Lateral fluid percussion: model of traumatic brain injury in mice

Deplete and repeat: microglial CSF1R inhibition and traumatic brain injury

Traumatic brain injury (TBI) is a public health burden affecting millions of people. Sustained neuroinflammation after TBI is often associated with poor outcome. As a result, increased attention has been placed on the role of immune cells in post-injury recovery. Microglia are highly dynamic after TBI and play a key role in the post-injury neuroinflammatory response. Therefore, microglia represent a malleable post-injury target that could substantially influence long-term outcome after TBI. This review highlights the cell specific role of microglia in TBI pathophysiology. Microglia have been manipulated via genetic deletion, drug inhibition, and pharmacological depletion in various pre-clinical TBI models. Notably, colony stimulating factor 1 (CSF1) and its receptor (CSF1R) have gained much traction in recent years as a pharmacological target on microglia. CSF1R is a transmembrane tyrosine kinase receptor that is essential for microglia proliferation, differentiation, and survival. Small molecule inhibitors targeting CSF1R result in a swift and effective depletion of microglia in rodents. Moreover, discontinuation of the inhibitors is sufficient for microglia repopulation. Attention is placed on summarizing studies that incorporate CSF1R inhibition of microglia. Indeed, microglia depletion affects multiple aspects of TBI pathophysiology, including neuroinflammation, oxidative stress, and functional recovery with measurable influence on astrocytes, peripheral immune cells, and neurons. Taken together, the data highlight an important role for microglia in sustaining neuroinflammation and increasing risk of oxidative stress, which lends to neuronal damage and behavioral deficits chronically after TBI. Ultimately, the insights gained from CSF1R depletion of microglia are critical for understanding the temporospatial role that microglia develop in mediating TBI pathophysiology and recovery.

Functional connectivity, tissue microstructure and T2 at 11.1 Tesla distinguishes neuroadaptive differences in two traumatic brain injury models in rats: A Translational Outcomes Project in NeuroTrauma (TOP-NT) UG3 phase study

The damage caused by contusive traumatic brain injuries (TBIs) is thought to involve breakdown in neuronal communication through focal and diffuse axonal injury along with alterations to the neuronal chemical environment, which adversely affects neuronal networks beyond the injury epicenter(s). In the present study, functional connectivity along with brain tissue microstructure coupled with T2 relaxometry were assessed in two experimental TBI models in rat, controlled cortical impact (CCI) and lateral fluid percussive injury (LFPI). Rats were scanned on an 11.1 Tesla scanner on days 2 and 30 following either CCI or LFPI. Naive controls were scanned once and used as a baseline comparison for both TBI groups. Scanning included functional magnetic resonance imaging (fMRI), diffusion weighted images (DWI), and multi-echo T2 images. fMRI scans were analyzed for functional connectivity across laterally and medially located region of interests (ROIs) across the cortical mantle, hippocampus, and dorsal striatum. DWI scans were processed to generate maps of fractional anisotropy, mean, axial, and radial diffusivities (FA, MD, AD, RD). The analyses focused on cortical and white matter (WM) regions at or near the TBI epicenter. Our results indicate that rats exposed to CCI and LFPI had significantly increased contralateral intra-cortical connectivity at 2 days post-injury. This was observed across similar areas of the cortex in both groups. The increased contralateral connectivity was still observed by day 30 in CCI, but not LFPI rats. Although both CCI and LFPI had changes in WM and cortical FA and diffusivities, WM changes were most predominant in CCI and cortical changes in LFPI. Our results provide support for the use of multimodal MR imaging for different types of contusive and skull-penetrating injury.

Selective neuroimmune modulation by type I interferon drives neuropathology and neurologic dysfunction following traumatic brain injury

Accumulating evidence suggests that type I interferon (IFN-I) signaling is a key contributor to immune cell-mediated neuropathology in neurodegenerative diseases. Recently, we demonstrated a robust upregulation of type I interferon-stimulated genes in microglia and astrocytes following experimental traumatic brain injury (TBI). The specific molecular and cellular mechanisms by which IFN-I signaling impacts the neuroimmune response and neuropathology following TBI remains unknown. Using the lateral fluid percussion injury model (FPI) in adult male mice, we demonstrated that IFN α/β receptor (IFNAR) deficiency resulted in selective and sustained blockade of type I interferon-stimulated genes following TBI as well as decreased microgliosis and monocyte infiltration. Molecular alteration of reactive microglia also occurred with diminished expression of genes needed for MHC class I antigen processing and presentation following TBI. This was associated with decreased accumulation of cytotoxic T cells in the brain. The IFNAR-dependent modulation of the neuroimmune response was accompanied by protection from secondary neuronal death, white matter disruption, and neurobehavioral dysfunction. These data support further efforts to leverage the IFN-I pathway for novel, targeted therapy of TBI.

Cortical Brain Injury Causes Retrograde Degeneration of Afferent Basal Forebrain Cholinergic Neurons via the p75NTR

Traumatic brain injury (TBI) elicits neuronal loss at the site of injury and progressive neuronal loss in the penumbra. However, the consequences of TBI on afferent neurons projecting to the injured tissue from distal locations is unknown. Basal forebrain cholinergic neurons (BFCNs) extend long projections to multiple brain regions including the cortex, regulate many cognitive functions, and are compromised in numerous neurodegenerative disorders. To determine the consequence of cortical injury on these afferent neurons, we used the fluid percussion injury model of traumatic brain injury and assessed the effects on BFCN survival and axon integrity in male and female mice. Survival or death of BF neurons can be regulated by neurotrophins or proneurotrophins, respectively. The injury elicited an induction of proNGF and proBDNF in the cortex and a loss of BFCNs ipsilateral to the injury compared with sham uninjured mice. The p75NTR knock-out mice did not show loss of BFCN neurons, indicating a retrograde degenerative effect of the cortical injury on the afferent BFCNs mediated through p75NTR. In contrast, locus ceruleus neurons, which also project throughout the cortex, were unaffected by the injury, suggesting specificity in retrograde degeneration after cortical TBI. Proneurotrophins (proNTs) provided directly to basal forebrain axons in microfluidic cultures triggered retrograde axonal degeneration and cell death, which did not occur in the absence of p75NTR. This study shows that after traumatic brain injury, proNTs induced in the injured cortex promote BFCN axonal degeneration and retrograde neuron loss through p75NTR.

Mature and Myelinating Oligodendrocytes Are Specifically Vulnerable to Mild Fluid Percussion Injury in Mice

Myelin loss and oligodendrocyte death are well documented in patients with traumatic brain injury (TBI), as well as in experimental animal models after moderate-to-severe TBI. In comparison, mild TBI (mTBI) does not necessarily result in myelin loss or oligodendrocyte death, but causes structural alterations in the myelin. To gain more insight into the impact of mTBI on oligodendrocyte lineage in the adult brain, we subjected mice to mild lateral fluid percussion injury (mFPI) and characterized the early impact (1 and 3 days post-injury) on oligodendrocytes in the corpus callosum using multiple oligodendrocyte lineage markers (platelet-derived growth factor receptor [PDGFR]-α, glutathione S-transferase [GST]-π, CC1, breast carcinoma-amplified sequence 1 [BCAS1], myelin basic protein [MBP], myelin-associated glycoprotein [MAG], proteolipid protein [PLP], and FluoroMyelin™). Two regions of the corpus callosum in relation to the impact site were analyzed: areas near (focal) and anterior (distal) to the impact site. mFPI did not result in oligodendrocyte death in either the focal or distal corpus callosum, nor impact on oligodendrocyte precursors (PDGFR-α+) and GST-π+ oligodendrocyte numbers. In the focal but not distal corpus callosum, mFPI caused a decrease in CC1+ as well as BCAS1+ actively myelinating oligodendrocytes and reduced FluoroMyelin intensity without altering myelin protein expression (MBP, PLP, and MAG). Disruption in node-paranode organization and loss of Nav1.6+ nodes were observed in both the focal and distal regions, even in areas without obvious axonal damage. Altogether, our study shows regional differences in mature and myelinating oligodendrocyte in response to mFPI. Further, mFPI elicits a widespread impact on node-paranode organization that affects regions both close to and remotely located from the site of injury.

