Traumatic brain injury - modeling neuropsychiatric symptoms in rodents

Carry-Over Effect of Deep Cerebellar Stimulation-Mediated Motor Recovery in a Rodent Model of Traumatic Brain Injury

BACKGROUND

We previously demonstrated that deep brain stimulation (DBS) of lateral cerebellar nucleus (LCN) can enhance motor recovery and functional reorganization of perilesional cortex in rodent models of stroke or TBI.

OBJECTIVE

Considering the treatment-related neuroplasticity observed at the perilesional cortex, we hypothesize that chronic LCN DBS-enhanced motor recovery observed will carry-over even after DBS has been deactivated.

METHODS

Here, we directly tested the enduring effects of LCN DBS in male Long Evans rats that underwent controlled cortical impact (CCI) injury targeting sensorimotor cortex opposite their dominant forepaw followed by unilateral implantation of a macroelectrode into the LCN opposite the lesion. Animals were randomized to DBS or sham treatment for 4 weeks during which the motor performance were characterize by behavioral metrics. After 4 weeks, stimulation was turned off, with assessments continuing for an additional 2 weeks. Afterward, all animals were euthanized, and tissue was harvested for further analyses.

RESULTS

Treated animals showed significantly greater motor improvement across all behavioral metrics relative to untreated animals during the 4-week treatment, with functional gains persisting across 2-week post-treatment. This motor recovery was associated with the increase in CaMKIIα and BDNF positive cell density across perilesional cortex in treated animals.

CONCLUSIONS

LCN DBS enhanced post-TBI motor recovery, the effect of which was persisted up to 2 weeks beyond stimulation offset. Such evidence should be considered in relation to future translational efforts as, unlike typical DBS applications, treatment may only need to be provided until such time as a new function plateau is achieved.

Single episode of moderate to severe traumatic brain injury leads to chronic neurological deficits and Alzheimer's-like pathological dementia

Traumatic brain injury (TBI) is one of the foremost causes of disability and mortality globally. While the scientific and medical emphasis is to save lives and avoid disability during acute period of injury, a severe health problem can manifest years after injury. For instance, TBI increases the risk of cognitive impairment in the elderly. Remote TBI history was reported to be a cause of the accelerated clinical trajectory of Alzheimer's disease-related dementia (ADRD) resulting in earlier onset of cognitive impairment and increased AD-associated pathological markers like greater amyloid deposition and cortical thinning. It is not well understood whether a single TBI event may increase the risk of dementia. Moreover, the cellular signaling pathways remain elusive for the chronic effects of TBI on cognition. We have hypothesized that a single TBI induces sustained neuroinflammation and disrupts cellular communication in a way that results later in ADRD pathology. To test this, we induced TBI in young adult CD1 mice and assessed the behavioral outcomes after 11 months followed by pathological, histological, transcriptomic, and MRI assessment. On MRI scans, these mice showed significant loss of tissue, reduced CBF, and higher white matter injury compared to sham mice. We found these brains showed progressive atrophy, markers of ADRD, sustained astrogliosis, loss of neuronal plasticity, and growth factors even after 1-year post-TBI. Because of progressive neurodegeneration, these mice had motor deficits, showed cognitive impairments, and wandered randomly in open field. We, therefore, conclude that progressive pathology after adulthood TBI leads to neurodegenerative conditions such as ADRD and impairs neuronal functions.

Genetic diversity drives extreme responses to traumatic brain injury and post-traumatic epilepsy

Traumatic brain injury (TBI) is a complex and heterogeneous condition that can cause wide-spectral neurological sequelae such as behavioral deficits, sleep abnormalities, and post-traumatic epilepsy (PTE). However, understanding the interaction of TBI phenome is challenging because few animal models can recapitulate the heterogeneity of TBI outcomes. We leveraged the genetically diverse recombinant inbred Collaborative Cross (CC) mice panel and systematically characterized TBI-related outcomes in males from 12 strains of CC and the reference C57BL/6J mice. We identified unprecedented extreme responses in multiple clinically relevant traits across CC strains, including weight change, mortality, locomotor activity, cognition, and sleep. Notably, we identified CC031 mouse strain as the first rodent model of PTE that exhibit frequent and progressive post-traumatic seizures after moderate TBI induced by lateral fluid percussion. Multivariate analysis pinpointed novel biological interactions and three principal components across TBI-related modalities. Estimate of the proportion of TBI phenotypic variability attributable to strain revealed large range of heritability, including >70% heritability of open arm entry time of elevated plus maze. Our work provides novel resources and models that can facilitate genetic mapping and the understanding of the pathobiology of TBI and PTE.

Neurobehavioral and inflammatory responses following traumatic brain injury in male and female mice

Traumatic brain injury (TBI) is a leading cause of mortality and is associated with a high rate of functional comorbidities, including motor, cognitive, anxiety, depression, and emotional disorders. TBI pathophysiology and recovery are complicated and involve several mechanistic pathways that control neurobehavioral outcomes. In this study, male and female C57Bl/6 J mice were subjected to a controlled cortical impact model of TBI or sham injury and evaluated for different neurobehavioral and inflammatory outcomes over a month. We demonstrate that TBI mice have increased motor dysfunction at early and late time points following the injury as compared to the sham group. Anxiety-like symptoms were time- and task-dependent, with both sexes having increased anxiety-like behavior 2 weeks post-injury. Cognitive functions measured by T-maze presented greater deficits in TBI mice, while there was no sex or injury-related difference in depressive-like behaviors. Notably, a significant effect of sex was found in empathy-like behavior, with females showing more allogrooming and freezing behavior in the consoling and fear observational tests, respectively. Evaluating the impact of the injury-induced brain damage demonstrated a greater injury volume and neuronal degeneration in males compared to females one month after TBI. Moreover, male mice showed higher peripheral inflammatory responses, as represented by elevated serum levels of peripheral leukocytes and inflammatory markers. These results will have significant implications for understanding TBI's long-term consequences on neurobehavioral and inflammatory responses, which are sex-specific and can be considered for individualized therapeutic strategies in treating TBI.

Associations of mTBI and post-traumatic stress to amygdala structure and functional connectivity in military Service Members

INTRODUCTION

Traumatic brain injury (TBI) is one of the highest public health priorities, especially among military personnel where comorbidity with post-traumatic stress symptoms and resulting consequences is high. Brain injury and post-traumatic stress symptoms are both characterized by dysfunctional brain networks, with the amygdala specifically implicated as a region with both structural and functional abnormalities.

METHODS

This study examined the structural volumetrics and resting state functional connectivity of 68 Active Duty Service Members with or without chronic mild TBI (mTBI) and comorbid symptoms of Post-Traumatic Stress (PTS).

RESULTS AND DISCUSSION

Structural analysis of the amygdala revealed no significant differences in volume between mTBI and healthy comparison participants with and without post-traumatic stress symptoms. Resting state functional connectivity with bilateral amygdala revealed decreased anterior network connectivity and increased posterior network connectivity in the mTBI group compared to the healthy comparison group. Within the mTBI group, there were significant regions of correlation with amygdala that were modulated by PTS severity, including networks implicated in emotional processing and executive functioning. An examination of a priori regions of amygdala connectivity in the default mode network, task positive network, and subcortical structures showed interacting influences of TBI and PTS, only between right amygdala and right putamen. These results suggest that mTBI and PTS are associated with hypo-frontal and hyper-posterior amygdala connectivity. Additionally, comorbidity of these conditions appears to compound these neural activity patterns. PTS in mTBI may change neural resource recruitment for information processing between the amygdala and other brain regions and networks, not only during emotional processing, but also at rest.

Deferiprone attenuates neuropathology and improves outcome following traumatic brain injury

BACKGROUND AND PURPOSE

Traumatic brain injury (TBI) remains a leading cause of mortality and morbidity in young adults. The role of iron in potentiating neurodegeneration following TBI has gained recent interest as iron deposition has been detected in the injured brain in the weeks to months post-TBI, in both the preclinical and clinical setting. A failure in iron homeostasis can lead to oxidative stress, inflammation and excitotoxicity; and whether this is a cause or consequence of the long-term effects of TBI remains unknown.

EXPERIMENTAL APPROACH

We investigated the role of iron and the effect of therapeutic intervention using a brain-permeable iron chelator, deferiprone, in a controlled cortical impact mouse model of TBI. An extensive assessment of cognitive, motor and anxiety/depressive outcome measures were examined, and neuropathological and biochemical changes, over a 3-month period post-TBI.

