Traumatic brain injuries

Vision impairment after traumatic brain injury: present knowledge and future directions

Traumatic brain injury (TBI) is a major cause of mortality and morbidity in the USA as well as in the world. As a result of TBI, the visual system is also affected often causing complete or partial visual loss, which in turn affects the quality of life. It may also lead to ocular motor dysfunction, defective accommodation, and impaired visual perception. As a part of the therapeutic strategy, early rehabilitative optometric intervention is important. Orthoptic therapy, medication, stem cell therapy, motor and attention trainings are the available treatment options. Gene therapy is one of the most promising emerging strategies. Use of state-of-the-art nanomedicine approaches to deliver drug(s) and/or gene(s) might enhance the therapeutic efficacy of the present and future modalities. More research is needed in these fields to improve the outcome of this debilitating condition. This review focuses on different visual pathologies caused by TBI, advances in pre-clinical and clinical research, and available treatment options.

Sports psychiatry: mental health and mental disorders in athletes and exercise treatment of mental disorders

Sports psychiatry has developed for the past 3 decades as an emerging field within psychiatry and sports medicine. An International society has been established in 1994 and also national interest groups were implemented, mostly within the national organizations for psychiatry, some also containing the topic of exercise treatment of mental disorders. Where are we now 30 years later? We systematically but also selectively review the medical literature on exercise, sport, psychiatry, mental health and mental disorders and related topics. The number of publications in the field has increased exponentially. Most topics keep remaining on the agenda, e.g., head trauma and concussion, drug abuse and doping, performance enhancement, overtraining, ADHD or eating disorders. Supported by the growing literature, evidence-based recommendations have become available now in many clinical areas. A relatively new phenomenon is muscle dysmorphia, observed in weightlifters, bodybuilders but also in college students and gym users. Further, sports therapy of mental disorders has been studied by more and more high-quality randomized controlled clinical trials. Mostly as a complementary treatment, however, for some disorders already with a 1a evidence level, e.g., depression, dementia or MCI but also post-traumatic stress disorder. Being grown up and accepted nowadays, sports psychiatry still represents a fast-developing field. The reverse side of the coin, sport therapy of mental disorders has received a scientific basis now. Who else than sports psychiatry could advance sport therapy of mental disorders? We need this enthusiasm for sports and psychiatry for our patients with mental disorders and it is time now for a broadening of the scope. Optimized psychiatric prevention and treatment of athletes and ideal sport-related support for individuals with mental disorders should be our main purpose and goal.

The Use of Pigs as a Translational Model for Studying Neurodegenerative Diseases

In recent years, the move to study neurodegenerative disease using larger animal models with brains that are more similar to humans has gained interest. While pigs have been used for various biomedical applications and research, it has only been recently that they have been used to study neurodegenerative diseases due to their neuroanatomically similar gyrencephalic brains and similar neurophysiological processes as seen in humans. This review focuses on the use of pigs in the study of Alzheimer’s disease (AD) and traumatic brain injury (TBI). AD is considered the most common neurodegenerative disease in elderly populations. Head impacts from falls are the most common form of injury in the elderly and recent literature has shown an association between repetitive head impacts and the development of AD. This review summarizes research into the pathological mechanisms underlying AD and TBI as well as the advantages and disadvantages of using pigs in the neuroscientific study of these disease processes. With the lack of successful therapeutics for neurodegenerative diseases, and an increasing elderly population, the use of pigs may provide a better translational model for understanding and treating these diseases.

Infections after a traumatic brain injury: The complex interplay between the immune and neurological systems

Traumatic brain injury (TBI) is a serious global health issue, being the leading cause of death and disability for individuals under the age of 45, and one of the largest causes of global neurological disability. In addition to the brain injury itself, it is increasingly appreciated that a TBI may also alter the systemic immune response in a way that renders TBI patients more vulnerable to infections in the acute post-injury period. Such infections pose an additional challenge to the patient, increasing rates of mortality and morbidity, and worsening neurological outcomes. Hospitalization, surgical interventions, and a state of immunosuppression induced by injury to the central nervous system (CNS), may all contribute to the high rate of infections seen in the population with TBI. Ongoing research to better understand the immunomodulators that underlie TBI-induced immunosuppression may aid in the development of effective therapeutic strategies to improve the recovery trajectory for patients. This review first describes the clinical scenario, posing the question of whether TBI patients are more susceptible to infections such as pneumonia, and if so, why? We then consider how cross-talk between the injured brain and the systemic immune system occurs, and further, how the additional immune challenge of an acquired infection can contribute to ongoing neuroinflammation and neurodegeneration after a TBI. Experimental models combining TBI with infection are discussed, as well as current treatment options available for this double-barreled insult. The aims of this review are to summarize current understanding of the bidirectional relationship between the CNS and the immune system when faced with a mechanical trauma combined with a concomitant infection, and to highlight key outstanding questions that remain in the field.

The changing nature of concussion in rugby union: Looking back to look forward

Introduction

Concussion is regularly observed in rugby union and has generated a growing public health concern, yet remains one of the least understood injuries facing the sports medicine community. Evidence suggests that multiple concussions may increase susceptibility to long-term neurological complications that present decades after the initial injury for reasons that remain unclear. We aimed to determine the incidence rate and risk factors for concussion amongst community-level rugby union-15s players active during the 1980s given that it may help to better understand the risks and mechanisms of injury.

Methods

Injury data were collected from clubs by the coach at the time of injury in players using a 15-item questionnaire (1982–1984).

Results

Seventy games were recorded throughout 1982–1983 and 1983–1984 rugby union seasons. Forty-two documented concussions accounted for ∼6% of injuries corresponding to an incidence rate of 0.64 per 1000 playing hours, more than a third lower than the ‘modern-day’ equivalent. Tackling (relative risk 1.60, p < 0.05), collisions (relative risk 0.95, p < 0.05) and gum shield use (relative risk 1.69, p < 0.05) were independently associated with concussion whereas no associations were observed for ground condition, quarter of play or players playing out of position ( p > 0.05).

Conclusion

Despite limitations due to the retrospective focus and reliance on questionnaire data notwithstanding raised awareness of concussion, the incidence rate of concussion during the 1980s appears to be appreciably lower compared to the present-day game. This is the likely outcome of improvements in the clinical understanding of concussion, data collection tools, reporting methods and clinical management of concussive injuries, including changes to both player and game. However, the findings of this study help better understand the risks and mechanisms of injury once encountered by rugby union players active during the 1980s, of which some of those risks are still apparent.

