Mossy cell hypertrophy and synaptic changes in the hilus following mild diffuse traumatic brain injury in pigs

The Neurovascular Unit Dysfunction in the Molecular Mechanisms of Epileptogenesis and Targeted Therapy

Epilepsy is a multifaceted neurological syndrome characterized by recurrent, spontaneous, and synchronous seizures. The pathogenesis of epilepsy, known as epileptogenesis, involves intricate changes in neurons, neuroglia, and endothelium, leading to structural and functional disorders within neurovascular units and culminating in the development of spontaneous epilepsy. Although current research on epilepsy treatments primarily centers around anti-seizure drugs, it is imperative to seek effective interventions capable of disrupting epileptogenesis. To this end, a comprehensive exploration of the changes and the molecular mechanisms underlying epileptogenesis holds the promise of identifying vital biomarkers for accurate diagnosis and potential therapeutic targets. Emphasizing early diagnosis and timely intervention is paramount, as it stands to significantly improve patient prognosis and alleviate the socioeconomic burden. In this review, we highlight the changes and molecular mechanisms of the neurovascular unit in epileptogenesis and provide a theoretical basis for identifying biomarkers and drug targets.

Maladaptation of dentate gyrus mossy cells mediates contextual discrimination deficit after traumatic stress

Fear overgeneralization is a maladaptive response to traumatic stress that is associated with the inability to discriminate between threat and safety contexts, a hallmark feature of post-traumatic stress disorder (PTSD). However, the neural mechanisms underlying this deficit remain unclear. Here, we show that traumatic stress exposure impairs contextual discrimination between threat and safety contexts in the learned helplessness (LH) model. Mossy cells (MCs) in the dorsal hippocampus are suppressed in response to traumatic stress. Bidirectional manipulation of MC activity in the LH model reveals that MC inhibition is causally linked to impaired contextual discrimination. Mechanistically, MC inhibition increases the number of active granule cells in a given context, significantly overlapping context-specific ensembles. Our study demonstrates that maladaptive inhibition of MCs after traumatic stress is a substantial mechanism underlying fear overgeneralization with contextual discrimination deficit, suggesting a potential therapeutic target for cognitive symptoms of PTSD.

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

INTRODUCTION

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.

MATERIAL AND METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Cytoarchitectureal changes in hippocampal subregions of the NZB/W F1 mouse model of lupus

Over 50% of clinical patients affected by the systemic lupus erythematosus disease display impaired neurological cognitive functions and psychiatric disorders, a form called neuropsychiatric systemic lupus erythematosus. Hippocampus is one of the brain structures most sensitive to the cognitive deficits and psychiatric disorders related to neuropsychiatric lupus. The purpose of this study was to compare, layer by layer, neuron morphology in lupus mice model NZB/W F1 versus Wild Type mice. By a morphometric of cells identified on Nissl-stained sections, we evaluated structural alterations between NZB/W F1 and Wild Type mice in seven hippocampal subregions: Molecular dentate gyrus, Granular dentate gyrus, Polymorph dentate gyrus, Oriens layer, Pyramidal layer, Radiatum layer and Lacunosum molecular layer. By principal component analysis we distinguished healthy Wild Type from NZB/W F1 mice. In NZB/W F1 mice hippocampal cytoarchitecture, the neuronal cells resulted larger in size and more regular than those of Wild Type. In NZB/W F1, neurons were usually denser than in WT. The Pyramidal layer neurons were much denser in Wild Type than in NZB/W F1. Application of principal component analysis, allowed to distinguish NZB/W F1 lupus mice from healthy, showing as NZBW subjects presented a scattered distribution and intrasubject variability. Our results show a hypertrophy of the NZB/W F1 hippocampal neurons associated with an increase in perikaryal size within the CA1, CA2, CA3 region and the DG. These results help advance our understanding on hippocampal organization and structure in the NZB/W F1 lupus model, suggesting the hypothesis that the different subregions could be differentially affected in neuropsychiatric systemic lupus erythematosus disease. Leveraging an in-depth analysis of the morphology of neural cells in the hippocampal subregions and applying dimensionality reduction using PCA, we propose an efficient methodology to distinguish pathological NZBW mice from WT mice."