Models of traumatic brain injury-highlights and drawbacks

Traumatic brain injury (TBI) is the leading cause for high morbidity and mortality rates in young adults, survivors may suffer from long-term physical, cognitive, and/or psychological disorders. Establishing better models of TBI would further our understanding of the pathophysiology of TBI and develop new potential treatments. A multitude of animal TBI models have been used to replicate the various aspects of human TBI. Although numerous experimental neuroprotective strategies were identified to be effective in animal models, a majority of strategies have failed in phase II or phase III clinical trials. This failure in clinical translation highlights the necessity of revisiting the current status of animal models of TBI and therapeutic strategies. In this review, we elucidate approaches for the generation of animal models and cell models of TBI and summarize their strengths and limitations with the aim of exploring clinically meaningful neuroprotective strategies.

Posttraumatic and Idiopathic Spike-Wave Discharges in Rats: Discrimination by Morphology and Thalamus Involvement

The possibility of epileptiform activity generation by the thalamocortical neuronal network after focal brain injuries, including traumatic brain injury (TBI), is actively debated. Presumably, posttraumatic spike-wave discharges (SWDs) involve a cortico-thalamocortical neuronal network. Differentiation of posttraumatic and idiopathic (i.e., spontaneously generated) SWDs is imperative for understanding posttraumatic epileptogenic mechanisms. Experiments were performed on male Sprague-Dawley rats with electrodes implanted into the somatosensory cortex and the thalamic ventral posterolateral nucleus. Local field potentials were recorded for 7 days before and 7 days after TBI (lateral fluid percussion injury, 2.5 atm). The morphology of 365 SWDs (89 idiopathic before craniotomy, and 262 posttraumatic that appeared only after TBI) and their appearance in the thalamus were analyzed. The occurrence of SWDs in the thalamus determined their spike-wave form and bilateral lateralization in the neocortex. Posttraumatic discharges were characterized by more "mature" characteristics as compared to spontaneously generated discharges: higher proportions of bilateral spreading, well-defined spike-wave form, and thalamus involvement. Based on SWD parameters, the etiology could be established with an accuracy of 75% (AUC 0.79). Our results support the hypothesis that the formation of posttraumatic SWDs involves a cortico-thalamocortical neuronal network. The results form a basis for further research of mechanisms associated with posttraumatic epileptiform activity and epileptogenesis.

Acute Haemostatic Depletion and Failure in Patients with Traumatic Brain Injury (TBI): Pathophysiological and Clinical Considerations

BACKGROUND

Because of the aging population, the number of low falls in elderly people with pre-existing anticoagulation is rising, often leading to traumatic brain injury (TBI) with a social and economic burden. Hemostatic disorders and disbalances seem to play a pivotal role in bleeding progression. Interrelationships between anticoagulatoric medication, coagulopathy, and bleeding progression seem to be a promising aim of therapy.

METHODS

We conducted a selective search of the literature in databases like Medline (Pubmed), Cochrane Library and current European treatment recommendations using relevant terms or their combination.

RESULTS

Patients with isolated TBI are at risk for developing coagulopathy in the clinical course. Pre-injury intake of anticoagulants is leading to a significant increase in coagulopathy, so every third patient with TBI in this population suffers from coagulopathy, leading to hemorrhagic progression and delayed traumatic intracranial hemorrhage. In an assessment of coagulopathy, viscoelastic tests such as TEG or ROTEM seem to be more beneficial than conventional coagulation assays alone, especially because of their timely and more specific gain of information about coagulopathy. Furthermore, results of point-of-care diagnostic make rapid "goal-directed therapy" possible with promising results in subgroups of patients with TBI.

CONCLUSIONS

The use of innovative technologies such as viscoelastic tests in the assessment of hemostatic disorders and implementation of treatment algorithms seem to be beneficial in patients with TBI, but further studies are needed to evaluate their impact on secondary brain injury and mortality.

What Happens in TBI? A Wide Talk on Animal Models and Future Perspective

Traumatic brain injury (TBI) is a global healthcare concern and a leading cause of death. The most common causes of TBI include road accidents, sports injuries, violence in warzones, and falls. TBI induces neuronal cell death independent of age, gender, and genetic background. TBI survivor patients often experience long-term behavioral changes like cognitive and emotional changes. TBI affects social activity, reducing the quality and duration of life. Over the last 40 years, several rodent models have been developed to mimic different clinical outcomes of human TBI for a better understanding of pathophysiology and to check the efficacy of drugs used for TBI. However, promising neuroprotective approaches that have been used preclinically have been found to be less beneficial in clinical trials. So, there is an urgent need to find a suitable animal model for establishing a new therapeutic intervention useful for TBI. In this review, we have demonstrated the etiology of TBI and post- TBI social life alteration, and also discussed various preclinical TBI models of rodents, zebrafish, and drosophila.

Chemical Kindling as an Experimental Model to Assess the Conventional Drugs in the Treatment of Post-traumatic Epilepsy

BACKGROUND

Traumatic brain injury (TBI) is one of the leading causes of morbidity and mortality today, which will surpass many infectious diseases in the coming years/decades. Posttraumatic epilepsy (PTE) is one of the most common debilitating consequences of TBI. PTE is a secondary, acquired epilepsy that causes recurrent, spontaneous seizures more than a week after TBI. The extent of head injury in individuals who develop PTE is unknown; however, trauma is thought to account for 20% of symptomatic epilepsy worldwide. Understanding the mechanisms of epilepsy following TBI is crucial for the discovery of new anticonvulsant drugs for the treatment of PTE, as well as for improving the quality of life of patients with PTE.

OBJECTIVE

This review article explains the rationale for the usage of a chemical model to access new treatments for post-traumatic epilepsy.

RESULTS

There are multiple methods to control and manage PTE. The essential and available remedy for the management of epilepsy is the use of antiepileptic drugs. Antiepileptic drugs (AEDs) decrease the frequency of seizures without affecting the disease's causality. Antiepileptic drugs are administrated for the prevention and treatment of PTE; however, 30% of epilepsy patients are drug-resistant, and AED side effects are significant in PTE patients. There are different types of animal models, such as the liquid percussion model, intracortical ferric chloride injection, and cortical subincision model, to study PTE and neurophysiological mechanisms underlying the development of epilepsy after head injury. However, these animal models do not easily mimic the pathological events occurring in epilepsy. Therefore, animal models of PTE are an inappropriate tool for screening new and putatively effective AEDs. Chemical kindling is the most common animal model used to study epilepsy. There is a strong similarity between the kindling model and different types of human epilepsy.

CONCLUSION

Today, researchers use experimental animal models to evaluate new anticonvulsant drugs. The chemical kindling models, such as pentylenetetrazol, bicuculline, and picrotoxin-induced seizures, are important experimental models to analyze the impact of putative antiepileptic drugs.