G, Calderon O, Moreno-Gonzalez I. Modifiable Risk Factors for Alzheimer's Disease

Since first described in the early 1900s, Alzheimer's disease (AD) has risen exponentially in prevalence and concern. Research still drives to understand the etiology and pathogenesis of this disease and what risk factors can attribute to AD. With a majority of AD cases being of sporadic origin, the increasing exponential growth of an aged population and a lack of treatment, it is imperative to discover an easy accessible preventative method for AD. Some risk factors can increase the propensity of AD such as aging, sex, and genetics. Moreover, there are also modifiable risk factors-in terms of treatable medical conditions and lifestyle choices-that play a role in developing AD. These risk factors have their own biological mechanisms that may contribute to AD etiology and pathological consequences. In this review article, we will discuss modifiable risk factors and discuss the current literature of how each of these factors interplay into AD development and progression and if strategically analyzed and treated, could aid in protection against this neurodegenerative disease.

Head trauma in sports - clinical characteristics, epidemiology and biomarkers

Traumatic brain injury (TBI) is clinically divided into a spectrum of severities, with mild TBI being the least severe form and a frequent occurrence in contact sports, such as ice hockey, American football, rugby, horse riding and boxing. Mild TBI is caused by blunt nonpenetrating head trauma that causes movement of the brain and stretching and tearing of axons, with diffuse axonal injury being a central pathogenic mechanism. Mild TBI is in principle synonymous with concussion; both have similar criteria in which the most important elements are acute alteration or loss of consciousness and/or post-traumatic amnesia following head trauma and no apparent brain changes on standard neuroimaging. Symptoms in mild TBI are highly variable and there are no validated imaging or fluid biomarkers to determine whether or not a patient with a normal computerized tomography scan of the brain has neuronal damage. Mild TBI typically resolves within a few weeks but 10-15% of concussion patients develop postconcussive syndrome. Repetitive mild TBI, which is frequent in contact sports, is a risk factor for a complicated recovery process. This overview paper discusses the relationships between repetitive head impacts in contact sports, mild TBI and chronic neurological symptoms. What are these conditions, how common are they, how are they linked and can they be objectified using imaging or fluid-based biomarkers? It gives an update on the current state of research on these questions with a specific focus on clinical characteristics, epidemiology and biomarkers.

A Review of Tics Presenting Subsequent to Traumatic Brain Injury

Purpose of review

This review summarizes case reports of patients with tics emerging subsequent to traumatic brain injury (TBI), with respect to demographics, post-TBI symptoms, tic onset latency and topography, clinical history, neuroimaging results and treatment outcome.

Recent findings

Patients were 22 adults and 3 youth. Trauma onset appeared to fall mostly in adulthood. Two-thirds of patients were male and head trauma was related to motor vehicle accidents in most cases. Loss of consciousness was reported in just below half (48.0%) of cases. Associated physical and cognitive symptoms (e.g., impaired memory, reduced sensory perception, poor balance, muscle weakness, attention problems, aggression/impulsivity, obsessions and compulsions, depression and anxiety) were commonly reported. The latency between head trauma and tic onset varied, but generally ranged from one day post-trauma to approximately one year post-trauma. Sole presentation of motor tics was common, with rostral to caudal development of motor tics in other cases. Simple and/or complex vocal tics were present in several cases, often emerging after motor tics. Post-trauma obsessive-compulsive symptoms were noted in five cases (20.0%). A personal or family history of tics was reported in four cases. Damage to the basal ganglia, ventricular system, and temporal region was observed across ten patients (40.0%). Pharmacological intervention varied, with tic symptoms deemed to have significantly or somewhat improved in 12 cases (48.0%). A comparison of post-TBI symptoms in youth with head trauma history relative to those with peripheral injury suggests tic symptoms are not a common post-TBI symptom in youth.

Summary

Ultimately, there has been limited study on the link between traumatic brain injury and tic expression, and methodological issues preclude the ability to draw definitive conclusions regarding this relationship. Nevertheless, findings do suggest there may be heterogeneity in brain dysfunction associated with tic expression. Future case reports should utilize more systematic and thorough assessment of TBI and tics using validated measures, evaluate medication effects using single-case designs, and perform more longitudinal follow-up of cases with repeated neuroimaging.

Intraparenchymal Application of Mature B Lymphocytes Improves Structural and Functional Outcome after Contusion Traumatic Brain Injury

Cerebral contusion causes neurological dysfunction mediated in part by inflammatory responses to injury. B lymphocytes are dynamic regulators of the immune system that have not been systematically studied in traumatic brain injury (TBI). We showed previously that topically applied mature B cells have immunomodulatory properties and strongly promote tissue regeneration, including cutaneous nerve growth, in acute and chronic skin wounds. Using a mouse controlled cortical impact (CCI) model, we assessed a possible beneficial role of exogenously applied B cells on histopathological and functional outcome after TBI. Mice were injected intraparenchymally at the lesion site with 2 × 10⁶ mature naïve syngeneic splenic B cells, then subjected to CCI. Control CCI mice received equal numbers of T cells or saline, and sham-injured mice (craniotomy only) were given B cells or saline. Sham-injured groups performed similarly in motor and learning tests. Injured mice administered B cells showed significantly improved post-injury rotarod, Y maze, and Morris water maze (MWM) performance compared with saline- or T-cell-treated CCI groups. Moreover, lesion volume in mice treated with B cells was significantly reduced by 40% at 35 days post-TBI compared with saline and T cell controls, and astrogliosis and microglial activation were decreased. In vivo tracking of exogenous B cells showed that they have a limited life span of approximately 14 days in situ and do not appear to proliferate. The data suggest proof of principle that local administration of B lymphocytes may represent a therapeutic option for treatment of cerebral contusion, especially when clinical management involves procedures that allow access to the injury site.

Early stage of diffusional kurtosis imaging and dynamic contrast-enhanced magnetic resonance imaging correlated with long-term neurocognitive function after experimental traumatic brain injury

Development of a reliable biomarker for prognostic monitoring of cognitive impairment after traumatic brain injury (TBI) is of great importance. The aim of the study was to explore the value of early diffusional kurtosis imaging (DKI) and dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in evaluation of chronic cognitive function after TBI. MRI was performed on TBI and control rats at 7 days post-injury. MRI parameters were measured in bilateral cortex, hippocampus, thalamus and corpus callosum (CC). All the rats underwent Morris water maze (MWM) at 6 months after injury. Immunohistochemistry (IHC) analysis of neuron [NeuN], astroglia [GFAP], microglia [Iba-1], and myelin [MBP] was performed after the MWM test. Our study revealed that, TBI group showed higher volume transfer coefficient (K^trans) value in ipsilateral cortex (P < 0.0001) and no detectable changes in other regions-of-interest (ROIs), compared with control group. DKI showed higher MK in all ipsilateral ROIs (P < 0.05), higher MD in ipsilateral cortex, hippocampus and CC (P < 0.05 for all) in TBI group. TBI group had worse performance in MWM test at 6 months post-injury(P < 0.05). IHC analysis showed lower NeuN, and higher GFAP and Iba-1 in all ipsilateral ROIs (P < 0.05) in TBI rats. NeuN, and GFAP and Iba-1 correlated significantly with MK value in ipsilateral regions of cortex. The MK value of ipsilateral cortex and CC and K^trans value of ipsilateral cortex also correlated significantly with time in the target quadrant. Therefore, our study indicated that early DKI and DCE-MRI could be used to assess the microstructural changes associated with long-term cognitive outcome following TBI.

