Head Injury Model Research Articles

Increased protein kinase Mζ expression by Minocycline and N-acetylcysteine restores late-phase long-term potentiation and spatial learning after closed head injury in mice.

Cognitive deficits frequently arise after traumatic brain injury. The murine closed head injury (CHI) models these deficits since injured mice cannot acquire Barnes maze. Dosing of minocycline plus N-acetylcysteine beginning 12 hours post-CHI (MN12) restores Barnes maze acquisition by an unknown mechanism. Increased hippocampal synaptic efficacy is needed to acquire Barnes maze, synaptic long-term potentiation (LTP) models this increased synaptic efficacy in vitro . LTP has an early phase (E-LTP) lasting up to one hour that is mediated by second messengers that is followed by a late phase (L-LTP) that needs new synthesis of protein kinase M zeta (PKMζ). PKMζ has constitutive kinase activity because it lacks the autoinhibitory regulatory domain found in other PKCs. Due to its constitutive activity, the amount of PKMζ kinase activity is determined by PKMζ protein levels. We report that CHI bilaterally decreases PKMζ levels in the CA3 and CA1 hippocampus. MN12 increases CA1 PKMζ expression. CHI inhibits E-LTP in slices from the ipsilesional hippocampus and inhibits L-LTP in slices from both hippocamppi. MN12 treatment reestablishes both E-LTP and L-LTP in slices from the injured MN12-treated hippocampus. The restoration of L-LTP from injured MN12-treated hippocampus is mediated by PKMζ because L-LTP is blocked by the specific PKMζ inhibitor, ζ-stat. Hippocampal ζ-stat infusions also prevents Barnes maze acquisition in injured, MN12-treated mice. These data suggest that post-injury minocycline plus N-acetylcysteine targets PKMζ to improve synaptic plasticity and cognition in mice with closed-head injury.

Effect of impact kinematic filters on brain strain responses in contact sports.

Impact kinematics are widely employed to investigate mechanisms of traumatic brain injury (TBI). However, they are susceptible to noise and artefacts; thus, require data filtering. Few studies have focused on how data filtering affects brain strain most relevant to TBI. Here, we report that impact-induced brain strains are much less sensitive to data filtering than kinematics based on three filtering methods: CFC180, lowpass 200Hz, and a new method called Head Exposure to Acceleration Database in Sport (HEADSport). Using mouthguard-measured head impacts in elite rugby (N=5694), average Euclidean distances between the three filtered angular velocity profiles and their unfiltered counterparts are used to identify three groups of impacts with large variations: 90-95th, 95-99th, and >99th percentile. From each group, 20 impacts are randomly selected for simulation using the anisotropic Worcester Head Injury Model (WHIM) V1.0. HEADSport and CFC180 are the most and least effective, respectively, in suppressing "unphysical artefacts" shown as sharp spikes with a rather short impulse duration (e.g., <3 ms) in angular velocity. However, maximum principal strain (MPS), especially that in the corpus callosum, is much less sensitive to data filtering compared to kinematic peaks (e.g., reduction of 3% vs. 47% and 90% for peak angular velocity and acceleration with HEADSport for impacts of >99th percentile). These findings confirm that the brain acts as a low-pass filter, itself, to suppress high frequency noise in impact kinematics. Therefore, brain strain can serve as a common metric for TBI biomechanical studies to maximize relevance to the injury, as it is not sensitive to kinematic filters.

Effects of Repetitive Mild Traumatic Brain Injury on Corticotropin-Releasing Factor Modulation of Lateral Habenula Excitability and Motivated Behavior.

Mild traumatic brain injury (mTBI) is a significant health burden due to mTBI-related chronic debilitating cognitive and psychiatric morbidities. Recent evidence from our laboratory suggests a possible dysregulation within reward/motivational circuit function at the level of a subcortical structure, the lateral habenula (LHb), where we demonstrated a causal role for hyperactive LHb in mTBI-induced motivational deficits in self-care grooming behavior in young adult male mice when exposed to mTBI during late adolescence (at ∼8 weeks old). In this study, we extended this observation by further characterizing neurobehavioral effects of this repetitive closed head injury model of mTBI in both young adult male and female mice on LHb excitability, corticotropin releasing factor (CRF) modulation of LHb activity, and behavioral responses of motivation to self-care behavior and approach versus avoidance behavior in the presence of a social- or threat-related stimulus. We show that mTBI increases LHb spontaneous tonic activity in female mice similar to what we previously observed in male mice, as well as promoting LHb neuronal hyperexcitability and hyperpolarization-induced LHb bursting in both male and female mice. Interestingly, mTBI only increases LHb intrinsic excitability in male mice coincident with higher levels of the hyperpolarization-activated cation currents (HCN/Ih) and reduces levels of the M-type potassium currents while potentiating M-currents without altering intrinsic excitability in LHb neurons of female mice. Because persistent dysregulation of brain CRF systems is suggested to contribute to chronic psychiatric morbidities and that LHb neurons are highly responsive to CRF, we tested whether the LHb CRF subsystem becomes engaged following mTBI. We found that in vitro inhibition of CRF receptor type 1 (CRFR1) within the LHb reverses mTBI-induced enhancement of LHb tonic activity and hyperexcitability in both sexes, suggesting that an augmented intra-LHb CRF-CRFR1-mediated signaling contributes to the overall LHb hyperactivity following mTBI. Behaviorally, mTBI diminishes motivation for self-care grooming in female mice as in male mice. mTBI also alters defensive behaviors in the looming shadow task by shifting the innate defensive behaviors toward more passive action locking rather than escape behaviors in response to an aerial threat in both male and female mice, as well as prolonging the latency to escape responses in female mice. While this model of mTBI reduces social preference in male mice, it induces higher social novelty seeking during the novel social encounters in both male and female mice. Overall, our study provides further translational validity for the use of this pre-clinical model of mTBI for investigation of mTBI-related reward circuit dysfunction and mood/motivation-related behavioral deficits in both sexes while uncovering a few sexually dimorphic neurobehavioral effects of this model that may differentially affect young males and females when exposed to this type of mTBI during late adolescence.

