Involvement of pro- and anti-inflammatory cytokines and chemokines in the pathophysiology of traumatic brain injury

Role of fibrinogen in cerebrovascular dysfunction after traumatic brain injury

Traumatic brain injury (TBI) has been associated with various neurological disorders. However, the role of cerebrovascular dysfunction and its mechanisms associated with TBI are still not well understood. Inflammation is the main cause of vascular dysfunction. It affects properties of blood components and the vascular wall leading to changes in blood flow and in interaction of blood components and vascular endothelium exacerbating microcirculatory complications during inflammatory diseases. One of the markers of inflammation is a plasma adhesion protein, fibrinogen (Fg). At elevated levels, Fg can also cause inflammatory responses. One of the manifestations of inflammatory responses is an increase in microvascular permeability leading to accumulation of plasma proteins in the subendothelial matrix and causing vascular remodelling. This has a most devastating effect on cerebral circulation after TBI that is accompanied with an elevation of plasma level of Fg and with an increased cerebrovascular permeability in injury penumbra impairing the normal healing process. This study reviews cerebrovascular alterations after TBI, considers the consequences of increased blood-brain barrier permeability, defines the role of elevated level of Fg and discusses the potential mechanisms of its action leading to vascular dysfunction, which subsequently can cause impairment in neuronal function. Thus, possible mechanisms of vasculo-neuronal dysfunction after TBI are considered.

Traumatic brain injury: oxidative stress and neuroprotection

SIGNIFICANCE

A vast amount of circumstantial evidence implicates high energy oxidants and oxidative stress as mediators of secondary damage associated with traumatic brain injury. The excessive production of reactive oxygen species due to excitotoxicity and exhaustion of the endogenous antioxidant system induces peroxidation of cellular and vascular structures, protein oxidation, cleavage of DNA, and inhibition of the mitochondrial electron transport chain.

RECENT ADVANCES

Different integrated responses exist in the brain to detect oxidative stress, which is controlled by several genes termed vitagens. Vitagens encode for cytoprotective heat shock proteins, and thioredoxin and sirtuins.

CRITICAL ISSUES AND FUTURE DIRECTIONS

This article discusses selected aspects of secondary brain injury after trauma and outlines key mechanisms associated with toxicity, oxidative stress, inflammation, and necrosis. Finally, this review discusses the role of different oxidants and presents potential clinically relevant molecular targets that could be harnessed to treat secondary injury associated with brain trauma.

Decreased neuroinflammation and increased brain energy homeostasis following environmental enrichment after mild traumatic brain injury is associated with improvement in cognitive function

Background

Persistent neuroinflammation and disruptions in brain energy metabolism is commonly seen in traumatic brain injury (TBI). Because of the lack of success of most TBI interventions and the documented benefits of environmental enrichment (EE) in enhancing brain plasticity, here we focused our study on use of EE in regulating injury-induced neuroinflammation and disruptions in energy metabolism in the prefrontal cortex and hippocampus. Adult male Wistar rats were used in the study and randomly assigned to receive either: mild TBI (mTBI) using the controlled cortical injury model or sham surgery. Following surgery, rats from each group were further randomized to either: EE housing or standard laboratory housing (CON). After 4 weeks of recovery, cognitive testing was performed using the non-matching-to-sample and delayed non-matching-to-sample tasks. After completion of behavioral testing, levels of the pro-inflammatory cytokines IL-1β and TNF-α and the anti-inflammatory cytokine IL-10 were measured. In addition, levels of AMPK (adenosine monophosphate-activated protein kinase), phosphorylated AMPK and uMtCK (ubiquitous mitochondrial creatine kinase) were assessed as measures of brain energy homeostasis.

Results

Our results showed that EE: (1) decreased the pro-inflammatory cytokines IL-1β and TNF-α and enhanced levels of the anti-inflammatory cytokine IL-10 after mTBI; (2) mitigated mTBI-induced cognitive impairment; and (3) attenuated mTBI-induced downregulation in pAMPK/AMPK ratio and uMtCK levels.

Conclusions

Our data demonstrated the potential of EE to modulate the persistent: (1) neuroinflammatory response seen following mTBI, and (2) persistent disturbance in brain energy homeostasis. It is possible that through the mechanism of modulating neuroinflammation, EE housing was able to restore the disruption in energy metabolism and enhanced functional recovery after mTBI.

Anti-inflammatory and immunomodulatory mechanisms of mesenchymal stem cell transplantation in experimental traumatic brain injury

Background

Previous studies have shown beneficial effects of mesenchymal stem cell (MSC) transplantation in central nervous system (CNS) injuries, including traumatic brain injury (TBI). Potential repair mechanisms involve transdifferentiation to replace damaged neural cells and production of growth factors by MSCs. However, few studies have simultaneously focused on the effects of MSCs on immune cells and inflammation-associated cytokines in CNS injury, especially in an experimental TBI model. In this study, we investigated the anti-inflammatory and immunomodulatory properties of MSCs in TBI-induced neuroinflammation by systemic transplantation of MSCs into a rat TBI model.

Methods/results

MSCs were transplanted intravenously into rats 2 h after TBI. Modified neurologic severity score (mNSS) tests were performed to measure behavioral outcomes. The effect of MSC treatment on neuroinflammation was analyzed by immunohistochemical analysis of astrocytes, microglia/macrophages, neutrophils and T lymphocytes and by measuring cytokine levels [interleukin (IL)-1α, IL-1β, IL-4, IL-6, IL-10, IL-17, tumor necrosis factor-α, interferon-γ, RANTES, macrophage chemotactic protein-1, macrophage inflammatory protein 2 and transforming growth factor-β1] in brain homogenates. The immunosuppression-related factors TNF-α stimulated gene/protein 6 (TSG-6) and nuclear factor-κB (NF-κB) were examined by reverse transcription-polymerase chain reaction and Western blotting. Intravenous MSC transplantation after TBI was associated with a lower density of microglia/macrophages and peripheral infiltrating leukocytes at the injury site, reduced levels of proinflammatory cytokines and increased anti-inflammatory cytokines, possibly mediated by enhanced expression of TSG-6, which may suppress activation of the NF-κB signaling pathway.

Conclusions

The results of this study suggest that MSCs have the ability to modulate inflammation-associated immune cells and cytokines in TBI-induced cerebral inflammatory responses. This study thus offers a new insight into the mechanisms responsible for the immunomodulatory effect of MSC transplantation, with implications for functional neurological recovery after TBI.