Epilepsy Characteristics in Neurodevelopmental Disorders: Research from Patient Cohorts and Animal Models Focusing on Autism Spectrum Disorder

Epilepsy, a heterogeneous group of brain-related diseases, has continued to significantly burden society and families. Epilepsy comorbid with neurodevelopmental disorders (NDDs) is believed to occur due to multifaceted pathophysiological mechanisms involving disruptions in the excitation and inhibition (E/I) balance impeding widespread functional neuronal circuitry. Although the field has received much attention from the scientific community recently, the research has not yet translated into actionable therapeutics to completely cure epilepsy, particularly those comorbid with NDDs. In this review, we sought to elucidate the basic causes underlying epilepsy as well as those contributing to the association of epilepsy with NDDs. Comprehensive emphasis is put on some key neurodevelopmental genes implicated in epilepsy, such as MeCP2, SYNGAP1, FMR1, SHANK1-3 and TSC1, along with a few others, and the main electrophysiological and behavioral deficits are highlighted. For these genes, the progress made in developing appropriate and valid rodent models to accelerate basic research is also detailed. Further, we discuss the recent development in the therapeutic management of epilepsy and provide a briefing on the challenges and caveats in identifying and testing species-specific epilepsy models.

Brain Trauma, Glucocorticoids and Neuroinflammation: Dangerous Liaisons for the Hippocampus

Glucocorticoid-dependent mechanisms of inflammation-mediated distant hippocampal damage are discussed with a focus on the consequences of traumatic brain injury. The effects of glucocorticoids on specific neuronal populations in the hippocampus depend on their concentration, duration of exposure and cell type. Previous stress and elevated level of glucocorticoids prior to pro-inflammatory impact, as well as long-term though moderate elevation of glucocorticoids, may inflate pro-inflammatory effects. Glucocorticoid-mediated long-lasting neuronal circuit changes in the hippocampus after brain trauma are involved in late post-traumatic pathology development, such as epilepsy, depression and cognitive impairment. Complex and diverse actions of the hypothalamic–pituitary–adrenal axis on neuroinflammation may be essential for late post-traumatic pathology. These mechanisms are applicable to remote hippocampal damage occurring after other types of focal brain damage (stroke, epilepsy) or central nervous system diseases without obvious focal injury. Thus, the liaisons of excessive glucocorticoids/dysfunctional hypothalamic–pituitary–adrenal axis with neuroinflammation, dangerous to the hippocampus, may be crucial to distant hippocampal damage in many brain diseases. Taking into account that the hippocampus controls both the cognitive functions and the emotional state, further research on potential links between glucocorticoid signaling and inflammatory processes in the brain and respective mechanisms is vital.

A novel simple traumatic brain injury mouse model

Background

Traumatic brain injury, one of the leading causes of death in adults under 40 years of age in the world, is frequently caused by mechanical shock, resulting in diffuse neuronal damage and long-term cognitive dysfunction. Many existing TBI animal models revival with expensive equipment or special room are needed or the processes of operations are complex and not easy to be widely used. Therefore, a simpler TBI model needs to be designed.

Methods

Our TBI model is an innovation of the modeling method through air guns shutting rubber bullets. A core facet is the application of our designed rubber bullet impact device. It could focus the hitting power to the fixed site of the brain, thus triggering a mild closed head injury. Moreover, the degree of damage can be adjusted by the times of shots.

Results

Our model induced blood-brain barrier leakage and diffused neuronal damage. Besides, it led to an increased level of Tau phosphorylation and resulted in cognitive dysfunction within several weeks post-injury.

Conclusion

Our TBI model is not only simple and time-saving but also can simulate mild brain injuries in clinical. It is suitable for exploring pathobiological mechanisms as well as a screening of potential therapies for TBI.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41016-022-00273-5.

Anticholinergics: A potential option for preventing posttraumatic epilepsy

Interest in the use of anticholinergics to prevent the development of epilepsy after traumatic brain injury (TBI) has grown since recent basic studies have shown their effectiveness in modifying the epileptogenic process. These studies demonstrated that treatment with anticholinergics, in the acute phase after brain injury, decreases seizure frequency, and severity, and the number of spontaneous recurrent seizures (SRS). Therefore, anticholinergics may reduce the risk of developing posttraumatic epilepsy (PTE). In this brief review, we summarize the role of the cholinergic system in epilepsy and the key findings from using anticholinergic drugs to prevent PTE in animal models and new clinical trial protocols. Furthermore, we discuss why treatment with anticholinergics is more likely to prevent PTE than treatment for other epilepsies.

The functional indexes of RBCs and microcirculation in the traumatic brain injury with the action of 2-ethil-6-methil-3-hydroxypiridin succinate

RESEARCH AIM

To study the RBCs functional and metabolic parameters and the microcirculatory brain structure at traumatic brain injury (TBI) under the action of 2-ethyl-6-methyl-3-hydroxypyridine succinate.

METHODS

A closed TBI was modeled by the free fall of a load on the parietooccipital regions of head. We made studies of the influence of 2-ethil-6-methil-3-hydroxipiridin succinate on aggregation and electrophoretic mobility of RBCs, catalase activity, malonic dialdehyde concentration, adenosine triphosphate and 2.3-biphosphoglycerate (2.3 - BPG) concentrations in RBCs. The state of parenchyma and microcirculatory brain mainstream in post-traumatic period of TBI have been studied on micro-preparations.

RESULTS

The use of 2-ethyl-6-methyl-3-hydroxypyridine succinate under conditions of head injury leads to a decrease in MDA concentration and in aggregation of RBCs, to an increase in the 2.3-BPG concentration and RBC electrophoretic mobility compared to the control (group value). The most pronounced changes under the action of 2-ethyl-6-methyl-3-hydroxypyridine succinate were observed 3-7 days after the TBI. Significant indicators of the restoration of the microvasculature and brain tissue provoked by the use of 2-ethyl-6-methyl-3-hydroxypyridine succinate of were evident from the 7th day unlike the control group, where the restoration of structural morphological parameters was observed only on the 12th day of the post-traumatic period. Fast recovery of blood flow under the action of 2-ethyl-6-methyl-3-hydroxypyridine succinate ensured effective restoration of neurons and glia in comparison with the control group.

CONCLUSIONS

Early and long-term cytoprotective correction intensifies the oxygen transport function of the blood, prevents and / or reduces disorders of microvessels, neurons and glia in the post-traumatic period, thereby provides correction of hypoxic state and drives to the restoration of brain tissues homeostasis.

Animal models of traumatic brain injury: a review of pathophysiology to biomarkers and treatments

Traumatic brain injury (TBI) is one of the main causes of death and disability in both civilian and military population. TBI may occur via a variety of etiologies, all of which involve trauma to the head. However, the neuroprotective drugs which were found to be very effective in animal TBI models failed in phase II or phase III clinical trials, emphasizing a compelling need to review the current status of animal TBI models and therapeutic strategies. No single animal model can adequately mimic all aspects of human TBI owing to the heterogeneity of clinical TBI. However, due to the ethical limitations, it is difficult to precisely emulate the TBI mechanisms that occur in humans. Therefore, many animal models with varying severity and mechanisms of brain injury have been developed, and each model has its own pros and cons in its implementation for TBI research. These challenges pose a need for study of continued TBI mechanisms, brain injury severity, duration, treatment strategies, and optimization of animal models across the neurotrauma research community. The aim of this review is to discuss (1) causes of TBI, (2) its prevalence in military and civilian population, (3) classification and pathophysiology of TBI, (4) biomarkers and detection methods, (5) animal models of TBI, and (6) the advantages and disadvantages of each model and the species used, as well as possible treatments.