Distinct Serum Glial Fibrillary Acidic Protein and Neurofilament Light Time-Courses After Rapid Head Rotations.

Traumatic brain injury (TBI) causes significant neurophysiological deficits and is typically associated with rapid head accelerations common in sports-related incidents and automobile accidents. There are over 1.5 million TBIs in the United States each year, with children aged 0-4 being particularly vulnerable. TBI diagnosis is currently achieved through interpretation of clinical signs and symptoms and neuroimaging; however, there is increasing interest in minimally invasive fluid biomarkers to detect TBI objectively across all ages. Pre-clinical porcine models offer controlled conditions to evaluate TBI with known biomechanical conditions and without comorbidities. The objective of the current study was to establish pediatric porcine healthy reference ranges (RRs) of common human serum TBI biomarkers and to report their acute time-course after nonimpact rotational head injury. A retrospective analysis was completed to quantify biomarker concentrations in porcine serum samples collected from 4-week-old female (n = 215) and uncastrated male (n = 6) Yorkshire piglets. Subjects were assigned to one of three experimental groups (sham, sagittal-single, sagittal-multiple) or to a baseline only group. A rapid nonimpact rotational head injury model was used to produce mild-to-moderate TBI in piglets following a single rotation and moderate-to-severe TBI following multiple rotations. The Quanterix Simoa Human Neurology 4-Plex A assay was used to quantify glial fibrillary acidic protein (GFAP), neurofilament light (Nf-L), tau, and ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1). The 95% healthy RRs for females were calculated and validated for GFAP (6.3-69.4 pg/mL), Nf-L (9.5-67.2 pg/mL), and UCH-L1 (3.8-533.7 pg/mL). Rising early, GFAP increased significantly above the healthy RRs for sagittal-single (to 164 and 243 pg/mL) and increased significantly higher in sagittal-multiple (to 494 and 413 pg/mL) groups at 30 min and 1 h postinjury, respectively, returning to healthy RRs by 1-week postinjury. Rising later, Nf-L increased significantly above the healthy RRs by 1 day in sagittal-single (to 69 pg/mL) and sagittal-multiple groups (to 140 pg/mL) and rising further at 1 week (single = 231 pg/mL, multiple = 481 pg/mL). Sagittal-single and sagittal-multiple UCH-L1 serum samples did not differ from shams or the healthy RRs. Sex differences were observed but inconsistent. Serum GFAP and Nf-L levels had distinct time-courses following head rotations in piglets, and both corresponded to load exposure. We conclude that serum GFAP and Nf-L offer promise for early TBI diagnosis and intervention decisions for TBI and other neurological trauma.

Effect of Human Head Shape on the Risk of Traumatic Brain Injury: A Gaussian Process Regression-Based Machine Learning Approach.

