A better mild traumatic brain injury model in the rat

Diffusion Tensor Imaging-Based Studies at the Group-Level Applied to Animal Models of Neurodegenerative Diseases

The understanding of human and non-human microstructural brain alterations in the course of neurodegenerative diseases has substantially improved by the non-invasive magnetic resonance imaging (MRI) technique of diffusion tensor imaging (DTI). Animal models (including disease or knockout models) allow for a variety of experimental manipulations, which are not applicable to humans. Thus, the DTI approach provides a promising tool for cross-species cross-sectional and longitudinal investigations of the neurobiological targets and mechanisms of neurodegeneration. This overview with a systematic review focuses on the principles of DTI analysis as used in studies at the group level in living preclinical models of neurodegeneration. The translational aspect from in-vivo animal models toward (clinical) applications in humans is covered as well as the DTI-based research of the non-human brains' microstructure, the methodological aspects in data processing and analysis, and data interpretation at different abstraction levels. The aim of integrating DTI in multiparametric or multimodal imaging protocols will allow the interrogation of DTI data in terms of directional flow of information and may identify the microstructural underpinnings of neurodegeneration-related patterns.

Cavitation-induced traumatic cerebral contusion and intracerebral hemorrhage in the rat brain by using an off-the-shelf clinical shockwave device

Traumatic cerebral contusion and intracerebral hemorrhages (ICH) commonly result from traumatic brain injury and are associated with high morbidity and mortality rates. Current animal models require craniotomy and provide less control over injury severity. This study proposes a highly reproducible and controllable traumatic contusion and ICH model using non-invasive extracorporeal shockwaves (ESWs). Rat heads were exposed to ESWs generated by an off-the-shelf clinical device plus intravenous injection of microbubbles to enhance the cavitation effect for non-invasive induction of injury. Results indicate that injury severity can be effectively adjusted by using different ESW parameters. Moreover, the location or depth of injury can be purposefully determined by changing the focus of the concave ESW probe. Traumatic contusion and ICH were confirmed by H&E staining. Interestingly, the numbers of TUNEL-positive cells (apoptotic cell death) peaked one day after ESW exposure, while Iba1-positive cells (reactive microglia) and GFAP-positive cells (astrogliosis) respectively peaked seven and fourteen days after exposure. Cytokine assay showed significantly increased expressions of IL-1β, IL-6, and TNF-α. The extent of brain edema was characterized with magnetic resonance imaging. Conclusively, the proposed non-invasive and highly reproducible preclinical model effectively simulates the mechanism of closed head injury and provides focused traumatic contusion and ICH.

Multispectral imaging of cortical vascular and hemodynamic responses to a shock wave: observation of spreading depolarization and oxygen supply-demand mismatch

Blast-induced traumatic brain injury has been a recent major concern in neurotraumatology. However, its pathophysiology and mechanism are not understood partly due to insufficient information on the brain pathophysiology during/immediately after shock wave exposure. We transcranially applied a laser-induced shock wave (LISW, ∼19  Pa  ·  s) to the left frontal region in a rat and performed multispectral imaging of the ipsilateral cortex through a cranial window (n  =  4). For the spectral data obtained, we conducted multiple regression analysis aided by Monte Carlo simulation to evaluate vascular diameters, regional hemoglobin concentration (rCHb), tissue oxygen saturation (StO2), oxygen extraction fraction, and light-scattering signals as a signature of cortical spreading depolarization (CSD). Immediately after LISW exposure, rCHb and StO2 were significantly decreased with distinct venular constriction. CSD was then generated and was accompanied by distinct hyperemia/hyperoxemia. This was followed by oligemia with arteriolar constriction, but it soon recovered (within ∼20  min). However, severe hypoxemia was persistently observed during the post-CSD period (∼1  h). These observations indicate that inadequate oxygen supply and/or excessive oxygen consumption continued even after blood supply was restored in the cortex. Such a hypoxemic state and/or a hypermetabolic state might be associated with brain damage caused by a shock wave.

Repeated In Vitro Impact Conditioning of Astrocytes Decreases the Expression and Accumulation of Extracellular Matrix

Pathological changes to the physical and chemical properties of brain extracellular matrix (ECM) occur following injury. It is generally assumed that astrocytes play an important role in these changes. What remain unclear are the triggers that lead to changes in the regulation of ECM by astrocytes following injury. We hypothesize that mechanical stimulation triggers genotypic and phenotypic changes to astrocytes that could ultimately reshape the ECM composition of the central nervous system following injury. To explore astrocyte mechanobiology, an in vitro drop test bioreactor was employed to condition primary rat astrocytes using short duration (10 ms), high deceleration (150G) and strain (20%) impact stimuli. Experiments were designed to explore the effect of single and repeated impact (single vs. double) on mechano-sensitive behavior including cell viability; ECM gene (collagens I and IV, fibronectin, neurocan, versican) and reactivity gene [glial fibrillary acidic protein (GFAP), S100B, vimentin] expression; matrix regulatory cytokine secretion [matrix metalloproteinase 2 (MMP-2), tissue inhibitor of metalloproteinases 1 (TIMP1), transforming growth factor beta 1 (TGFβ1)]; and matrix accumulation [collagen and glycosaminoglycan (GAG)]. Experiments revealed that both ECM and reactive gliosis gene expression was significantly decreased in response to impact conditioning. The decreases for several genes, including collagen, versican, and GFAP were sensitive to impact number, suggesting mechano-sensitivity to repeated impact conditioning. The measured decreases in ECM gene expression were supported by longer-term in vitro experiments that demonstrated significant decreases in chondroitin sulfate proteoglycan (CSPG) and collagen accumulation within impact conditioned 3-D scaffolds accompanied by a 25% decrease in elastic modulus. Overall, the general trend across all samples was towards altered ECM and reactive gliosis gene expression in response to impact. These results suggest that the regulation of ECM production by astrocytes is sensitive to mechanical stimuli, and that repeated impact conditioning may increase this sensitivity.