KEY RESULTS

Lesion volume was significantly reduced at 3 months, which was preceded by a reduction in astrogliosis, microglia/macrophages and preservation of neurons in the injured brain at 2 weeks and/or 1 month post-TBI in mice receiving oral deferiprone. Deferiprone treatment showed significant improvements in neurological severity scores, locomotor/gait performance and cognitive function, and attenuated anxiety-like symptoms post-TBI. Deferiprone reduced iron levels, lipid peroxidation/oxidative stress and altered expression of neurotrophins in the injured brain over this period.

CONCLUSION AND IMPLICATIONS

Our findings support a detrimental role of iron in the injured brain and suggest that deferiprone (or similar iron chelators) may be promising therapeutic approaches to improve survival, functional outcomes and quality of life following TBI.

Repeated Mild TBI in Adolescent Rats Reveals Sex Differences in Acute and Chronic Behavioral Deficits

High school students who participate in contact sports are vulnerable to sustaining multiple concussions and exhibit deficits in cognitive function in both the acute and chronic phases and in emotional behavior in the chronic phase. Further, boys are more likely to suffer cognitive problems whereas girls tend to report depression and anxiety. The effects of repetitive mild TBI in adolescent (35-40-day old) male and female Sprague-Dawley rats on object location and spatial working memory (hippocampal-dependent) and object recognition memory (hippocampal-independent) at 1-and-4-weeks post-injury along with trait-dependent anxiety- and depressive-like behaviors at 5 weeks were examined. Compared to sham-injured rats, male brain-injured rats demonstrated significant impairment in both hippocampal-dependent and -independent memory tasks at both time points, whereas female brain-injured rats only exhibited impairment in these tests at the 4-week time point. In contrast, depressive-like behaviors were present in the forced swim test in only the female brain-injured animals at 5 weeks post-injury; anxiety-like behaviors were not evident in either male or female brain-injured animals. Histological analysis at 6 weeks after injury revealed that repeated mild TBI in male and female adolescent rats resulted in increased reactivity of astrocytes and microglia within the corpus callosum below the impact site and in the stratum oriens and stratum pyramidale of the CA2 region of the dorsal hippocampus. Together, these data are indicative of the differences in the temporal pattern of post-traumatic behavioral deficits between male and female animals and that female animals may be more likely to develop deficits in the chronic post-traumatic period.

Traumatic brain injury-induced submissive behavior in rats: link to depression and anxiety

Traumatic brain injury (TBI) affects millions of people worldwide, many of whom are affected with post-TBI mood disorders or behavioral changes, including aggression or social withdrawal. Diminished functionality can persist for decades after TBI and delay rehabilitation and resumption of employment. It has been established that there is a relationship between these mental disorders and brain injury. However, the etiology and causal relationships behind these conditions are poorly understood. Rodent models provide a helpful tool for researching mood disorders and social impairment due to their natural tendencies to form social hierarchies. Here, we present a rat model of mental complications after TBI using a suite of behavioral tests to examine the causal relationships between changes in social behavior, including aggressive, hierarchical, depressive, and anxious behavior. For this purpose, we used multivariate analysis to identify causal relationships between the above post-TBI psychiatric sequelae. We performed statistical analysis using principal component analysis, discriminant analysis, and correlation analysis, and built a model to predict dominant-submissive behavior based on the behavioral tests. This model displayed a predictive accuracy of 93.3% for determining dominant-submissive behavior in experimental groups. Machine learning algorithms determined that in rats, aggression is not a principal prognostic factor for dominant-submissive behavior. Alternatively, dominant-submissive behavior is determined solely by the rats' depressive-anxious state and exploratory activity. We expect the causal approach used in this study will guide future studies into mood conditions and behavioral changes following TBI.

Titrating the Translational Relevance of a Low-Level Repetitive Head Impact Model

Recently, there has been increased attention in the scientific community to the phenomenon of sub-concussive impacts, those hits to the head that do not cause the signs and symptoms of a concussion. Some authors suggest that sub-concussive impacts may alter behavior and cognition, if sustained repetitively, but the mechanisms underlying these changes are not well-defined. Here, we adapt our well-established weight drop model of repetitive mild traumatic brain injury (rmTBI) to attempt to produce a model of low-level repetitive head impacts (RHI). The model was modified to eliminate differences in latency to right following impact and gross behavioral changes after a single cluster of hits. Further, we varied our model in terms of repetition of impact over a 4-h span to mimic the repeated sub-concussive impacts that may be experienced by an athlete within a single day of play. To understand the effects of a single cluster of RHIs, as well as the effect of an increased impact frequency within the cluster, we evaluated classical behavioral measures, serum biomarkers, cortical protein quantification, and immunohistochemistry both acutely and sub-acutely following the impacts. In the absence of gross behavioral changes, the impact protocol did generate pathology, in a dose-dependent fashion, in the brain. Evaluation of serum biomarkers revealed limited changes in GFAP and NF-L, which suggests that their diagnostic utility may not emerge until the exposure to low-level head impacts reaches a certain threshold. Robust decreases in both IL-1β and IL-6 were observed in the serum and the cortex, indicating downregulation of inflammatory pathways. These experiments yield initial data on pathology and biomarkers in a mouse model of low-level RHIs, with relevance to sports settings, providing a starting point for further exploration of the potential role of anti-inflammatory processes in low-level RHI outcomes, and how these markers may evolve with repeated exposure.

Multidimensional nature of dominant behavior: Insights from behavioral neuroscience

Social interactions for many species of animals are critical for survival, wellbeing, and reproduction. Optimal navigation of a social system increases chances for survival and reproduction, therefore there is strong incentive to fit into social structures. Social animals rely heavily on dominant-submissive behaviors in establishment of stable social hierarchies. There is a link between extreme manifestation of dominance/submissiveness and behavioral deviations. To understand neural substrates affiliated with a specific hierarchical rank, there is a real need for reliable animal behavioral models. Different paradigms have been consolidated over time to study the neurobiology of social rank behavior in a standardized manner using rodent models to unravel the neural pathways and substrates involved in normal and abnormal intraspecific social interactions. This review summarizes and discusses the commonly used behavioral tests and new directions for the assessment of dominance in rodents. We discuss the hierarchy inheritable nature and other critical issues regarding hierarchical rank manifestation which may help in designing social-rank-related studies that serve as promising pre-clinical tools in behavioral psychiatry.

Measuring Anxiety-Like Behaviors in Rodent Models of Traumatic Brain Injury

Anxiety is a common complaint following acquired traumatic brain injury (TBI). However, the measurement of dysfunctional anxiety behavioral states following experimental TBI in rodents is complex. Some studies report increased anxiety after TBI, whereas others find a decreased anxiety-like state, often described as increased risk-taking behavior or impulsivity. These inconsistencies may reflect a lack of standardization of experimental injury models or of behavioral testing techniques. Here, we review the most commonly employed unconditioned tests of anxiety and discuss them in a context of experimental TBI. Special attention is given to the effects of repeated testing, and consideration of potential sensory and motor confounds in injured rodents. The use of multiple tests and alternative data analysis methods are discussed, as well as the potential for the application of common data elements (CDEs) as a means of providing a format for documentation of experimental details and procedures of each published research report. CDEs may improve the rigor, reproducibility, as well as endpoint for better relating findings with clinical TBI phenotypes and the final goal of translation. While this may not resolve all incongruities in findings across laboratories, it is seen as a way forward for standardized and universal data collection for improvement of data quality and sharing, and advance therapies for neuropsychiatric symptoms that often present for decades following TBI.

Dauricine alleviated secondary brain injury after intracerebral hemorrhage by upregulating GPX4 expression and inhibiting ferroptosis of nerve cells

Intracerebral hemorrhage (ICH) is a severe stroke subtype with high disability and mortality, and no effective treatment is available. Previous research on intracerebral hemorrhage secondary brain injury drugs mainly targeted at cell apoptosis, inflammation and oxidative stress, but did not achieve good effects. In recent years, ferroptosis has become a focus concern in neurological diseases. Ferroptosis is a new type of programmed cell death caused by iron-dependent accumulation of lipid peroxides, in which glutathione peroxidase 4 (GPX4) is a key protein affecting ferroptosis. In this study, we used the STRING protein database to predict the proteins that may be co-expressed with GPX4, and studied the ability of Dauricine(Dau) to up-regulate the expression of GPX4 against ferroptosis and neuroprotection after intracerebral hemorrhage in normal cells in vitro, glutathione peroxidase 4 (GPX4) knockdown cells and collagenase injection in vivo in mouse models of intracerebral hemorrhage. The results showed that glutathione reductase (GSR) was a possible co-expression protein with GPX4. Dau could up-regulate the expression of glutathione peroxidase 4 (GPX4) in intracerebral hemorrhage(ICH) model, normal cells and GPX4 knockdown cells in vitro, and simultaneously up-regulate the expression of GSR in ICH mice. Dau could also reduce the levels of iron and lipid peroxidation, and have a neuroprotective effect on intracerebral hemorrhage(ICH) mice. It was tesified that Dauricine(Dau) could inhibit ferroptosis of nerve cells and alleviate brain injury after intracerebral hemorrhage by upregulating glutathione peroxidase 4 (GPX4) and glutathione reductase (GSR) co-expression. Therefore, Dau may be an effective drug for inhibiting ferroptosis and treating intracerebral hemorrhage.