Tumor necrosis factor in traumatic brain injury: effects of genetic deletion of p55 or p75 receptor

The role of tumor necrosis factor (TNF) and its receptors after traumatic brain injury (TBI) remains unclear. We evaluated the effects of genetic deletion of either p55 or p75 TNF receptor on neurobehavioral outcome, histopathology, DNA damage and apoptosis-related cell death/survival gene expression (bcl-2/bax), and microglia/macrophage (M/M) activation in wild-type (WT) and knockout mice after TBI. Injured p55 (-/-) mice showed a significant attenuation while p75 (-/-) mice showed a significant worsening of sensorimotor deficits compared with WT mice over 4 weeks postinjury. At the same time point, contusion volume in p55 (-/-) mice (11.1±3.3 mm(3)) was significantly reduced compared with WT (19.7±3.4 mm(3)) and p75 (-/-) mice (20.9±3.2 mm(3)). At 4 hours postinjury, bcl-2/bax ratio mRNA expression was increased in p55 (-/-) compared with p75 (-/-) mice and was associated with reduced DNA damage terminal deoxynucleotidyl transferaseYmediated dUTP nick end labeling (TUNEL-positivity), reduced CD11b expression and increased Ym1 expression at 24 hours postinjury in p55 (-/-) compared with p75 (-/-) mice, indicative of a protective M/M response. These data suggest that TNF may exacerbate neurobehavioral deficits and tissue damage via p55 TNF receptor whose inhibition may represent a specific therapeutic target after TBI.

Review: the long-term consequences of microglial activation following acute traumatic brain injury

The brain is vulnerable to a number of acute insults, with traumatic brain injury being among the commonest. Neuroinflammation is a common response to acute injury and microglial activation is a key component of the inflammatory response. In the acute and subacute phase it is likely that this response is protective and forms an important part of the normal tissue reaction. However, there is considerable literature demonstrating an association between acute traumatic brain injury to the brain and subsequent cognitive decline. This article will review the epidemiological literature relating to both single and repetitive head injury. It will focus on the neuropathological features associated with long-term complications of a single blunt force head injury, repetitive head injury and blast head injury, with particular reference to chronic traumatic encephalopathy, including dementia pugilistica. Neuroinflammation has been postulated as a key mechanism linking acute traumatic brain injury with subsequent neurodegenerative disease, and this review will consider the response to injury in the acute phase and how this may be detrimental in the longer term, and discuss potential genetic factors which may influence this cellular response. Finally, this article will consider future directions for research and potential future therapies.

Traumatic brain injury, neuroinflammation, and post-traumatic headaches

Concussions following head and/or neck injury are common, and although most people with mild injuries recover uneventfully, a subset of individuals develop persistent post-concussive symptoms that often include headaches. Post-traumatic headaches vary in presentation and may progress to become chronic and in some cases debilitating. Little is known about the pathogenesis of post-traumatic headaches, although shared pathophysiology with that of the brain injury is suspected. Following primary injury to brain tissues, inflammation rapidly ensues; while this inflammatory response initially provides a defensive/reparative function, it can persist beyond its beneficial effect, potentially leading to secondary injuries because of alterations in neuronal excitability, axonal integrity, central processing, and other changes. These changes may account for the neurological symptoms often observed after traumatic brain injury, including headaches. This review considers selected aspects of the inflammatory response following traumatic brain injury, with an emphasis on the role of glial cells as mediators of maladaptive post-traumatic inflammation.

Beneficial effects of minocycline and botulinum toxin-induced constraint physical therapy following experimental traumatic brain injury

BACKGROUND

Effective recovery from functional impairments caused by traumatic brain injury (TBI) requires appropriate rehabilitation therapy. Multiple pathways are involved in secondary injury and recovery suggesting a role for multimodal approaches.

OBJECTIVE

Here, we examined the efficacy of the anti-inflammatory agent minocycline and botulinum toxin (botox)-induced limb constraint with structured physical therapy, delivered alone or in combination, after a severe TBI produced by a controlled cortical impact in rats.

METHODS

Minocycline was administered at 25 mg/kg daily for 2 weeks beginning 1 day after TBI or sham surgery. For constraint/physical therapy, botox-type A was injected into the nonaffected forearm muscle 1 day after injury and 2 weeks of physical therapy commenced at 5 days after injury. Functional evaluations were conducted 8 weeks after injury.

RESULTS

Minocycline, either as a monotherapy or as combination treatment with botox/physical therapy significantly reduced impairments of spatial learning and memory in the water maze test, whereas botox/physical therapy reduced forelimb motor asymmetry and improved manual dexterity in the cylinder and vermicelli handling tests, A synergistic effect between the 2 treatments was observed when rats performed tasks requiring dexterity. Inflammation was attenuated in the peri-contusion cortex and hippocampus in all TBI groups receiving mono or combination therapies, though there was no significant difference in lesion size among groups.

CONCLUSION

These data provide a rationale for incorporating anti-inflammatory treatment during rehabilitation therapy.

Elevated plasma MCP-1 concentration following traumatic brain injury as a potential "predisposition" factor associated with an increased risk for subsequent development of Alzheimer's disease

We explored whether changes in the expression profile of peripheral blood plasma proteins may provide a clinical, readily accessible "window" into the brain, reflecting molecular alterations following traumatic brain injury (TBI) that might contribute to TBI complications. We recruited fourteen TBI and ten control civilian participants for the study, and also analyzed banked plasma specimens from 20 veterans with TBI and 20 control cases. Using antibody arrays and ELISA assays, we explored differentially-regulated protein species in the plasma of TBI compared to healthy controls from the two independent cohorts. We found three protein biomarker species, monocyte chemotactic protein-1 (MCP-1), insulin-like growth factor-binding protein-3, and epidermal growth factor receptor, that are differentially regulated in plasma specimens of the TBI cases. A three-biomarker panel using all three proteins provides the best potential criterion for separating TBI and control cases. Plasma MCP-1 contents are correlated with the severity of TBI and the index of compromised axonal fiber integrity in the frontal cortex. Based on these findings, we evaluated postmortem brain specimens from 7 mild cognitive impairment (MCI) and 7 neurologically normal cases. We found elevated MCP-1 expression in the frontal cortex of MCI cases that are at high risk for developing Alzheimer's disease. Our findings suggest that additional application of the three-biomarker panel to current diagnostic criteria may lead to improved TBI detection and more sensitive outcome measures for clinical trials. Induction of MCP-1 in response to TBI might be a potential predisposing factor that may increase the risk for development of Alzheimer's disease.