Persistence of Hyper-Ramified Microglia in Porcine Cortical Gray Matter after Mild Traumatic Brain Injury

Traumatic brain injury (TBI) is a major contributor to morbidity and mortality in the United States as several million people visit the emergency department every year due to TBI exposures. Unfortunately, there is still no consensus on the pathology underlying mild TBI, the most common severity sub-type of TBI. Previous preclinical and post-mortem human studies have detailed the presence of diffuse axonal injury following TBI, suggesting that white matter pathology is the predominant pathology of diffuse brain injury. However, the inertial loading produced by TBI results in strain fields in both gray and white matter. In order to further characterize gray matter pathology in mild TBI, our lab used a pig model (n = 25) of closed-head rotational acceleration-induced TBI to evaluate blood-brain barrier disruptions, neurodegeneration, astrogliosis, and microglial reactivity in the cerebral cortex out to 1 year post-injury. Immunohistochemical staining revealed the presence of a hyper-ramified microglial phenotype-more branches, junctions, endpoints, and longer summed process length-at 30 days post injury (DPI) out to 1 year post injury in the cingulate gyrus (p < 0.05), and at acute and subacute timepoints in the inferior temporal gyrus (p < 0.05). Interestingly, we did not find neuronal loss or astroglial reactivity paired with these chronic microglia changes. However, we observed an increase in fibrinogen reactivity-a measure of blood-brain barrier disruption-predominately in the gray matter at 3 DPI (p = 0.0003) which resolved to sham levels by 7 DPI out to chronic timepoints. Future studies should employ gene expression assays, neuroimaging, and behavioral assays to elucidate the effects of these hyper-ramified microglia, particularly related to neuroplasticity and responses to potential subsequent insults. Further understanding of the brain's inflammatory activity after mild TBI will hopefully provide understanding of pathophysiology that translates to clinical treatment for TBI.

Multimodal Neuromonitoring and Neurocritical Care in Swine to Enhance Translational Relevance in Brain Trauma Research

Neurocritical care significantly impacts outcomes after moderate-to-severe acquired brain injury, but it is rarely applied in preclinical studies. We created a comprehensive neurointensive care unit (neuroICU) for use in swine to account for the influence of neurocritical care, collect clinically relevant monitoring data, and create a paradigm that is capable of validating therapeutics/diagnostics in the unique neurocritical care space. Our multidisciplinary team of neuroscientists, neurointensivists, and veterinarians adapted/optimized the clinical neuroICU (e.g., multimodal neuromonitoring) and critical care pathways (e.g., managing cerebral perfusion pressure with sedation, ventilation, and hypertonic saline) for use in swine. Moreover, this neurocritical care paradigm enabled the first demonstration of an extended preclinical study period for moderate-to-severe traumatic brain injury with coma beyond 8 h. There are many similarities with humans that make swine an ideal model species for brain injury studies, including a large brain mass, gyrencephalic cortex, high white matter volume, and topography of basal cisterns, amongst other critical factors. Here we describe the neurocritical care techniques we developed and the medical management of swine following subarachnoid hemorrhage and traumatic brain injury with coma. Incorporating neurocritical care in swine studies will reduce the translational gap for therapeutics and diagnostics specifically tailored for moderate-to-severe acquired brain injury.