Protective Effect of Lutein/Zeaxanthin Isomers in Traumatic Brain Injury in Mice

Previous studies revealed that oxidative stress and inflammation are the main contributors to secondary injury after traumatic brain injury (TBI). In an earlier study, we reported that lutein/zeaxanthin isomers (L/Zi) exert antioxidative and anti-inflammatory effects by activating the nuclear factor-kappa B (NF-κB) and nuclear factor-erythroid 2-related factor 2 (Nrf2) pathways. However, its precise role and underlying mechanisms were largely unknown after TBI. This study was conducted to investigate the potential mechanism of L/Zi isomers in a TBI model induced by a cold injury model in mice. To investigate the effects of L/Zi, male C57BL/6j mice-induced brain injury using the cold trauma model was allocated into two groups (n = 7): (i) TBI + vehicle group and (ii) TBI + L/Zi group (20 mg/kg BW). Brain samples were collected 24 h later for analyses. L/Zi given immediately after the injury decreased infarct volume and blood-brain barrier (BBB) permeability; L/Zi treatment also significantly reduced proinflammatory cytokines, including interleukin1 beta (IL-1β), interleukin 6 (IL-6), and NF-κB levels and increased growth-associated protein 43 (GAP-43), neural cell adhesion molecule (NCAM), brain-derived neurotrophic factor (BDNF), and Nrf2 levels compared with vehicle control. These data suggest that L/Zi improves mitochondrial function in TBI models, possibly decreasing inflammation and activating the Nrf2 pathway.

A Role for the Amygdala in Impairments of Affective Behaviors Following Mild Traumatic Brain Injury

Mild traumatic brain injury (TBI) results in chronic affective disorders such as depression, anxiety, and fear that persist up to years following injury and significantly impair the quality of life for patients. Although a great deal of research has contributed to defining symptoms of mild TBI, there are no adequate drug therapies for brain-injured individuals. Preclinical studies have modeled these deficits in affective behaviors post-injury to understand the underlying mechanisms with a view to developing appropriate treatment strategies. These studies have also unveiled sex differences that contribute to the varying phenotypes associated with each behavior. Although clinical and preclinical studies have viewed these behavioral deficits as separate entities with unique neurobiological mechanisms, mechanistic similarities suggest that a novel approach is needed to advance research on drug therapy. This review will discuss the circuitry involved in the expression of deficits in affective behaviors following mild TBI in humans and animals and provide evidence that the manifestation of impairment in these behaviors stems from an amygdala-dependent emotional processing deficit. It will highlight mechanistic similarities between these different types of affective behaviors that can potentially advance mild TBI drug therapy by investigating treatments for the deficits in affective behaviors as one entity, requiring the same treatment.

A roadmap of brain recovery in a mouse model of concussion: insights from neuroimaging

Concussion or mild traumatic brain injury is the most common form of traumatic brain injury with potentially long-term consequences. Current objective diagnosis and treatment options are limited to clinical assessment, cognitive rest, and symptom management, which raises the real danger of concussed patients being released back into activities where subsequent and cumulative injuries may cause disproportionate damages. This study conducted a cross-sectional multi-modal examination investigation of the temporal changes in behavioural and brain changes in a mouse model of concussion using magnetic resonance imaging. Sham and concussed mice were assessed at day 2, day 7, and day 14 post-sham or injury procedures following a single concussion event for motor deficits, psychological symptoms with open field assessment, T2-weighted structural imaging, diffusion tensor imaging (DTI), neurite orientation density dispersion imaging (NODDI), stimulus-evoked and resting-state functional magnetic resonance imaging (fMRI). Overall, a mismatch in the temporal onsets and durations of the behavioural symptoms and structural/functional changes in the brain was seen. Deficits in behaviour persisted until day 7 post-concussion but recovered at day 14 post-concussion. DTI and NODDI changes were most extensive at day 7 and persisted in some regions at day 14 post-concussion. A persistent increase in connectivity was seen at day 2 and day 14 on rsfMRI. Stimulus-invoked fMRI detected increased cortical activation at day 7 and 14 post-concussion. Our results demonstrate the capabilities of advanced MRI in detecting the effects of a single concussive impact in the brain, and highlight a mismatch in the onset and temporal evolution of behaviour, structure, and function after a concussion. These results have significant translational impact in developing methods for the detection of human concussion and the time course of brain recovery.

Depression following traumatic brain injury: a comprehensive overview

Traumatic brain injury (TBI) represents a major health concern affecting the neuropsychological health; TBI is accompanied by drastic long-term adverse complications that can influence many aspects of the life of affected individuals. A substantial number of studies have shown that mood disorders, particularly depression, are the most frequent complications encountered in individuals with TBI. Post-traumatic depression (P-TD) is present in approximately 30% of individuals with TBI, with the majority of individuals experiencing symptoms of depression during the first year following head injury. To date, the mechanisms of P-TD are far from being fully understood, and effective treatments that completely halt this condition are still lacking. The aim of this review is to outline the current state of knowledge on the prevalence and risk factors of P-TD, to discuss the accompanying brain changes at the anatomical, molecular and functional levels, and to discuss current approaches used for the treatment of P-TD.

Neural Markers of Vulnerability to Anxiety Outcomes after Traumatic Brain Injury

Anxiety outcomes after traumatic brain injury (TBI) are complex, and the underlying neural mechanisms are poorly understood. Here, we developed a multi-dimensional behavioral profiling approach to investigate anxiety-like outcomes in mice that takes into account individual variability. Departing from the tradition of comparing outcomes in TBI versus sham groups, we identified a subgroup within the TBI group that is vulnerable to anxiety dysfunction, and present increased exploration of the anxiogenic zone compared to sham controls or resilient injured animals, by applying dimensionality reduction, clustering, and post hoc validation to behavioral data obtained from multiple assays for anxiety at several post-injury time points. These vulnerable animals expressed distinct molecular profiles in the corticolimbic network, with downregulation in gamma-aminobutyric acid and glutamate and upregulation in neuropeptide Y markers. Indeed, among vulnerable animals, not resilient or sham controls, severity of anxiety-related outcomes correlated strongly with expression of molecular markers. Our results establish a foundational approach, with predictive power, for reliably identifying maladaptive anxiety outcomes after TBI and uncovering neural signatures of vulnerability to anxiety.

Chronic traumatic encephalopathy-a blueprint for the bridge between neurological and psychiatric disorders

Chronic traumatic encephalopathy (CTE) is a perplexing condition characterized by a broad and diverse range of neuropathology and psychopathology. While there are no agreed upon or validated clinical criteria for CTE, case series of CTE have described a wide range of neuropsychiatric symptoms that have been attributed to repetitive traumatic brain injuries (rTBI). However, the direct links between the psychopathology of psychiatric and neurological conditions from rTBI to CTE remains poorly understood. Prior studies suggest that repetitive cerebral injuries are associated with damage to neural circuitry involved in emotional and memory processes, but these studies do not offer longitudinal assessments that prove causation. More recent studies on novel targets, such as transmission of misfolded proteins, as well as newly advanced non-invasive imaging techniques may offer more direct evidence of the pathogenesis of CTE by tracing the progression of pathology and display of related behavioral impairments. Understanding this interface in the context of rTBI can play an important role in future approaches to the definition, assessment, prevention, and treatment of CTE and mental illnesses.