Exogenous administration of PACAP alleviates traumatic brain injury in rats through a mechanism involving the TLR4/MyD88/NF-κB pathway

Pituitary adenylate cyclase-activating polypeptide (PACAP) is effective in reducing axonal damage associated with traumatic brain injury (TBI), and has immunomodulatory properties. Toll-like receptor 4 (TLR4) is an important mediator of the innate immune response. It significantly contributes to neuroinflammation induced by brain injury. However, it remains unknown whether exogenous PACAP can modulate TBI through the TLR4/adapter protein myeloid differentiation factor 88 (MyD88)/nuclear factor-κB (NF-κB) signaling pathway. In this study, we investigated the potential neuroprotective mechanisms of PACAP pretreatment in a weight-drop model of TBI. PACAP38 was microinjected intracerebroventricularly before TBI. Brain samples were extracted from the pericontusional area in the cortex and hippocampus. We found that TBI induced significant upregulation of TLR4, with peak expression occurring 24 h post-trauma, and that pretreatment with PACAP significantly improved motor and cognitive dysfunction, attenuated neuronal apoptosis, and decreased brain edema. Pretreatment with PACAP inhibited upregulation of TLR4 and its downstream signaling molecules MyD88, p-IκB, and NF-κB, and suppressed increases in the levels of the downstream inflammatory agents interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), in the brain tissue around the injured cortex and in the hippocampus. Administration of PACAP both in vitro and in vivo attenuated the ability of the TLR4 agonist lipopolysaccharide (LPS) to increase TLR4 protein levels. Therefore, PACAP exerts a neuroprotective effect in this rat model of TBI, by inhibiting a secondary inflammatory response mediated by the TLR4/MyD88/NF-κB signaling pathway in microglia and neurons, thereby reducing neuronal death and improving the outcome following TBI.

Analysis of functional pathways altered after mild traumatic brain injury

Concussive injury (or mild traumatic brain injury; mTBI) can exhibit features of focal or diffuse injury patterns. We compared and contrasted the cellular and molecular responses after mild controlled cortical impact (mCCI; a focal injury) or fluid percussion injury (FPI; a diffuse injury) in rats. The rationale for this comparative analysis was to investigate the brain's response to mild diffuse versus mild focal injury to identify common molecular changes triggered by these injury modalities and to determine the functional pathways altered after injury that may provide novel targets for therapeutic intervention. Microarrays containing probes against 21,792 unique messenger RNAs (mRNAs) were used to investigate the changes in cortical mRNA expression levels at 3 and 24 h postinjury. Of the 354 mRNAs with significantly altered expression levels after mCCI, over 89% (316 mRNAs) were also contained within the mild FPI (mFPI) data set. However, mFPI initiated a more widespread molecular response, with over 2300 mRNAs differentially expressed. Bioinformatic analysis of annotated gene ontology molecular function and biological pathway terms showed a significant overrepresentation of genes belonging to inflammation, stress, and signaling categories in both data sets. We therefore examined changes in the protein levels of a panel of 23 cytokines and chemokines in cortical extracts using a Luminex-based bead immunoassay and detected significant increases in macrophage inflammatory protein (MIP)-1α (CCL3), GRO-KC (CXCL1), interleukin (IL)-1α, IL-1β, and IL-6. Immunohistochemical localization of MIP-1α and IL-1β showed marked increases at 3 h postinjury in the cortical vasculature and microglia, respectively, that were largely resolved by 24 h postinjury. Our findings demonstrate that both focal and diffuse mTBI trigger many shared pathobiological processes (e.g., inflammatory responses) that could be targeted for mechanism-based therapeutic interventions.

Time-dependent changes of protein biomarker levels in the cerebrospinal fluid after blast traumatic brain injury

Time-dependent changes of protein biomarkers in the cerebrospinal fluid (CSF) can be used to identify the pathological processes in traumatic brain injury (TBI) as well as to follow the progression of the disease. We obtained CSF from a large animal model (swine) of blast-induced traumatic brain injury prior to and at 6, 24, 72 h, and 2 wk after a single exposure to blast overpressure, and determined changes in the CSF levels of neurofilament-heavy chain, neuron-specific enolase, brain-specific creatine kinase, glial fibrillary acidic protein, calcium-binding protein β (S100β), Claudin-5, vascular endothelial growth factor, and von Willebrand factor using reverse phase protein microarray. We detected biphasic temporal patterns in the CSF concentrations of all tested protein markers except S100β. The CSF levels of all markers were significantly increased 6 h after the injury compared to preinjury levels. Values were then decreased at 24 h, prior to a second increase in all markers but S100β at 72 h. At 2 wk postinjury, the CSF concentrations of all biomarkers were decreased once again; brain-specific creatine kinase, Claudin-5, von Willebrand factor, and S100β levels were no longer significantly higher than their preinjury values while neurofilament-heavy chain, neuron-specific enolase, vascular endothelial growth factor, and glial fibrillary acidic protein levels remained significantly elevated compared to baseline. Our findings implicate neuronal and glial cell damage, compromised vascular permeability, and inflammation in blast-induced traumatic brain injury, as well as demonstrate the value of determining the temporal pattern of biomarker changes that may be of diagnostic value.

Reactive oxygen species-activated nanoprodrug of Ibuprofen for targeting traumatic brain injury in mice

Traumatic brain injury (TBI) is an enormous public health problem, with 1.7 million new cases of TBI recorded annually by the Centers for Disease Control. However, TBI has proven to be an extremely challenging condition to treat. Here, we apply a nanoprodrug strategy in a mouse model of TBI. The novel nanoprodrug contains a derivative of the nonsteroidal anti-inflammatory drug (NSAID) ibuprofen in an emulsion with the antioxidant α-tocopherol. The ibuprofen derivative, Ibu2TEG, contains a tetra ethylene glycol (TEG) spacer consisting of biodegradable ester bonds. The biodegradable ester bonds ensure that the prodrug molecules break down hydrolytically or enzymatically. The drug is labeled with the fluorescent reporter Cy5.5 using nonbiodegradable bonds to 1-octadecanethiol, allowing us to reliably track its accumulation in the brain after TBI. We delivered a moderate injury using a highly reproducible mouse model of closed-skull controlled cortical impact to the parietal region of the cortex, followed by an injection of the nanoprodrug at a dose of 0.2 mg per mouse. The blood brain barrier is known to exhibit increased permeability at the site of injury. We tested for accumulation of the fluorescent drug particles at the site of injury using confocal and bioluminescence imaging of whole brains and brain slices 36 hours after administration. We demonstrated that the drug does accumulate preferentially in the region of injured tissue, likely due to an enhanced permeability and retention (EPR) phenomenon. The use of a nanoprodrug approach to deliver therapeutics in TBI represents a promising potential therapeutic modality.