Understanding microglial responses in large animal models of traumatic brain injury: an underutilized resource for preclinical and translational research

Traumatic brain injury (TBI) often results in prolonged or permanent brain dysfunction with over 2.8 million affected annually in the U.S., including over 56,000 deaths, with over 5 million total survivors exhibiting chronic deficits. Mild TBI (also known as concussion) accounts for over 75% of all TBIs every year. Mild TBI is a heterogeneous disorder, and long-term outcomes are dependent on the type and severity of the initial physical event and compounded by secondary pathophysiological consequences, such as reactive astrocytosis, edema, hypoxia, excitotoxicity, and neuroinflammation. Neuroinflammation has gained increasing attention for its role in secondary injury as inflammatory pathways can have both detrimental and beneficial roles. For example, microglia-resident immune cells of the central nervous system (CNS)-influence cell death pathways and may contribute to progressive neurodegeneration but also aid in debris clearance and neuroplasticity. In this review, we will discuss the acute and chronic role of microglia after mild TBI, including critical protective responses, deleterious effects, and how these processes vary over time. These descriptions are contextualized based on interspecies variation, sex differences, and prospects for therapy. We also highlight recent work from our lab that was the first to describe microglial responses out to chronic timepoints after diffuse mild TBI in a clinically relevant large animal model. The scaled head rotational acceleration of our large animal model, paired with the gyrencephalic architecture and appropriate white:gray matter ratio, allows us to produce pathology with the same anatomical patterns and distribution of human TBI, and serves as an exemplary model to examine complex neuroimmune response post-TBI. An improved understanding of microglial influences in TBI could aid in the development of targeted therapeutics to accentuate positive effects while attenuating detrimental post-injury responses over time.

A multiscale tissue assessment in a rat model of mild traumatic brain injury

Diffusion tensor imaging (DTI) has demonstrated the potential to assess the pathophysiology of mild traumatic brain injury (mTBI) but correlations of DTI findings and pathological changes in mTBI are unclear. We evaluated the potential of ex vivo DTI to detect tissue damage in a mild mTBI rat model by exploiting multiscale imaging methods, histology and scanning micro-X-ray diffraction (SμXRD) 35 days after sham-operation (n = 2) or mTBI (n = 3). There were changes in DTI parameters rostral to the injury site. When examined by histology and SμXRD, there was evidence of axonal damage, reduced myelin density, gliosis, and ultrastructural alterations in myelin that were ongoing at the experimental time point of 35 days postinjury. We assessed the relationship between the 3 imaging modalities by multiple linear regression analysis. In this analysis, DTI and histological parameters were moderately related, whereas SμXRD parameters correlated weakly with DTI and histology. These findings suggest that while DTI appears to distinguish tissue changes at the microstructural level related to the loss of myelinated axons and gliosis, its ability to visualize alterations in myelin ultrastructure is limited. The use of several imaging techniques represents a novel approach to reveal tissue damage and provides new insights into mTBI detection.

Non-Linear Device Head Coupling and Temporal Delays in Large Animal Acceleration Models of Traumatic Brain Injury

Accurate characterization of head kinematics following an external blow represents a fundamental aspect of traumatic brain injury (TBI) research. The majority of previous large animal studies have assumed an equivalent relationship between the device delivering the impulsive load and subsequent head kinematics rather than performing direct measurement (sensors or videography). The current study therefore examined factors affecting device/head coupling kinematics in an acceleration TBI model. Experiment 1 indicated ~ 50% reduction in peak angular velocity for swine head relative to the device, with an approximate doubling in temporal duration. The peak angular velocity for the head was not significantly altered by variations in restraint device (straps vs. cables), animal positioning or body mass. In Experiment 2, reducing the impulsive load by 32% resulted in only a 14% reduction in angular velocity of the head (approximately 69% head/device coupling ratio), with more pronounced differences qualitatively observed for angular momentum. A temporal delay was identified in initial device/head coupling, potentially a result of soft tissue deformation. Finally, similar head kinematics were obtained regardless of mounting the sensor directly to the skull or through the scalp (Experiment 3). Current findings highlight the importance of direct measurement of head kinematics for future studies.