Sex as a Biological Variable in Preclinical Modeling of Blast-Related Traumatic Brain Injury

Approaches to furthering our understanding of the bioeffects, behavioral changes, and treatment options following exposure to blast are a worldwide priority. Of particular need is a more concerted effort to employ animal models to determine possible sex differences, which have been reported in the clinical literature. In this review, clinical and preclinical reports concerning blast injury effects are summarized in relation to sex as a biological variable (SABV). The review outlines approaches that explore the pertinent role of sex chromosomes and gonadal steroids for delineating sex as a biological independent variable. Next, underlying biological factors that need exploration for blast effects in light of SABV are outlined, including pituitary, autonomic, vascular, and inflammation factors that all have evidence as having important SABV relevance. A major second consideration for the study of SABV and preclinical blast effects is the notable lack of consistent model design—a wide range of devices have been employed with questionable relevance to real-life scenarios—as well as poor standardization for reporting of blast parameters. Hence, the review also provides current views regarding optimal design of shock tubes for approaching the problem of primary blast effects and sex differences and outlines a plan for the regularization of reporting. Standardization and clear description of blast parameters will provide greater comparability across models, as well as unify consensus for important sex difference bioeffects.

The closed-head impact model of engineered rotational acceleration (CHIMERA) as an application for traumatic brain injury pre-clinical research: A status report

Closed-head traumatic brain injury (TBI) is a worldwide concern with increasing prevalence and cost to society. Rotational acceleration is a primary mechanism in TBI that results from tissue strains that give rise to diffuse axonal injury. The Closed-Head Impact Model of Engineered Rotational Acceleration (CHIMERA) was recently introduced as a method for the study of impact acceleration effects in pre-clinical TBI research. This review provides a survey of the published literature implementing the CHIMERA device and describes pathological, imaging, neurophysiological, and behavioral findings. Findings show CHIMERA inflicts damage in white matter tracts as a key area of injury. Behaviorally, repeated studies have shown motor deficits and more chronic cognitive effects after CHIMERA injury. Good progress with model application has been accomplished by investigators attending to what is required for model validation. However, the majority of CHIMERA studies only utilize adult male mice. To further establish this model, more work with female animals and various age groups need to be performed, as well as studies to further establish and standardize methodologies for validation of the models for clinical relevance. Common data elements to standardize the reporting methodology for the CHIMERA literature are suggested.

DPP-4 inhibitor reduces striatal microglial deramification after sensorimotor cortex injury induced by external force impact

Dipeptidyl peptidase-4 inhibitors (or gliptins), a class of antidiabetic drugs, have recently been shown to have protective actions in the central nervous system. Their cellular and molecular mechanisms responsible for these effects are largely unknown. In the present study, two structurally different gliptins, sitagliptin and vildagliptin, were examined for their therapeutic actions in a controlled cortical impact (CCI) model of moderate traumatic brain injury (TBI) in mice. Early post-CCI treatment with sitagliptin, but not vildagliptin, significantly reduced body asymmetry, locomotor hyperactivity, and brain lesion volume. Sitagliptin attenuated post-CCI microglial deramification in the ipsilateral dorsolateral (DL) striatum, while vildagliptin had no effect. Sitagliptin also reduced striatal expression of galectin-3 and monocyte chemoattractant protein 1(MCP-1), and increased the cortical and striatal levels of the anti-inflammatory cytokine IL-10 on the ipsilateral side. These data support a differential protective effect of sitagliptin against TBI, possibly mediated by an anti-inflammatory effect in striatum to preserve connective network. Both sitagliptin and vildagliptin produced similar increases of active glucagon-like peptide-1 (GLP-1) in blood and brain. Increasing active GLP-1 may not be the sole molecular mechanisms for the neurotherapeutic effect of sitagliptin in TBI.

Longitudinal Functional Assessment of Brain Injury Induced by High-Intensity Ultrasound Pulse Sequences

Exposure of the brain to high-intensity stress waves creates the potential for long-term functional deficits not related to thermal or cavitational damage. Possible sources of such exposure include overpressure from blast explosions or high-intensity focused ultrasound (HIFU). While current ultrasound clinical protocols do not normally produce long-term neurological deficits, the rapid expansion of potential therapeutic applications and ultrasound pulse-train protocols highlights the importance of establishing a safety envelope beyond which therapeutic ultrasound can cause neurological deficits not detectable by standard histological assessment for thermal and cavitational damage. In this study, we assessed the neuroinflammatory response, behavioral effects, and brain micro-electrocorticographic (µECoG) signals in mice following exposure to a train of transcranial pulses above normal clinical parameters. We found that the HIFU exposure induced a mild regional neuroinflammation not localized to the primary focal site, and impaired locomotor and exploratory behavior for up to 1 month post-exposure. In addition, low frequency (δ) and high frequency (β, γ) oscillations recorded by ECoG were altered at acute and chronic time points following HIFU application. ECoG signal changes on the hemisphere ipsilateral to HIFU exposure are of greater magnitude than the contralateral hemisphere, and persist for up to three months. These results are useful for describing the upper limit of transcranial ultrasound protocols, and the neurological sequelae of injury induced by high-intensity stress waves.

Sex differences in cued fear responses and parvalbumin cell density in the hippocampus following repetitive concussive brain injuries in C57BL/6J mice

There is strong evidence to suggest a link between repeated head trauma and cognitive and emotional disorders, and Repetitive concussive brain injuries (rCBI) may also be a risk factor for depression and anxiety disorders. Animal models of brain injury afford the opportunity for controlled study of the effects of injury on functional outcomes. In this study, male and cycling female C57BL/6J mice sustained rCBI (3x) at 24-hr intervals and were tested in a context and cued fear conditioning paradigm, open field (OF), elevated zero maze and tail suspension test. All mice with rCBI showed less freezing behavior than sham control mice during the fear conditioning context test. Injured male, but not female mice also froze less in response to the auditory cue (tone). Injured mice were hyperactive in an OF environment and spent more time in the open quadrants of the elevated zero maze, suggesting decreased anxiety, but there were no differences between injured mice and sham-controls in depressive-like activity on the tail suspension test. Pathologically, injured mice showed increased astrogliosis in the injured cortex and white matter tracts (optic tracts and corpus callosum). There were no changes in the number of parvalbumin-positive interneurons in the cortex or amygdala, but injured male mice had fewer parvalbumin-positive neurons in the hippocampus. Parvalbumin-reactive interneurons of the hippocampus have been previously demonstrated to be involved in hippocampal-cortical interactions required for memory consolidation, and it is possible memory changes in the fear-conditioning paradigm following rCBI are the result of more subtle imbalances in excitation and inhibition both within the amygdala and hippocampus, and between more widespread brain regions that are injured following a diffuse brain injury.

Therapeutic effects of chrysin in a rat model of traumatic brain injury: A behavioral, biochemical, and histological study

AIMS

Oxidative stress and apoptosis have major roles in the progression of traumatic brain injury (TBI)-associated motor and cognitive deficits. The present study was aimed to elucidate the putative effects of chrysin, a natural flavonoid compound, against TBI-induced motor and cognitive dysfunctions and possible involved mechanisms.

MAIN METHODS

Chrysin (25, 50 or 100 mg/kg) was orally administered to rats starting immediately following TBI induction by Marmarou's weight-drop technique and continuously for 3 or 14 days. Neurological functions, motor coordination, learning and memory performances, histological changes, cell apoptosis, expression of pro- and anti-apoptotic proteins, and oxidative status were assayed at scheduled time points after experimental TBI.

KEY FINDINGS

The results indicated that treatment with chrysin improved learning and memory disabilities in passive avoidance task, and ameliorated motor coordination impairment in rotarod test after TBI. These beneficial effects were accompanied by increased the concentrations of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione (GSH), decreased malondialdehyde (MDA) content, prevented neuronal loss, diminished apoptotic index, elevated the expression of anti-apoptotic Bcl-2 protein, and reduced the expression of pro-apoptotic Bax protein in the cerebral cortex and hippocampus tissues.

SIGNIFICANCE

Our findings suggest that both anti-oxidative and anti-apoptotic properties of chrysin (especially in the dose of 100 mg/kg) are possible mechanisms that improve cognitive/motor deficits and prevent neuronal cell death after TBI.