Computational head injury models are promising tools for understanding and predicting traumatic brain injuries. However, most available head injury models are "average" models that employ a single set of head geometry (e.g., 50th-percentile U.S. male) without considering variability in these parameters across the human population. A significant variability of head shapes exists in U.S. Army soldiers, evident from the Anthropometric Survey of U.S. Army Personnel (ANSUR II). The objective of this study is to elucidate the effects of head shape on the predicted risk of traumatic brain injury from computational head injury models. Magnetic resonance imaging scans of 25 human subjects are collected. These images are registered to the standard MNI152 brain atlas, and the resulting transformation matrix components (called head shape parameters) are used to quantify head shapes of the subjects. A generative machine learning model is used to generate 25 additional head shape parameter datasets to augment our database. Head injury models are developed for these head shapes, and a rapid injurious head rotation event is simulated to obtain several brain injury predictor variables (BIPVs): Peak cumulative maximum principal strain (CMPS), average CMPS, and the volume fraction of brain exceeding an injurious CMPS threshold. A Gaussian process regression model is trained between head shape parameters and BIPVs, which is then used to study the relative sensitivity of the various BIPVs on individual head shape parameters. We distinguish head shape parameters into 2 types: Scaling components ${T_{xx}}$, ${T_{yy}}$, and ${T_{zz}}$ that capture the breadth, length, and height of the head, respectively, and shearing components (${T_{xy}},{T_{xz}},{T_{yx}},{T_{yz}},{T_{zx}}$, and ${T_{zy}}$) that capture the relative skewness of the head shape. An overall positive correlation is evident between scaling components and BIPVs. Notably, a very high, positive correlation is seen between the BIPVs and the head volume. As an example, a 57% increase in peak CMPS was noted between the smallest and the largest investigated head volume parameters. The variation in shearing components ${T_{xy}},{T_{xz}},{T_{yx}},{T_{yz}},{T_{zx}}$, and ${T_{zy}}$ on average does not cause notable changes in the BIPVs. From the Gaussian process regression model, all 3 BIPVs showed an increasing trend with each of the 3 scaling components, but the BIPVs are found to be most sensitive to the height dimension of the head. From the Sobol sensitivity analysis, the ${T_{zz}}$ scaling parameter contributes nearly 60% to the total variance in peak and average CMPS; ${T_{yy}}$ contributes approximately 20%, whereas ${T_{xx}}$ contributes less than 5%. The remaining contribution is from the 6 shearing components. Unlike peak and average CMPS, the VF-CMPS BIPV is associated with relatively evenly distributed Sobol indices across the 3 scaling parameters. Furthermore, the contribution of shearing components on the total variance in this case is negligible. Head shape has a considerable influence on the injury predictions of computational head injury models. Available "average" head injury models based on a 50th-percentile U.S. male are likely associated with considerable uncertainty. In general, larger head sizes correspond to greater BIPV magnitudes, which point to potentially a greater injury risk under rapid neck rotation for people with larger heads.

Development and validation of a nomogram for predicting mortality in patients with acute severe traumatic brain injury: A retrospective analysis.

Recent evidence links the prognosis of traumatic brain injury (TBI) to various factors, including baseline clinical characteristics, TBI specifics, and neuroimaging outcomes. This study focuses on identifying risk factors for short-term survival in severe traumatic brain injury (sTBI) cases and developing a prognostic model. Analyzing 430 acute sTBI patients from January 2018 to December 2023 at the 904th Hospital's Neurosurgery Department, this retrospective case-control study separated patients into survival outcomes: 288 deceased and 142 survivors. It evaluated baseline, clinical, hematological, and radiological data to identify risk and protective factors through univariate and Lasso regression. A multivariate model was then formulated to pinpoint independent prognostic factors, assessing their relationships via Spearman's correlation. The model's accuracy was gauged using the Receiver Operating Characteristic (ROC) curve, with additional statistical analyses for quantitative factors and model effectiveness. Internal validation employed ROC, calibration curves, Decision Curve Analysis (DCA), and Clinical Impact Curves (CIC) to assess model discrimination, utility, and accuracy. The International Mission for Prognosis and Analysis of Clinical Trials in TBI (IMPACT) and Corticosteroid Randomization After Significant Head injury (CRASH) models were also compared through multivariate regression. Factors like unilateral and bilateral pupillary non-reactivity at admission, the derived neutrophil to lymphocyte ratio (dNLR), platelet to lymphocyte ratio (PLR), D-dimer to fibrinogen ratio (DFR), infratentorial hematoma, and Helsinki CT score were identified as independent risk factors (OR > 1), whereas serum albumin emerged as a protective factor (OR < 1). The model showed superior predictive performance with an AUC of 0.955 and surpassed both IMPACT and CRASH models in predictive accuracy. Internal validation confirmed the model's high discriminative capability, clinical relevance, and effectiveness. Short-term survival in sTBI is significantly influenced by factors such as pupillary response, dNLR, PLR, DFR, serum albumin levels, infratentorial hematoma occurrence, and Helsinki CT scores at admission. The developed nomogram accurately predicts sTBI outcomes, offering significant clinical utility.

Temporal variations in immune and inflammatory markers following rodent juvenile traumatic brain injury

