Administration of excitatory amino acid antagonists via microdialysis attenuates the increase in glucose utilization seen following concussive brain injury

Can Long-Term Outcomes of Posttraumatic Headache be Predicted?

PURPOSE OF REVIEW

Headache is one of the most common symptoms of traumatic brain injury, and it is more common in patients with mild, rather than moderate or severe, traumatic brain injury. Posttraumatic headache can be the most persistent symptom of traumatic brain injury. In this article, we review the current understanding of posttraumatic headache, summarize the current knowledge of its pathophysiology and treatment, and review the research regarding predictors of long-term outcomes.

RECENT FINDINGS

To date, posttraumatic headache has been treated based on the semiology of the primary headache disorder that it most resembles, but the pathophysiology is likely to be different, and the long-term prognosis differs as well. No models exist to predict long-term outcomes, and few studies have highlighted risk factors for the development of acute and persistent posttraumatic headaches. Further research is needed to elucidate the pathophysiology and identify specific treatments for posttraumatic headache to be able to predict long-term outcomes. In addition, the effect of managing comorbid traumatic brain injury symptoms on posttraumatic headache management should be further studied. Posttraumatic headache can be a persistent symptom of traumatic brain injury, especially mild traumatic brain injury. It has traditionally been treated based on the semiology of the primary headache disorder it most closely resembles, but further research is needed to elucidate the pathophysiology of posttraumatic headache and determine risk factors to better predict long-term outcomes.

Traumatic Brain Injury: A Comprehensive Review of Biomechanics and Molecular Pathophysiology

Traumatic brain injury (TBI) is a critical public health concern with profound consequences for affected individuals. This comprehensive literature review delves into TBI intricacies, encompassing primary injury biomechanics and the molecular pathophysiology of the secondary injury cascade. Primary TBI involves a complex interplay of forces, including impact loading, blast overpressure, and impulsive loading, leading to diverse injury patterns. These forces can be categorized into inertial (e.g., rotational acceleration causing focal and diffuse injuries) and contact forces (primarily causing focal injuries like skull fractures). Understanding their interactions is crucial for effective injury management. The secondary injury cascade in TBI comprises multifaceted molecular and cellular responses, including altered ion concentrations, dysfunctional neurotransmitter networks, oxidative stress, and cellular energy disturbances. These disruptions impair synaptic function, neurotransmission, and neuroplasticity, resulting in cognitive and behavioral deficits. Moreover, neuroinflammatory responses play a pivotal role in exacerbating damage. As we endeavor to bridge the knowledge gap between biomechanics and molecular pathophysiology, further research is imperative to unravel the nuanced interplay between mechanical forces and their consequences at the molecular and cellular levels, ultimately guiding the development of targeted therapeutic strategies to mitigate the debilitating effects of TBI. In this study, we aim to provide a concise review of the bridge between biomechanical processes causing primary injury and the ensuing molecular pathophysiology of secondary injury, while detailing the subsequent clinical course for this patient population. This knowledge is crucial for advancing our understanding of TBI and developing effective interventions to improve outcomes for those affected.

Brain Temperature as an Indicator of Cognitive Function in Traumatic Brain Injury Patients

Whether brain temperature noninvasively extracted by magnetic resonance imaging has a role in identifying brain changes in the later phases of mild to moderate traumatic brain injury (TBI) is not known. This prospective study aimed to evaluate if TBI patients in subacute and chronic phases had altered brain temperature measured by whole-brain magnetic resonance spectroscopic imaging (WB-MRSI) and if the measurable brain temperature had any relationship with cognitive function scores. WB-MRSI was performed on eight TBI patients and fifteen age- and sex-matched control subjects. Brain temperature (T) was extracted from the brain's major metabolites and compared between the two groups. The T of the patients was tested for correlation with cognitive function test scores. The results showed significantly lower brain temperature in the TBI patients (p < 0.05). Brain temperature derived from N-acetylaspartate (TNAA) strongly correlated with the 2 s paced auditory serial addition test (PASAT-2s) score (p < 0.05). The observation of lower brain temperature in TBI patients may be due to decreased metabolic activity resulting from glucose and oxygen depletion. The correlation of brain temperature with PASAT-2s may imply that noninvasive brain temperature may become a noninvasive index reflecting cognitive performance.

Single Versus Repetitive Traumatic Brain Injury: Current Knowledge on the Chronic Outcomes, Neuropathology and the Role of TDP-43 Proteinopathy

Traumatic brain injury (TBI) is one of the most important causes of death and disability in adults and thus an important public health problem. Following TBI, secondary pathophysiological processes develop over time and condition the development of different neurodegenerative entities. Previous studies suggest that neurobehavioral changes occurring after a single TBI are the basis for the development of Alzheimer's disease, while repetitive TBI is considered to be a contributing factor for chronic traumatic encephalopathy development. However, pathophysiological processes that determine the evolvement of a particular chronic entity are still unclear. Human post-mortem studies have found combinations of amyloid, tau, Lewi bodies, and TAR DNA-binding protein 43 (TDP-43) pathologies after both single and repetitive TBI. This review focuses on the pathological changes of TDP-43 after single and repetitive brain traumas. Numerous studies have shown that TDP-43 proteinopathy noticeably occurs after repetitive head trauma. A relatively small number of available preclinical research on single brain injury are not in complete agreement with the results from the human samples, which makes it difficult to draw specific conclusions. Also, as TBI is considered a heterogeneous type of injury, different experimental trauma models and injury intensities may cause differences in the cascade of secondary injury, which should be considered in future studies. Experimental and post-mortem studies of TDP-43 pathobiology should be carried out, preferably in the same laboratories, to determine its involvement in the development of neurodegenerative conditions after one and repetitive TBI, especially in the context of the development of new therapeutic options.

The Role of the Glucose Potassium Ratio in the Management of Traumatic Brain Injury

Objective

Traumatic brain injury (TBI) has become a worldwide public health issue, raising concerns about which tool might be useful to guide initial management at hospital admission, especially to decide whether the patient would benefit from an opportune surgical intervention. Recently, the glucose-to-potassium ratio has more accurate predictive values than other biomarkers and is useful for its simplicity to obtain. To correlate each biomarker with the outcome for every patient with TBI.

Methods

The analysis included patients treated in a single institution between 2020 and 2021, diagnosed with mild TBI that required neurosurgery, moderate or severe TBI. Blood samples were obtained at admission, and the glucose-to-potassium ratio was calculated retrospectively. Then, these values and other variables were compared with the outcome at 6 and 12 months. Extracranial lesions that directly contributed to the outcome, a Glasgow Coma Scale of 3 and below, hemodynamic instability, and cardiac arrest were exclusion criteria.

