‐drop mouse model of repetitive mTBI. We hypothesized that an increasing number of injuries would lead to an increase in neural immune signaling, pathological markers, and glial activation in the hippocampus.MethodFemale 3xTg mice at 3‐4mo of age were subjected to 1x, 3x, or 5x weight‐drop closed head injuries (CHI) spaced once‐daily. Animals were sacrificed and brains harvested at 30min, 4h, 24h, or 1‐month after the final CHI (n = 7‐10/time point/injury group). 32 cytokines, 10 MAPK phospho‐proteins, Aβ42, Aβ40, phospho‐tau (pThr181), and total tau were measured by Luminex in hippocampal tissues. GFAP was measured by ELISA. CBF was non‐invasively measured immediately prior to sacrifice.ResultWe observed a steady increase in both total tau and phospho‐tau and a trend of increased GFAP in the hippocampus after repeated injuries. We then identified groups of cytokines and MAPK phospho‐proteins which co‐vary with either GFAP or phospho‐tau. GFAP‐associated cytokines showed a rapid acute increase after injury then a return to basal levels by 24h, while GFAP‐associated MAPK dynamics changed with repeated injury. Cytokines and MAPK phospho‐proteins showed a notably high degree of cross‐correlation 4h after repeated injury, when GFAP levels were at their highest. Multivariate analysis revealed that high levels of GFAP were associated with low CBF while increased phospho‐tau in the frontal cortex was associated with high CBF.ConclusionTogether, our data indicate an increase in hippocampal neural immune signaling and astrocyte reactivity after repetitive brain injury. Immune signaling changes may be causally linked to spatial learning and memory deficits after repetitive mTBI.

0285 Sleep health in veteran population with and without mild traumatic brain injury

Abstract Introduction Sleep duration is frequently observed in military and Veteran populations. Some of this effect may result from exposure to traumatic brain injury (TBI) during military service. However, other features of combat deployment, circadian disruption, and chronic stress may contribute to poor sleep independent of the effects of TBI. In this study we tested whether combat deployment with or without TBI exposure was associated with poor sleep compared to civilian controls. Methods In a prospective study of Operation Enduring Freedom/Iraqi Freedom/ New Dawn Veterans with repeated blast mild TBI (mTBI) conducted at the VA Puget Sound Healthcare System, self-reported sleep quality was assessed with the Pittsburgh Sleep Quality Index (PSQI). Age-matched civilians (CONciv) non-TBI deployed Veterans (CONdep) were included in the study for comparison. The outcomes of interest included the PSQI sum score and its key components scored as 0-3. One way ANOVA and paired comparison with Bonferroni adjustment for each component were performed . Results A total of 104 mTBI, 36 CONdep and 15 CONciv participants were included. Poor overall sleep quality (PSQI sum&amp;gt;5) was most frequently reported by mTBI participants, followed by CONdep and CONciv participants (80 % vs. 50 vs. 11, p&amp;lt; 0.0001). Across virtually every sleep feature, sleep impairment was most pronounced in mTBI participants followed by CONdep: PSQI sum (mTBI VS. CONdep vs. CONvic= 11.6 vs. 6.5 vs. 3, p&amp;lt; 0.0001), sleep duration (5.5 hrs vs. 6.6 vs. 7.1, p&amp;lt; 0.0001), sleep onset insomnia (2.1 vs. 1.3 vs. 0.3, p&amp;lt; 0.0001) , sleep maintenance insomnia (2.5 vs. 1.4 vs. 0.7, p&amp;lt; 0.0001), daytime sleepiness (1.3 vs. 0.6 vs. 0.4, p&amp;lt; 0.0001), daytime function (1.8 vs. 0.9 vs. 0.3, p&amp;lt; 0.0001) and sleep disturbance by pain (1.5 vs. 0.7 vs. 0.1, p&amp;lt; 0.0001). Both mTBI and CONdep groups had significantly worse sleep quality than the CONciv group. Conclusion Veterans with repetitive mTBI exhibited overall poor sleep quality and impaired sleep in multiple sleep domains. Deployed Veterans without TBI, but exhibited similar, but less severe sleep disruption. Future studies should explore how poor sleep quality may be related to the long-term effects of TBI and military deployment. Support (if any)

Repetitive mild traumatic brain injuries in children of abuse

Repetitive mild traumatic brain injuries in children of abuse