CDC's guideline on pediatric mild traumatic brain injury: Recommendations for neurologists

Purpose of review

In September 2018, the Centers for Disease Control and Prevention (CDC) published an evidence-based guideline on the diagnosis and management of mild traumatic brain injury (mTBI) among children.

Recent findings

Based on a systematic review of the evidence that covers research published over a 25-year span (1990-2015), the CDC Pediatric mTBI Guideline strives to optimize the care of pediatric patients with mTBI. The guideline was developed using a rigorous methodology developed by the American Academy of Neurology.

Summary

Clinical practice recommendations in the CDC Pediatric mTBI Guideline can help guide neurologists with critical diagnostic and management decisions and to implement evidence-based strategies for the recovery of their young patients with this injury.

Differential responses to increasing numbers of mild traumatic brain injury in a rodent closed-head injury model

Following mild traumatic brain injury (mTBI), further mild impacts can exacerbate negative outcomes. To compare chronic damage and deficits following increasing numbers of repeated mTBIs, a closed-head weight-drop model of repeated mTBI was used to deliver 1, 2 or 3 mTBIs to adult female rats at 24 h intervals. Outcomes were assessed at 3 months following the first mTBI. No gross motor, sensory or reflex deficits were identified (p > 0.05), consistent with current literature. Cognitive function assessed using a Morris water maze revealed chronic memory deficits following 1 and 2, but not 3 mTBI compared to shams (p ≤ 0.05). Oxidative damage to DNA was assessed immunohistochemically in the dentate hilus of the hippocampus and splenium of the corpus callosum; no changes were observed. IBA1-positive microglia were increased in size in the cortex following 1 mTBI and in the corpus callosum following 2 mTBI compared to shams (p ≤ 0.05); no changes were observed in the dentate hilus. Glial fibrillary acidic protein (GFAP)-positive astrocyte immunoreactivity was assessed in all three brain regions and no chronic changes were observed. Integrity of myelin ultrastructure in the corpus callosum was assessed using transmission electron microscopy. G ratio was decreased following 2 mTBIs compared to shams (p ≤ 0.05) at post hoc level only. The changing patterns of damage and deficits following increasing numbers of mTBI may reflect dynamic responses to small numbers of mTBIs or a conditioning effect such that increasing numbers of mTBIs do not necessarily result in worsening pathology. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/. Cover Image for this issue: doi: 10.1111/jnc.14508.

Relating brain connectivity with persistent symptoms in pediatric concussion

Persistent post‐concussion symptoms (PCS) in children following a mild traumatic brain injury (mTBI) are a growing public health concern. There is a pressing need to understand the neural underpinning of PCS. Here, we examined whole‐brain functional connectivity from resting‐state fMRI with behavioral assessments in a cohort of 110 children with mTBI. Children with mTBI and controls had similar levels of connectivity. PCS symptoms and behaviors including poor cognition and sleep were associated with connectivity within functional brain networks. The identification of a single “positive‐negative” dimension linking connectivity with behaviors enables better prognosis and stratification toward personalized therapeutic interventions.

Dissemination of brain inflammation in traumatic brain injury

Traumatic brain injury (TBI) is recognized as a global health problem due to its increasing occurrence, challenging treatment, and persistent impacts on brain pathophysiology. Neural cell death in patients with TBI swiftly causes inflammation in the injured brain areas, which is recognized as focal brain inflammation. Focal brain inflammation causes secondary brain injury by exacerbating brain edema and neuronal death, while also exerting divergent beneficial effects, such as sealing the damaged limitans and removing cellular debris. Recent evidence from patients with TBI and studies on animal models suggest that brain inflammation after TBI is not only restricted to the focal lesion but also disseminates to remote areas of the brain. The dissemination of inflammation has been detected within days after the primary injury and persists chronically. This state of inflammation may be related to remote complications of TBI in patients, such as hyperthermia and hypopituitarism, and may lead to progressive neurodegeneration, such as chronic traumatic encephalopathy. Future studies should focus on understanding the mechanisms that govern the initiation and propagation of brain inflammation after TBI and its impacts on post-trauma brain pathology.

Analysis of trauma patients with unplanned returns to the operating room

Objectives

Trauma patients undergoing damage-control surgery may have a planned return to the operating room. In contrast, little is known about unplanned returns to the operating room (uROR) in trauma. The aim of this study was to identify risk factors for uROR in trauma patients. It is hypothesized that blunt trauma patients with uROR have higher mortality when compared to penetrating trauma patients with uROR. Additionally, it is hypothesized that trauma patients with uROR after thoracotomy have higher mortality than patients with uROR after laparotomy.

Material and Methods

A retrospective analysis of the National Trauma Data Bank from 2011-2015 including any adult patient with an uROR was performed.

Results

From 3.447.320 patients, 9.269 (0.2%) were identified to have uROR. In a multivariable logistic regression analysis, 27 independent predictors were identified for risk of uROR with the strongest independent risk factor being compartment syndrome (OR= 10.50, CI= 9.35-11.78, p <0.001). Blunt (compared to penetrating) mechanism was associated with higher risk for mortality in patents with uROR (OR= 1.69, CI= 1.14-2.51, p <0.001) as was re-incision thoracotomy (RT) compared to re-incision laparotomy (RL) (OR= 2.22, CI= 1.29-3.84, p <0.001).

Conclusion

The strongest risk factor for uROR in trauma is compartment syndrome. Both a blunt (compared to penetrating) mechanism and RT (compared to RL) are independent risk factors for mortality in patients undergoing an uROR.

Management of concussion in soccer

BACKGROUND

When participating in contact sports, (mild) head trauma is a common incident-observed in both professional and amateur sports. When head trauma results in transient neurological impairment, a sports-related concussion has occurred. Acute concussion, repetitive concussions, as well as cumulative "sub-concussive" head impacts may increase the risk of developing cognitive and behavioral deficits for athletes, as well as accelerated cerebral degeneration. While this concept has been well established for classic contact sports like American Football, Rugby, or Boxing, there is still an awareness gap for the role of sports-related concussion in the context of the world's most popular sport-Soccer.