Results

Forty-seven patients who reached the criteria were examined, 35 (74%) had a favorable outcome and 12 (26%) a poor one. The only biomarker significantly related to the outcome was the glucose-to-potassium ratio in both the bivariate and multivariate analysis (p=0.04; odds ratio, 8.61; 95% confidence interval, 1.07-69.6).

Conclusion

An increase in the glucose-to-potassium ratio was the only biomarker associated with poor outcomes and increased mortality.

Astrocytes in Post-traumatic Stress Disorder

Although posttraumatic stress disorder (PTSD) is on the rise, traumatic events and their consequences are often hidden or minimized by patients for reasons linked to PTSD itself. Traumatic experiences can be broadly classified into mental stress (MS) and traumatic brain injury (TBI), but the cellular mechanisms of MS- or TBI-induced PTSD remain unknown. Recent evidence has shown that the morphological remodeling of astrocytes accompanies and arguably contributes to fearful memories and stress-related disorders. In this review, we summarize the roles of astrocytes in the pathogenesis of MS-PTSD and TBI-PTSD. Astrocytes synthesize and secrete neurotrophic, pro- and anti-inflammatory factors and regulate the microenvironment of the nervous tissue through metabolic pathways, ionostatic control, and homeostatic clearance of neurotransmitters. Stress or trauma-associated impairment of these vital astrocytic functions contribute to the pathophysiological evolution of PTSD and may present therapeutic targets.

The Kynurenine Pathway in Traumatic Brain Injury: Implications for Psychiatric Outcomes

Traumatic brain injury (TBI) is an established risk factor for the development of psychiatric disorders, especially depression and anxiety. However, the mechanistic pathways underlying this risk remain unclear, limiting treatment options and hindering the identification of clinically useful biomarkers. One salient pathophysiological process implicated in both primary psychiatric disorders and TBI is inflammation. An important consequence of inflammation is the increased breakdown of tryptophan to kynurenine and, subsequently, the metabolism of kynurenine into several neuroactive metabolites, including the neurotoxic NMDA receptor agonist quinolinic acid and the neuroprotective NMDA receptor antagonist kynurenic acid. Here, we review studies of the kynurenine pathway (KP) in TBI and examine their potential clinical implications. The weight of the literature suggests that there is increased production of neurotoxic kynurenines such as quinolinic acid in TBI of all severities and that elevated quinolinic acid concentrations in both the cerebrospinal fluid and blood are a negative prognostic indicator, being associated with death, magnetic resonance imaging abnormalities, increased depressive and anxiety symptoms, and prolonged recovery. We hypothesize that an imbalance in KP metabolism is also one molecular pathway through which the TBI-induced neurometabolic cascade may predispose to the development of psychiatric sequelae. If this model is correct, KP metabolites could serve to predict who is likely to develop psychiatric illness while drugs that target the KP could help to prevent or treat depression and anxiety arising in the context of TBI.

The Roles of Neurotrophins in Traumatic Brain Injury

Neurotrophins are a collection of structurally and functionally related proteins. They play important roles in many aspects of neural development, survival, and plasticity. Traumatic brain injury (TBI) leads to different levels of central nervous tissue destruction and cellular repair through various compensatory mechanisms promoted by the injured brain. Many studies have shown that neurotrophins are key modulators of neuroinflammation, apoptosis, blood–brain barrier permeability, memory capacity, and neurite regeneration. The expression of neurotrophins following TBI is affected by the severity of injury, genetic polymorphism, and different post-traumatic time points. Emerging research is focused on the potential therapeutic applications of neurotrophins in managing TBI. We conducted a comprehensive review by organizing the studies that demonstrate the role of neurotrophins in the management of TBI.

Stimulant Therapy Utilization for Neurocognitive Deficits in Mild Traumatic Brain Injury

CONTEXT

There are 3.8 million mild traumatic brain injuries (mTBIs) that occur each year in the United States. Many are left with prolonged life-altering neurocognitive deficits, including difficulties in attention, concentration, mental fatigue, and distractibility. With extensive data on the safety and efficacy of stimulant medications in treating attention deficit, concentration difficulties and distractibility seen with attention deficit disorder, it is not surprising that interest continues regarding the application of stimulant medications for the persistent neurocognitive deficits in some mTBIs.

EVIDENCE ACQUISITION

Studies were extracted from PubMed based on the topics of neurocognitive impairment, mTBI, stimulant use in mTBI, stimulants, and the association between attention deficit/hyperactivity disorder and mTBI. The search criteria included a date range of 1999 to 2020 in the English language.

STUDY DESIGN

Literature review.

LEVEL OF EVIDENCE

Level 4.

RESULTS

Currently, there is very limited literature, and no guidelines for evaluating the use of stimulant medication for the treatment of prolonged neurocognitive impairments due to mTBI. However, a limited number of studies have demonstrated efficacy and safety of stimulants in the treatment of neurocognitive sequelae of mTBI in the adult, pediatric, military, and athletic populations.

CONCLUSION

There is limited evidence to suggest stimulant medication may be beneficial in patients with mTBI with persistent neurocognitive symtpoms. The decision to utilize stimulant medication for mTBI patients remains physician and patient preference dependent. Given the limited encouraging data currently available, physicians may consider stimulant medication in appropriate patients to facilitate the recovery of prolonged neurocognitive deficits, while remaining cognizant of potential adverse effects.

Dietary Supplementation for Para-Athletes: A Systematic Review

The use of dietary supplements is high among athletes and non-athletes alike, as well as able-bodied individuals and those with impairments. However, evidence is lacking in the use of dietary supplements for sport performance in a para-athlete population (e.g., those training for the Paralympics or similar competition). Our objective was to examine the literature regarding evidence for various sport supplements in a para-athlete population. A comprehensive literature search was conducted using PubMed, SPORTDiscus, MedLine, and Rehabilitation and Sports Medicine Source. Fifteen studies met our inclusion criteria and were included in our review. Seven varieties of supplements were investigated in the studies reviewed, including caffeine, creatine, buffering agents, fish oil, leucine, and vitamin D. The evidence for each of these supplements remains inconclusive, with varying results between studies. Limitations of research in this area include the heterogeneity of the subjects within the population regarding functionality and impairment. Very few studies included individuals with impairments other than spinal cord injury. Overall, more research is needed to strengthen the evidence for or against supplement use in para-athletes. Future research is also recommended on performance in para-athlete populations with classifiable impairments other than spinal cord injuries.