Traumatic brain injury (TBI) is one of the leading causes of death and disability in the juvenile population. TBI is associated with elevations in inflammatory signaling. However, the temporal changes in immune and inflammatory markers following TBI, particularly in juvenile studies utilizing the Closed Head Injury Model of Engineered Rotational Acceleration (CHIMERA), have not been fully elucidated. The current study aimed to determine the time course of changes to immune cell expression throughout the first four days following juvenile TBI via the CHIMERA. Male Long Evans rats sustained either a TBI or a Sham TBI via the CHIMERA on post-natal day (PND) 30. Sham animals were euthanized at 3 hours (h) post-injury. TBI animals were euthanized at 0, 3, 6, 12, 24, or 96 h post-injury. Hippocampus samples were collected for use in QRT-PCR. The mRNA expression of cytokines IL1b and TNF-α was significantly elevated at 6 h, and C1q C chain (C1QC), a dendritic cell marker, was significantly elevated at 24 h. The mRNA expression of CD68, a marker for macrophages, was significantly elevated at 6, 24, and 96 h post-injury compared to Sham. CD3G, a marker for T cells, was significantly elevated at 6 hours post-injury. However, the mRNA expression of PTPRC, a marker for leukocytes, was not significantly altered throughout the time periods evaluated. To follow up on these studies, juvenile rats were injured and brains and blood were harvested 48 h post-injury comparing Sham and TBI. Peripheral blood lymphocytes were obtained and sorted by marker-specific antibodies. In the peripheral blood, there was a significantly higher number of CD3+ total T cells, CD3+/CD8 cytotoxic T cells, and CD3+/CD4+ helper T cells in the TBI group compared to the Sham, but CD45R+ total B cells and natural killer (NK) cells were not significantly different. Superior hemi-sected cortices were also used for immune cell extraction. There was a significantly lower number of NK cells and CD45R+ total B cells in the TBI group compared to the Sham, but CD45+ leukocytes and CD3+ total T cells were not significantly different. Further work is needed to understand the relationship between the reduction of specific cells in the brain with the elevation of cells in the peripheral blood. This work is supported by T32HL105324 to AMS. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Cerebral and Peripheral Immune Cell Changes following Rodent Juvenile Traumatic Brain Injury.

Traumatic brain injury (TBI) is one of the leading causes of death and disability. TBI is associated with neuroinflammation, but temporal changes in immune and inflammatory signaling following TBI have not been fully elucidated. Furthermore, there have been no previous studies on changes in immune cell populations following TBI via the Closed Head Injury Model of Engineered Rotational Acceleration (CHIMERA). The current study aimed to determine the time course changes to inflammatory marker mRNA expression in the acute period following TBI in juvenile rats and to determine acute changes to brain and circulating immune cell populations. For this study, post-natal day (PND)-30 male Long Evans rats sustained a TBI or Sham TBI and were euthanized at 0, 3, 6, 12, 24, or 96 h post-injury. Prefrontal cortex and hippocampus samples were used to determine mRNA expression changes of inflammatory factors. The mRNA expression of the pro-inflammatory cytokine TNF-α was significantly elevated at 6 h post-injury in both regions evaluated. To evaluate immune cell populations, male Long Evans rats were euthanized at 48 h post-injury, and brain and blood samples were used for cell sorting by marker-specific antibodies. In the peripheral blood, there was an elevation in CD3+ total T cells, CD45R+ total B cells, and CD3+CD4+ helper T cells in the TBI subjects. However, there were no changes to natural killer cells or CD3+CD8+ cytotoxic T cell populations. In the brain, there was a reduction in CD11b/c+ monocytes/macrophages, but no changes in other immune cell populations. At 48 h post-injury, the TBI subjects also demonstrated expansion of the thymic medulla. These changes in the cerebral and blood immune cell populations and thymic medulla expansion may implicate the subacute recovery timeframe as a vulnerable window for the immune system in the pediatric population.

Comparative analysis of CRASH and IMPACT in predicting the outcome of 340 patients with traumatic brain injury.

Both the International Mission for Prognosis and Analysis of Clinical Trials (IMPACT) and the Corticosteroid randomization after significant head injury (CRASH) models are globally acknowledged prognostic algorithms for assessing traumatic brain injury (TBI) outcomes. The aim of this study is to externalize the validation process and juxtapose the prognostic accuracy of the CRASH and IMPACT models in moderate-to-severe TBI patients in the Chinese population. We conducted a retrospective study encompassing a cohort of 340 adult TBI patients (aged > 18 years), presenting with Glasgow Coma Scale (GCS) scores ranging from 3 to 12. The data were accrued over 2 years (2020-2022). The primary endpoints were 14-day mortality rates and 6-month Glasgow Outcome Scale (GOS) scores. Analytical metrics, including the area under the receiver operating characteristic curve for discrimination and the Brier score for predictive precision were employed to quantitatively evaluate the model performance. Mortality rates at the 14-day and 6-month intervals, as well as the 6-month unfavorable GOS outcomes, were established to be 22.06, 40.29, and 65.59%, respectively. The IMPACT models had area under the curves (AUCs) of 0.873, 0.912, and 0.927 for the 6-month unfavorable GOS outcomes, with respective Brier scores of 0.14, 0.12, and 0.11. On the other hand, the AUCs associated with the six-month mortality were 0.883, 0.909, and 0.912, and the corresponding Brier scores were 0.15, 0.14, and 0.13, respectively. The CRASH models exhibited AUCs of 0.862 and 0.878 for the 6-month adverse outcomes, with uniform Brier scores of 0.18. The 14-day mortality rates had AUCs of 0.867 and 0.87, and corresponding Brier scores of 0.21 and 0.22, respectively. Both the CRASH and IMPACT algorithms offer reliable prognostic estimations for patients suffering from craniocerebral injuries. However, compared to the CRASH model, the IMPACT model has superior predictive accuracy, albeit at the cost of increased computational intricacy.