Neuroinflammation and Neuronal Loss in the Hippocampus Are Associated with Immediate Posttraumatic Seizures and Corticosterone Elevation in Rats

Hippocampal damage after traumatic brain injury (TBI) is associated with late posttraumatic conditions, such as depression, cognitive decline and epilepsy. Mechanisms of selective hippocampal damage after TBI are not well understood. In this study, using rat TBI model (lateral fluid percussion cortical injury), we assessed potential association of immediate posttraumatic seizures and changes in corticosterone (CS) levels with neuroinflammation and neuronal cell loss in the hippocampus. Indices of distant hippocampal damage (neurodegeneration and neuroinflammation) were assessed using histological analysis (Nissl staining, Iba-1 immunohistochemical staining) and ELISA (IL-1β and CS) 1, 3, 7 and 14 days after TBI or sham operation in male Wistar rats (n = 146). IL-1β was elevated only in the ipsilateral hippocampus on day 1 after trauma. CS peak was detected on day 3 in blood, the ipsilateral and contralateral hippocampus. Neuronal cell loss in the hippocampus was demonstrated bilaterally; in the ipsilateral hippocampus it started earlier than in the contralateral. Microglial activation was evident in the hippocampus bilaterally on day 7 after TBI. The duration of immediate seizures correlated with CS elevation, levels of IL-1β and neuronal loss in the hippocampus. The data suggest potential association of immediate post-traumatic seizures with CS-dependent neuroinflammation-mediated distant hippocampal damage.

An In Vivo Study of a Rat Fluid-Percussion-Induced Traumatic Brain Injury Model with [11C]PBR28 and [18F]flumazenil PET Imaging

Traumatic brain injury (TBI) modelled by lateral fluid percussion-induction (LFPI) in rats is a widely used experimental rodent model to explore and understand the underlying cellular and molecular alterations in the brain caused by TBI in humans. Current improvements in imaging with positron emission tomography (PET) have made it possible to map certain features of TBI-induced cellular and molecular changes equally in humans and animals. The PET imaging technique is an apt supplement to nanotheranostic-based treatment alternatives that are emerging to tackle TBI. The present study aims to investigate whether the two radioligands, [¹¹C]PBR28 and [¹⁸F]flumazenil, are able to accurately quantify in vivo molecular-cellular changes in a rodent TBI-model for two different biochemical targets of the processes. In addition, it serves to observe any palpable variations associated with primary and secondary injury sites, and in the affected versus the contralateral hemispheres. As [¹¹C]PBR28 is a radioligand of the 18 kD translocator protein, the up-regulation of which is coupled to the level of neuroinflammation in the brain, and [¹⁸F]flumazenil is a radioligand for GABA_A-benzodiazepine receptors, whose level mirrors interneuronal activity and eventually cell death, the use of the two radioligands may reveal two critical features of TBI. An up-regulation in the [¹¹C]PBR28 uptake triggered by the LFP in the injured (right) hemisphere was noted on day 14, while the uptake of [¹⁸F]flumazenil was down-regulated on day 14. When comparing the left (contralateral) and right (LFPI) hemispheres, the differences between the two in neuroinflammation were obvious. Our results demonstrate a potential way to measure the molecular alterations in a rodent-based TBI model using PET imaging with [¹¹C]PBR28 and [¹⁸F]flumazenil. These radioligands are promising options that can be eventually used in exploring the complex in vivo pharmacokinetics and delivery mechanisms of nanoparticles in TBI treatment.

The Role of Estradiol in Traumatic Brain Injury: Mechanism and Treatment Potential

Patients surviving traumatic brain injury (TBI) face numerous neurological and neuropsychological problems significantly affecting their quality of life. Extensive studies over the past decades have investigated pharmacological treatment options in different animal models, targeting various pathological consequences of TBI. Sex and gender are known to influence the outcome of TBI in animal models and in patients, respectively. Apart from its well-known effects on reproduction, 17β-estradiol (E2) has a neuroprotective role in brain injury. Hence, in this review, we focus on the effect of E2 in TBI in humans and animals. First, we discuss the clinical classification and pathomechanism of TBI, the research in animal models, and the neuroprotective role of E2. Based on the results of animal studies and clinical trials, we discuss possible E2 targets from early to late events in the pathomechanism of TBI, including neuroinflammation and possible disturbances of the endocrine system. Finally, the potential relevance of selective estrogenic compounds in the treatment of TBI will be discussed.

APOE4 genetic polymorphism results in impaired recovery in a repeated mild traumatic brain injury model and treatment with Bryostatin-1 improves outcomes

After traumatic brain injury (TBI), some people have worse recovery than others. Single nucleotide polymorphisms (SNPs) in Apolipoprotein E (APOE) are known to increase risk for developing Alzheimer’s disease, however there is controversy from human and rodent studies as to whether ApoE4 is a risk factor for worse outcomes after brain trauma. To resolve these conflicting studies we have explored the effect of the human APOE4 gene in a reproducible mouse model that mimics common human injuries. We have investigated cellular and behavioral outcomes in genetically engineered human APOE targeted replacement (TR) mice following repeated mild TBI (rmTBI) using a lateral fluid percussion injury model. Relative to injured APOE3 TR mice, injured APOE4 TR mice had more inflammation, neurodegeneration, apoptosis, p-tau, and activated microglia and less total brain-derived neurotrophic factor (BDNF) in the cortex and/or hippocampus at 1 and/or 21 days post-injury. We utilized a novel personalized approach to treating APOE4 susceptible mice by administering Bryostatin-1, which improved cellular as well as motor and cognitive behavior outcomes at 1 DPI in the APOE4 injured mice. This study demonstrates that APOE4 is a risk factor for poor outcomes after rmTBI and highlights how personalized therapeutics can be a powerful treatment option.

A Translational Study on Acute Traumatic Brain Injury: High Incidence of Epileptiform Activity on Human and Rat Electrocorticograms and Histological Correlates in Rats

Background: In humans, early pathological activity on invasive electrocorticograms (ECoGs) and its putative association with pathomorphology in the early period of traumatic brain injury (TBI) remains obscure. Methods: We assessed pathological activity on scalp electroencephalograms (EEGs) and ECoGs in patients with acute TBI, early electrophysiological changes after lateral fluid percussion brain injury (FPI), and electrophysiological correlates of hippocampal damage (microgliosis and neuronal loss), a week after TBI in rats. Results: Epileptiform activity on ECoGs was evident in 86% of patients during the acute period of TBI, ECoGs being more sensitive to epileptiform and periodic discharges. A “brush-like” ECoG pattern superimposed over rhythmic delta activity and periodic discharge was described for the first time in acute TBI. In rats, FPI increased high-amplitude spike incidence in the neocortex and, most expressed, in the ipsilateral hippocampus, induced hippocampal microgliosis and neuronal loss, ipsilateral dentate gyrus being most vulnerable, a week after TBI. Epileptiform spike incidence correlated with microglial cell density and neuronal loss in the ipsilateral hippocampus. Conclusion: Epileptiform activity is frequent in the acute period of TBI period and is associated with distant hippocampal damage on a microscopic level. This damage is probably involved in late consequences of TBI. The FPI model is suitable for exploring pathogenetic mechanisms of post-traumatic disorders.

Temperature-sensitive bone mesenchymal stem cells combined with mild hypothermia reduces neurological deficit in rats of severe traumatic brain injury

BACKGROUND

To explore the combined influences of temperature-sensitive bone mesenchymal stem cells (tsBMSCs) and mild hypothermia (MH) on neurological function and glucose metabolism in rats with severe traumatic brain injury (TBI).

METHODS

SD rats were randomly divided into sham, TBI, TBI + MH, TBI + BMSCs and TBI + MH +tsBMSCs groups. Then, the brain water content, serum-specific proteins (S100β, NSE, LDH, and CK), and blood glucose at different time points were measured. Furthermore, GLUT-3 expression was detected by Western blotting, and apoptotic rate was determined by TUNEL staining.

RESULTS

After TBI rat establishment, the brain injury resulted in significant increases in mNSS scores and brain water content, and upregulations in serum levels of S100β, NSE, LDH and CK, and blood glucose, with the elevated cell apoptotic rate in the injured cortex. However, these changes were reversed by MH alone, BMSCs alone, or combination treatment of MH and tsBMSCs in varying degrees, and the combination treatment was superior to the treatment with BMSCs or MH alone.