METHODS

Here, we review the relevance of sport-related concussion for Soccer as well as its diagnosis and management. Finally, we provide insight into future directions for research in this field.

RESULTS

Soccer fulfills the criteria of a contact sport and is characterized by a high incidence of concussion. There is ample evidence that these events cause functional and structural cerebral disorders. Furthermore, heading, as a repeat sub-concussive impact, has been linked to structural brain changes and neurocognitive impairment. As a consequence, recommendations for the diagnosis and management of concussion in soccer have been formulated by consensus groups. In order to minimize the risk of repetitive concussion in soccer the rapid and reliable side-line diagnosis of concussion with adoption of a strict remove-from-play protocol is essential, followed by a supervised, graduated return-to-play protocol. Recent studies, however, demonstrate that adherence to these recommendations by players, coaches, clubs, and officials is insufficient, calling for stricter enforcement. In addition, future research to solidify the pathophysiological relevance of concussion for soccer athletes seems to be needed. Advanced neuroimaging and neurochemical biomarker analyses (e.g. S100β, tau and neurofilament light (NfL)) may assist in detecting concussion-related structural brain changes and selecting athletes at risk for irreversible damage.

CONCLUSION

Sports-related concussion represents a genuine neurosurgical field of interest. Given the high socioeconomic relevance, neurosurgeons should get involved in prevention and management of concussion in soccer.

Considerations for Athletic Trainers: A Review of Guidance on Mild Traumatic Brain Injury Among Children From the Centers for Disease Control and Prevention and the National Athletic Trainers' Association

The Centers for Disease Control and Prevention recently published an evidence-based guideline, "Diagnosis and Management of Mild Traumatic Brain Injury (mTBI) Among Children." The guideline has many applications for athletic trainers. The following commentary provides considerations for athletic trainers regarding the guideline in conjunction with the current National Athletic Trainers' Association position statement "Management of Sport Concussion" and the "Consensus Statement on Concussion in Sport-The 5th International Conference on Concussion in Sport Held in Berlin, October 2016."

Inflammasome proteins as biomarkers of traumatic brain injury

BACKGROUND

The inflammasome plays an important role in the inflammatory innate immune response after central nervous system (CNS) injury. Inhibition of the inflammasome after traumatic brain injury (TBI) results in improved outcomes by lowering the levels of caspase-1 and interleukin (IL)-1b. We have previously shown that inflammasome proteins are elevated in the cerebrospinal fluid (CSF) of patients with TBI and that higher levels of these proteins were consistent with poorer outcomes after TBI when compared to patients that presented these inflammasome proteins at lower levels.

METHODS AND FINDINGS

Here we extend our work by analyzing serum from 21 TBI patients and CSF from 18 TBI patients compared to 120 serum samples and 30 CSF samples from no-TBI donor controls for the expression of caspase-1, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), interleukin(IL)-1b and IL-18. Analysis was carried out using the Ella Simple Plex system (Protein Simple) to determine the sensitivity and specificity of inflammasome proteins as biomarkers of TBI. Receiver operator characteristic (ROC) curves, confidence intervals and likelihood ratios for each biomarker was determined. ROC curves, confidence intervals, sensitivity and specificity for each biomarker examined revealed that caspase-1 (0.93 area under the curve (AUC)) and ASC (0.90 AUC) in serum and ASC (1.0 AUC) and IL-18 (0.84 AUC) in CSF are promising biomarkers of TBI pathology. Importantly, higher protein levels (above 547.6 pg/ml) of ASC (0.91 AUC) were consistent with poorer outcomes after TBI as determined by the Glasgow Outcome Scale-Extended (GOSE).

CONCLUSION

These findings indicate that inflammasome proteins are excellent diagnostic and predictive biomarkers of TBI.

Seeking to improve care for young patients: Development of tools to support the implementation of the CDC Pediatric mTBI Guideline

INTRODUCTION

The Centers for Disease Control and Prevention (CDC) Pediatric Mild Traumatic Brain Injury (mTBI) Guideline was created to help standardize diagnosis, prognosis, and management and treatment of pediatric mTBI. This paper describes the process CDC used to develop educational tools, and a dissemination and implementation strategy, in support of the CDC Pediatric mTBI Guideline.

METHODS

Two qualitative data collection projects with healthcare providers who care for pediatric patients were conducted. In-depth interviews were used in both projects. Project One examined healthcare providers' guideline use and dissemination preferences. Project Two assessed perceptions of the CDC Pediatric mTBI Guideline educational tools.

RESULTS

Project One brought to light four key areas related to Guideline usage and dissemination preferences, specifically a need for: (1) partnership with professional medical societies; (2) integration into electronic health records, mobile apps, and websites; (3) development of continuing medical education (CME) opportunities; and (4) dissemination through healthcare system leadership. In Project Two, healthcare providers reported that the CDC Pediatric mTBI Guideline educational tools were well-organized, clear and easy to navigate, and informative. Healthcare providers also requested more information on the Guideline methodology.

DISCUSSION

Assessment of pediatric healthcare providers' current use of clinical guidelines and preferences for educational tools yielded important insights that helped inform CDC's dissemination and implementation strategy for the Pediatric mTBI Guideline.

PRACTICAL APPLICATIONS

The findings from these data collection projects can also inform other guideline implementation and dissemination efforts among healthcare providers.

Military-related risk factors for dementia

INTRODUCTION

In recent years, there has been growing discussion to better understand the pathophysiological mechanisms of traumatic brain injury and post-traumatic stress disorder and how they may be linked to an increased risk of neurodegenerative diseases including Alzheimer's disease in veterans.

METHODS

Building on that discussion, and subsequent to a special issue of Alzheimer's & Dementia published in June 2014, which focused on military risk factors, the Alzheimer's Association convened a continued discussion of the scientific community on December 1, 2016.

RESULTS

During this meeting, participants presented and evaluated progress made since 2012 and identified outstanding knowledge gaps regarding factors that may impact veterans' risk for later life dementia.

DISCUSSION

The following is a summary of the invited presentations and moderated discussions of both the review of scientific understanding and identification of gaps to inform further investigations.

Passive Immunotherapies for Central Nervous System Disorders: Current Delivery Challenges and New Approaches

Passive immunotherapy, i.e., the administration of exogenous antibodies that recognize a specific target antigen, has gained significant momentum as a potential treatment strategy for several central nervous system (CNS) disorders, including Alzheimer's disease, Parkinson's disease, Huntington's disease, and brain cancer, among others. Advances in antibody engineering to create therapeutic antibody fragments or antibody conjugates have introduced new strategies that may also be applied to treat CNS disorders. However, drug delivery to the CNS for antibodies and other macromolecules has thus far proven challenging, due in large part to the blood-brain barrier and blood-cerebrospinal fluid barriers that greatly restrict transport of peripherally administered molecules from the systemic circulation into the CNS. Here, we summarize the various passive immunotherapy approaches under study for the treatment of CNS disorders, with a primary focus on disease-specific and target site-specific challenges to drug delivery and new, cutting edge methods.