Investigation of Neuroprotective Efficacy of Dexpanthenol in an Experimental Head Injury Model.

Dexpanthenol (DXP), which has known neuroprotective effects, has been shown to be beneficial in various experimental models and ischaemic diseases. The aim of this study was to investigate the possible neuroprotective effects of DXP in a traumatic brain injury (TBI) model. Thirty-six Wistar-Albino female rats, approximately 6 months old, weighing 220-285 g were used. All rats were subjected to closed head trauma by dropping a weight of 350 g on the parietal region from a height of 50 cm at an angle of 180 degrees in the prepared head trauma model setup. The rats were divided into four groups as control (group 1), trauma (group 2), trauma + DXP (group 3), and DXP (group 4). In group 3, DXP was administered intraperitoneally at a dose of 500 mg/kg for six times at 30 minutes, 6, 12, 24, 36, and 48 hours. In group 4, DXP was administered intraperitoneally simultaneously with group 3 without causing head trauma. Blood samples were taken from all rats 72 hours later for biochemical examination. After blood samples were taken, rats were decapitated under general anaesthesia. Cerebral tissue samples were taken from decapitated rats for immunohistochemical and histopathological examination. Cytokine markers were found to be increased in posttraumatic brain tissue. Malondialdehyde and glutathione reductase levels were lower in group 3 compared to group 2. In addition, superoxide dismutase, glutathione peroxidase and catalase levels were significantly higher in group 3 compared to group 2. In histological evaluation, congestion in the piamater layer, cell infiltration, vascular congestion, hemorrhage and neuronal degeneration were significantly decreased in group 3 compared to group 2. DXP seems to be beneficial in neurological recovery in terms of histological and oxidative changes after head trauma in rats. DXP should be further evaluated for its possible therapeutic effect in TBI.

Glial cells react to closed head injury in a distinct and spatiotemporally orchestrated manner

Traumatic brain injury (TBI) is a leading cause of mortality and disability worldwide. Acute neuroinflammation is a prominent reaction after TBI and is mostly initiated by brain-resident glial cells such as microglia, NG2-glia and astrocytes. The magnitude of this reaction paves the way for long-lasting consequences such as chronic neurological pathologies, for which therapeutic options remain limited. The neuroinflammatory response to TBI is mostly studied with craniotomy-based animal models that are very robust but also rather artificial. Here, we aimed to analyze the reaction of glial cells in a highly translational but variable closed head injury (CHI) model and were able to correlate the severity of the trauma to the degree of glial response. Furthermore, we could show that the different glial cell types react in a temporally and spatially orchestrated manner in terms of morphological changes, proliferation, and cell numbers in the first 15 days after the lesion. Interestingly, NG2-glia, the only proliferating cells in the healthy brain parenchyma, divided at a rate that was correlated with the size of the injury. Our findings describe the previously uncharacterized posttraumatic response of the major brain glial cell types in CHI in order to gain a detailed understanding of the course of neuroinflammatory events; such knowledge may open novel avenues for future therapeutic approaches in TBI.

Testing the Efficacy of Minocycline Treatment in an Awake, Female Rat Model of Repetitive Mild Head Injury

Minocycline is being tested in clinical trials for the treatment of stroke and traumatic brain injury. As an antibiotic it reduces microglia activation. Can minocycline be used to treat mild repetitive head injury? To that end, minocycline was tested in a novel, closed-head, momentum exchange model of repetitive mild head injury in female rats impacted while fully awake. Magnetic resonance imaging (MRI) revealed there was no brain damage or contusion attesting to the mild nature of the head impacts in this model. It was hypothesized that drug treatment would reduce edema and brain neuroinflammation. Female rats maintained on a reverse light-dark cycle were head impacted three times while fully awake with and without drug treatment. The impacts, separated by 24 hrs each, were delivered under red light illumination. Within 1-2 hrs of the last impact, rats were assessed for changes in water diffusion using diffusion weighted imaging. The data were registered to a 3D MRI rat atlas with 173 segmented brain areas providing site specific information on altered brain gray matter microarchitecture. Postmortem histology was performed 18 days post head injury. Head injury without minocycline treatment was characterized by multiple areas of increased fractional anisotropy, evidence of cytotoxic edema. Treatment with minocycline reversed these measures in many of the same areas and several others (e.g., hippocampus, basal ganglia, prefrontal cortex, sensory and motor cortices and thalamus). Histology for gliosis showed no evidence of neuroinflammation in the thalamus, hippocampus and cerebellum for control or experimental groups in this female model of mild head injury. These studies provide clear evidence that treatment with minocycline within hours after mild repetitive head injury significantly reduce measures of cytotoxic edema in a female rat model of mild repetitive head injury.