CONCLUSION

Combination therapy of tsBMSCs and MH can reduce the neuronal apoptosis in severe TBI rats, with the suppression of serum biomarkers and hyperglycemia, contributing to the recovery of neurological functions.

ABBREVIATIONS

tsBMSCs: temperature-sensitive bone mesenchymal stem cells; MH: mild hypothermia; TBI: traumatic brain injury; mNSS: modified Neurological Severity Score.

Induction of Diffuse Axonal Brain Injury in Rats Based on Rotational Acceleration

Traumatic brain injury (TBI) is a major cause of death and disability. Diffuse axonal injury (DAI) is the predominant mechanism of injury in a large percentage of TBI patients requiring hospitalization. DAI involves widespread axonal damage from shaking, rotation or blast injury, leading to rapid axonal stretch injury and secondary axonal changes that are associated with a long-lasting impact on functional recovery. Historically, experimental models of DAI without focal injury have been difficult to design. Here we validate a simple, reproducible and reliable rodent model of DAI that causes widespread white matter damage without skull fractures or contusions.

Experimental Traumatic Brain Injury Induces Chronic Glutamatergic Dysfunction in Amygdala Circuitry Known to Regulate Anxiety-Like Behavior

Up to 50% of traumatic brain injury (TBI) survivors demonstrate persisting and late-onset anxiety disorders indicative of limbic system dysregulation, yet the pathophysiology underlying the symptoms is unclear. We hypothesize that the development of TBI-induced anxiety-like behavior in an experimental model of TBI is mediated by changes in glutamate neurotransmission within the amygdala. Adult, male Sprague-Dawley rats underwent midline fluid percussion injury or sham surgery. Anxiety-like behavior was assessed at 7 and 28 days post-injury (DPI) followed by assessment of real-time glutamate neurotransmission in the basolateral amygdala (BLA) and central nucleus of the amygdala (CeA) using glutamate-selective microelectrode arrays. The expression of anxiety-like behavior at 28 DPI coincided with decreased evoked glutamate release and slower glutamate clearance in the CeA, not BLA. Numerous factors contribute to the changes in glutamate neurotransmission over time. In two additional animal cohorts, protein levels of glutamatergic transporters (Glt-1 and GLAST) and presynaptic modulators of glutamate release (mGluR2, TrkB, BDNF, and glucocorticoid receptors) were quantified using automated capillary western techniques at 28 DPI. Astrocytosis and microglial activation have been shown to drive maladaptive glutamate signaling and were histologically assessed over 28 DPI. Alterations in glutamate neurotransmission could not be explained by changes in protein levels for glutamate transporters, mGluR2 receptors, astrocytosis, and microglial activation. Presynaptic modulators, BDNF and TrkB, were significantly decreased at 28 DPI in the amygdala. Dysfunction in presynaptic regulation of glutamate neurotransmission may contribute to anxiety-related behavior and serve as a therapeutic target to improve circuit function.

Animal Models of Post-Traumatic Epilepsy

Traumatic brain injury is the leading cause of morbidity and mortality worldwide, with the incidence of post-traumatic epilepsy increasing with the severity of the head injury. Post-traumatic epilepsy (PTE) is defined as a recurrent seizure disorder secondary to trauma to the brain and has been described as one of the most devastating complications associated with TBI (Traumatic Brain Injury). The goal of this review is to characterize current animal models of PTE and provide succinct protocols for the development of each of the currently available animal models. The development of translational and effective animal models for post-traumatic epilepsy is critical in both elucidating the underlying pathophysiology associated with PTE and providing efficacious clinical breakthroughs in the management of PTE.

Motor Effects of Minimal Traumatic Brain Injury in Mice

Traumatic brain injury (TBI) is considered to be the leading cause of disability and death among young people. Up to 30% of mTBI patients report motor impairments, such as altered coordination and impaired balance and gait. The objective of the present study was to characterize motor performance and motor learning changes, in order to achieve a more thorough understanding of the possible motor consequences of mTBI in humans. Mice were exposed to traumatic brain injury using the weight-drop model and subsequently subjected to a battery of behavioral motor tests. Immunohistochemistry was conducted in order to evaluate neuronal survival and synaptic connectivity. TBI mice showed a different walking pattern on the Erasmus ladder task, without any significant impairment in motor performance and motor learning. In the running wheels, mTBI mice showed reduced activity during the second dark phase and increased activity during the second light phase compared to the control mice. There was no difference in the sum of wheel revolutions throughout the experiment. On the Cat-Walk paradigm, the mice showed a wider frontal base of support post mTBI. The same mice spent a significantly greater percent of time standing on three paws post mTBI compared with controls. mTBI mice also showed a decrease in the number of neurons in the temporal cortex compared with the control group. In summary, mTBI mice suffered from mild motor impairments, minor changes in the circadian clock, and neuronal damage. A more in-depth examination of the mechanisms by which mTBI compensate for motor deficits is necessary.

The p53 inactivators pifithrin-μ and pifithrin-α mitigate TBI-induced neuronal damage through regulation of oxidative stress, neuroinflammation, autophagy and mitophagy

Traumatic brain injury (TBI) is one of the most common causes of death and disability worldwide. We investigated whether inhibition of p53 using pifithrin (PFT)-α or PFT-μ provides neuroprotective effects via p53 transcriptional dependent or -independent mechanisms, respectively. Sprague Dawley rats were subjected to controlled cortical impact TBI followed by the administration of PFTα or PFT-μ (2 mg/kg, i.v.) at 5 h after TBI. Brain contusion volume, as well as sensory and motor functions were evaluated at 24 h after TBI. TBI-induced impairments were mitigated by both PFT-α and PFT-μ. Fluoro-Jade C staining was used to label degenerating neurons within the TBI-induced cortical contusion region that, together with Annexin V positive neurons, were reduced by PFT-μ. Double immunofluorescence staining similarly demonstrated that PFT-μ significantly increased HO-1 positive neurons and mRNA expression in the cortical contusion region as well as decreased numbers of 4-hydroxynonenal (4HNE)-positive cells. Levels of mRNA encoding for p53, autophagy, mitophagy, anti-oxidant, anti-inflammatory related genes and proteins were measured by RT-qPCR and immunohistochemical staining, respectively. PFT-α, but not PFT-μ, significantly lowered p53 mRNA expression. Both PFT-α and PFT-μ lowered TBI-induced pro-inflammatory cytokines (IL-1β and IL-6) mRNA levels as well as TBI-induced autophagic marker localization (LC3 and p62). Finally, treatment with PFT-μ mitigated TBI-induced declines in mRNA levels of PINK-1 and SOD2. Our data suggest that both PFT-μ and PFT-α provide neuroprotective actions through regulation of oxidative stress, neuroinflammation, autophagy, and mitophagy mechanisms, and that PFT-μ, in particular, holds promise as a TBI treatment strategy.

BDNF Val66Met Genetic Polymorphism Results in Poor Recovery Following Repeated Mild Traumatic Brain Injury in a Mouse Model and Treatment With AAV-BDNF Improves Outcomes

Clinicians have long noticed that some Traumatic Brain Injury (TBI) patients have worse symptoms and take a longer time to recover than others, for reasons unexplained by known factors. Identifying what makes some individuals more susceptible is critical to understanding the underlying mechanisms through which TBI causes deleterious effects. We have sought to determine the effect of a single nucleotide polymorphism (SNP) in Brain-derived neurotrophic factor (BDNF) at amino acid 66 (rs6265) on recovery after TBI. There is controversy from human studies as to whether the BDNF Val66Val or Val66Met allele is the risk factor for worse outcomes after brain trauma. We therefore investigated cellular and behavioral outcomes in genetically engineered mice following repeated mild TBI (rmTBI) using a lateral fluid percussion (LFP) injury model. We found that relative to injured Val66Val carriers, injured Val66Met carriers had a larger inflammation volume and increased levels of neurodegeneration, apoptosis, p-tau, activated microglia, and gliosis in the cortex and/or hippocampus at 1 and/or 21 days post-injury (DPI). We therefore concluded that the Val66Met genetic polymorphism is a risk factor for poor outcomes after rmTBI. In order to determine the mechanism for these differences, we investigated levels of the apoptotic-inducing pro BDNF and survival-inducing mature BDNF isoforms and found that Met carriers had less total BDNF in the cortex and a higher pro/mature ratio of BDNF in the hippocampus. We then developed a personalized approach to treating genetically susceptible individuals by overexpressing wildtype BDNF in injured Val66Met mice using an AAV-BDNF virus. This intervention improved cellular, motor, and cognitive behavior outcomes at 21 DPI and increased levels of mature BDNF and phosphorylation of mature BDNF's receptor trkB. This study lays the groundwork for further investigation into the genetics that play a role in the extent of injury after rmTBI and highlights how personalized therapeutics may be targeted for recovery in susceptible individuals.