Post-Traumatic Epilepsy and Comorbidities: Advanced Models, Molecular Mechanisms, Biomarkers, and Novel Therapeutic Interventions

Post-traumatic epilepsy (PTE) is one of the most devastating long-term, network consequences of traumatic brain injury (TBI). There is currently no approved treatment that can prevent onset of spontaneous seizures associated with brain injury, and many cases of PTE are refractory to antiseizure medications. Post-traumatic epileptogenesis is an enduring process by which a normal brain exhibits hypersynchronous excitability after a head injury incident. Understanding the neural networks and molecular pathologies involved in epileptogenesis are key to preventing its development or modifying disease progression. In this article, we describe a critical appraisal of the current state of PTE research with an emphasis on experimental models, molecular mechanisms of post-traumatic epileptogenesis, potential biomarkers, and the burden of PTE-associated comorbidities. The goal of epilepsy research is to identify new therapeutic strategies that can prevent PTE development or interrupt the epileptogenic process and relieve associated neuropsychiatric comorbidities. Therefore, we also describe current preclinical and clinical data on the treatment of PTE sequelae. Differences in injury patterns, latency period, and biomarkers are outlined in the context of animal model validation, pathophysiology, seizure frequency, and behavior. Improving TBI recovery and preventing seizure onset are complex and challenging tasks; however, much progress has been made within this decade demonstrating disease modifying, anti-inflammatory, and neuroprotective strategies, suggesting this goal is pragmatic. Our understanding of PTE is continuously evolving, and improved preclinical models allow for accelerated testing of critically needed novel therapeutic interventions in military and civilian persons at high risk for PTE and its devastating comorbidities.

Relationships between injury kinematics, neurological recovery, and pathology following concussion

Mild traumatic brain injury affects millions of individuals annually primarily through falls, traffic collisions, or blunt trauma and can generate symptoms that persist for years. Closed-head rotational loading is the most common cause of mild traumatic brain injury and is defined by a rapid rotational acceleration of brain tissue within an intact skull. Injury kinematics-the mechanical descriptors of injury-inducing motion-explain movement of the head, which govern energy transfer, and, therefore, determine injury severity. However, the relationship between closed-head rotational injury kinematics-such as angular velocity, angular acceleration, and injury duration-and outcome after mild traumatic brain injury is not completely understood. To address this gap in knowledge, we analysed archived surgical records of 24 swine experiencing a diffuse closed-head rotational acceleration mild traumatic brain injury against 12 sham animals. Kinematics were contrasted against acute recovery outcomes, specifically apnea time, extubation time, standing time, and recovery duration. Compared to controls, animals experiencing a mild traumatic brain injury were far more likely to have apnea (P < 0.001), shorter time to extubation (P = 0.023), and longer time from extubation to standing (P = 0.006). Using least absolute shrinkage and selection operator-based regressions, kinematic parameters, including maximum negative angular velocity and time from peak angular velocity to maximum angular deceleration, were selected to explain variation in apnea time, standing time, and recovery duration. Simplified linear models employing the least absolute shrinkage and selection operator-selected variables explained a modest degree of variation in apnea time (adjusted R 2 = 0.18), standing time (adjusted R 2 = 0.19), and recovery duration (adjusted R 2 = 0.27). Neuropathology was correlated with multiple injury kinematics, with maximum angular acceleration exhibiting the strongest correlation (R 2 = 0.66). Together, these data suggest the interplay between multiple injury kinematics, including maximum negative angular velocity (immediately preceding cessation of head motion) and time from peak angular velocity to maximum angular deceleration, best explain acute recovery metrics and neuropathology after mild traumatic brain injury in swine. Future experiments that independently manipulate individual kinematic parameters could be instrumental in developing translational diagnostics for clinical mild traumatic brain injury.