Glucose transporters in brain in health and disease

Energy demand of neurons in brain that is covered by glucose supply from the blood is ensured by glucose transporters in capillaries and brain cells. In brain, the facilitative diffusion glucose transporters GLUT1-6 and GLUT8, and the Na⁺-d-glucose cotransporters SGLT1 are expressed. The glucose transporters mediate uptake of d-glucose across the blood-brain barrier and delivery of d-glucose to astrocytes and neurons. They are critically involved in regulatory adaptations to varying energy demands in response to differing neuronal activities and glucose supply. In this review, a comprehensive overview about verified and proposed roles of cerebral glucose transporters during health and diseases is presented. Our current knowledge is mainly based on experiments performed in rodents. First, the functional properties of human glucose transporters expressed in brain and their cerebral locations are described. Thereafter, proposed physiological functions of GLUT1, GLUT2, GLUT3, GLUT4, and SGLT1 for energy supply to neurons, glucose sensing, central regulation of glucohomeostasis, and feeding behavior are compiled, and their roles in learning and memory formation are discussed. In addition, diseases are described in which functional changes of cerebral glucose transporters are relevant. These are GLUT1 deficiency syndrome (GLUT1-SD), diabetes mellitus, Alzheimer’s disease (AD), stroke, and traumatic brain injury (TBI). GLUT1-SD is caused by defect mutations in GLUT1. Diabetes and AD are associated with changed expression of glucose transporters in brain, and transporter-related energy deficiency of neurons may contribute to pathogenesis of AD. Stroke and TBI are associated with changes of glucose transporter expression that influence clinical outcome.

Sugar as a therapeutic target for the cognitive restoration following traumatic brain injury

PURPOSE OF REVIEW

This review aims to discuss examples of changes in glucose (sugar) metabolism after traumatic brain injury (TBI). It will attempt to provide an understanding of what changes in glucose metabolism mean for the injured brain. It will further identify potential therapeutic target(s) emanating from our growing understanding of glucose pathways and their roles in TBI.

RECENT FINDINGS

Although a significant fraction of glucose is utilized for the energy production in the brain, a small fraction is utilized in other, often ignored pathways. Recent studies have unraveled unexpected biological effects of glucose through these pathways, including redox regulation, genetic and epigenetic regulation, glycation of proteins, nucleotide synthesis and amino acid synthesis.

SUMMARY

A number of regulatory players in minor glucose metabolic pathways, such as folate and chondroitin sulfate proteoglycans, have recently been identified as potential targets to restore cognitive functions. Targeting of these players should be combined with the supplementation of alternative energy substrates to achieve the maximal cognitive restoration after TBI. This multimodal therapeutic strategy deserves testing in various models of TBI.

VIDEO ABSTRACT

Supplemental digital video content 1: Video that demonstrates an effective therapeutic strategy for the cognitive restoration after TBI. http://links.lww.com/CONR/A46.

Dysregulated Glucose Metabolism as a Therapeutic Target to Reduce Post-traumatic Epilepsy

Traumatic brain injury (TBI) is a significant cause of disability worldwide and can lead to post-traumatic epilepsy. Multiple molecular, cellular, and network pathologies occur following injury which may contribute to epileptogenesis. Efforts to identify mechanisms of disease progression and biomarkers which predict clinical outcomes have focused heavily on metabolic changes. Advances in imaging approaches, combined with well-established biochemical methodologies, have revealed a complex landscape of metabolic changes that occur acutely after TBI and then evolve in the days to weeks after. Based on this rich clinical and preclinical data, combined with the success of metabolic therapies like the ketogenic diet in treating epilepsy, interest has grown in determining whether manipulating metabolic activity following TBI may have therapeutic value to prevent post-traumatic epileptogenesis. Here, we focus on changes in glucose utilization and glycolytic activity in the brain following TBI and during seizures. We review relevant literature and outline potential paths forward to utilize glycolytic inhibitors as a disease-modifying therapy for post-traumatic epilepsy.

Remote Changes in Cortical Excitability after Experimental Traumatic Brain Injury and Functional Reorganization

Although cognitive and behavioral deficits are well known to occur following traumatic brain injury (TBI), motor deficits that occur even after mild trauma are far less known, yet are equally persistent. This study was aimed at making progress toward determining how the brain reorganizes in response to TBI. We used the adult rat controlled cortical impact injury model to study the ipsilesional forelimb map evoked by electrical stimulation of the affected limb, as well as the contralesional forelimb map evoked by stimulation of the unaffected limb, both before injury and at 1, 2, 3, and 4 weeks after using functional magnetic resonance imaging (fMRI). End-point c-FOS immunohistochemistry data following 1 h of constant stimulation of the unaffected limb were acquired in the same rats to avoid any potential confounds due to altered cerebrovascular coupling. Single and paired-pulse sensory evoked potential (SEP) data were recorded from skull electrodes over the contralesional cortex in a parallel series of rats before injury, at 3 days, and at 1, 2, 3, and 4 weeks after injury in order to determine whether alterations in cortical excitability accompanied reorganization of the cortical map. The results show a transient trans-hemispheric shift in the ipsilesional cortical map as indicated by fMRI, remote contralesional increases in cortical excitability that occur in spatially similar regions to altered fMRI activity and greater c-FOS activation, and reduced or absent ipsilesional cortical activity chronically. The contralesional changes also were indicated by reduced SEP latency within 3 days after injury, but not by blood oxygenation level-dependent fMRI until much later. Detailed interrogation of cortical excitability using paired-pulse electrophysiology showed that the contralesional cortex undergoes both an early and a late post-injury period of hyper-excitability in response to injury, interspersed by a period of relatively normal activity. From these data, we postulate a cross-hemispheric mechanism by which remote cortex excitability inhibits ipsilesional activation by rebalanced cortical excitation-inhibition.

The Role of Gaseous Molecules in Traumatic Brain Injury: An Updated Review

Traumatic brain injury (TBI) affects millions of people in China each year. TBI has a high mortality and often times a serious prognosis. The causative mechanisms of TBI during development and recovery from an injury remain vague, leaving challenges for the medical community to provide treatment options that improve prognosis and provide an optimal recovery. Biological gaseous molecules including nitric oxide (NO), carbon monoxide (CO), hydrogen sulfide (H₂S), and molecular hydrogen (H₂) have been found to play critical roles in physiological and pathological conditions in mammals. Accumulating evidence has found that these gaseous molecules can execute neuroprotection in many central nervous system (CNS) conditions due to their highly permeable properties allowing them to enter the brain. Considering the complicated mechanisms and the serious prognosis of TBI, effective and adequate therapeutic approaches are urgently needed. These four gaseous molecules can be potential attractive therapeutic intervention on TBI. In this review, we will present a comprehensive overview on the role of these four biological gasses in the development of TBI and their potential therapeutic applications.