Time course images of cellular injury and recovery in murine brain with high-resolution GRIN lens system

Time course, in vivo imaging of brain cells is crucial to fully understand the progression of secondary cellular damage and recovery in murine models of injury. We have combined high-resolution gradient index lens technology with a model of diffuse axonal injury in rodents to enable repeated visualization of fine features of individual cells in three-dimensional space over several weeks. For example, we recorded changes in morphology in the same axons in the external capsule numerous times over 30 to 60 days, before and after induced traumatic brain injury. We observed the expansion of secondary injury and limited recovery of individual axons in this subcortical white matter tract over time. In another application, changes in microglial activation state were visualized in the penumbra region of mice before and after ischemia induced by middle carotid artery occlusion. The ability to collect a series of high-resolution images of cellular features of the same cells pre- and post-injury enables a unique opportunity to study the progression of damage, spontaneous healing, and effects of therapeutics in mouse models of neurodegenerative disease and brain injury.

Therapeutic hypercapnia reduces blood-brain barrier damage possibly via protein kinase Cε in rats with lateral fluid percussion injury

Background

This study investigated whether therapeutic hypercapnia (TH) ameliorated blood–brain barrier (BBB) damage and improved the neurologic outcome in a rat model of lateral fluid percussion injury (FPI), and explored the possible underlying mechanism.

Methods

Rats underwent lateral FPI and received inhalation of 30%O₂–70%N₂ or 30%O₂–N₂ plus CO₂ to maintain arterial blood CO₂ tension (PaCO₂) between 80 and 100 mmHg for 3 h. To further explore the possible mechanisms for the protective effects of TH, a PKC inhibitor staurosporine or PKCαβ inhibitor GÖ6976 was administered via intracerebral ventricular injection.

Results

TH significantly improved neurological function 24 h, 48 h, 7 d, and 14 d after FPI. The wet/dry ratio, computed tomography values, Evans blue content, and histological lesion volume were significantly reduced by TH. Moreover, numbers of survived neurons and the expression of tight junction proteins (ZO-1, occludin, and claudin-5) were significantly elevated after TH treatment at 48-h post-FPI. TH significantly increased the expression of protein kinase Cε (PKCε) at 48-h post-FPI, but did not significantly change the expression of PKCα and PKCβII. PKC inhibitor staurosporine (but not the selective PKCαβ inhibitor-GÖ6976) inhibited the protective effect of TH.

Conclusions

Therapeutic hypercapnia is a promising candidate that should be further evaluated for clinical treatment. It not only protects the traumatic penumbra from secondary injury and improves histological structure but also maintains the integrity of BBB and reduces neurologic deficits after trauma in a rat model of FPI.

Loss of Par1b/MARK2 primes microglia during brain development and enhances their sensitivity to injury

Background

Microglia, the resident immune cells of the brain, exhibit various morphologies that correlate with their functions under physiological and pathological conditions. In conditions such as aging and stress, microglia priming occurs, which leads to altered morphology and lower threshold for activation upon further insult. However, the molecular mechanisms that lead to microglia priming are unclear.

Methods

To understand the role of Par1b/MARK2 in microglia, we first expressed shRNA targeting luciferase or Par1b/MARK2 in primary microglial cells and imaged the cells using fluorescent microscopy to analyze for morphological changes. A phagocytosis assay was then used to assess functional changes. We then moved in vivo and used a Par1b/MARK2 knockout mouse model to assess for changes in microglia density, morphology, and phagocytosis using immunohistochemistry, confocal imaging, and 3D image reconstruction. Next, we used two-photon in vivo imaging in live Par1b/MARK2 deficient mice to examine microglia dynamics. In addition, a controlled-cortical impact injury was performed on wild-type and Par1b/MARK2-deficient mice and microglial response was determined by confocal imaging. Finally, to help rule out non-cell autonomous effects, we analyzed apoptosis by confocal imaging, cytokine levels by multiplex ELISA, and blood-brain barrier permeability using Evans Blue assay.

Results

Here, we show that loss of the cell polarity protein Par1b/MARK2 facilitates the activation of primary microglia in culture. We next found that microglia in Par1b/MARK2 deficient mice show increased density and a hypertrophic morphology. These morphological changes are accompanied with alterations in microglia functional responses including increased phagocytosis of neuronal particles early in development and decreased surveillance of the brain parenchyma, all reminiscent of a primed phenotype. Consistent with this, we found that microglia in Par1b/MARK2 deficient mice have a significantly lower threshold for activation upon injury.

Conclusions

Together, our studies show that loss of Par1b/MARK2 switches microglia from a surveillant to a primed state during development, resulting in an increased neuroinflammatory response to insults.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1390-3) contains supplementary material, which is available to authorized users.

Transplantation of Embryonic Neural Stem Cells and Differentiated Cells in a Controlled Cortical Impact (CCI) Model of Adult Mouse Somatosensory Cortex

Traumatic brain injury (TBI) is a major cause of death worldwide. Depending on the severity of the injury, TBI can reflect a broad range of consequences such as speech impairment, memory disturbances, and premature death. In this study, embryonic neural stem cells (ENSC) were isolated from E14 mouse embryos and cultured to produce neurospheres which were induced to generate differentiated cells (DC). As a cell replacement treatment option, we aimed to transplant ENSC or DC into the adult injured C57BL/6 mouse cortex controlled cortical impact (CCI) model, 7 days post-trauma, in comparison to saline injection (control). The effect of grafted cells on neuroinflammation and neurogenesis was investigated at 1 and 4 weeks post-transplantation. Results showed that microglia were activated following mild CCI, but not enhanced after engraftment of ENSC or DC. Indeed, ipsilateral lesioned somatosensory area expressed high levels of Iba-1+ microglia within the different groups after 1 and 4 weeks. On the other hand, treatment with ENSC or DC demonstrated a significant reduction in astrogliosis. The levels of GFAP expressing astrocytes started decreasing early (1 week) in the ENSC group and then were similarly low at 4 weeks in both ENSC and DC. Moreover, neurogenesis was significantly enhanced in ENSC and DC groups. Indeed, a significant increase in the number of DCX expressing progenitor cells was observed at 1 week in the ENSC group, and in DC and ENSC groups at 4 weeks. Furthermore, the number of mature neuronal cells (NeuN+) significantly increased in DC group at 4 weeks whereas they decreased in ENSC group at 1 week. Therefore, injection of ENSC or DC post-CCI caused decreased astrogliosis and suggested an increased neurogenesis via inducing neural progenitor proliferation and expression rather than neuronal maturation. Thus, ENSC may play a role in replacing lost cells and brain repair following TBI by improving neurogenesis and reducing neuroinflammation, reflecting an optimal environment for transplanted and newly born cells.