Single cell molecular alterations reveal target cells and pathways of concussive brain injury

The complex neuropathology of traumatic brain injury (TBI) is difficult to dissect, given the convoluted cytoarchitecture of affected brain regions such as the hippocampus. Hippocampal dysfunction during TBI results in cognitive decline that may escalate to other neurological disorders, the molecular basis of which is hidden in the genomic programs of individual cells. Using the unbiased single cell sequencing method Drop-seq, we report that concussive TBI affects previously undefined cell populations, in addition to classical hippocampal cell types. TBI also impacts cell type-specific genes and pathways and alters gene co-expression across cell types, suggesting hidden pathogenic mechanisms and therapeutic target pathways. Modulating the thyroid hormone pathway as informed by the T4 transporter transthyretin Ttr mitigates TBI-associated genomic and behavioral abnormalities. Thus, single cell genomics provides unique information about how TBI impacts diverse hippocampal cell types, adding new insights into the pathogenic pathways amenable to therapeutics in TBI and related disorders.

Post-mortem in situ stability of serum markers of cerebral damage and acute phase response

The aim of the given study was to test the in situ stability of biochemical markers of cerebral damage and acute phase response in the early post-mortem interval to assess their usability for forensic pathology. A monocentric, prospective study investigated post-mortem femoral venous blood samples at four time points obtained within 48 h post-mortem starting at the death of 20 deceased, using commercial immunoassays for the ten parameters: S100 calcium-binding protein B (S100B), glial fibrillary acidic protein (GFAP), neuron-specific enolase (NSE), brain-derived neurotrophic factor (BDNF), interleukin-6 (IL-6), C-reactive protein (CRP), procalcitonin (PCT), ferritin, soluble tumor necrosis factor receptor type 1 (sTNFR1), and lactate dehydrogenase (LDH). Significant changes in serum levels were observed only later than 2 h after death for all markers. Inter-laboratory comparability was high, and intra-assay precision was sufficient for most markers. Most of the biomarker levels depended on the severity of hemolysis and lipemia but were robust against freeze-thaw cycles. Serum levels increased with longer post-mortem intervals for S100B, NSE, ferritin, sTNFR1, and LDH (for all p < 0.001) but decreased over this period for CRP (p = 0.089) and PCT (p < 0.001). Largely unchanged median values were found for GFAP (p = 0.139), BDNF (p = 0.106), and IL-6 (p = 0.094). Serum levels of CRP (p = 0.059) and LDH (p = 0.109) did not differ significantly between the final ante-mortem (resuscitation) and the first post-mortem sample (moment of death). Collecting the post-mortem blood sample as soon as possible will reduce the influence of post-mortem blood changes. Serum GFAP for detection of cerebral damage as well as serum IL-6 and CRP as proof of acute phase response seemed to be preferable due to their in situ stability in the first 2 days after death.

Heading in soccer increases serum neurofilament light protein and SCAT3 symptom metrics

Objectives

To determine the effect of heading a soccer ball on serum neurofilament light (NF-L) protein, plasma tau protein and symptom metrics including total number of symptoms reported and symptom severity scores on the Standardized Concussion Assessment Tool— 3rd edition (SCAT3).

Methods

Eleven male collegiate soccer players were recruited to take part in three experimental conditions including heading, sham and control conditions. Participants were required to perform 40 headers in 20 min in the heading condition, and control 40 soccer balls directed at them with their hands, chest or thigh in the sham condition. No ball contact was made during the control condition. Blood sampling and SCAT3 symptom assessments were completed prior to and 1 hour following conditions. A subset of participants returned 3 weeks following the heading condition for blood sampling.

Results

NF-L was elevated at 1 hour (p=0.004) and 1 month (p=0.04) following the heading condition, and at 1 hour (p=0.02) following the control condition. Tau levels remained unchanged following all conditions. The total number of symptoms (TS) and symptom severity (SS) scores from the SCAT3 were both elevated following the heading condition (p=0.01 and p=0.03, respectively). Both TS and SS decreased following sham (p=0.04 and p=0.04) and control conditions (p=0.04 and p=0.04).

Conclusion

An acute bout of soccer heading is associated with increased NF-L concentrations at 1 hour and 1 month following the session and can lead to symptoms commonly reported following sport-related concussion.

Acute Inflammatory Biomarker Responses to Diffuse Traumatic Brain Injury in the Rat Monitored by a Novel Microdialysis Technique

Neuroinflammation is a major contributor to the progressive brain injury process induced by traumatic brain injury (TBI), and may play an important role in the pathophysiology of axonal injury. The immediate neuroinflammatory cascade cannot be characterized in the human setting. Therefore, we used the midline fluid percussion injury model of diffuse TBI in rats and a novel microdialysis (MD) method providing stable diffusion-driven biomarker sampling. Immediately post-injury, bilateral amphiphilic tri-block polymer coated MD probes (100 kDa cut off membrane) were inserted and perfused with Dextran 500 kDa-supplemented artificial cerebrospinal fluid (CSF) to optimize protein capture. Six hourly samples were analyzed for 27 inflammatory biomarkers (9 chemokines, 13 cytokines, and 5 growth factors) using a commercial multiplex biomarker kit. TBI (n = 6) resulted in a significant increase compared with sham-injured controls (n = 6) for five chemokines (eotaxin/CCL11, fractalkine/CX3CL1, LIX/CXCL5, monocyte chemoattractant protein [MCP]1α/CCL2, macrophage inflammatory protein [MIP]1α /CCL3), 10 cytokines (interleukin [IL]-1α, IL-1β, IL-4, IL-6, IL-10, IL-13, IL-17α, IL-18, interferon [IFN]-γ, tumor necrosis factor [TNF]-α), and four growth factors (epidermal growth factor [EGF], granulocyte-macrophage colony-stimulating factor [GM-CSF], leptin, vascular endothelial growth factor [VEGF]). Therefore, diffuse TBI was associated with an increased level of 18 of the 27 inflammatory biomarkers at one through six time points, during the observation period whereas the remaining 9 biomarkers were unaltered. The study shows that diffuse TBI induces an acute increase in a number of inflammatory biomarkers. The novel MD technique provides stable MD sampling suitable for further studies on the early neuroinflammatory cascade in TBI.