Diverse changes in microglia morphology and axonal pathology during the course of 1 year after mild traumatic brain injury in pigs

Over 2.8 million people experience mild traumatic brain injury (TBI) in the United States each year, which may lead to long-term neurological dysfunction. The mechanical forces that are caused by TBI propagate through the brain to produce diffuse axonal injury (DAI) and trigger secondary neuroinflammatory cascades. The cascades may persist from acute to chronic time points after injury, altering the homeostasis of the brain. However, the relationship between the hallmark axonal pathology of diffuse TBI and potential changes in glial cell activation or morphology have not been established in a clinically relevant large animal model at chronic time points. In this study, we assessed the tissue from pigs subjected to rapid head rotation in the coronal plane to generate mild TBI. Neuropathological assessments for axonal pathology, microglial morphological changes, and astrocyte reactivity were conducted in specimens out to 1-year post-injury. We detected an increase in overall amyloid precursor protein pathology, as well as periventricular white matter and fimbria/fornix pathology after a single mild TBI. We did not detect the changes in corpus callosum integrity or astrocyte reactivity. However, detailed microglial skeletal analysis revealed changes in morphology, most notably increases in the number of microglial branches, junctions, and endpoints. These subtle changes were most evident in periventricular white matter and certain hippocampal subfields, and were observed out to 1-year post-injury in some cases. These ongoing morphological alterations suggest persistent change in neuroimmune homeostasis. Additional studies are needed to characterize the underlying molecular and neurophysiological alterations, as well as potential contributions to neurological deficits.

The Immune System's Role in the Consequences of Mild Traumatic Brain Injury (Concussion)

Mild traumatic brain injury (mild TBI), often referred to as concussion, is the most common form of TBI and affects millions of people each year. A history of mild TBI increases the risk of developing emotional and neurocognitive disorders later in life that can impact on day to day living. These include anxiety and depression, as well as neurodegenerative conditions such as chronic traumatic encephalopathy (CTE) and Alzheimer's disease (AD). Actions of brain resident or peripherally recruited immune cells are proposed to be key regulators across these diseases and mood disorders. Here, we will assess the impact of mild TBI on brain and patient health, and evaluate the recent evidence for immune cell involvement in its pathogenesis.

Relationships between injury kinematics, neurological recovery, and pathology following concussion

Mild traumatic brain injury affects millions of individuals annually primarily through falls, traffic collisions, or blunt trauma and can generate symptoms that persist for years. Closed-head rotational loading is the most common cause of mild traumatic brain injury and is defined by a rapid rotational acceleration of brain tissue within an intact skull. Injury kinematics-the mechanical descriptors of injury-inducing motion-explain movement of the head, which govern energy transfer, and, therefore, determine injury severity. However, the relationship between closed-head rotational injury kinematics-such as angular velocity, angular acceleration, and injury duration-and outcome after mild traumatic brain injury is not completely understood. To address this gap in knowledge, we analysed archived surgical records of 24 swine experiencing a diffuse closed-head rotational acceleration mild traumatic brain injury against 12 sham animals. Kinematics were contrasted against acute recovery outcomes, specifically apnea time, extubation time, standing time, and recovery duration. Compared to controls, animals experiencing a mild traumatic brain injury were far more likely to have apnea (P < 0.001), shorter time to extubation (P = 0.023), and longer time from extubation to standing (P = 0.006). Using least absolute shrinkage and selection operator-based regressions, kinematic parameters, including maximum negative angular velocity and time from peak angular velocity to maximum angular deceleration, were selected to explain variation in apnea time, standing time, and recovery duration. Simplified linear models employing the least absolute shrinkage and selection operator-selected variables explained a modest degree of variation in apnea time (adjusted R ² = 0.18), standing time (adjusted R ² = 0.19), and recovery duration (adjusted R ² = 0.27). Neuropathology was correlated with multiple injury kinematics, with maximum angular acceleration exhibiting the strongest correlation (R ² = 0.66). Together, these data suggest the interplay between multiple injury kinematics, including maximum negative angular velocity (immediately preceding cessation of head motion) and time from peak angular velocity to maximum angular deceleration, best explain acute recovery metrics and neuropathology after mild traumatic brain injury in swine. Future experiments that independently manipulate individual kinematic parameters could be instrumental in developing translational diagnostics for clinical mild traumatic brain injury.