The Microtubule-Modulating Drug Epothilone D Alters Dendritic Spine Morphology in a Mouse Model of Mild Traumatic Brain Injury

Microtubule dynamics underpin a plethora of roles involved in the intricate development, structure, function, and maintenance of the central nervous system. Within the injured brain, microtubules are vulnerable to misalignment and dissolution in neurons and have been implicated in injury-induced glial responses and adaptive neuroplasticity in the aftermath of injury. Unfortunately, there is a current lack of therapeutic options for treating traumatic brain injury (TBI). Thus, using a clinically relevant model of mild TBI, lateral fluid percussion injury (FPI) in adult male Thy1-YFPH mice, we investigated the potential therapeutic effects of the brain-penetrant microtubule-stabilizing agent, epothilone D. At 7 days following a single mild lateral FPI the ipsilateral hemisphere was characterized by mild astroglial activation and a stereotypical and widespread pattern of axonal damage in the internal and external capsule white matter tracts. These alterations occurred in the absence of other overt signs of trauma: there were no alterations in cortical thickness or in the number of cortical projection neurons, axons or dendrites expressing YFP. Interestingly, a single low dose of epothilone D administered immediately following FPI (and sham-operation) caused significant alterations in the dendritic spines of layer 5 cortical projection neurons, while the astroglial response and axonal pathology were unaffected. Specifically, spine length was significantly decreased, whereas the density of mushroom spines was significantly increased following epothilone D treatment. Together, these findings have implications for the use of microtubule stabilizing agents in manipulating injury-induced synaptic plasticity and indicate that further study into the viability of microtubule stabilization as a therapeutic strategy in combating TBI is warranted.

Polarization of Microglia to the M2 Phenotype in a Peroxisome Proliferator-Activated Receptor Gamma-Dependent Manner Attenuates Axonal Injury Induced by Traumatic Brain Injury in Mice

Increasing evidence indicates that activated microglia play an important role in the inflammatory response following traumatic brain injury (TBI). Inhibiting M1 and stimulating M2 activated microglia have demonstrated protective effects in several animal models of central nervous system diseases. However, it is not clear whether the polarization of microglia to M2 attenuates axonal injury following TBI. In this study, we used a lateral fluid percussion injury device to induce axonal injury in mice. Mice were randomly assigned to the sham, TBI, TBI + rosiglitazone (peroxisome proliferator-activated receptor gamma [PPAR-γ] agonist), and TBI + GW9662 (PPAR-γ antagonist) groups. Axonal injury was assessed using immunohistochemical staining for beta amyloid precursor protein. The inflammatory response was assessed by enzyme-linked immunosorbent assay, microglia polarization was assessed using specific markers of M1 and M2 microglia, and neurological function was assessed using the neurological severity score. Following TBI, microglia of the M1 phenotype increased significantly, while those of the M2 phenotype decreased. Rosiglitazone-induced PPAR-γ activation promoted microglia polarization to the M2 phenotype, which reduced the inflammatory response, attenuated axonal injury in the cerebral cortex, and improved neurological function. Conversely, GW9662 inhibited the polarization of microglia to M2 and aggravated inflammation and axonal injury. Our in vitro findings in lipopolysaccharide-induced microglia were consistent with those of our in vivo experiments. In conclusion, the polarization of microglia to the M2 phenotype via PPAR-γ activation attenuated axonal injury following TBI in mice, which may be a potential therapeutic approach for TBI-induced axonal injury.

Combined Blockade of Interleukin-1α and -1β Signaling Protects Mice from Cognitive Dysfunction after Traumatic Brain Injury

Diffuse activation of interleukin-1 inflammatory cytokine signaling after traumatic brain injury (TBI) elicits progressive neurodegeneration and neuropsychiatric dysfunction, and thus represents a potential opportunity for therapeutic intervention. Although interleukin (IL)-1α and IL-1β both activate the common type 1 IL-1 receptor (IL-1RI), they manifest distinct injury-specific roles in some models of neurodegeneration. Despite its potential relevance to treating patients with TBI, however, the individual contributions of IL-1α and IL-1β to TBI-pathology have not been previously investigated. To address this need, we applied genetic and pharmacologic approaches in mice to dissect the individual contributions of IL-1α, IL-β, and IL-1RI signaling to the pathophysiology of fluid percussion–mediated TBI, a model of mixed focal and diffuse TBI. IL-1RI ablation conferred a greater protective effect on brain cytokine expression and cognitive function after TBI than did individual IL-1α or IL-1β ablation. This protective effect was recapitulated by treatment with the drug anakinra, a recombinant naturally occurring IL-1RI antagonist. Our data thus suggest that broad targeting of IL-1RI signaling is more likely to reduce neuroinflammation and preserve cognitive function after TBI than are approaches that individually target IL-1α or IL-1β signaling.

Implantation of Neuronal Stem Cells Enhances Object Recognition without Increasing Neurogenesis after Lateral Fluid Percussion Injury in Mice

Cognitive deficits after traumatic brain injury (TBI) are debilitating and contribute to the morbidity and loss of productivity of over 10 million people worldwide. Cell transplantation has been linked to enhanced cognitive function after experimental traumatic brain injury, yet the mechanism of recovery is poorly understood. Since the hippocampus is a critical structure for learning and memory, supports adult neurogenesis, and is particularly vulnerable after TBI, we hypothesized that stem cell transplantation after TBI enhances cognitive recovery by modulation of endogenous hippocampal neurogenesis. We performed lateral fluid percussion injury (LFPI) in adult mice and transplanted embryonic stem cell-derived neural progenitor cells (NPC). Our data confirm an injury-induced cognitive deficit in novel object recognition, a hippocampal-dependent learning task, which is reversed one week after NPC transplantation. While LFPI alone promotes hippocampal neurogenesis, as revealed by doublecortin immunolabeling of immature neurons, subsequent NPC transplantation prevents increased neurogenesis and is not associated with morphological maturation of endogenous injury-induced immature neurons. Thus, NPC transplantation enhances cognitive recovery early after LFPI without a concomitant increase in neuron numbers or maturation.

Gambogic amide, a selective TrkA agonist, does not improve outcomes from traumatic brain injury in mice

OBJECTIVES

There is evidence that treatment with nerve growth factor (NGF) may reduce neuroinflammation and apoptosis after a traumatic brain injury (TBI). NGF is thought to exert its effects via binding to either TrkA or p75 neurotrophin receptors. This study aimed to investigate the effects of a selective TrkA agonist, gambogic amide (GA), on TBI pathology and outcomes in mice following lateral fluid percussion injury.

METHODS

Male C57BL/6 mice were given either a TBI or sham injury, and then received subcutaneous injections of either 2 mg/kg of GA or vehicle at 1, 24, and 48 h post-injury. Following behavioural studies, mice were euthanized at 72 h post-injury for analysis of neuroinflammatory, apoptotic, and neurite outgrowth markers.

RESULTS

Behavioural testing revealed that GA did not mitigate motor deficits after TBI. TBI caused an increase in cortical and hippocampal expression of several markers of neuroinflammation and apoptosis compared to sham groups. GA treatment did not attenuate these increases in expression, possibly contributed to by our finding of TrkA receptor down-regulation post-TBI.

CONCLUSIONS

These findings suggest that GA treatment may not be suitable for attenuating TBI pathology and improving outcomes.