Absence of TLR4 reduces neurovascular unit and secondary inflammatory process after traumatic brain injury in mice

Background

Traumatic brain injury (TBI) initiates a neuroinflammatory cascade that contributes to neuronal damage and behavioral impairment. Toll-like receptors (TLRs) are signaling receptors in the innate immune system, although emerging evidence indicates their role in brain injury. We have therefore investigated the role played by TLR4 signaling pathway in the development of mechanisms of secondary inflammatory process in traumatic brain injury (TBI) differ in mice that lack a functional TLR4 signaling pathway.

Methods/Principal Findings

Controlled cortical impact injury was performed on TLR4 knockout (KO) mice (C57BL/10ScNJ) and wild-type (WT) mice (C57BL/10ScNJ). TBI outcome was evaluated by determination of infarct volume and assessment of neurological scores. Brains were collected at 24 h after TBI. When compared to WT mice, TLR4 KO mice had lower infarct volumes and better outcomes in neurological and behavioral tests (evaluated by EBST and rotarod test). Mice that lacked TLR4 had minor expression of TBI-induced GFAP, Chymase, Tryptase, IL-1β, iNOS, PARP and Nitrotyrosine mediators implicated in brain damage. The translocation of expression of p-JNK, IκB-α and NF-κB pathway were also lower in brains from TLR4 KO mice. When compared to WT mice, resulted in significant augmentation of all the above described parameters. In addition, apoptosis levels in TLR4 KO mice had minor expression of Bax while on the contrary with Bcl-2.

Conclusions/Significance

Our results clearly demonstrated that absence of TLR4 reduces the development of neuroinflammation, tissues injury events associated with brain trauma and may play a neuroprotective role in TBI in mice.

The neuropathology and neurobiology of traumatic brain injury

The acute and long-term consequences of traumatic brain injury (TBI) have received increased attention in recent years. In this Review, we discuss the neuropathology and neural mechanisms associated with TBI, drawing on findings from sports-induced TBI in athletes, in whom acute TBI damages axons and elicits both regenerative and degenerative tissue responses in the brain and in whom repeated concussions may initiate a long-term neurodegenerative process called dementia pugilistica or chronic traumatic encephalopathy (CTE). We also consider how the neuropathology and neurobiology of CTE in many ways resembles other neurodegenerative illnesses such as Alzheimer's disease, particularly with respect to mismetabolism and aggregation of tau, β-amyloid, and TDP-43. Finally, we explore how translational research in animal models of acceleration/deceleration types of injury relevant for concussion together with clinical studies employing imaging and biochemical markers may further elucidate the neurobiology of TBI and CTE.

Animal models of traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of mortality and morbidity both in civilian life and on the battlefield worldwide. Survivors of TBI frequently experience long-term disabling changes in cognition, sensorimotor function and personality. Over the past three decades, animal models have been developed to replicate the various aspects of human TBI, to better understand the underlying pathophysiology and to explore potential treatments. Nevertheless, promising neuroprotective drugs that were identified as being effective in animal TBI models have all failed in Phase II or Phase III clinical trials. This failure in clinical translation of preclinical studies highlights a compelling need to revisit the current status of animal models of TBI and therapeutic strategies.

Post-injury conditioning with lipopolysaccharide or lipooligosaccharide reduces inflammation in the brain

BACKGROUND

Traumatic brain injury (TBI) is a leading cause of mortality and disability in the Western world. The first stage of TBI results from the mechanical damage from an impact or blast. A second stage occurs as an inflammatory response to the primary injury and presents an opportunity for clinical intervention. In this study, we investigated the effect of pre- and post-injury treatment with lipopolysaccharide (LPS) from Escherichia coli and lipooligosaccharide (LOS) from Neisseria meningitidis on levels of cerebral inflammatory cells, circulating blood cells, and pro- and anti-inflammatory cytokine levels in a rat model of neuroinflammation induced by intrastriatal injection of IL-1β to mimic the second stage of TBI.

METHODS

LPS or LOS was administered intravenously (IV) or intranasally (IN) 2h pre- or post-injection of IL-1β. The rats were euthanized 12h following IL-1β injection. Brain sections were immunostained with antibody to ED-1, a microglia cell marker. Cells in whole blood were assessed with a VetScan HM2 analyzer, and cytokine levels in sera were analyzed with a Bio-Plex system.

RESULTS

Pre- and post-injury IV administration of LPS or LOS significantly reduced microglia in the brain, and IN pre-treatment with LPS or LOS showed a statistical trend towards reducing microglia. Pre- and post-treatment IV with LOS increased circulating levels of IL-2 and IL-4, whereas IN post-treatment with LPS reduced levels of the inflammatory cytokines, TNF-α and IFN-γ.

CONCLUSIONS

The findings strongly support continued investigation of post-conditioning with LPS or LOS as potential neuroprotective treatments for neuroinflammation from TBI.

Neuroinflammation: beneficial and detrimental effects after traumatic brain injury

Traumatic brain injury (TBI) is the major cause of death and severe disability in young adults and infants worldwide and many survivors also have mild to moderate neurological deficits which impair their lives. This review highlights the primary and secondary lesions constituting craniocerebral trauma and the main elements of neuroinflammation, one of the most important secondary events evolving after the initial traumatic insult. Neuroinflammation has dual and opposing roles in outcome after TBI, being both beneficial and harmful, its effects often differing between the acute and more delayed phases after injury. Since each patient with TBI has a unique and complex pattern of cerebral damage, developing pharmacological intervention strategies targeted at the multiple cellular and molecular events in the neuroinflammatory cascade is difficult. While there have been very few successful outcomes to date in human clinical trials of drugs developed to treat TBI in general, those that have been devised to modulate neuroinflammation are discussed.