Chronic Histopathological and Behavioral Outcomes of Experimental Traumatic Brain Injury in Adult Male Animals

The purpose of this review is to survey the use of experimental animal models for studying the chronic histopathological and behavioral consequences of traumatic brain injury (TBI). The strategies employed to study the long-term consequences of TBI are described, along with a summary of the evidence available to date from common experimental TBI models: fluid percussion injury; controlled cortical impact; blast TBI; and closed-head injury. For each model, evidence is organized according to outcome. Histopathological outcomes included are gross changes in morphology/histology, ventricular enlargement, gray/white matter shrinkage, axonal injury, cerebrovascular histopathology, inflammation, and neurogenesis. Behavioral outcomes included are overall neurological function, motor function, cognitive function, frontal lobe function, and stress-related outcomes. A brief discussion is provided comparing the most common experimental models of TBI and highlighting the utility of each model in understanding specific aspects of TBI pathology. The majority of experimental TBI studies collect data in the acute postinjury period, but few continue into the chronic period. Available evidence from long-term studies suggests that many of the experimental TBI models can lead to progressive changes in histopathology and behavior. The studies described in this review contribute to our understanding of chronic TBI pathology.

Identification of serum microRNA signatures for diagnosis of mild traumatic brain injury in a closed head injury model

Wars in Iraq and Afghanistan have highlighted the problems of diagnosis and treatment of mild traumatic brain injury (mTBI). MTBI is a heterogeneous injury that may lead to the development of neurological and behavioral disorders. In the absence of specific diagnostic markers, mTBI is often unnoticed or misdiagnosed. In this study, mice were induced with increasing levels of mTBI and microRNA (miRNA) changes in the serum were determined. MTBI was induced by varying weight and fall height of the impactor rod resulting in four different severity grades of the mTBI. Injuries were characterized as mild by assessing with the neurobehavioral severity scale-revised (NSS-R) at day 1 post injury. Open field locomotion and acoustic startle response showed behavioral and sensory motor deficits in 3 of the 4 injury groups at day 1 post injury. All of the animals recovered after day 1 with no significant neurobehavioral alteration by day 30 post injury. Serum microRNA (miRNA) profiles clearly differentiated injured from uninjured animals. Overall, the number of miRNAs that were significantly modulated in injured animals over the sham controls increased with the severity of the injury. Thirteen miRNAs were found to identify mTBI regardless of its severity within the mild spectrum of injury. Bioinformatics analyses revealed that the more severe brain injuries were associated with a greater number of miRNAs involved in brain related functions. The evaluation of serum miRNA may help to identify the severity of brain injury and the risk of developing adverse effects after TBI.

Assessing neuro-systemic & behavioral components in the pathophysiology of blast-related brain injury

Among the U.S. military personnel, blast injury is among the leading causes of brain injury. During the past decade, it has become apparent that even blast injury as a form of mild traumatic brain injury (mTBI) may lead to multiple different adverse outcomes, such as neuropsychiatric symptoms and long-term cognitive disability. Blast injury is characterized by blast overpressure, blast duration, and blast impulse. While the blast injuries of a victim close to the explosion will be severe, majority of victims are usually at a distance leading to milder form described as mild blast TBI (mbTBI). A major feature of mbTBI is its complex manifestation occurring in concert at different organ levels involving systemic, cerebral, neuronal, and neuropsychiatric responses; some of which are shared with other forms of brain trauma such as acute brain injury and other neuropsychiatric disorders such as post-traumatic stress disorder. The pathophysiology of blast injury exposure involves complex cascades of chronic psychological stress, autonomic dysfunction, and neuro/systemic inflammation. These factors render blast injury as an arduous challenge in terms of diagnosis and treatment as well as identification of sensitive and specific biomarkers distinguishing mTBI from other non-TBI pathologies and from neuropsychiatric disorders with similar symptoms. This is due to the “distinct” but shared and partially identified biochemical pathways and neuro-histopathological changes that might be linked to behavioral deficits observed. Taken together, this article aims to provide an overview of the current status of the cellular and pathological mechanisms involved in blast overpressure injury and argues for the urgent need to identify potential biomarkers that can hint at the different mechanisms involved.