Altered brain connectivity, neuroinflammation and AD‐related markers following 7 days after repetitive mild traumatic brain injury in young wild‐type mice

AbstractBackgroundTraumatic brain injuries (TBI) substantially increase the risk for neurodegenerative disorders including tauopathies and synucleinopathies. Repetitive mild TBI (rmTBI) exacerbate damage in brain impacting cognitive and emotional processes through lifetime. Therefore, there is a critical need to identify the molecular mechanisms underlying TBI‐mediated brain dysfunction. In doing so, we can develop effective therapies as the etiology for dementia remain poorly understood. Our goal is to identify early, unbiased, and novel biomarkers of brain dysfunction following rmTBI. These include defects in the brain connectome and protein expression in the areas most functionally susceptible to damage following rmTBI.MethodTo do this, we exposed young male and female C57BL/6J wild‐type mice to two rmTBI (2 × 0.6 J impacts/24 h apart) using the closed head injury model of engineered rotational acceleration (CHIMERA) or sham procedures. We measured changes in brain functional connectivity (FC) using resting state functional MRI (rsfMRI) and graph theory, examined microstructural differences in white and grey matter regions through diffusion tensor imaging (DTI) analyses, surveyed neuropathological proteins using NanoString‐GeoMx Digital spatial protein profiling spatial profiling (DSP).ResultThe rsfMRI data revealed that rmTBI induces aberrant changes in the graph metrics such as node clustering coefficient, global and local efficiency, participation coefficient, eigenvector centrality, and betweenness centrality in brain regions processing visual, auditory, and somatosensory information. The optic tract and thalamus were the most affected regions showing significant differences in phospho‐tau (S199), neuroinflammatory markers (GFAP, Iba‐1, GPNMB), and other proteolytic (cathepsin‐D) and proliferation (ki‐67) cell markers. We identified extensive white matter damage, defects in brain FC, and exacerbated anatomically distinct protein profiles.ConclusionThese findings align with results reported in individuals with TBI such as diffuse axonal damage, glial activation, and functional network disruption in the visual tract and specific thalamic regions. Upcoming studies will evaluate the potential use of using brain imaging along with molecular markers to predict longitudinal damage after rmTBI.

Characterization of Traumatic Brain Injury in a Gyrencephalic Ferret Model Using the Novel Closed Head Injury Model of Engineered Rotational Acceleration (CHIMERA).

Traumatic brain injury (TBI) results from mechanical force to the brain and leads to a series of biochemical responses that further damage neurons and supporting cells. Clinically, most TBIs result from an impact to the intact skull, making closed head TBI pre-clinical models highly relevant. However, most of these closed head TBI models use lissencephalic rodents, which may not transduce biomechanical load in the same manner as gyrencephalic humans. To address this translational gap, this study aimed to characterize acute axonal injury and microglial responses in ferrets-the smallest gyrencephalic mammal. Injury was induced in male ferrets (Mustela furo; 1.20-1.51 kg; 6-9 months old) with the novel Closed Head Injury Model of Engineered Rotational Acceleration (CHIMERA) model. Animals were randomly allocated to either sham (n = 4), a 22J (joules) impact (n = 4), or a 27J impact (n = 4). Axonal injury was examined histologically with amyloid precursor protein (APP), neurofilament M (RMO 14.9) (RMO-14), and phosphorylated tau (AT180) and the microglial response with ionized calcium-binding adaptor molecule 1 at 24 h post-injury in gray and white matter regions. Graded axonal injury was observed with modest increases in APP and RMO-14 immunoreactivity in the 22J TBI group, mostly within the corpus callosum and fornix and more extensive diffuse axonal injury encompassing gray matter structures like the thalamus and hypothalamus in the 27J group. Accompanying microglial activation was only observed in the 27J group, most prominently within the white matter tracts in response to the larger amounts of axonal injury. The 27J, but not the 22J, group showed an increase in AT180 within the base of the sulci post-injury. This could suggest that the strain may be highest in this region, demonstrating the different responses in gyrencephalic compared to lissencephalic brains. The CHIMERA model in ferrets mimic many of the histopathological features of human closed head TBI acutely and provides a promising model to investigate the pathophysiology of TBI.

Repeated mild traumatic brain injury causes sex-specific increases in cell proliferation and inflammation in juvenile rats

Childhood represents a period of significant growth and maturation for the brain, and is also associated with a heightened risk for mild traumatic brain injuries (mTBI). There is also concern that repeated-mTBI (r-mTBI) may have a long-term impact on developmental trajectories. Using an awake closed head injury (ACHI) model, that uses rapid head acceleration to induce a mTBI, we investigated the acute effects of repeated-mTBI (r-mTBI) on neurological function and cellular proliferation in juvenile male and female Long-Evans rats. We found that r-mTBI did not lead to cumulative neurological deficits with the model. R-mTBI animals exhibited an increase in BrdU + (bromodeoxyuridine positive) cells in the dentate gyrus (DG), and that this increase was more robust in male animals. This increase was not sustained, and cell proliferation returning to normal by PID3. A greater increase in BrdU + cells was observed in the dorsal DG in both male and female r-mTBI animals at PID1. Using Ki-67 expression as an endogenous marker of cellular proliferation, a robust proliferative response following r-mTBI was observed in male animals at PID1 that persisted until PID3, and was not constrained to the DG alone. Triple labeling experiments (Iba1+, GFAP+, Brdu+) revealed that a high proportion of these proliferating cells were microglia/macrophages, indicating there was a heightened inflammatory response. Overall, these findings suggest that rapid head acceleration with the ACHI model produces an mTBI, but that the acute neurological deficits do not increase in severity with repeated administration. R-mTBI transiently increases cellular proliferation in the hippocampus, particularly in male animals, and the pattern of cell proliferation suggests that this represents a neuroinflammatory response that is focused around the mid-brain rather than peripheral cortical regions. These results add to growing literature indicating sex differences in proliferative and inflammatory responses between females and males. Targeting proliferation as a therapeutic avenue may help reduce the short term impact of r-mTBI, but there may be sex-specific considerations.