Late exercise reduces neuroinflammation and cognitive dysfunction after traumatic brain injury

Delayed secondary biochemical and cellular changes after traumatic brain injury continue for months to years, and are associated with chronic neuroinflammation and progressive neurodegeneration. Physical activity can reduce inflammation and facilitate recovery after brain injury. Here, we investigated the time-dependent effects, and underlying mechanisms of post-traumatic exercise initiation on outcome after moderate traumatic brain injury using a well-characterized mouse controlled cortical impact model. Late exercise initiation beginning at 5weeks after trauma, but not early initiation of exercise at 1week, significantly reduced working and retention memory impairment at 3months, and decreased lesion volume compared to non-exercise injury controls. Cognitive recovery was associated with attenuation of classical inflammatory pathways, activation of alternative inflammatory responses and enhancement of neurogenesis. In contrast, early initiation of exercise failed to alter behavioral recovery or lesion size, while increasing the neurotoxic pro-inflammatory responses. These data underscore the critical importance of timing of exercise initiation after trauma and its relation to neuroinflammation, and challenge the widely held view that effective neuroprotection requires early intervention.

Inflammation and white matter degeneration persist for years after a single traumatic brain injury

A single traumatic brain injury is associated with an increased risk of dementia and, in a proportion of patients surviving a year or more from injury, the development of hallmark Alzheimer's disease-like pathologies. However, the pathological processes linking traumatic brain injury and neurodegenerative disease remain poorly understood. Growing evidence supports a role for neuroinflammation in the development of Alzheimer's disease. In contrast, little is known about the neuroinflammatory response to brain injury and, in particular, its temporal dynamics and any potential role in neurodegeneration. Cases of traumatic brain injury with survivals ranging from 10 h to 47 years post injury (n = 52) and age-matched, uninjured control subjects (n = 44) were selected from the Glasgow Traumatic Brain Injury archive. From these, sections of the corpus callosum and adjacent parasaggital cortex were examined for microglial density and morphology, and for indices of white matter pathology and integrity. With survival of ≥3 months from injury, cases with traumatic brain injury frequently displayed extensive, densely packed, reactive microglia (CR3/43- and/or CD68-immunoreactive), a pathology not seen in control subjects or acutely injured cases. Of particular note, these reactive microglia were present in 28% of cases with survival of >1 year and up to 18 years post-trauma. In cases displaying this inflammatory pathology, evidence of ongoing white matter degradation could also be observed. Moreover, there was a 25% reduction in the corpus callosum thickness with survival >1 year post-injury. These data present striking evidence of persistent inflammation and ongoing white matter degeneration for many years after just a single traumatic brain injury in humans. Future studies to determine whether inflammation occurs in response to or, conversely, promotes white matter degeneration will be important. These findings may provide parallels for studying neurodegenerative disease, with traumatic brain injury patients serving as a model for longitudinal investigations, in particular with a view to identifying potential therapeutic interventions.

Midbrain raphe stimulation improves behavioral and anatomical recovery from fluid-percussion brain injury

The midbrain median raphe (MR) and dorsal raphe (DR) nuclei were tested for their capacity to regulate recovery from traumatic brain injury (TBI). An implanted, wireless self-powered stimulator delivered intermittent 8-Hz pulse trains for 7 days to the rat's MR or DR, beginning 4-6 h after a moderate parasagittal (right) fluid-percussion injury. MR stimulation was also examined with a higher frequency (24 Hz) or a delayed start (7 days after injury). Controls had sham injuries, inactive stimulators, or both. The stimulation caused no apparent acute responses or adverse long-term changes. In water-maze trials conducted 5 weeks post-injury, early 8-Hz MR and DR stimulation restored the rate of acquisition of reference memory for a hidden platform of fixed location. Short-term spatial working memory, for a variably located hidden platform, was restored only by early 8-Hz MR stimulation. All stimulation protocols reversed injury-induced asymmetry of spontaneous forelimb reaching movements tested 6 weeks post-injury. Post-mortem histological measurement at 8 weeks post-injury revealed volume losses in parietal-occipital cortex and decussating white matter (corpus callosum plus external capsule), but not hippocampus. The cortical losses were significantly reversed by early 8-Hz MR and DR stimulation, the white matter losses by all forms of MR stimulation. The generally most effective protocol, 8-Hz MR stimulation, was tested 3 days post-injury for its acute effect on forebrain cyclic adenosine monophosphate (cAMP), a key trophic signaling molecule. This procedure reversed injury-induced declines of cAMP levels in both cortex and hippocampus. In conclusion, midbrain raphe nuclei can enduringly enhance recovery from early disseminated TBI, possibly in part through increased signaling by cAMP in efferent targets. A neurosurgical treatment for TBI using interim electrical stimulation in raphe repair centers is suggested.

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.

Association of CXCL1 promoter polymorphism with ischaemic stroke in Korean population

This is a pilot study analysing association of chemokine gene polymorphisms (CXCL1, rs3117604; CXCL2, rs3806792; CCL2, rs2857656 and rs3760396; CCL5, rs2107538) in Korean patients with ischemic stroke (IS) (n = 120) and age-matched controls (n = 267). The CXCL1 gene and particularly T allele of rs3117604 was associated with IS.

Neuropathology of mild traumatic brain injury: relationship to neuroimaging findings

Neuroimaging identified abnormalities associated with traumatic brain injury (TBI) are but gross indicators that reflect underlying trauma-induced neuropathology at the cellular level. This review examines how cellular pathology relates to neuroimaging findings with the objective of more closely relating how neuroimaging findings reveal underlying neuropathology. Throughout this review an attempt will be made to relate what is directly known from post-mortem microscopic and gross anatomical studies of TBI of all severity levels to the types of lesions and abnormalities observed in contemporary neuroimaging of TBI, with an emphasis on mild traumatic brain injury (mTBI). However, it is impossible to discuss the neuropathology of mTBI without discussing what occurs with more severe injury and viewing pathological changes on some continuum from the mildest to the most severe. Historical milestones in understanding the neuropathology of mTBI are reviewed along with implications for future directions in the examination of neuroimaging and neuropathological correlates of TBI.