Utilizing a Structural Mechanics Approach to Assess the Primary Effects of Injury Loads Onto the Axon and Its Components

Diffuse axonal injury (DAI) occurs as a result of the transmission of rapid dynamic loads from the head to the brain and specifically to its neurons. Despite being one of the most common and most deleterious types of traumatic brain injury (TBI), the inherent cell injury mechanism is yet to be understood. Experimental observations have led to the formulation of different hypotheses, such as mechanoporation of the axolemma and microtubules (MTs) breakage. With the goal of singling out the mechanical aspect of DAI and to resolve the ambiguity behind its injury mechanism, a composite finite element (FE) model of a representative volume of an axon was developed. Once calibrated and validated against published experimental data, the axonal model was used to simulate injury scenarios. The resulting strain distributions along its components were then studied in dependence of strain rate and of typical modeling choices such as the applied MT constraints and tau proteins failure. Results show that oversimplifying the MT bundle kinematic entails a systematic attenuation (cf = 2.33) of the computed maximum MT strain. Nevertheless, altogether, results support the hypothesis of axolemma mechanoporation as a cell-injury trigger. Moreover, for the first time the interconnection between the axolemma and the MT bundle is shown to play a role in damage localization. The proposed FE axonal model is a valuable tool to understand the axonal injury mechanism from a mechanical perspective and could be used in turn for the definition of well-informed injury criteria at the tissue and organ level.

Protein biomarkers of epileptogenicity after traumatic brain injury

Traumatic brain injury (TBI) is a major risk factor for acquired epilepsy. Post-traumatic epilepsy (PTE) develops over time in up to 50% of patients with severe TBI. PTE is mostly unresponsive to traditional anti-seizure treatments suggesting distinct, injury-induced pathomechanisms in the development of this condition. Moderate and severe TBIs cause significant tissue damage, bleeding, neuron and glia death, as well as axonal, vascular, and metabolic abnormalities. These changes trigger a complex biological response aimed at curtailing the physical damage and restoring homeostasis and functionality. Although a positive correlation exists between the type and severity of TBI and PTE, there is only an incomplete understanding of the time-dependent sequelae of TBI pathobiologies and their role in epileptogenesis. Determining the temporal profile of protein biomarkers in the blood (serum or plasma) and cerebrospinal fluid (CSF) can help to identify pathobiologies underlying the development of PTE, high-risk individuals, and disease modifying therapies. Here we review the pathobiological sequelae of TBI in the context of blood- and CSF-based protein biomarkers, their potential role in epileptogenesis, and discuss future directions aimed at improving the diagnosis and treatment of PTE.

Metabolic aspects of neuronal degeneration: From a NAD+ point of view

Cellular metabolism maintains the life of cells, allowing energy production required for building cellular constituents and maintaining homeostasis under constantly changing external environments. Neuronal cells maintain their structure and function for the entire life of organisms and the loss of neurons, with limited neurogenesis in adults, directly causes loss of complexity in the neuronal networks. The nervous system organizes the neurons by placing cell bodies containing nuclei of similar types of neurons in discrete regions. Accordingly, axons must travel great distances to connect different types of neurons and peripheral organs. The enormous surface area of neurons makes them high-energy demanding to keep their membrane potential. Distal axon survival is dependent on axonal transport that is another energy demanding process. All of these factors make metabolic stress a potential risk factor for neuronal death and neuronal degeneration often associated with metabolic diseases. This review discusses recent findings on metabolic dysregulations under neuronal degeneration and pathways protecting neurons in these conditions.

Hallmarks of Brain Aging: Adaptive and Pathological Modification by Metabolic States

During aging, the cellular milieu of the brain exhibits tell-tale signs of compromised bioenergetics, impaired adaptive neuroplasticity and resilience, aberrant neuronal network activity, dysregulation of neuronal Ca2+ homeostasis, the accrual of oxidatively modified molecules and organelles, and inflammation. These alterations render the aging brain vulnerable to Alzheimer's and Parkinson's diseases and stroke. Emerging findings are revealing mechanisms by which sedentary overindulgent lifestyles accelerate brain aging, whereas lifestyles that include intermittent bioenergetic challenges (exercise, fasting, and intellectual challenges) foster healthy brain aging. Here we provide an overview of the cellular and molecular biology of brain aging, how those processes interface with disease-specific neurodegenerative pathways, and how metabolic states influence brain health.

Microglial Lectins in Health and Neurological Diseases

Microglia are the innate sentinels of the central nervous system (CNS) and are responsible for the homeostasis and immune defense of the CNS. Under the influence of the local environment and cell-cell interaction, microglia exhibit a multidimensional and context-dependent phenotypes that can be cytotoxic and neuroprotective. Recent studies suggest that microglia express multitudinous types of lectins, including galectins, Siglecs, mannose-binding lectins (MBLs) and other glycan binding proteins. Because most studies that examine lectins focus on the peripheral system, the functions of lectins have not been critically investigated in the CNS. In addition, the types of brain cells that contribute to the altered levels of lectins present in diseases are often unclear. In this review, we will discuss how galectins, Siglecs, selectins and MBLs contribute to the dynamic functions of microglia. The interacting ligands of these lectins are complex glycoconjugates, which consist of glycoproteins and glycolipids that are expressed on microglia or surrounding cells. The current understanding of the heterogeneity and functions of glycans in the brain is limited. Galectins are a group of pleotropic proteins that recognize both β-galactoside-containing glycans and non- β-galactoside-containing proteins. The function and regulation of galectins have been implicated in immunomodulation, neuroinflammation, apoptosis, phagocytosis and oxidative bursts. Most Siglecs are expressed at a low level on the plasma membrane and bind to sialic acid residues for immunosurveillance and cell-cell communication. Siglecs are classified based on their inhibitory and activatory downstream signaling properties. Inhibitory Siglecs negatively regulate microglia activation upon recognizing the intact sialic acid patterns and vice versa. MBLs are expressed upon infection in cytoplasm and can be secreted in order to recognize molecules containing terminal mannose as an innate immune defense machinery. Most importantly, multiple studies have reported dysregulation of lectins in neurological disorders. Here, we reviewed recent studies on microglial lectins and their functions in CNS health and disease, and suggest that these lectin families are novel, potent therapeutic targets for neurological diseases.