Aerobic Exercise for Adolescents With Prolonged Symptoms After Mild Traumatic Brain Injury: An Exploratory Randomized Clinical Trial

OBJECTIVE

To describe the methodology and report primary outcomes of an exploratory randomized clinical trial (RCT) of aerobic training for management of prolonged symptoms after a mild traumatic brain injury (mTBI) in adolescents.

SETTING

Outpatient research setting.

PARTICIPANTS

Thirty adolescents between the ages of 12 and 17 years who sustained a mTBI and had between 4 and 16 weeks of persistent symptoms.

DESIGN

Partially blinded, pilot RCT of subsymptom exacerbation aerobic training compared with a full-body stretching program.

MAIN MEASURES

The primary outcome was postinjury symptom improvement assessed by the adolescent's self-reported Post-Concussion Symptom Inventory (PCSI) repeated for at least 6 weeks of the intervention. Parent-reported PCSI and adherence are also described.

RESULTS

Twenty-two percent of eligible participants enrolled in the trial. Repeated-measures analysis of variance via mixed-models analysis demonstrated a significant group × time interaction with self-reported PCSI ratings, indicating a greater rate of improvement in the subsymptom exacerbation aerobic training group than in the full-body stretching group (F = 4.11, P = .044). Adherence to the home exercise programs was lower in the subsymptom exacerbation aerobic training group compared with the full-body stretching group (mean [SD] times per week = 4.42 [1.95] vs 5.85 [1.37], P < .0001) over the duration of the study.

CONCLUSION

Findings from this exploratory RCT suggest subsymptom exacerbation aerobic training is potentially beneficial for adolescents with persistent symptoms after an mTBI. These findings and other recent research support the potential benefit of active rehabilitation programs for adolescents with persistent symptoms after an mTBI. Larger replication studies are needed to verify findings and improve generalizability. Future work should focus on determining the optimal type, timing, and intensity of active rehabilitation programs and characteristics of individuals most likely to benefit.

Concussion: pathophysiology and clinical translation

The majority of the 3.8 million estimated annual traumatic brain injuries (TBI) in the United States are mild TBIs, or concussions, and they occur primarily in adolescents and young adults. A concussion is a brain injury associated with rapid brain movement and characteristic clinical symptoms, with no associated objective biomarkers or overt pathologic brain changes, thereby making it difficult to diagnose by neuroimaging or other objective diagnostic tests. Most concussion symptoms are transient and resolve within 1-2 weeks. Concussions share similar acute pathophysiologic perturbations to more severe TBI: there is a rapid release of neurotransmitters, which causes ionic disequilibrium across neuronal membranes. Re-establishing ionic homeostasis consumes energy and leads to dynamic changes in cerebral glucose uptake. The magnitude and duration of these changes are related to injury severity, with milder injuries showing faster normalization. Cerebral sex differences add further variation to concussion manifestation. Relative to the male brain, the female brain has higher overall cerebral blood flow, and demonstrates regional differences in glucose metabolism, inflammatory responses, and connectivity. Understanding the pathophysiology and clinical translation of concussion can move research towards management paradigms that will minimize the risk for prolonged recovery and repeat injury.

Vestibular dysfunction and concussion

The assessment and treatment of sport-related concussion (SRC) often requires a multifaceted approach. Vestibular dysfunction represents an important profile of symptoms and pathology following SRC, with high prevalence and association with prolonged recovery. Signs and symptoms of vestibular dysfunction may include dizziness, vertigo, disequilibrium, nausea, and visual impairment. Identifying the central and peripheral vestibular mechanisms responsible for pathology can aid in management of SRC. The most common vestibular disturbances after SRC include benign paroxysmal positional vertigo, vestibulo-ocular reflex impairment, visual motion sensitivity, and balance impairment. A variety of evidence-based screening and assessment tools can help to identify the various types of vestibular pathology in SRC. When vestibular dysfunction is identified, there is emerging support for applying targeted vestibular rehabilitation to manage this condition.

Glucose metabolism in pediatric traumatic brain injury

Traumatic brain injury is the number one cause of death and disability among the pediatric population in the USA. The heterogeneity of the pediatric population is reflected by both the normal cerebral maturation and the age differences in the causes of TBI, which generate unique age-related pathophysiology responses and recovery profiles. This review will address the normal changes in cerebral glucose metabolism throughout developmental phases and how TBI alters glucose metabolism. Evidence has shown that TBI disrupts the biochemical processing of glucose to energy. This brings to question, "What is the optimal substrate to manage a pediatric TBI patient?" Issues related to glycemic control and alternative substrate metabolism are addressed specifically in regard to pediatric TBI. Research into pediatric glucose metabolism after TBI is limited, and understanding these age-related differences within the pediatric population have great potential to improve support for the injured younger brain.

Functional Neuroimaging in Traumatic Brain Injury: From Nodes to Networks

Since the invention of functional magnetic resonance imaging (fMRI), thousands of studies in healthy and clinical samples have enlightened our understanding of the organization of cognition in the human brain and neuroplastic changes following brain disease and injury. Increasingly, studies involve analyses rooted in complex systems theory and analysis applied to clinical samples. Given the complexity in available approaches, concise descriptions of the theoretical motivation of network techniques and their relationship to traditional approaches and theory are necessary. To this end, this review concerns the use of fMRI to understand basic cognitive function and dysfunction in the human brain scaling from emphasis on basic units (or "nodes") in the brain to interactions within and between brain networks. First, major themes and theoretical issues in the scientific study of the injured brain are introduced to contextualize these analyses, particularly concerning functional "brain reorganization." Then, analytic approaches ranging from the voxel level to the systems level using graph theory and related approaches are reviewed as complementary approaches to examine neurocognitive processes following TBI. Next, some major findings relevant to functional reorganization hypotheses are discussed. Finally, major open issues in functional network analyses in neurotrauma are discussed in theoretical, analytic, and translational terms.