Application of Delayed Contrast Extravasation Magnetic Resonance Imaging for Depicting Subtle Blood-Brain Barrier Disruption in a Traumatic Brain Injury Model.

The blood-brain barrier (BBB) is composed of brain microvasculature that provides selective transport of solutes from the systemic circulation into the central nervous system to protect the brain and spinal microenvironment. Damage to the BBB in the acute phase after traumatic brain injury (TBI) is recognized as a major underlying mechanism leading to secondary long-term damage. Because of the lack of technological ability to detect subtle BBB disruption (BBBd) in the chronic phase, however, the presence of chronic BBBd is disputable. Thus, the dynamics and course of long-term BBBd post-TBI remains elusive. Thirty C57BL/6 male mice subjected to TBI using our weight drop closed head injury model and 19 naïve controls were scanned by magnetic resonance imaging (MRI) up to 540 days after injury. The BBB maps were calculated from delayed contrast extravasation MRI (DCM) with high spatial resolution and high sensitivity to subtle BBBd, enabling depiction and quantification of BBB permeability. At each time point, 2-6 animals were sacrificed and their brains were extracted, sectioned, and stained for BBB biomarkers including: blood microvessel coverage by astrocyte using GFAP, AQP4, ZO-1 gaps, and IgG leakage. We found that DCM provided depiction of subtle yet significant BBBd up to 1.5 years after TBI, with significantly higher sensitivity than standard contrast-enhanced T1-weighted and T2-weighted MRI (BBBd volumes main effect DCM/T1/T2 p < 0.0001 F(2,70) = 107.3, time point p < 0.0001 F(2,133, 18.66) = 23.53). In 33% of the cases, both in the acute and chronic stages, there was no detectable enhancement on standard T1-MRI, nor detectable hyperintensities on T2-MRI, whereas DCM showed significant BBBd volumes. The BBBd values of TBI mice at the chronic stage were found significantly higher compared with age matched naïve animals at 30, 60, and 540 days. The calculated BBB maps were histologically validated by determining significant correlation between the calculated levels of disruption and a diverse set of histopathological parameters obtained from different brain regions, presenting different components of the BBB. Cumulative evidence from recent years points to BBBd as a central component of the pathophysiology of TBI. Therefore, it is expected that routine use of highly sensitive non-invasive techniques to measure BBBd, such as DCM with advanced analysis methods, may enhance our understanding of the changes in BBB function after TBI. Application of the DCM technology to other CNS disorders, as well as to normal aging, may shed light on the involvement of chronic subtle BBBd in these conditions.

Acute Extra-Arachnoid Subdural Hematomas in Patients 50 Years and Older: When Subdurals Act Like Epidurals

Some patients with subdural hematoma (SDH) with acute extra-arachnoid lesions and without concomitant subarachnoid blood or contusions may present in similarly grave neurological condition compared with the general population of patients with SDH. However, these patients often make an impressive neurological recovery. This study compared neurological outcomes in patients with extra-arachnoid SDH with all other SDH patients. We compared a prospective series of extra-arachnoid SDH patients without subarachnoid hemorrhage or other concomitant intracranial injury with a Transforming Research and Clinical Knowledge in TBI control group with SDH only. We performed inverse probability weighting for key characteristics and ordinal regression with and without controlling for midline shift comparing neurological outcomes (Extended Glasgow Outcome Scale score) at 2 weeks. We used the Corticosteroid Randomization After Significant Head Injury prognostic model to predict mortality based on age, Glasgow Coma Scale score, pupil reactivity, and major extracranial injury. Mean midline shift was significantly different between extra-arachnoid SDH and control groups (7.2 mm vs. 2.7 mm, P < 0.001). After weighting for group allocation and controlling for midline shift, extra-arachnoid SDH patients had 5.68 greater odds (P < 0.001) of a better 2-week Extended Glasgow Outcome Scale score than control patients. Mortality in the extra-arachnoid SDH group was less than predicted by the Corticosteroid Randomization After Significant Head Injury prognostic model (10% vs. 21% predicted). Patients with extra-arachnoid SDH have significantly better 2-week neurological outcomes and lower mortality than predicted by the Corticosteroid Randomization After Significant Head Injury model. Neurosurgeons should consider surgery for this patient subset even in cases of poor neurological examination, older age, and large hematoma with high degree of midline shift.