Nasal application of HSV encoding human preproenkephalin blocks craniofacial pain in a rat model of traumatic brain injury

According to Centers for Disease Control and Prevention, each year, an estimated 1.7 million Americans sustain a traumatic brain injury (TBI), which frequently leads to chronic craniofacial pain. In this study we examine a gene therapy approach to the treatment of post-TBI craniofacial neuropathic pain using nasal application of a herpes simplex virus (HSV)-based vector expressing human proenkephalin (SHPE) to target the trigeminal ganglia. Mild TBI was induced in rats by the use of a modified fluid percussion model. Two days after mild TBI, following the development of facial mechanical allodynia, animals received either an intranasal application of vehicle or recombinant HSV encoding human preproenkephalin or lacZ reporter gene encoding control vector (SHZ.1). Compared with baseline response thresholds, mild TBI in SHZ.1 or vehicle-treated animals induced a robust craniofacial allodynia lasting at least 45 days. On the other hand, nasal SHPE application 2 days post-TBI attenuated facial allodynia, reaching significance by day 4-7 and maintaining this effect throughout the duration of the experiment. Immunohistochemical examination revealed strong expression of human proenkephalin in trigeminal ganglia of SHPE, but not SHZ.1-treated rats. This study demonstrates that intranasal administration of HSV-based gene vectors may be a viable, non-invasive means of treating chronic craniofacial pain, including post-TBI pain.

Validation of Acoustic Wave Induced Traumatic Brain Injury in Rats

BACKGROUND

This study looked to validate the acoustic wave technology of the Storz-D-Actor that inflicted a consistent closed-head, traumatic brain injury (TBI) in rats. We studied a range of single pulse pressures administered to the rats and observed the resulting decline in motor skills and memory. Histology was observed to measure and confirm the injury insult.

METHODS

Four different acoustic wave pressures were studied using a single pulse: 0, 3.4, 4.2 and 5.0 bar (n = 10 rats per treatment group). The pulse was administered to the left frontal cortex. Rotarod tests were used to monitor the rats' motor skills while the water maze test was used to monitor memory deficits. The rats were then sacrificed ten days post-treatment for histological analysis of TBI infarct size.

RESULTS

The behavioral tests showed that acoustic wave technology administered an effective insult causing significant decreases in motor abilities and memory. Histology showed dose-dependent damage to the cortex infarct areas only.

CONCLUSIONS

This study illustrates that the Storz D-Actor effectively induces a repeatable TBI infarct, avoiding the invasive procedure of a craniotomy often used in TBI research.

Animal models of chronic traumatic encephalopathy

Repeated head impacts have been suggested to be associated with the development of the neurodegenerative disorder, chronic traumatic encephalopathy (CTE). CTE is characterized by the accumulation of hyperphosphorylated tau within the brain, with accompanying cognitive and behavioral deficits. How a history of repeated head impacts can lead to the later development of CTE is not yet known, and as such appropriate animal models are required. Over the last decade a number of rodent models of repeated mild traumatic brain injury have been developed that are broadly based on traditional traumatic brain injury models, in controlled cortical impact, fluid percussion and weight drop models, with adaptations to allow for better modeling of the mechanical forces associated with concussion.

Mesenchymal Stem Cells in the Treatment of Traumatic Brain Injury

Traumatic brain injury (TBI) is characterized by a disruption in the normal function of the brain due to an injury following a trauma, which can potentially cause severe physical, cognitive, and emotional impairment. The primary insult to the brain initiates secondary injury cascades consisting of multiple complex biochemical responses of the brain that significantly influence the overall severity of the brain damage and clinical sequelae. The use of mesenchymal stem cells (MSCs) offers huge potential for application in the treatment of TBI. MSCs have immunosuppressive properties that reduce inflammation in injured tissue. As such, they could be used to modulate the secondary mechanisms of injury and halt the progression of the secondary insult in the brain after injury. Particularly, MSCs are capable of secreting growth factors that facilitate the regrowth of neurons in the brain. The relative abundance of harvest sources of MSCs also makes them particularly appealing. Recently, numerous studies have investigated the effects of infusion of MSCs into animal models of TBI. The results have shown significant improvement in the motor function of the damaged brain tissues. In this review, we summarize the recent advances in the application of MSCs in the treatment of TBI. The review starts with a brief introduction of the pathophysiology of TBI, followed by the biology of MSCs, and the application of MSCs in TBI treatment. The challenges associated with the application of MSCs in the treatment of TBI and strategies to address those challenges in the future have also been discussed.

From blast to bench: A translational mini-review of posttraumatic headache

Current events within the military and professional sports have resulted in an increased recognition of the long-term and debilitating consequences of traumatic brain injury. Mild traumatic brain injury accounts for the majority of head injuries, and posttraumatic headache is the most common adverse effect. It is estimated that between 30% to 90% of traumatic brain injuries result in posttraumatic headache, and for a significant number of people this headache disorder can continue for up to and over a year post injury. Often, the most severe and chronic posttraumatic headache has a migraine-like phenotype and is difficult to resolve. In this review we discuss the preclinical findings from animal models of posttraumatic headache. We also describe potential mechanisms by which traumatic brain injury leads to chronic posttraumatic headache, including neuroinflammatory mediators and migraine-associated neuropeptides. There are surprisingly few preclinical studies that have investigated overlapping mechanisms between posttraumatic headache and migraine, especially considering the prevalence and debilitating nature of posttraumatic headache. Given this context, posttraumatic headache is a field with many emerging opportunities for growth. The frequency of posttraumatic headache in the general and military population is rising, and further preclinical research is required to understand, ameliorate, and treat this disabling disorder. © 2017 Wiley Periodicals, Inc.

Overview of Traumatic Brain Injury: An Immunological Context

Traumatic brain injury (TBI) afflicts people of all ages and genders, and the severity of injury ranges from concussion/mild TBI to severe TBI. Across all spectrums, TBI has wide-ranging, and variable symptomology and outcomes. Treatment options are lacking for the early neuropathology associated with TBIs and for the chronic neuropathological and neurobehavioral deficits. Inflammation and neuroinflammation appear to be major mediators of TBI outcomes. These systems are being intensively studies using animal models and human translational studies, in the hopes of understanding the mechanisms of TBI, and developing therapeutic strategies to improve the outcomes of the millions of people impacted by TBIs each year. This manuscript provides an overview of the epidemiology and outcomes of TBI, and presents data obtained from animal and human studies focusing on an inflammatory and immunological context. Such a context is timely, as recent studies blur the traditional understanding of an “immune-privileged” central nervous system. In presenting the evidence for specific, adaptive immune response after TBI, it is hoped that future studies will be interpreted using a broader perspective that includes the contributions of the peripheral immune system, to central nervous system disorders, notably TBI and post-traumatic syndromes.

MicroRNAs as diagnostic markers and therapeutic targets for traumatic brain injury

Traumatic brain injury (TBI) is characterized by primary damage to the brain from the external mechanical force and by subsequent secondary injury due to various molecular and pathophysiological responses that eventually lead to neuronal cell death. Secondary brain injury events may occur minutes, hours, or even days after the trauma, and provide valuable therapeutic targets to prevent further neuronal degeneration. At the present time, there is no effective treatment for TBI due, in part, to the widespread impact of numerous complex secondary biochemical and pathophysiological events occurring at different time points following the initial injury. MicroRNAs control a range of physiological and pathological functions such as development, differentiation, apoptosis and metabolism, and may serve as potential targets for progress assessment and intervention against TBI to mitigate secondary damage to the brain. This has implications regarding improving the diagnostic accuracy of brain impairment and long-term outcomes as well as potential novel treatments. Recent human studies have identified specific microRNAs in serum/plasma (miR-425-p, -21, -93, -191 and -499) and cerebro-spinal fluid (CSF) (miR-328, -362-3p, -451, -486a) as possible indicators of the diagnosis, severity, and prognosis of TBI. Experimental animal studies have examined specific microRNAs as biomarkers and therapeutic targets for moderate and mild TBI (e.g., miR-21, miR-23b). MicroRNA profiling was altered by voluntary exercise. Differences in basal microRNA expression in the brain of adult and aged animals and alterations in response to TBI (e.g., miR-21) have also been reported. Further large-scale studies with TBI patients are needed to provide more information on the changes in microRNA profiles in different age groups (children, adults, and elderly).