Traumatic Brain Injury Disrupts Pain Signaling in the Brainstem and Spinal Cord

Chronic pain is a common consequence of traumatic brain injury (TBI) that can increase the suffering of a patient and pose a significant challenge to rehabilitative efforts. Unfortunately, the mechanisms linking TBI to pain are poorly understood, and specific treatments for TBI-related pain are still lacking. Our laboratory has shown that TBI causes pain sensitization in areas distant to the site of primary injury, and that changes in spinal gene expression may underlie this sensitization. The aim of this study was to examine the roles that pain modulatory pathways descending from the brainstem play in pain after TBI. Deficiencies in one type of descending inhibition, diffuse noxious inhibitory control (DNIC), have been suggested to be responsible for the development of chronic pain by allowing excess and uncontrolled afferent nociceptive inputs. Here we expand our knowledge of pain after TBI in two ways: (1) by outlining the neuropathology in pain-related centers of the brain and spinal cord involved in DNIC using the rat lateral fluid percussion (LFP) model of TBI, and (2) by evaluating the effects of a potent histone acetyl transferase inhibitor, anacardic acid (AA), on LFP-induced pain behaviors and neuropathology when administered for several days after TBI. The results revealed that TBI induces transient mechanical allodynia and a chronic persistent loss of DNIC. Further, while short-term AA treatment can block acute nociceptive sensitization and some early neuropathological changes, this treatment neither prevented the loss of DNIC nor did it alter long-term neuropathological changes in the brain or spinal cord.

Neuroendocrine Abnormalities Following Traumatic Brain Injury: An Important Contributor to Neuropsychiatric Sequelae

Neuropsychiatric symptoms following traumatic brain injury (TBI) are common and contribute negatively to TBI outcomes by reducing overall quality of life. The development of neurobehavioral sequelae, such as concentration deficits, depression, anxiety, fatigue, and loss of emotional well-being has historically been attributed to an ambiguous "post-concussive syndrome," considered secondary to frank structural injury and axonal damage. However, recent research suggests that neuroendocrine dysfunction, specifically hypopituitarism, plays an important role in the etiology of these symptoms. This post-head trauma hypopituitarism (PHTH) has been shown in the past two decades to be a clinically prevalent phenomenon, and given the parallels between neuropsychiatric symptoms associated with non-TBI-induced hypopituitarism and those following TBI, it is now acknowledged that PHTH is likely a substantial contributor to these impairments. The current paper seeks to provide an overview of hypothesized pathophysiological mechanisms underlying neuroendocrine abnormalities after TBI, and to emphasize the significance of this phenomenon in the development of the neurobehavioral problems frequently seen after head trauma.

Neurofilament light and tau as blood biomarkers for sports-related concussion

Objective

To compare neurofilament light (NfL) and tau as blood-based biomarkers for acute sports-related concussion (SRC) and determine whether their concentrations at different time points after the injury are associated with prolonged time to return to play (RTP).

Methods

A total of 288 professional hockey players were followed longitudinally from September 1, 2012, to April 30, 2015. Data collection and biomarker analyses were conducted between 2015 and 2017. Associations were tested between blood concentrations of NfL and tau, and RTP time. Serum concentrations of S100B and neuron-specific enolase (NSE) were also measured for comparison.

Results

Of 288 players, 105 sustained an SRC. Of these, 87 underwent blood sampling 1, 12, 36, and 144 hours after SRC and at the RTP time point. Serum NfL concentrations 1, 12, 36, and 144 hours after SRC were related to prolonged RTP time, and could separate players with RTP >10 days from those with RTP ≤10 days (area under the receiver operating characteristic curve [AUROC] 0.82). Also, serum NfL 144 hours after SRC discriminated players who resigned from the game due to persistent postconcussion symptoms (PCS) from those who returned to play (AUROC 0.89). Plasma tau 1 hour after SRC was related to RTP but less strongly than NfL, while S100B and NSE showed no such associations.

Conclusion

Serum NfL outperformed tau, S100B, and NSE as a biomarker for SRC. From a clinical standpoint, serum NfL may be useful to identify individuals at risk of prolonged PCS, and may aid in biomarker-informed decisions with regard to when RTP should be considered.

The Inflammatory Continuum of Traumatic Brain Injury and Alzheimer's Disease

The post-injury inflammatory response is a key mediator in long-term recovery from traumatic brain injury (TBI). Moreover, the immune response to TBI, mediated by microglia and macrophages, is influenced by existing brain pathology and by secondary immune challenges. For example, recent evidence shows that the presence of beta-amyloid and phosphorylated tau protein, two hallmark features of AD that increase during normal aging, substantially alter the macrophage response to TBI. Additional data demonstrate that post-injury microglia are “primed” and become hyper-reactive following a subsequent acute immune challenge thereby worsening recovery. These alterations may increase the incidence of neuropsychiatric complications after TBI and may also increase the frequency of neurodegenerative pathology. Therefore, the purpose of this review is to summarize experimental studies examining the relationship between TBI and development of AD-like pathology with an emphasis on the acute and chronic microglial and macrophage response following injury. Furthermore, studies will be highlighted that examine the degree to which beta-amyloid and tau accumulation as well as pre- and post-injury immune stressors influence outcome after TBI. Collectively, the studies described in this review suggest that the brain’s immune response to injury is a key mediator in recovery, and if compromised by previous, coincident, or subsequent immune stressors, post-injury pathology and behavioral recovery will be altered.

Prospective study of myelin water fraction changes after mild traumatic brain injury in collegiate contact sports

OBJECTIVEMild traumatic brain injury (mTBI) in athletes, including concussion, is increasingly being found to have long-term sequelae. Current imaging techniques have not been able to identify early damage caused by mTBI that is predictive of long-term symptoms or chronic traumatic encephalopathy. In this preliminary feasibility study, the authors investigated the use of an emerging magnetic resonance imaging (MRI) technique, multicomponent driven equilibrium single pulse observation of T1 and T2 (mcDESPOT), in visualizing acute and chronic white matter changes after mTBI in collegiate football and rugby players.METHODSThis study was a nonrandomized, nonblinded prospective trial designed to quantify changes in the myelin water fraction (MWF), used as a surrogate MRI measure of myelin content, in a group of male collegiate football and rugby players, classified here as a contact sport player (CSP) cohort, at the time of mTBI diagnosis and 3 months after injury when the acute symptoms of the injury had resolved. In addition, differences in the MWF between the CSP cohort and a control cohort of noncontact sport players (NCSPs) were quantified. T-tests and a threshold-free cluster enhancement (TFCE) statistical analysis technique were used to identify brain structures with significant changes in the MWF between the CSP and NCSP cohorts and between immediately postinjury and follow-up images obtained in the CSP cohort.RESULTSBrain MR images of 12 right-handed male CSPs were analyzed and compared with brain images of 10 right-handed male NCSPs from the same institution. A comparison of CSP and NCSP baseline images using TFCE showed significantly higher MWFs in the bilateral basal ganglia, anterior and posterior corpora callosa, left corticospinal tract, and left anterior and superior temporal lobe (p < 0.05). At the 3-month follow-up examination, images from the CSP cohort still showed significantly higher MWFs than those identified on baseline images from the NCSP cohort in the bilateral basal ganglia, anterior and posterior corpora callosa, and left anterior temporal lobe, and also in the bilateral corticospinal tracts, parahippocampal gyrus, and bilateral juxtapositional (previously known as supplemental motor) areas (p < 0.05). In the CSP cohort, a t-test comparing the MWF at the time of injury and 3 months later showed a significant increase in the overall MWF at follow-up (p < 0.005). These increases were greatest in the bilateral basal ganglia and deep white matter. MWF decreases were seen in more superficial white matter (p < 0.005).CONCLUSIONSIn this preliminary study, MWF was found to be increased in the brains of CSPs compared with the brains of controls, suggesting acute/chronic MWF alterations in CSPs from previous injuries. Increases in the MWF were also demonstrated in the brains of CSPs 3 months after the players sustained an mTBI. The full clinical significance of an increased MWF and whether this reflects axon neuropathology or disorderly remyelination leading to hypermyelination has yet to be determined.