Neuroinflammation after traumatic brain injury: opportunities for therapeutic intervention

Traumatic brain injury (TBI) remains one of the leading causes of mortality and morbidity worldwide, yet despite extensive efforts to develop neuroprotective therapies for this devastating disorder there have been no successful outcomes in human clinical trials to date. Following the primary mechanical insult TBI results in delayed secondary injury events due to neurochemical, metabolic and cellular changes that account for many of the neurological deficits observed after TBI. The development of secondary injury represents a window of opportunity for therapeutic intervention to prevent progressive tissue damage and loss of function after injury. To establish effective neuroprotective treatments for TBI it is essential to fully understand the complex cellular and molecular events that contribute to secondary injury. Neuroinflammation is well established as a key secondary injury mechanism after TBI, and it has been long considered to contribute to the damage sustained following brain injury. However, experimental and clinical research indicates that neuroinflammation after TBI can have both detrimental and beneficial effects, and these likely differ in the acute and delayed phases after injury. The key to developing future anti-inflammatory based neuroprotective treatments for TBI is to minimize the detrimental and neurotoxic effects of neuroinflammation while promoting the beneficial and neurotrophic effects, thereby creating optimal conditions for regeneration and repair after injury. This review outlines how post-traumatic neuroinflammation contributes to secondary injury after TBI, and discusses the complex and varied responses of the primary innate immune cells of the brain, microglia, to injury. In addition, emerging experimental anti-inflammatory and multipotential drug treatment strategies for TBI are discussed, as well as some of the challenges faced by the research community to translate promising neuroprotective drug treatments to the clinic.

Rod microglia: elongation, alignment, and coupling to form trains across the somatosensory cortex after experimental diffuse brain injury

BACKGROUND

Since their discovery, the morphology of microglia has been interpreted to mirror their function, with ramified microglia constantly surveying the micro-environment and rapidly activating when changes occur. In 1899, Franz Nissl discovered what we now recognize as a distinct microglial activation state, microglial rod cells (Stäbchenzellen), which he observed adjacent to neurons. These rod-shaped microglia are typically found in human autopsy cases of paralysis of the insane, a disease of the pre-penicillin era, and best known today from HIV-1-infected brains. Microglial rod cells have been implicated in cortical 'synaptic stripping' but their exact role has remained unclear. This is due at least in part to a scarcity of experimental models. Now we have noted these rod microglia after experimental diffuse brain injury in brain regions that have an associated sensory sensitivity. Here, we describe the time course, location, and surrounding architecture associated with rod microglia following experimental diffuse traumatic brain injury (TBI).

METHODS

Rats were subjected to a moderate midline fluid percussion injury (mFPI), which resulted in transient suppression of their righting reflex (6 to 10 min). Multiple immunohistochemistry protocols targeting microglia with Iba1 and other known microglia markers were undertaken to identify the morphological activation of microglia. Additionally, labeling with Iba1 and cell markers for neurons and astrocytes identified the architecture that surrounds these rod cells.

RESULTS

We identified an abundance of Iba1-positive microglia with rod morphology in the primary sensory barrel fields (S1BF). Although present for at least 4 weeks post mFPI, they developed over the first week, peaking at 7 days post-injury. In the absence of contusion, Iba1-positive microglia appear to elongate with their processes extending from the apical and basal ends. These cells then abut one another and lay adjacent to cytoarchitecture of dendrites and axons, with no alignment with astrocytes and oligodendrocytes. Iba1-positive rod microglial cells differentially express other known markers for reactive microglia including OX-6 and CD68.

CONCLUSION

Diffuse traumatic brain injury induces a distinct rod microglia morphology, unique phenotype, and novel association between cells; these observations entice further investigation for impact on neurological outcome.

Increased expression of ferritin in cerebral cortex after human traumatic brain injury

Despite numerous researches and improvements in the past few years, the precise mechanisms underlying secondary brain injury after trauma remain obscure. Iron is essential for almost all types of cells, including nerve cells. However, excess of iron has been proved to contribute to the brain injury following trauma in animal models. As a key iron-handling protein in the brain, ferritin might be involved in iron-induced pathophysiological process of various brain disorders. Therefore, the current study was aimed to investigate the expression of ferritin in the human contused brain. Nineteen contused brain samples were obtained from 19 patients undergoing surgery for brain contusions 3 h-17 d after trauma, and three normal temporal pole samples from 3 patients with petroclival meningioma were collected as controls. Expression of ferritin-H-chain was measured by quantitative real-time polymerase chain reaction (PCR), western blot and immunohistochemistry, respectively. Perl's reaction was taken for iron staining. The results showed that human traumatic brain injury (TBI) could up-regulate ferritin-H-chain in pericontusional cortex. A marked increase of ferritin was detected in the early group (≤12 h), and remained elevated for a long time till after 48 h post-injury. The location of ferritin-H-chain was found mainly at the neuron-like cells and seldom at glia-like cells. Perl's reaction showed that most of the iron-positive cells were glia-like cells. These findings suggested that iron and ferritin might be involved in the secondary brain injury and could be therapeutic targets for patients with TBI.

New perspectives on central and peripheral immune responses to acute traumatic brain injury

Traumatic injury to the brain (TBI) results in a complex set of responses involving various symptoms and long-term consequences. TBI of any form can cause cognitive, behavioral and immunologic changes in later life, which underscores the problem of underdiagnosis of mild TBI that can cause long-term neurological deficits. TBI disrupts the blood–brain barrier (BBB) leading to infiltration of immune cells into the brain and subsequent inflammation and neurodegeneration. TBI-induced peripheral immune responses can also result in multiorgan damage. Despite worldwide research efforts, the methods of diagnosis, monitoring and treatment for TBI are still relatively ineffective. In this review, we delve into the mechanism of how TBI-induced central and peripheral immune responses affect the disease outcome and discuss recent developments in the continuing effort to combat the consequences of TBI and new ways to enhance repair of the damaged brain.

Effects of therapeutic hypothermia on inflammasome signaling after traumatic brain injury

Traumatic brain injury (TBI) activates the NALP1/NLRP1 inflammasome, which is an important component of the early innate inflammatory response to injury. We investigated the influence of therapeutic hypothermia on inflammasome activation after TBI. Adult male Sprague-Dawley rats were subjected to moderate fluid percussion brain injury. Temperature manipulation (33°C or 37°C) was initiated 30 minutes after TBI and maintained for 4 hours. At 4 or 24 hours after TBI, traumatized cortex and hippocampus were prepared for immunoblot or immunohistochemical analysis. In the normothermic groups, caspase-1, caspase-11 and expression of the purinergic receptor P2X7 increased at 24 hours after TBI. Posttraumatic hypothermia lead to decreased expression of these proteins at 24 hours compared with normothermic levels. Immunocytochemical studies showed that posttraumatic hypothermia also decreased caspase-1 staining in cerebral cortical neurons compared with normothermic TBI. Cultured cortical neurons subjected to stretch injury demonstrated significant secretion of caspase-1 into the culture medium and caspase-3 activation, both results reduced by hypothermic treatment. Posttraumatic hypothermia decreases inflammasome signaling in neurons and reduces the innate immune response to TBI at 24 hours after injury. Therapeutic hypothermia may protect the injured central nervous system by targeting the detrimental consequences of the innate immune response to injury.