Cognitive and neuropsychiatric impairments vary as a function of injury severity at 12 months post-experimental diffuse traumatic brain injury: Implications for dementia development

Traumatic brain injury (TBI) is a common risk factor for later neurodegeneration, which can manifest as dementia. Despite this, little is known about the time-course of development of functional deficits, particularly cognitive and neuropsychiatric impairments, and whether these differ depending on the nature of the initiating insult. Therefore, this study investigated long term functional impairment at 12 months post-injury following diffuse TBI of different severities. Male Sprague-Dawley rats (420-480 g; 10-12 weeks) were either given a sham surgery (n = 14) or subjected to Marmarou's impact acceleration model of diffuse TBI for a single mild TBI (n = 12), repetitive mild TBI (3 mild diffuse injuries at 5 day intervals) (n = 14) or moderate to severe TBI (n = 14). At 12 months after injury, they were tested on a functional battery encompassing motor, neuropsychiatric (anxiety and depressive-like) and cognitive function. Our results showed that moderate to severe TBI animals exhibited significant impairments in cognitive flexibility (p = 0.009) on the Barnes maze when compared to age-matched sham animals. Neither repetitive mild TBI nor single mild TBI animals showed significant functional impairments when compared to shams. Thus, this study provides the first insight into chronic functional impairments associated with different severities of diffuse TBI, with moderate to severe TBI being a higher risk factor for impaired cognitive function at 12 months post-injury. Taken together, this may have implications for risk of dementia development following different severities of injury.

Chronic Neurobehavioral Sex Differences in a Murine Model of Repetitive Concussive Brain Injury

Traumatic brain injury (TBI) resulting from repeated head trauma is frequently characterized by diffuse axonal injury and long-term motor, cognitive and neuropsychiatric symptoms. Given the delay, often decades, between repeated head traumas and the presentation of symptoms in TBI patients, animal models of repeated injuries should be studied longitudinally to properly assess the longer-term effects of multiple concussive injuries on functional outcomes. In this study, male and cycling female C57BL/6J mice underwent repeated (three) concussive brain injuries (rCBI) delivered via a Leica ImpactOne cortical impact device and were assessed chronically on motor (open field and rotarod), cognitive (y-maze and active place avoidance), and neuropsychiatric (marble-burying, elevated zero maze and tail suspension) tests. Motor deficits were significant on the rotarod on the day following the injuries, and slight impairment remained for up to 6 months. All mice that sustained rCBI had significant cognitive deficits on the active place avoidance test and showed greater agitation (less immobility) in the tail suspension test. Only injured male mice were significantly hyperactive in the open field, and had increased time spent in the open quadrants of the elevated zero maze. One year after the injuries, mice of both sexes exhibited persistent pathological changes by the presence of Prussian blue staining (indication of prior microbleeds), primarily in the cortex at the site of the injury, and increased GFAP staining in the perilesional cortex and axonal tracts (corpus callosum and optic tracts). These data demonstrate that a pathological phenotype with motor, cognitive, and neuropsychiatric symptoms can be observed in an animal model of rCBI for at least one year post-injury, providing a pre-clinical setting for the study of the link between multiple brain injuries and neurodegenerative disorders. Furthermore, this is the first study to include both sexes in a pre-clinical long-term rCBI model, and female mice are less impaired functionally than males.

Berberine Protects Secondary Injury in Mice with Traumatic Brain Injury Through Anti-oxidative and Anti-inflammatory Modulation

Traumatic brain injury (TBI) is one of the major causes of death and disability worldwide. Novel and effective therapy is needed to prevent the secondary spread of damage beyond the initial injury. The aim of this study was to investigate whether berberine has a neuroprotective effect on secondary injury post-TBI, and to explore its potential mechanism in this protection. The mice were randomly divided into Sham-saline, TBI-saline and TBI-Berberine (50 mg/kg). TBI was induced by Feeney's weight-drop technique. Saline or berberine was administered via oral gavage starting 1 h post-TBI and continuously for 21 days. Motor coordination, spatial learning and memory were assessed using beam-walking test and Morris water maze test, respectively. Brain sections were processed for lesion volume assessment, and expression of neuronal nuclei (NeuN), cyclooxygenase 2 (COX-2), inducible nitric oxide synthase (iNOS), 8-hydroxy-2-deoxyguanosine (8-OHdG), ionized calcium-binding adapter molecule 1 (Iba1) and glial fibrillary acidic protein (GFAP) were detected via immunohistochemistry and immunofluorescence. There were statistically significant improvement in motor coordination, spatial learning and memory in the TBI-Berberine group, compared to the TBI-saline group. Treatment with berberine significantly reduced cortical lesion volume, neuronal loss, COX-2, iNOS and 8-OHdG expression in both the cortical lesion border zone (LBZ) and ipsilateral hippocampal CA1 region (CA1), compared to TBI-saline. Berberine treatment also significantly decreased Iba1- and GFAP-positive cell number in both the cortical LBZ and ipsilateral CA1, relative to saline controls. These results indicated that berberine exerted neuroprotective effects on secondary injury in mice with TBI probably through anti-oxidative and anti-inflammatory properties.

FGF21 Protects the Blood-Brain Barrier by Upregulating PPARγ via FGFR1/β-klotho after Traumatic Brain Injury

Blood-brain barrier (BBB) disruption and dysfunction result in brain edema, which is responsible for more than half of all deaths after severe traumatic brain injury (TBI). Fibroblast growth factor 21 (FGF21) has a potential neuroprotective function in the brain. However, the effects and underlying possible mechanism of action on BBB integrity following TBI remain unknown. The purpose of the current study was to determine the effects of FGF21 on BBB protection and TBI treatment. The effects of recombinant human FGF21 (rhFGF21) on BBB integrity and on tight junction (TJ) and adhesion junction (AJ) proteins were investigated both in a TBI mouse model and an in vitro BBB disruption model established with tumor necrosis factor alpha (TNF-α)-induced human brain microvascular endothelial cells (HBMECs). The ability of rhFGF21 to form an FGF21/FGFR1/β-klotho complex was confirmed by in vitro β-klotho small interfering RNA (siRNA) transfection and FGFR1 co-immunoprecipitation. In addition, the specific FGFR1 and peroxisome proliferator-activated receptor gamma (PPARγ) inhibitors PD173074 and GW9662, respectively, were applied to further explore the possible mechanism of rhFGF21 in BBB maintenance after TBI. rhFGF21 markedly reduced neurofunctional behavior deficits and cerebral edema degree, preserved BBB integrity, and recued brain tissue loss and neuron apoptosis in the mouse model after TBI. Both in vivo and in vitro, rhFGF21 upregulated TJ and AJ proteins, thereby preserving the BBB. Moreover, rhFGF21 activated PPARγ in TNF-α-induced HBMECs through formation of an FGF21/FGFR1/β-klotho complex. rhFGF21 protected the BBB through FGF21/FGFR1/β-klotho complex formation and PPARγ activation, which upregulated TJ and AJ proteins.

Effective Treatment of Traumatic Brain Injury in Rowett Nude Rats with Stromal Vascular Fraction Transplantation

Traumatic brain injury (TBI) affects 1.9 million Americans, including blast TBI that is the signature injury of the Iraq and Afghanistan wars. Our project investigated whether stromal vascular fraction (SVF) can assist in post-TBI recovery. We utilized strong acoustic waves (5.0 bar) to induce TBI in the cortex of adult Rowett Nude (RNU) rats. One hour post-TBI, harvested human SVF (500,000 cells suspended in 0.5 mL lactated Ringers) was incubated with Q-Tracker cell label and administered into tail veins of RNU rats. For comparison, we utilized rats that received SVF 72 h post-TBI, and a control group that received lactated Ringers solution. Rotarod and water maze assays were used to monitor motor coordination and spatial memories. Rats treated immediately after TBI showed no signs of motor skills and memory regression. SVF treatment 72 h post-TBI enabled the rats maintain their motor skills, while controls treated with lactated Ringers were 25% worse statistically in both assays. Histological analysis showed the presence of Q-dot labeled human cells near the infarct in both SVF treatment groups; however, labeled cells were twice as numerous in the one hour group. Our study suggests that immediate treatment with SVF would serve as potential therapeutic agents in TBI.

Alpha-1-antitrypsin: a novel predictor for long-term recovery of chronic disorder of consciousness

BACKGROUND

The aim of this manuscript was to explore the molecular basis and identify novel biomarkers for the diagnosis and prognosis of patients with chronic disorder of consciousness.

METHODS

A coupled isobaric tag for relative and absolute quantitation-based approach was used to screen differentially expressed proteins (DEPs) between patients with chronic disorder of consciousness and healthy individuals. Candidate proteins were identified and measured. The Coma Recovery Scale-Revised (CRS-R) score was used to quantify the severity, and long-term recovery was assessed by Glasgow Outcome Scale (GOS).