Notch signaling inhibitor DAPT provides protection against acute craniocerebral injury

Notch signaling pathway is involved in many physiological and pathological processes. The γ-secretase inhibitor DAPT inhibits Notch signaling pathway and promotes nerve regeneration after cerebral ischemia. However, neuroprotective effects of DAPT against acute craniocerebral injury remain unclear. In this study, we established rat model of acute craniocerebral injury, and found that with the increase of damage grade, the expression of Notch and downstream protein Hes1 and Hes5 expression gradually increased. After the administration of DAPT, the expression of Notch, Hes1 and Hes5 was inhibited, apoptosis and oxidative stress decreased, neurological function and cognitive function improved. These results suggest that Notch signaling can be used as an indicator to assess the severity of post-traumatic brain injury. Notch inhibitor DAPT can reduce oxidative stress and apoptosis after acute craniocerebral injury, and is a potential drug for the treatment of acute craniocerebral injury.

Minocycline plus N-Acetylcysteine Reduce Behavioral Deficits and Improve Histology with a Clinically Useful Time Window

There are no drugs to manage traumatic brain injury (TBI) presently. A major problem in developing therapeutics is that drugs to manage TBI lack sufficient potency when dosed within a clinically relevant time window. Previous studies have shown that minocycline (MINO, 45 mg/kg) plus N-acetylcysteine (NAC, 150 mg/kg) synergistically improved cognition and memory, modulated inflammation, and prevented loss of oligodendrocytes that remyelinated damaged white matter when first dosed 1 h after controlled cortical impact (CCI) in rats. We show that MINO (45 mg/kg) plus NAC (150 mg/kg) also prevent brain injury in a mouse closed head injury (CHI) TBI model. Using the CHI model, the concentrations of MINO and NAC were titrated to determine that MINO (22.5 mg/kg) plus NAC (75 mg/kg) was more potent than the original formulation. MINO (22.5 mg/kg) plus NAC (75 mg/kg) also limited injury in the rat CCI model. The therapeutic time window of MINO plus NAC was then tested in the CHI and CCI models. Mice and rats could acquire an active place avoidance task when MINO plus NAC was first dosed at 12 h post-injury. A first dose at 12 h also limited gray matter injury in the hippocampus and preserved myelin in multiple white matter tracts. Mice and rats acquired Barnes maze when MINO plus NAC was first dosed at 24 h post-injury. These data suggest that MINO (22.5 mg/kg) plus NAC (75 mg/kg) remain potent when dosed at clinically useful time windows. Both MINO and NAC are drugs approved by the Food and Drug Administration and have been administered safely to patients in clinical trials at the doses in the new formulation. This suggests that the drug combination of MINO plus NAC may be effective in treating patients with TBI.

Thyroid hormone and the brain: Mechanisms of action in development and role in protection and promotion of recovery after brain injury

Thyroid hormone (TH) is essential for normal brain development and may also promote recovery and neuronal regeneration after brain injury. TH acts predominantly through the nuclear receptors, TH receptor alpha (THRA) and beta (THRB). Additional factors that impact TH action in the brain include metabolism, activation of thyroxine (T4) to triiodothyronine (T3) by the enzyme 5'-deiodinase Type 2 (Dio2), inactivation by the enzyme 5-deiodinase Type 3 (Dio3) to reverse T3 (rT3), which occurs in glial cells, and uptake by the Mct8 transporter in neurons. Traumatic brain injury (TBI) is associated with inflammation, metabolic alterations and neural death. In clinical studies, central hypothyroidism, due to hypothalamic and pituitary dysfunction, has been found in some individuals after brain injury. TH has been shown, in animal models, to be protective for the damage incurred from brain injury and may have a role to limit injury and promote recovery. Although clinical trials have not yet been reported, findings from in vitro and in vivo models inform potential treatment strategies utilizing TH for protection and promotion of recovery after brain injury.

Hyperthermia and Mild Traumatic Brain Injury: Effects on Inflammation and the Cerebral Vasculature

Mild traumatic brain injury (mTBI) or concussion represents the majority of brain trauma in the United States. The pathophysiology of mTBI is complex and may include both focal and diffuse injury patterns. In addition to altered circuit dysfunction and traumatic axonal injury (TAI), chronic neuroinflammation has also been implicated in the pathophysiology of mTBI. Recently, our laboratory has reported the detrimental effects of mild hyperthermic mTBI in terms of worsening histopathological and behavioral outcomes. To clarify the role of temperature-sensitive neuroinflammatory processes on these consequences, we evaluated the effects of elevated brain temperature (39°C) on altered microglia/macrophage phenotype patterns after mTBI, changes in leukocyte recruitment, and TAI. Sprague-Dawley male rats underwent mild parasagittal fluid-percussion injury under normothermic (37°C) or hyperthermic (39°C) conditions. Cortical and hippocampal regions were analyzed using several cellular and molecular outcome measures. At 24 h, the ratio of iNOS-positive (M1 type phenotype) to arginase-positive (M2 type phenotype) cells after hyperthermic mTBI showed an increase compared with normothermia by flow cytometry. Inflammatory response gene arrays also demonstrated a significant increase in several classes of pro-inflammatory genes with hyperthermia treatment over normothermia. The injury-induced expression of chemokine ligand 2 (Ccl2) and alpha-2-macroglobulin were also increased with hyperthermic mTBI. With western blot analysis, an increase in CD18 and intercellular cell adhesion molecule-1 (ICAM-1) with hyperthermia and a significant increase in Iba1 reactive microglia are reported in the cerebral cortex. Together, these results demonstrate significant differences in the cellular and molecular consequences of raised brain temperature at the time of mTBI. The observed polarization toward a M1-phenotype with mild hyperthermia would be expected to augment chronic inflammatory cascades, sustained functional deficits, and increased vulnerability to secondary insults. Mild elevations in brain temperature may contribute to the more severe and longer lasting consequences of mTBI or concussion reported in some patients.