Neurotrauma: The Crosstalk between Neurotrophins and Inflammation in the Acutely Injured Brain

Traumatic brain injury (TBI) is a major cause of morbidity and mortality among young individuals worldwide. Understanding the pathophysiology of neurotrauma is crucial for the development of more effective therapeutic strategies. After the trauma occurs, immediate neurologic damage is produced by the traumatic forces; this primary injury triggers a secondary wave of biochemical cascades together with metabolic and cellular changes, called secondary neural injury. In the scenario of the acutely injured brain, the ongoing secondary injury results in ischemia and edema culminating in an uncontrollable increase in intracranial pressure. These areas of secondary injury progression, or areas of “traumatic penumbra”, represent crucial targets for therapeutic interventions. Neurotrophins are a class of signaling molecules that promote survival and/or maintenance of neurons. They also stimulate axonal growth, synaptic plasticity, and neurotransmitter synthesis and release. Therefore, this review focuses on the role of neurotrophins in the acute post-injury response. Here, we discuss possible endogenous neuroprotective mechanisms of neurotrophins in the prevailing environment surrounding the injured areas, and highlight the crosstalk between neurotrophins and inflammation with focus on neurovascular unit cells, particularly pericytes. The perspective is that neurotrophins may represent promising targets for research on neuroprotective and neurorestorative processes in the short-term following TBI.

The Pathophysiology of Concussion

Concussion is a significant issue in medicine and the media today. With growing interest on the long-term effects of sports participation, it is important to understand what occurs in the brain after an impact of any degree. While some of the basic pathophysiology has been elucidated, much is still unknown about what happens in the brain after traumatic brain injury, particularly with milder injuries where no damage can be seen at the structural level on standard neuroimaging. Understanding the chain of events from a cellular level using studies investigating more severe injuries can help to drive research efforts in understanding the symptomatology that is seen in the acute phase after concussion, as well as point to mechanisms that may underlie persistent post-concussive symptoms. This review discusses the basic neuropathology that occurs after traumatic brain injury at the cellular level. We also present the pathology of chronic traumatic encephalopathy and its similarities to other neurodegenerative diseases. We conclude with recent imaging and biomarker findings looking at changes that may occur after repeated subconcussive blows, which may help to guide efforts in understanding if cumulative subconcussive mechanical forces upon the brain are detrimental in the long term or if concussive symptoms mark the threshold for brain injury.

Therapeutic Potentials of Synapses after Traumatic Brain Injury: A Comprehensive Review

Massive studies have focused on the understanding of the pathobiology of cellular and molecular changes and injury mechanisms after traumatic brain injury (TBI), but very few studies have specially discussed the role of synapses in the context of TBI. This paper specifically highlights the role and therapeutic potentials of synapses after TBI. First, we review and conclude how synapses interact with constant structural, metabolic, neuroendocrine, and inflammatory mechanisms after TBI. Second, we briefly describe several key synaptic proteins involved in neuroplasticity, which may be novel neuronal targets for specific intervention. Third, we address therapeutic interventions in association with synapses after TBI. Finally, we concisely discuss the study gaps in the synapses after TBI, in hopes that this would provide more insights for future studies. Synapses play an important role in TBI; while the understandings on the synaptic participation in the treatments and prognosis of TBI are lacking, more studies in this area are warranted.

Moderate injury in motor-sensory cortex causes behavioral deficits accompanied by electrophysiological changes in mice adulthood

Moderate traumatic brain injury (TBI) in children often happen when there’s a sudden blow to the frontal bone, end with long unconscious which can last for hours and progressive cognitive deficits. However, with regard to the influences of moderate TBI during children adulthood, injury-induced alterations of locomotive ability, long-term memory performance, and hippocampal electrophysiological firing changes have not yet been fully identified. In this study, lateral fluid percussion (LFP) method was used to fabricate moderate TBI in motor and somatosensory cortex of the 6-weeks-old mice. The motor function, learning and memory function, extracellular CA1 neural spikes were assessed during acute and subacute phase. Moreover, histopathology was performed on day post injury (DPI) 16 to evaluate the effect of TBI on tissue and cell morphological changes in cortical and hippocampal CA1 subregions. After moderate LFP injury, the 6-weeks-old mice showed severe motor deficits at the early stage in acute phase but gradually recovered later during adulthood. At the time points in acute and subacute phase after TBI, novel object recognition (NOR) ability and spatial memory functions were consistently impaired in TBI mice; hippocampal firing frequency and burst probability were hampered. Analysis of the altered burst firing shows a clear hippocampal theta rhythm drop. These electrophysiological impacts were associated with substantially lowered NOR preference as compared to the sham group during adulthood. These results suggest that moderate TBI introduced at motorsenory cortex in 6-weeks-old mice causes obvious motor and cognitive deficits during their adulthood. While the locomotive ability progressively recovers, the cognitive deficits persisted while the mice mature as adult mice. The cognitive deficits may be attributed to the general suppressing of whole neural network, which could be labeled by marked reduction of excitability in hippocampal CA1 subregion.

Metabolic fate of glucose in rats with traumatic brain injury and pyruvate or glucose treatments: A NMR spectroscopy study

Administration of sodium pyruvate (SP; 9.08 μmol/kg, i.p.), ethyl pyruvate (EP; 0.34 μmol/kg, i.p.) or glucose (GLC; 11.1 μmol/kg, i.p.) to rats after unilateral controlled cortical impact (CCI) injury has been reported to reduce neuronal loss and improve cerebral metabolism. In the present study these doses of each fuel or 8% saline (SAL; 5.47 nmoles/kg) were administered immediately and at 1, 3, 6 and 23 h post-CCI. At 24 h all CCI groups and non-treated Sham injury controls were infused with [1,2 ¹³C] glucose for 68 min ¹³C nuclear magnetic resonance (NMR) spectra were obtained from cortex + hippocampus tissues from left (injured) and right (contralateral) hemispheres. All three fuels increased lactate labeling to a similar degree in the injured hemisphere. The amount of lactate labeled via the pentose phosphate and pyruvate recycling (PPP + PR) pathway increased in CCI-SAL and was not improved by SP, EP, and GLC treatments. Oxidative metabolism, as assessed by glutamate labeling, was reduced in CCI-SAL animals. The greatest improvement in oxidative metabolism was observed in animals treated with SP and fewer improvements after EP or GLC treatments. Compared to SAL, all three fuels restored glutamate and glutamine labeling via pyruvate carboxylase (PC), suggesting improved astrocyte metabolism following fuel treatment. Only SP treatments restored the amount of [4 ¹³C] glutamate labeled by the PPP + PR pathway to sham levels. Milder injury effects in the contralateral hemisphere appear normalized by either SP or EP treatments, as increases in the total pool of ¹³C lactate and labeling of lactate in glycolysis, or decreases in the ratio of PC/PDH labeling of glutamine, were found only for CCI-SAL and CCI-GLC groups compared to Sham. The doses of SP, EP and GLC examined in this study all enhanced lactate labeling and restored astrocyte-specific PC activity but differentially affected neuronal metabolism after CCI injury. The restoration of astrocyte metabolism by all three fuel treatments may partially underlie their abilities to improve cerebral glucose utilization and to reduce neuronal loss following CCI injury.