RESULTS

Between patients and controls, a total of 77 DEPs were identified. Based on the DEPs, a network containing 50 nodes and 207 edges was built, and alpha-1-antitrypsin was marked as the hub protein. The results indicated that alpha-1-antitrypsin correlated with the CRS-R score with a correlation coefficient of 0.631, and an outcome at 12 months (8.5 ± 2.1 ng/ml in patients with GOS 1-2 vs. 6.8 ± 1.6 ng/ml in those with GOS 3-5, p = 0.002).

CONCLUSIONS

The data confirm the diagnostic and prognostic potential of alpha-1-antitrypsin in chronic disorder of consciousness, which may contribute to the development of novel therapeutic agents.

Progression of histopathological and behavioral abnormalities following mild traumatic brain injury in the male ferret

White matter damage is an important consequence of traumatic brain injury (TBI) in humans. Unlike rodents, ferrets have a substantial amount of white matter and a gyrencephalic brain; therefore, they may represent an ideal small mammal model to study human-pertinent consequences of TBI. Here we report immunohistochemical and behavioral results after a controlled cortical impact (CCI) injury to the sensorimotor cortex of adult male ferrets. We assessed inflammation in the neocortex and white matter, and behavior at 1 day post injury and 1, 4, and 16 weeks post injury (WPI). CCI in the ferret produced inflammation that originated in the neocortex near the site of the injury and progressed deep into the white matter with time. The density of microglia and astrocytes increased in the neocortex near the injury, peaking at 4WPI and remaining elevated at 16WPI. Microglial morphology in the neocortex was significantly altered in the first 4 weeks, but showed a return toward normal at 16 weeks. Clusters of microglial cells in the white matter persisted until 16WPI. We assessed motor and cognitive behavior using the open field, novel object recognition, T-maze, and gait tests. A transient deficit in memory occurred at 4WPI, with a reduction of rearing and motor ability at 12 and 16WPI. Behavioral impairments coincide with features of the inflammatory changes in the neocortex revealed by immunohistochemistry. The ferret represents an important animal model to explore ongoing damage in the white matter and cerebral cortex after TBI.

HDAC1 Silence Promotes Neuroprotective Effects of Human Umbilical Cord-Derived Mesenchymal Stem Cells in a Mouse Model of Traumatic Brain Injury via PI3K/AKT Pathway

Stem cell transplantation is a promising therapy for traumatic brain injury (TBI), but low efficiency of survival and differentiation of transplanted stem cells limits its clinical application. Histone deacetylase 1 (HDAC1) plays important roles in self-renewal of stem cells as well as the recovery of brain disorders. However, little is known about the effects of HDAC1 on the survival and efficacy of human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) in vivo. In this study, our results showed that HDAC1 silence promoted hUC-MSCs engraftment in the hippocampus and increased the neuroprotective effects of hUC-MSCs in TBI mouse model, which was accompanied by improved neurological function, enhanced neurogenesis, decreased neural apoptosis, and reduced oxidative stress in the hippocampus. Further mechanistic studies revealed that the expressions of phosphorylated PTEN (p-PTEN), phosphorylated Akt (p-Akt), and phosphorylated GSK-3β (p-GSK-3β) were upregulated. Intriguingly, the neuroprotective effects of hUC-MSCs with HDAC1 silence on behavioral performance of TBI mice was markedly attenuated by LY294002, an inhibitor of the PI3K/AKT pathway. Taken together, our findings suggest that hUC-MSCs transplantation with HDAC1 silence may provide a potential strategy for treating TBI in the future.

Repeated Mild Closed Head Injuries Induce Long-Term White Matter Pathology and Neuronal Loss That Are Correlated With Behavioral Deficits

An estimated 5.3 million Americans are living with a disability from a traumatic brain injury (TBI). There is emerging evidence of the detrimental effects from repeated mild TBIs (rmTBIs). rmTBI manifests its own unique set of behavioral and neuropathological changes. A subset of individuals exposed to rmTBI develop permanent behavioral and pathological consequences, defined postmortem as chronic traumatic encephalopathy. We have combined components of two classic rodent models of TBI, the controlled cortical impact model and the weight drop model, to develop a repeated mild closed head injury (rmCHI) that produces long-term deficits in several behaviors that correlate with neuropathological changes. Mice receiving rmCHI performed differently from 1-hit or sham controls on the elevated plus maze; these deficits persist up to 6 months postinjury (MPI). rmCHI mice performed worse than 1-hit and control sham mice at 2 MPI and 6 MPI on the Morris water maze. Mice receiving rmCHI exhibited significant atrophy of the corpus callosum at both 2 MPI and 6 MPI, as assessed by stereological volume analysis. Stereological analysis also revealed significant loss of cortical neurons in comparison with 1-hit and controls. Moreover, both of these pathological changes correlated with behavioral impairments. In human tau transgenic mice, rmCHI induced increases in hyperphosphorylated paired helical filament 1 tau in the hippocampus. This suggests that strategies to restore myelination or reduce neuronal loss may ameliorate the behavioral deficits observed following rmCHI and that rmCHI may model chronic traumatic encephalopathy in human tau mice.

Depression following a traumatic brain injury: uncovering cytokine dysregulation as a pathogenic mechanism

A substantial number of individuals have long-lasting adverse effects from a traumatic brain injury (TBI). Depression is one of these long-term complications that influences many aspects of life. Depression can limit the ability to return to work, and even worsen cognitive function and contribute to dementia. The mechanistic cause for the increased depression risk associated with a TBI remains to be defined. As TBI results in chronic neuroinflammation, and priming of glia to a secondary challenge, the inflammatory theory of depression provides a promising framework for investigating the cause of depression following a TBI. Increases in cytokines similar to those seen in depression in the general population are also increased following a TBI. Biomarker levels of cytokines peak within hours-to-days after the injury, yet pro-inflammatory cytokines may still be elevated above physiological levels months-to-years following TBI, which is the time frame in which post-TBI depression can persist. As tumor necrosis factor α and interleukin 1 can signal directly at the neuronal synapse, pathophysiological levels of these cytokines can detrimentally alter neuronal synaptic physiology. The purpose of this review is to outline the current evidence for the inflammatory hypothesis of depression specifically as it relates to depression following a TBI. Moreover, we will illustrate the potential synaptic mechanisms by which tumor necrosis factor α and interleukin 1 could contribute to depression. The association of inflammation with the development of depression is compelling; however, in the context of post-TBI depression, the role of inflammation is understudied. This review attempts to highlight the need to understand and treat the psychological complications of a TBI, potentially by neuroimmune modulation, as the neuropsychiatric disabilities can have a great impact on the rehabilitation from the injury, and overall quality of life.

Repeated mild traumatic brain injury produces neuroinflammation, anxiety-like behaviour and impaired spatial memory in mice

PRIMARY OBJECTIVE

Repeated traumatic brain injuries (rmTBI) are frequently associated with debilitating neuropsychiatric conditions such as cognitive impairment, mood disorders, and post-traumatic stress disorder. We tested the hypothesis that repeated mild traumatic brain injury impairs spatial memory and enhances anxiety-like behaviour.

RESEARCH DESIGN

We used a between groups design using single (smTBI) or repeated (rmTBI) controlled cranial closed skull impacts to mice, compared to a control group.

METHODS AND PROCEDURES

We assessed the effects of smTBI and rmTBI using measures of motor performance (Rotarod Test [RT]), anxiety-like behaviour (Elevated Plus Maze [EPM] and Open Field [OF] tests), and spatial memory (Morris Water Maze [MWM]) within 12 days of the final injury. In separate groups of mice, astrocytosis and microglial activation were assessed 24 hours after the final injury using GFAP and IBA-1 immunohistochemistry.

MAIN OUTCOMES AND RESULTS

RmTBI impaired spatial memory in the MWM and increased anxiety-like behaviour in the EPM and OFT. In addition, rmTBI elevated GFAP and IBA-1 immunohistochemistry throughout the mouse brain. RmTBI produced astrocytosis and microglial activation, and elicited impaired spatial memory and anxiety-like behaviour.

CONCLUSIONS

rmTBI produces acute cognitive and anxiety-like disturbances associated with inflammatory changes in brain regions involved in spatial memory and anxiety.