Heparanase overexpression impairs inflammatory response and macrophage-mediated clearance of amyloid-β in murine brain

Neuroinflammation is typically observed in neurodegenerative diseases such as Alzheimer’s disease, as well as after traumatic injury and pathogen infection. Resident immune cells, microglia and astrocytes, are activated and joined by blood-borne monocytes that traverse the blood–brain barrier and convert into activated macrophages. The activated cells express various cytokines, chemokines and proteolytic enzymes. To study the role of heparan sulfate proteoglycans in neuroinflammation, we employed a transgenic mouse overexpressing heparanase, an endoglucuronidase that specifically degrades heparan sulfate side chains. Neuroinflammation was induced by systemic challenge with lipopolysaccharide, or by localized cerebral microinjection of aggregated amyloid-β peptide, implicated in Alzheimer’s disease. Lipopolysaccharide-treated control mice showed massive activation of resident microglia as well as recruitment of monocyte-derived macrophages into the brain parenchyma. Microinjection of aggregated amyloid-β elicited a similar inflammatory response, albeit restricted to the injection site, which led to dispersion and clearance of the amyloid. In the heparanase-overexpressing mice, all aspects of immune cell recruitment and activation were significantly attenuated in both inflammation models, as was amyloid dispersion. Accordingly, an in vitro blood–brain barrier model constructed from heparanase-overexpressing cerebral vascular cells showed impaired transmigration of monocytes compared to a corresponding assembly of control cells. Our data indicate that intact heparan sulfate chains are required at multiple sites to mediate neuroinflammatory responses, and further point to heparanase as a modulator of this process, with potential implications for Alzheimer’s disease.

IκBα deficiency in brain leads to elevated basal neuroinflammation and attenuated response following traumatic brain injury: implications for functional recovery

Background

The transcription factor NFκB is an important mediator of cell survival and inflammation in the immune system. In the central nervous system (CNS), NFκB signaling has been implicated in regulating neuronal survival following acute pathologic damage such as traumatic brain injury (TBI) and stroke. NFκB is normally bound by the principal inhibitory protein, IκBα, and sequestered in the cytoplasm. Activation of NFκB requires the degradation of IκBα, thereby freeing NFκB to translocate to the nucleus and activate the target genes. Mice deficient in IκBα display deregulated and sustained NFκB activation and early postnatal lethality, highlighting a critical role of IκBα in NFκB regulation.

Results

We investigated the role of IκBα in regulating NFκB activity in the brain and the effects of the NFκB/IκBα pathway in mediating neuroinflammation under both physiological and brain injury conditions. We report that astrocytes, but not neurons, exhibit prominent NFκB activity, and that basal NFκB activity in astrocytes is elevated in the absence of IκBα. By generating mice with brain-specific deletion of IκBα, we show that IκBα deficiency does not compromise normal brain development. However, basal neuroinflammation detected by GFAP and Iba1 immunoreactivity is elevated. This leads to impaired inflammatory responses following TBI and worsened brain damage including higher blood brain barrier permeability, increased injury volumes and enlarged ventricle volumes.

Conclusions

We conclude that, in the CNS, astrocyte is the primary cell type subject to NFκB regulation. We further demonstrate that IκBα plays an important role in regulating NFκB activity in the brain and a robust NFκB/IκBα-mediated neuroinflammatory response immediately following TBI is beneficial.

Morphological and genetic activation of microglia after diffuse traumatic brain injury in the rat

Traumatic brain injury (TBI) survivors experience long-term post-traumatic morbidities. In diffuse brain-injured rats, a chronic sensory sensitivity to whisker stimulation models the agitation of TBI survivors and provides anatomical landmarks across the whisker-barrel circuit to evaluate post-traumatic neuropathology. As a consequence of TBI, acute and chronic microglial activation can contribute to degenerative and reparative events underlying post-traumatic morbidity. Here we hypothesize that a temporal sequence of microglial activation states contributes to the circuit pathology responsible for post-traumatic morbidity, and test the hypothesis by examining microglial morphological activation and neuroinflammatory markers for activation states through gene expression and receptor-binding affinity. Adult male, Sprague-Dawley rats were subjected to a single moderate midline fluid percussion injury (FPI) or sham injury. Microglial activation was determined by immunohistochemistry, quantitative real-time PCR and receptor autoradiography in the primary somatosensory barrel field (S1BF) and ventral posterior medial nucleus (VPM) of the thalamus at 7 and 28 days following FPI. Morphological changes indicative of microglial activation, including swollen cell body with thicker, shrunken processes, were evident in S1BF and VPM at 7 and 28 days post-injury. Principally at 7 days post-injury in VPM, general inflammatory gene expression (major histocompatibility complex I, major histocompatibility complex II, translocator protein 18 kDa [TSPO]) is increased above sham level and TSPO gene expression confirmed by receptor autoradiography. Further, CD45, a marker of classical activation, and TGF-βI, an acquired deactivation marker, were elevated significantly above sham at 7 days post-injury. Daily administration of the anti-inflammatory ibuprofen (20mg/kg, i.p.) significantly reduced the expression of these genes. Evidence for alternative activation (arginase 1) was not observed. Thus, these data demonstrate concomitant classical activation and acquired deactivation phenotypes of microglia in diffuse TBI in the absence of overt contusion or cavitation. Anti-inflammatory treatment may further alleviate the neuropathological burden of post-traumatic inflammation.

Characterization and function of the human macrophage dopaminergic system: implications for CNS disease and drug abuse

Background

Perivascular macrophages and microglia are critical to CNS function. Drugs of abuse increase extracellular dopamine in the CNS, exposing these cells to elevated levels of dopamine. In rodent macrophages and human T-cells, dopamine was shown to modulate cellular functions through activation of dopamine receptors and other dopaminergic proteins. The expression of these proteins and the effects of dopamine on human macrophage functions had not been studied.