Early and Persistent Dendritic Hypertrophy in the Basolateral Amygdala following Experimental Diffuse Traumatic Brain Injury

In the pathophysiology of traumatic brain injury (TBI), the amygdala remains understudied, despite involvement in processing emotional and stressful stimuli associated with anxiety disorders, such as post-traumatic stress disorder (PTSD). Because the basolateral amygdala (BLA) integrates inputs from sensory and other limbic structures coordinating emotional learning and memory, injury-induced changes in circuitry may contribute to psychiatric sequelae of TBI. This study quantified temporal changes in dendritic complexity of BLA neurons after experimental diffuse TBI, modeled by midline fluid percussion injury. At post-injury days (PIDs) 1, 7, and 28, brain tissue from sham and brain-injured adult, male rats was processed for Golgi, glial fibrillary acidic protein (GFAP), or silver stain and analyzed to quantify BLA dendritic branch intersections, activated astrocytes, and regional neuropathology, respectively. Compared to sham, brain-injured rats at all PIDs showed enhanced dendritic branch intersections in both pyramidal and stellate BLA neuronal types, as evidenced by Sholl analysis. GFAP staining in the BLA was significantly increased at PID1 and 7 in comparison to sham. However, the BLA was relatively spared from neuropathology, demonstrated by an absence of argyrophilic accumulation over time, in contrast to other brain regions. These data suggest an early and persistent enhancement of dendritic complexity within the BLA after a single diffuse TBI. Increased dendritic complexity would alter information processing into and through the amygdala, contributing to emotional symptoms post-TBI, including PTSD.

Regional brain monitoring in the neurocritical care unit

Regional multimodality monitoring has evolved over the last several years as a tool to understand the mechanisms of brain injury and brain function at the cellular level. Multimodality monitoring offers an important augmentation to the clinical exam and is especially useful in comatose neurocritical care patients. Cerebral microdialysis, brain tissue oxygen monitoring, and cerebral blood flow monitoring all offer insight into permutations in brain chemistry and function that occur in the context of brain injury. These tools may allow for development of individual therapeutic strategies that are mechanistically driven and goal-directed. We present a summary of the discussions that took place during the Second Neurocritical Care Research Conference regarding regional brain monitoring.

Metabolic, enzymatic and gene involvement in cerebral glucose dysmetabolism after traumatic brain injury

In this study, the metabolic, enzymatic and gene changes causing cerebral glucose dysmetabolism following graded diffuse traumatic brain injury (TBI) were evaluated. TBI was induced in rats by dropping 450g from 1 (mild TBI; mTBI) or 2m height (severe TBI; sTBI). After 6, 12, 24, 48, and 120h gene expressions and enzymatic activities of glycolysis and pentose phosphate pathway (PPP) enzymes, and levels of lactate, ATP, ADP, ATP/ADP (indexing mitochondrial phosphorylating capacity), NADP(+), NADPH and GSH were determined in whole brain extracts (n=9 rats at each time for both TBI levels). Sham-operated animals (n=9) were used as controls. Results demonstrated that mTBI caused a late increase (48-120h post injury) of glycolytic gene expression and enzymatic activities, concomitantly with mitochondrial functional recovery (ATP and ATP/ADP normalization). No changes in lactate and PPP genes and enzymes, were accompanied by transient decrease in GSH, NADP(+), NADPH and NADPH/NADP(+). Animals following sTBI showed early increase (6-24h post injury) of glycolytic gene expression and enzymatic activities, occurring during mitochondrial malfunctioning (50% decrease in ATP and ATP/ADP). Higher lactate and lower GSH, NADP(+), NADPH, NADPH/NADP(+) than controls were recorded at anytime post injury (p<0.01). Both TBI levels caused metabolic and gene changes affecting glucose metabolism. Following mTBI, increased glucose flux through glycolysis is coupled to mitochondrial glucose oxidation. "True" hyperglycolysis occurs only after sTBI, where metabolic changes, caused by depressed mitochondrial phosphorylating capacity, act on genes causing net glycolytic flux increase uncoupled from mitochondrial glucose oxidation.

Metabolic Response of Pediatric Traumatic Brain Injury

Traumatic brain injury (TBI) in the pediatric brain presents unique challenges as the complex cascades of metabolic and biochemical responses to TBI are further complicated ongoing maturational changes of the developing brain. TBIs of all severities have been shown to significantly alter metabolism and hormones which impair the ability of the brain to process glucose for cellular energy. Under these conditions, the brain's primary fuel (glucose) becomes a less favorable fuel and the ability of the younger brain to revert to ketone metabolism can an advantage. This review addresses the potential of alternative substrate metabolic intervention as a logical pediatric TBI neuroprotective strategy.

Neurochemical cascade of concussion

PRIMARY OBJECTIVE

The aim of this literature review was to systematically describe the sequential metabolic changes that occur following concussive injury, as well as identify and characterize the major concepts associated with the neurochemical cascade.

RESEARCH DESIGN

Narrative literature review.

CONCLUSIONS

Concussive injury initiates a complex cascade of pathophysiological changes that include hyper-acute ionic flux, indiscriminant excitatory neurotransmitter release, acute hyperglycolysis and sub-acute metabolic depression. Additionally, these metabolic changes can subsequently lead to impaired neurotransmission, alternate fuel usage and modifications in synaptic plasticity and protein expression. The combination of these metabolic alterations has been proposed to cause the transient and prolonged neurological deficits that typically characterize concussion. Consequently, understanding the implications of the neurochemical cascade may lead to treatment and return-to-play guidelines that can minimize the chronic effects of concussive injury.

Glucose metabolism following human traumatic brain injury: methods of assessment and pathophysiological findings

The pathophysiology of traumatic brain (TBI) injury involves changes to glucose uptake into the brain and its subsequent metabolism. We review the methods used to study cerebral glucose metabolism with a focus on those used in clinical TBI studies. Arterio-venous measurements provide a global measure of glucose uptake into the brain. Microdialysis allows the in vivo sampling of brain extracellular fluid and is well suited to the longitudinal assessment of metabolism after TBI in the clinical setting. A recent novel development is the use of microdialysis to deliver glucose and other energy substrates labelled with carbon-13, which allows the metabolism of glucose and other substrates to be tracked. Positron emission tomography and magnetic resonance spectroscopy allow regional differences in metabolism to be assessed. We summarise the data published from these techniques and review their potential uses in the clinical setting.