Neuroinflammation in traumatic brain injury: A chronic response to an acute injury

Every year, approximately 1.4 million US citizens visit emergency rooms for traumatic brain injuries. Formerly known as an acute injury, chronic neurodegenerative symptoms such as compromised motor skills, decreased cognitive abilities, and emotional and behavioral changes have caused the scientific community to consider chronic aspects of the disorder. The injury causing impact prompts multiple cell death processes, starting with neuronal necrosis, and progressing to various secondary cell death mechanisms. Secondary cell death mechanisms, including excitotoxicity, oxidative stress, mitochondrial dysfunction, blood-brain barrier disruption, and inflammation accompany chronic traumatic brain injury (TBI) and often contribute to long-term disabilities. One hallmark of both acute and chronic TBI is neuroinflammation. In acute stages, neuroinflammation is beneficial and stimulates an anti-inflammatory response to the damage. Conversely, in chronic TBI, excessive inflammation stimulates the aforementioned secondary cell death. Converting inflammatory cells from pro-inflammatory to anti-inflammatory may expand the therapeutic window for treating TBI, as inflammation plays a role in all stages of the injury. By expanding current research on the role of inflammation in TBI, treatment options and clinical outcomes for afflicted individuals may improve. This paper is a review article. Referred literature in this paper has been listed in the references section. The data sets supporting the conclusions of this article are available online by searching various databases, including PubMed. Some original points in this article come from the laboratory practice in our research center and the authors' experiences.

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.

Cognitive Deficits and Inflammatory Response Resulting from Mild-to-Moderate Traumatic Brain Injury in Rats Are Exacerbated by Repeated Pre-Exposure to an Innate Stress Stimulus

Traumatic brain injury (TBI) is common in both military and civilian populations, and often results in neurobehavioral sequelae that impair quality of life in both patients and their families. Although individuals who are chronically exposed to stress are more likely to experience TBI, it is still unknown whether pre-injury stress influences the outcome after TBI. The present study tested whether behavioral and cognitive long-term outcome after TBI in rats is affected by prior exposure to an innate stress stimulus. Young adult male Sprague-Dawley rats were exposed to the predator odor 2,5-dihydro-2,4,5-trimethylthiazoline (TMT) or to water (WAT); exposure was repeated eight times at irregular intervals over a 2-week period. Rats were subsequently subjected to either mild-to-moderate bilateral brain injury (lateral fluid percussion [LFP]) or sham surgery (Sham). Four experimental groups were studied: Sham-WAT, Sham-TMT, LFP-WAT and LFP-TMT. Compared with Sham-WAT rats, LFP-WAT rats exhibited transient locomotor hyperactivity without signs of anxiety, minor spatial learning acquisition and hippocampal long-term potentiation deficits, and lower baseline activity of the hypothalamic-pituitary-adrenal axis with slightly stronger reactivity to restraint stress. Exposure to TMT had only negligible effects on Sham rats, whereas it exacerbated all deficits in LFP rats except for locomotor hyperactivity. Early brain inflammatory response (8 h post-trauma) was aggravated in rats pre-exposed to TMT, suggesting that increased brain inflammation may sustain functional deficits in these rats. Hence, these data suggest that pre-exposure to stressful conditions can aggravate long-term deficits induced by TBI, leading to severe stress response deficits, possibly due to dysregulated inflammatory response.

Protective Effects of Chinese Herbal Medicine Rhizoma drynariae in Rats After Traumatic Brain Injury and Identification of Active Compound

Traumatic brain injury (TBI) is a leading cause of death and disability in the USA. Effective therapeutic strategies for TBI are needed, and increasing attention is turning toward traditional herbal medicine. Rhizoma drynariae is a traditional Chinese medicine that has immunomodulatory and anti-inflammatory effects. Here, using the controlled cortical impact model of TBI in rats, we examined whether oral administration of R. drynariae can reduce TBI-induced brain injury in rats. We also identified the likely active compound among its four major phytochemicals in decoction. We found that post-treatment with R. drynariae decreased brain lesion volume, improved neurologic and cognitive function, and reduced anxiety- and depression-like behaviors. These changes were accompanied by reduced blood levels of IL-6 and increased IL-10. R. drynariae treatment also reversed the TBI-induced decrease in blood monocyte numbers and percentage of blood CD3 and CD4 T lymphocytes while inhibiting microglial/macrophage activation. Furthermore, by using ultra performance liquid chromatography and comparing retention times with authentic standards, we identified eriodictyol as the putative active compound of R. drynariae extract in the blood of rats with TBI. These novel findings indicate that the traditional Chinese herbal medicine R. drynariae protects brain against TBI-induced brain injury, possibly via immune-promoting, anti-inflammatory, and neuroprotective effects. Eriodictyol could be its active compound.

Aging with Traumatic Brain Injury: Effects of Age at Injury on Behavioral Outcome following Diffuse Brain Injury in Rats

Development and aging are influenced by external factors with the potential to impact health throughout the life span. Traumatic brain injury (TBI) can initiate and sustain a lifetime of physical and mental health symptoms. Over 1.7 million TBIs occur annually in the USA alone, with epidemiology suggesting a higher incidence for young age groups. Additionally, increasing life spans mean more years to age with TBI. While there is ongoing research of experimental pediatric and adult TBI, few studies to date have incorporated animal models of pediatric, adolescent, and adult TBI to understand the role of age at injury across the life span. Here, we explore repeated behavioral performance between rats exposed to diffuse TBI at five different ages. Our aim was to follow neurological morbidities across the rodent life span with respect to age at injury. A single cohort of male Sprague-Dawley rats (n = 69) was received at postnatal day (PND) 10. Subgroups of this cohort (n = 11-12/group) were subjected to a single moderate midline fluid percussion injury at age PND 17, PND 35, 2 months, 4 months, or 6 months. A control group of naïve rats (n = 12) was assembled from this cohort. The entire cohort was assessed for motor function by beam walk at 1.5, 3, 5, and 7 months of age. Anxiety-like behavior was assessed with the open field test at 8 months of age. Cognitive performance was assessed using the novel object location task at 8, 9, and 10 months of age. Depression-like behavior was assessed using the forced swim test at 10 months of age. Age at injury and time since injury differentially influenced motor, cognitive, and affective behavioral outcomes. Motor and cognitive deficits occurred in rats injured at earlier developmental time points, but not in rats injured in adulthood. In contrast, rats injured during adulthood showed increased anxiety-like behavior compared to uninjured control rats. A single diffuse TBI did not result in chronic depression-like behaviors or changes in body weight among any groups. The interplay of age at injury and aging with an injury are translationally important factors that influence behavioral performance as a quality of life metric. More complete understanding of these factors can direct rehabilitative efforts and personalized medicine for TBI survivors.

Sex differences in orbitofrontal connectivity in male and female veterans with TBI

More female soldiers are now serving in combat theaters than at any other time. However, little is known about possible sex differences underlying the neuropathology and manifestation of one of modern war’s signature injuries, traumatic brain injury (TBI). The paucity of information regarding sex differences in TBI is particularly evident when examining changes in executive function and emotion regulation associated with post concussive events. The current study objective was to observe whether patterns of orbitofrontal (OFC) functional connectivity would differ between female veterans with TBI and their male counterparts. The study further sought to determine whether OFC connectivity might be differentially associated with clinical measures of aggression and hostility. Seventeen female veterans and 24 male veterans, age 18 to 25, who met criteria for TBI completed resting state magnetic resonance imaging (MRI) and clinical assessment measures. Imaging data were analyzed using left and right seed regions of the OFC, and regression analyses were conducted to observe the relationship between resting state connectivity and self-reported aggression. Females and males in this study differed in OFC connectivity, with females demonstrating greater connectivity between left and right OFC and parietal and occipital regions and males demonstrating greater connectivity between left and right OFC and frontal and temporal regions. Significant associations between resting state connectivity and clinical measures were found only in male veterans. These findings suggest that TBI may interact with sex-specific patterns of brain connectivity in male and female veterans and exert divergent effects on clinical profiles of aggression post-injury.