Mitochondrial dysfunction underlies impaired neurovascular coupling following traumatic brain injury

Traumatic brain injury (TBI) involves an acute injury (primary damage), which may evolve in the hours to days after impact (secondary damage). Seizures and cortical spreading depolarization (CSD) are metabolically demanding processes that may worsen secondary brain injury. Metabolic stress has been associated with mitochondrial dysfunction, including impaired calcium homeostasis, reduced ATP production, and elevated ROS production. However, the association between mitochondrial impairment and vascular function after TBI is poorly understood. Here, we explored this association using a rodent closed head injury model. CSD is associated with neurobehavioral decline after TBI. Craniotomy was performed to elicit CSD via electrical stimulation or to induce seizures via 4-aminopyridine application. We measured vascular dysfunction following CSDs and seizures in TBI animals using laser doppler flowmetry. We observed a more profound reduction in local cortical blood flow in TBI animals compared to healthy controls. CSD resulted in mitochondrial dysfunction and pathological signs of increased oxidative stress adjacent to the vasculature. We explored these findings further using electron microscopy and found that TBI and CSDs resulted in vascular morphological changes and mitochondrial cristae damage in astrocytes, pericytes and endothelial cells. Overall, we provide evidence that CSDs induce mitochondrial dysfunction, impaired cortical blood flow, and neurobehavioral deficits in the setting of TBI.

A Morphologically Individualized Deep Learning Brain Injury Model.

The brain injury modeling community has recommended improving model subject specificity and simulation efficiency. Here, we extend an instantaneous (< 1 sec) convolutional neural network (CNN) brain model based on the anisotropic Worcester Head Injury Model (WHIM) V1.0 to account for strain differences due to individual morphological variations. Linear scaling factors relative to the generic WHIM along the three anatomical axes are used as additional CNN inputs. To generate training samples, the WHIM is randomly scaled to pair with augmented head impacts randomly generated from real-world data for simulation. An estimation of voxelized peak maximum principal strain of the whole-brain is said to be successful when the linear regression slope and Pearson's correlation coefficient relative to directly simulated do not deviate from 1.0 (when identical) by more than 0.1. Despite a modest training dataset (N = 1363 vs. ∼5.7 k previously), the individualized CNN achieves a success rate of 86.2% in cross-validation for scaled model responses, and 92.1% for independent generic model testing for impacts considered as complete capture of kinematic events. Using 11 scaled subject-specific models (with scaling factors determined from pre-established regression models based on head dimensions and sex and age information, and notably, without neuroimages), the morphologically individualized CNN remains accurate for impacts that also yield successful estimations for the generic WHIM. The individualized CNN instantly estimates subject-specific and spatially detailed peak strains of the entire brain and thus, supersedes others that report a scalar peak strain value incapable of informing the location of occurrence. This tool could be especially useful for youths and females due to their anticipated greater morphological differences relative to the generic model, even without the need for individual neuroimages. It has potential for a wide range of applications for injury mitigation purposes and the design of head protective gears. The voxelized strains also allow for convenient data sharing and promote collaboration among research groups.

Modified mouse model of repeated mild traumatic brain injury through a thinned-skull window and fluid percussion.

Mild traumatic brain injury (mTBI) is a clinically highly heterogeneous neurological disorder, none of the existing animal models can replicate the entire sequelae. This study aimed to develop a modified closed head injury (CHI) model of repeated mTBI (rmTBI) for investigating Ca2+ fluctuations of the affected neural network, the alternations of electrophysiology, and behavioral dysfunctions. The transcranial Ca2+ study protocol includes AAV-GCaMP6s infection in the right motor cortex, thinned-skull preparation, and two-photon laser scanning microscopy (TPLSM) imaging. The CHI rmTBI model is fabricated using the thinned-skull site and applying 2.0 atm fluid percussion with 48-h interval. The neurological dysfunction, minor motor performance, evident mood, spatial working, and reference deficits we found in this study mimic the clinically relevant syndromes after mTBI. Besides, our study revealed that there was a trend of transition from Ca2+ singlepeak to multipeak and plateau, and the total Ca2+ activities of multipeaks and plateaus (p < .001 vs. pre-rmTBI value) were significantly increased in ipsilateral layer 2/3 motor neurons after rm TBI. In parallel, there is a low-frequency power shift from delta to theta band (p < .01 vs. control) in the ipsilateral layer 2/3 of motor cortex of the rmTBI mice, and the overall firing rates significantly increased (p < .01 vs. control). Moreover, rmTBI causes slight cortical and hippocampal neuron damage and possibly induces neurogenesis in the dentate gyrus (DG). The alternations of Ca2+ and electrophysiological characteristics in layer 2/3 neuronal network, histopathological changes, and possible neurogenesis may play concertedly and partially contribute to the functional outcome post-rmTBI.