Glucose and oxygen metabolism after penetrating ballistic-like brain injury

Traumatic brain injury (TBI) is a major cause of death and disability in all age groups. Among TBI, penetrating traumatic brain injuries (PTBI) have the worst prognosis and represent the leading cause of TBI-related morbidity and death. However, there are no specific drugs/interventions due to unclear pathophysiology. To gain insights we looked at cerebral metabolism in a PTBI rat model: penetrating ballistic-like brain injury (PBBI). Early after injury, regional cerebral oxygen tension and consumption significantly decreased in the ipsilateral cortex in the PBBI group compared with the control group. At the same time point, glucose uptake was significantly reduced globally in the PBBI group compared with the control group. Examination of Fluorojade B-stained brain sections at 24 hours after PBBI revealed an incomplete overlap of metabolic impairment and neurodegeneration. As expected, the injury core had the most severe metabolic impairment and highest neurodegeneration. However, in the peri-lesional area, despite similar metabolic impairment, there was lesser neurodegeneration. Given our findings, the data suggest the presence of two distinct zones of primary injury, of which only one recovers. We anticipate the peri-lesional area encompassing the PBBI ischemic penumbra, could be salvaged by acute therapies.

Glycolysis and the significance of lactate in traumatic brain injury

In traumatic brain injury (TBI) patients, elevation of the brain extracellular lactate concentration and the lactate/pyruvate ratio are well-recognized, and are associated statistically with unfavorable clinical outcome. Brain extracellular lactate was conventionally regarded as a waste product of glucose, when glucose is metabolized via glycolysis (Embden-Meyerhof-Parnas pathway) to pyruvate, followed by conversion to lactate by the action of lactate dehydrogenase, and export of lactate into the extracellular fluid. In TBI, glycolytic lactate is ascribed to hypoxia or mitochondrial dysfunction, although the precise nature of the latter is incompletely understood. Seemingly in contrast to lactate's association with unfavorable outcome is a growing body of evidence that lactate can be beneficial. The idea that the brain can utilize lactate by feeding into the tricarboxylic acid (TCA) cycle of neurons, first published two decades ago, has become known as the astrocyte-neuron lactate shuttle hypothesis. Direct evidence of brain utilization of lactate was first obtained 5 years ago in a cerebral microdialysis study in TBI patients, where administration of (13)C-labeled lactate via the microdialysis catheter and simultaneous collection of the emerging microdialysates, with (13)C NMR analysis, revealed (13)C labeling in glutamine consistent with lactate utilization via the TCA cycle. This suggests that where neurons are too damaged to utilize the lactate produced from glucose by astrocytes, i.e., uncoupling of neuronal and glial metabolism, high extracellular levels of lactate would accumulate, explaining the association between high lactate and poor outcome. Recently, an intravenous exogenous lactate supplementation study in TBI patients revealed evidence for a beneficial effect judged by surrogate endpoints. Here we review the current state of knowledge about glycolysis and lactate in TBI, how it can be measured in patients, and whether it can be modulated to achieve better clinical outcome.

Systemic, local, and imaging biomarkers of brain injury: more needed, and better use of those already established?

Much progress has been made over the past two decades in the treatment of severe acute brain injury, including traumatic brain injury and subarachnoid hemorrhage, resulting in a higher proportion of patients surviving with better outcomes. This has arisen from a combination of factors. These include improvements in procedures at the scene (pre-hospital) and in the hospital emergency department, advances in neuromonitoring in the intensive care unit, both continuously at the bedside and intermittently in scans, evolution and refinement of protocol-driven therapy for better management of patients, and advances in surgical procedures and rehabilitation. Nevertheless, many patients still experience varying degrees of long-term disabilities post-injury with consequent demands on carers and resources, and there is room for improvement. Biomarkers are a key aspect of neuromonitoring. A broad definition of a biomarker is any observable feature that can be used to inform on the state of the patient, e.g., a molecular species, a feature on a scan, or a monitoring characteristic, e.g., cerebrovascular pressure reactivity index. Biomarkers are usually quantitative measures, which can be utilized in diagnosis and monitoring of response to treatment. They are thus crucial to the development of therapies and may be utilized as surrogate endpoints in Phase II clinical trials. To date, there is no specific drug treatment for acute brain injury, and many seemingly promising agents emerging from pre-clinical animal models have failed in clinical trials. Large Phase III studies of clinical outcomes are costly, consuming time and resources. It is therefore important that adequate Phase II clinical studies with informative surrogate endpoints are performed employing appropriate biomarkers. In this article, we review some of the available systemic, local, and imaging biomarkers and technologies relevant in acute brain injury patients, and highlight gaps in the current state of knowledge.

Glycolysis and the pentose phosphate pathway after human traumatic brain injury: microdialysis studies using 1,2-(13)C2 glucose

Increased 'anaerobic' glucose metabolism is observed after traumatic brain injury (TBI) attributed to increased glycolysis. An alternative route is the pentose phosphate pathway (PPP), which generates putatively protective and reparative molecules. To compare pathways we employed microdialysis to perfuse 1,2-(13)C2 glucose into the brains of 15 TBI patients and macroscopically normal brain in six patients undergoing surgery for benign tumors, and to simultaneously collect products for nuclear magnetic resonance (NMR) analysis. (13)C enrichment for glycolytic 2,3-(13)C2 lactate was the median 5.4% (interquartile range (IQR) 4.6-7.5%) in TBI brain and 4.2% (2.4-4.4%) in 'normal' brain (P<0.01). The ratio of PPP-derived 3-(13)C lactate to glycolytic 2,3-(13)C2 lactate was median 4.9% (3.6-8.2%) in TBI brain and 6.7% (6.3-8.9%) in 'normal' brain. An inverse relationship was seen for PPP-glycolytic lactate ratio versus PbtO2 (r=-0.5, P=0.04) in TBI brain. Thus, glycolytic lactate production was significantly greater in TBI than 'normal' brain. Several TBI patients exhibited PPP-lactate elevation above the 'normal' range. There was proportionally greater PPP-derived lactate production with decreasing PbtO2. The study raises questions about the roles of the PPP and glycolysis after TBI, and whether they can be manipulated to achieve a better outcome. This study is the first direct comparison of glycolysis and PPP in human brain.