Neuropsychiatric Symptom Modeling in Male and Female C57BL/6J Mice after Experimental Traumatic Brain Injury

Psychiatric symptoms such as anxiety and depression are frequent and persistent complaints following traumatic brain injury (TBI). Modeling these symptoms in animal models of TBI affords the opportunity to determine mechanisms underlying behavioral pathologies and to test potential therapeutic agents. However, testing these symptoms in animal models of TBI has yielded inconsistent results. The goal of the current study was to employ a battery of tests to measure multiple anxiety- and depressive-like symptoms following TBI in C57BL/6J mice, and to determine if male and female mice are differentially affected by the injury. Following controlled cortical impact (CCI) at a parietal location, neither male nor female mice showed depressive-like symptoms as measured by the Porsolt forced-swim test and sucrose preference test. Conclusions regarding anxiety-like behaviors were dependent upon the assay employed; CCI-induced thigmotaxis in the open field suggested an anxiogenic effect of the injury; however, results from the elevated zero maze, light-dark box, and marble-burying tests indicated that CCI reduced anxiety-like behaviors. Fewer anxiety-like behaviors were also associated with the female sex. Increased levels of activity were also measured in female mice and injured mice in these tests, and conclusions regarding anxiety should be taken with caution when experimental manipulations induce changes in baseline activity. These results underscore the irreconcilability of results from studies attempting to model TBI-induced neuropsychiatric symptoms. Changes in injury models or better attempts to replicate the clinical syndrome may improve the translational applicability of rodent models of TBI-induced anxiety and depression.

Social dysfunction after pediatric traumatic brain injury: A translational perspective

Social dysfunction is common after traumatic brain injury (TBI), contributing to reduced quality of life for survivors. Factors which influence the development or persistence of social deficits after injury remain poorly understood, particularly in the context of ongoing brain maturation during childhood and adolescence. Aberrant social interactions have recently been modeled in adult and juvenile rodents after experimental TBI, providing an opportunity to gain new insights into the underlying neurobiology of these behaviors. Here, we review our current understanding of social dysfunction in both humans and rodent models of TBI, with a focus on brain injuries acquired during early development. Modulators of social outcomes are discussed, including injury-related and environmental risk and resilience factors. Disruption of social brain network connectivity and aberrant neuroendocrine function are identified as potential mechanisms of social impairments after pediatric TBI. Throughout, we highlight the overlap and disparities between outcome measures and findings from clinical and experimental approaches, and explore the translational potential of future research to prevent or ameliorate social dysfunction after childhood TBI.

Automated monitoring of early neurobehavioral changes in mice following traumatic brain injury

Traumatic brain injury often causes a variety of behavioral and emotional impairments that can develop into chronic disorders. Therefore, there is a need to shift towards identifying early symptoms that can aid in the prediction of traumatic brain injury outcomes and behavioral endpoints in patients with traumatic brain injury after early interventions. In this study, we used the SmartCage system, an automated quantitative approach to assess behavior alterations in mice during an early phase of traumatic brain injury in their home cages. Female C57BL/6 adult mice were subjected to moderate controlled cortical impact (CCI) injury. The mice then received a battery of behavioral assessments including neurological score, locomotor activity, sleep/wake states, and anxiety-like behaviors on days 1, 2, and 7 after CCI. Histological analysis was performed on day 7 after the last assessment. Spontaneous activities on days 1 and 2 after injury were significantly decreased in the CCI group. The average percentage of sleep time spent in both dark and light cycles were significantly higher in the CCI group than in the sham group. For anxiety-like behaviors, the time spent in a light compartment and the number of transitions between the dark/light compartments were all significantly reduced in the CCI group than in the sham group. In addition, the mice suffering from CCI exhibited a preference of staying in the dark compartment of a dark/light cage. The CCI mice showed reduced neurological score and histological abnormalities, which are well correlated to the automated behavioral assessments. Our findings demonstrate that the automated SmartCage system provides sensitive and objective measures for early behavior changes in mice following traumatic brain injury.

Diminished amygdala activation and behavioral threat response following traumatic brain injury

Each year, approximately 3.8 million people suffer mild to moderate traumatic brain injuries (mTBI) that result in an array of neuropsychological symptoms and disorders. Despite these alarming statistics, the neurological bases of these persistent, debilitating neuropsychological symptoms are currently poorly understood. In this study we examined the effects of mTBI on the amygdala, a brain structure known to be critically involved in the processing of emotional stimuli. Seven days after lateral fluid percussion injury (LFPI), mice underwent a series of physiological and behavioral experiments to assess amygdala function. Brain-injured mice exhibited a decreased threat response in a cued fear conditioning paradigm, congruent with a decrease in amygdala excitability determined with basolateral amygdala (BLA) field excitatory post-synaptic potentials together with voltage-sensitive dye imaging (VSD). Furthermore, beyond exposing a general decrease in the excitability of the primary input of the amygdala, the lateral amygdala (LA), VSD also revealed a decrease in the relative strength or activation of internuclear amygdala circuit projections after LFPI. Thus, not only does activation of the LA require increased stimulation, but the proportion of this activation that is propagated to the primary output of the amygdala, the central amygdala, is also diminished following LFPI. Intracellular recordings revealed no changes in the intrinsic properties of BLA pyramidal neurons after LFPI. This data suggests that mild to moderate TBI has prominent effects on amygdala function and provides a potential neurological substrate for many of the neuropsychological symptoms suffered by TBI patients.

A Novel Closed-Head Model of Mild Traumatic Brain Injury Using Focal Primary Overpressure Blast to the Cranium in Mice

Mild traumatic brain injury (TBI) from focal head impact is the most common form of TBI in humans. Animal models, however, typically use direct impact to the exposed dura or skull, or blast to the entire head. We present a detailed characterization of a novel overpressure blast system to create focal closed-head mild TBI in mice. A high-pressure air pulse limited to a 7.5 mm diameter area on the left side of the head overlying the forebrain is delivered to anesthetized mice. The mouse eyes and ears are shielded, and its head and body are cushioned to minimize movement. This approach creates mild TBI by a pressure wave that acts on the brain, with minimal accompanying head acceleration-deceleration. A single 20-psi blast yields no functional deficits or brain injury, while a single 25-40 psi blast yields only slight motor deficits and brain damage. By contrast, a single 50-60 psi blast produces significant visual, motor, and neuropsychiatric impairments and axonal damage and microglial activation in major fiber tracts, but no contusive brain injury. This model thus reproduces the widespread axonal injury and functional impairments characteristic of closed-head mild TBI, without the complications of systemic or ocular blast effects or head acceleration that typically occur in other blast or impact models of closed-skull mild TBI. Accordingly, our model provides a simple way to examine the biomechanics, pathophysiology, and functional deficits that result from TBI and can serve as a reliable platform for testing therapies that reduce brain pathology and deficits.

Targeting different pathophysiological events after traumatic brain injury in mice: Role of melatonin and memantine

The tissue damage that emerges during traumatic brain injury (TBI) is a consequence of a variety of pathophysiological events, including free radical generation and over-activation of N-methyl-d-aspartate-type glutamate receptors (NMDAR). Considering the complex pathophysiology of TBI, we hypothesized that combination of neuroprotective compounds, targeting different events which appear during injury, may be a more promising approach for patients. In this context, both NMDAR antagonist memantine and free radical scavenger melatonin are safe in humans and promising agents for the treatment of TBI. Herein, we examined the effects of melatonin administered alone or in combination with memantine on the activation of signaling pathways, injury development and DNA fragmentation. Both compounds reduced brain injury moderately and the density of DNA fragmentation significantly. Notably, melatonin/memantine combination decreased brain injury and DNA fragmentation significantly, which was associated with reduced p38 and ERK-1/2 phosphorylation. As compared with melatonin and memantine groups, SAPK/JNK-1/2 phosphorylation was also reduced in melatonin/memantine combined animals. In addition, melatonin, memantine and their combination decreased iNOS activity significantly. Here, we provide evidence that melatonin/memantine combination protects brain from traumatic injury, which was associated with decreased DNA fragmentation, p38 phosphorylation and iNOS activity.

CT imaging and spontaneous behavior analysis after osmotic blood-brain barrier opening in Wistar rat

In our previous experiments we demonstrated that osmotic opening of the blood brain barrier (BBB) in rats by administration of mannitol into the internal carotid artery leads to cerebral edema. The aim of this study was to confirm objectively the development of brain edema and determine whether it affects spontaneous locomotor activity in rats (SLA). Brain edema was verified by computer tomography (CT) examination of the brain and SLA was observed during open field test. Twenty four adult male rats were divided into four groups of six: (1) control animals (C), (2) controls with anesthesia (CA), (3) controls with sham surgery (CS), (4) experimental - osmotic opening of the BBB (MA). Osmotic BBB disruption manifested by reducing the density of brain tissue (hypodensity), suggesting a higher water content in the brain tissue. SLA was compared between C, CA, CS and MA groups and between MA and CA groups. Significant difference was found only between the control group and MA group. In the first 30 min of the examination, rats after the mannitol administration revealed a marked limitation of spontaneous locomotor activity. Experimental results demonstrated reduction of spontaneous locomotor activity in rats with induced brain edema.