Cellular and molecular mechanisms of injury and spontaneous recovery

Until recently, most have assumed that traumatic brain injury (TBI) was singularly associated with the overt destruction of brain tissue resulting in subsequent morbidity or death. More recently, experimental and clinical studies have shown that the pathobiology of TBI is more complex, involving a host of cellular and subcellular changes that impact on neuronal function and viability while also affecting vascular reactivity and the activation of multiple biological response pathways. Here we review the brain's response to injury, examining both focal and diffuse changes and their implications for post-traumatic brain dysfunction and recovery. TBI-induced neuronal dysfunction and death as well as the diffuse involvement of multiple fiber projections are discussed together with considerations of how local axonal membrane changes or channelopathy translate into local ionic dysregulation and axonal disconnection. Concomitant changes in the cerebral microcirculation are also discussed and their relationship with the parallel changes in the brain's metabolism is considered. These cellular and subcellular events occurring within neurons and their blood supply are correlated with multiple biological response modifiers evoked by generalized post-traumatic inflammation and the parallel activation of oxidative stress processes. The chapter closes with considerations of recovery following focal or diffuse injury. Evidence for dynamic brain reorganization/repair is presented, with considerations of traumatically induced circuit disruption and their progression to either adaptive or in some cases, maladaptive reorganization.

The pathophysiology of traumatic brain injury at a glance

Traumatic brain injury (TBI) is defined as an impact, penetration or rapid movement of the brain within the skull that results in altered mental state. TBI occurs more than any other disease, including breast cancer, AIDS, Parkinson's disease and multiple sclerosis, and affects all age groups and both genders. In the US and Europe, the magnitude of this epidemic has drawn national attention owing to the publicity received by injured athletes and military personnel. This increased public awareness has uncovered a number of unanswered questions concerning TBI, and we are increasingly aware of the lack of treatment options for a crisis that affects millions. Although each case of TBI is unique and affected individuals display different degrees of injury, different regional patterns of injury and different recovery profiles, this review and accompanying poster aim to illustrate some of the common underlying neurochemical and metabolic responses to TBI. Recognition of these recurrent features could allow elucidation of potential therapeutic targets for early intervention.

Traumatic brain injury and diet

Increasing attention is being paid to nutritional and metabolic management of traumatic brain injury patients. The gross metabolic changes that occur after injury have been found to be influenced by both macronutrients, that is, dietary ratios of fat, carbohydrates, and protein, and micronutrients, for example, vitamins and minerals. Alterations in diet and nutritional strategies have been shown to decrease both morbidity and mortality after injury. Despite this knowledge, defining optimal nutritional support following traumatic brain injury continues to be an ongoing challenge.

Repeated mild traumatic brain injury: mechanisms of cerebral vulnerability

Among the 3.5 million annual new head injury cases is a subpopulation of children and young adults who experience repeated traumatic brain injury (TBI). The duration of vulnerability after a single TBI remains unknown, and biomarkers have yet to be determined. Decreases in glucose metabolism (cerebral metabolic rate of glucose [CMRglc]) are consistently observed after experimental and human TBI. In the current study, it is hypothesized that the duration of vulnerability is related to the duration of decreased CMRglc and that a single mild TBI (mTBI) increases the brain's vulnerability to a second insult for a period, during which a subsequent mTBI will worsen the outcome. Postnatal day 35 rats were given sham, single mTBI, or two mTBI at 24-h or 120-h intervals. (14)C-2-deoxy-D-glucose autoradiography was conducted at 1 or 3 days post-injury to calculate CMRglc. At 24 h after a single mTBI, CMRglc is decreased by 19% in both the parietal cortex and hippocampus, but approached sham levels by 3 days post-injury. When a second mTBI is introduced during the CMRglc depression of the first injury, the consequent CMRglc is depressed (36.5%) at 24 h and remains depressed (25%) at 3 days. In contrast, when the second mTBI is introduced after the metabolic recovery of the first injury, the consequent CMRglc depression is similar to that seen with a single injury. Results suggest that the duration of metabolic depression reflects the time-course of vulnerability to second injury in the juvenile brain and could serve as a valuable biomarker in establishing window of vulnerability guidelines.

An overview of the basic science of concussion and subconcussion: where we are and where we are going

There has been a growing interest in the diagnosis and management of mild traumatic brain injury (TBI), or concussion. Repetitive concussion and subconcussion have been linked to a spectrum of neurological sequelae, including postconcussion syndrome, chronic traumatic encephalopathy, mild cognitive impairment, and dementia pugilistica. A more common risk than chronic traumatic encephalopathy is the season-ending or career-ending effects of concussion or its mismanagement. To effectively prevent and treat the sequelae of concussion, it will be important to understand the basic processes involved. Reviewed in this paper are the forces behind the primary phase of injury in mild TBI, as well as the immediate and delayed cellular events responsible for the secondary phase of injury leading to neuronal dysfunction and possible cell death. Advanced neuroimaging sequences have recently been developed that have the potential to increase the sensitivity of standard MRI to detect both structural and functional abnormalities associated with concussion, and have provided further insight into the potential underlying pathophysiology. Also discussed are the potential long-term effects of repetitive mild TBI, particularly chronic traumatic encephalopathy. Much of the data regarding this syndrome is limited to postmortem analyses, and at present there is no animal model of chronic traumatic encephalopathy described in the literature. As this arena of TBI research continues to evolve, it will be imperative to appropriately model concussive and even subconcussive injuries in an attempt to understand, prevent, and treat the associated chronic neurodegenerative sequelae.

Understanding the neuroinflammatory response following concussion to develop treatment strategies

Mild traumatic brain injuries (mTBI) have been associated with long-term cognitive deficits relating to trauma-induced neurodegeneration. These long-term deficits include impaired memory and attention, changes in executive function, emotional instability, and sensorimotor deficits. Furthermore, individuals with concussions show a high co-morbidity with a host of psychiatric illnesses (e.g., depression, anxiety, addiction) and dementia. The neurological damage seen in mTBI patients is the result of the impact forces and mechanical injury, followed by a delayed neuroimmune response that can last hours, days, and even months after the injury. As part of the neuroimmune response, a cascade of pro- and anti-inflammatory cytokines are released and can be detected at the site of injury as well as subcortical, and often contralateral, regions. It has been suggested that the delayed neuroinflammatory response to concussions is more damaging then the initial impact itself. However, evidence exists for favorable consequences of cytokine production following traumatic brain injuries as well. In some cases, treatments that reduce the inflammatory response will also hinder the brain's intrinsic repair mechanisms. At present, there is no evidence-based pharmacological treatment for concussions in humans. The ability to treat concussions with drug therapy requires an in-depth understanding of the pathophysiological and neuroinflammatory changes that accompany concussive injuries. The use of neurotrophic factors [e.g., nerve growth factor (NGF)] and anti-inflammatory agents as an adjunct for the management of post-concussion symptomology will be explored in this review.