Methods

To study dopaminergic gene expression, qRT-PCR was performed on mRNA from primary human monocyte derived macrophages (MDM). Expression and localization of dopaminergic proteins was examined by immunoblotting isolated plasma membrane, total membrane and cytosolic proteins from MDM. To characterize dopamine-mediated changes in cytokine production in basal and inflammatory conditions, macrophages were treated with different concentrations of dopamine in the presence or absence of LPS and cytokine production was assayed by ELISA. Statistical significance was determined using two-tailed Students’ T-tests or Wilcoxen Signed Rank tests.

Results

These data show that MDM express mRNA for all five subtypes of dopamine receptors, and that dopamine receptors 3 and 4 are expressed on the plasma membrane. MDM also express mRNA for the dopamine transporter (DAT), vesicular monoamine transporter 2 (VMAT2), tyrosine hydroxylase (TH) and aromatic amino acid decarboxylase (AADC). DAT is expressed on the plasma membrane, VMAT2 on cellular membranes and TH and AADC are in the cytosol. Dopamine also alters macrophage cytokine production in both untreated and LPS-treated cells. Untreated macrophages show dopamine mediated increases IL-6 and CCL2. Macrophages treated with LPS show increased IL-6, CCL2, CXCL8 and IL-10 and decreased TNF-α.

Conclusions

Monocyte derived macrophages express dopamine receptors and other dopaminergic proteins through which dopamine may modulate macrophage functions. Thus, increased CNS dopamine levels due to drug abuse may exacerbate the development of neurological diseases including Alzheimer’s disease and HIV associated neurological disorders.

Temporal changes in cell marker expression and cellular infiltration in a controlled cortical impact model in adult male C57BL/6 mice

Background

Traumatic injury to the central nervous system (CNS) triggers a robust inflammatory response that leads to axonal damage and secondary degeneration of spared tissue. In contrast, some immune responses have neuroprotective effects. However, detailed information regarding the dynamics of immune responses after traumatic CNS injury is still unavailable.

Methods

In the present study, changes in the immune cells present in the injured brain, spleen, and cervical lymph nodes (CLNs), which are draining lymphatic organs from the CNS, were analyzed after controlled cortical impact (CCI) by flow cytometry and immunohistochemistry.

Results

The number of neutrophils and macrophages that infiltrated the injured brain immediately increased 1 d post-injury and declined rapidly thereafter. In the injured brain, resident microglia showed a bimodal increase during the first week and in the chronic phase (≥3 weeks) after injury. Increase in the Iba-1⁺ microglia/macrophages was observed around the injured site. Morphologic analysis showed that Iba-1⁺ cells were round at 1 week, whereas those at 3 weeks were more ramified. Furthermore, CD86⁺/CD11b⁺ M1-like microglia increased at 4 weeks after CCI, whereas CD206⁺/CD11b⁺ M2-like microglia increased at 1 week. These results suggest that different subsets of microglia increased in the acute and chronic phases after CCI. Dendritic cells and T cells increased transiently within 1 week in the injured brain. In the CLNs and the spleen, T cells showed dynamic changes after CCI. In particular, the alteration in the number of T cells in the CLNs showed a similar pattern, with a 1-week delay, to that of microglia in the injured brain.

Conclusion

The data from this study provide useful information on the dynamics of immune cells in CNS injuries.

Mouse brain PSA-NCAM levels are altered by graded-controlled cortical impact injury

Traumatic brain injury (TBI) is a worldwide endemic that results in unacceptably high morbidity and mortality. Secondary injury processes following primary injury are composed of intricate interactions between assorted molecules that ultimately dictate the degree of longer-term neurological deficits. One comparatively unexplored molecule that may contribute to exacerbation of injury or enhancement of recovery is the posttranslationally modified polysialic acid form of neural cell adhesion molecule, PSA-NCAM. This molecule is a critical modulator of central nervous system plasticity and reorganization after injury. In this study, we used controlled cortical impact (CCI) to produce moderate or severe TBI in the mouse. Immunoblotting and immunohistochemical analysis were used to track the early (2, 24, and 48 hour) and late (1 and 3 week) time course and location of changes in the levels of PSA-NCAM after TBI. Variable and heterogeneous short- and long-term increases or decreases in expression were found. In general, alterations in PSA-NCAM levels were seen in the cerebral cortex immediately after injury, and these reductions persisted in brain regions distal to the primary injury site, especially after severe injury. This information provides a starting point to dissect the role of PSA-NCAM in TBI-related pathology and recovery.

Serum-based protein biomarkers in blast-induced traumatic brain injury spectrum disorder

The biological consequences of exposure to explosive blast are extremely complex. Serum protein biomarkers in blast-induced traumatic brain injury (bTBI) can aid in determining injury severity, monitoring progress, and predicting outcome. Exposure to blast results in varying degrees of physical injury. Explosive blast can also induce psychological stress that can contribute to or amplify the extent of physical damage. Given the complexity, scale of injury, and variety of symptoms, bTBI may be best described as a spectrum disorder. In this focused review, we summarize the status of serum protein biomarkers in bTBI in the context of the classification and pathological changes of other forms of TBI. Finally, we recommend specific and easily implementable measures to accelerate serum protein biomarker discovery and validation in bTBI.

Noninvasive brain stimulation to modulate neuroplasticity in traumatic brain injury

OBJECTIVE

To review the use of noninvasive brain stimulation (NBS) as a therapeutic tool to enhance neuroplasticity following traumatic brain injury (TBI).

MATERIALS AND METHODS

Based on a literature search, we describe the pathophysiological events following TBI and the rationale for the use of transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) in this setting.

RESULTS

The pathophysiological mechanisms occurring after TBI vary across time and therefore require differential interventions. Theoretically, given the neurophysiological effects of both TMS and tDCS, these tools may: 1) decrease cortical hyperexcitability acutely after TBI; 2) modulate long-term synaptic plasticity as to avoid maladaptive consequences; and 3) combined with physical and behavioral therapy, facilitate cortical reorganization and consolidation of learning in specific neural networks. All of these interventions may help decrease the burden of disabling sequelae after brain injury.

CONCLUSIONS

Evidence from animal and human studies reveals the potential benefit of NBS in decreasing the extent of injury and enhancing plastic changes to facilitate learning and recovery of function in lesioned neural tissue. However, this evidence is mainly theoretical at this point. Given safety constraints, studies in TBI patients are necessary to address the role of NBS in this condition as well as to further elucidate its therapeutic effects and define optimal stimulation parameters.

Mean diffusivity in the amygdala correlates with anxiety in pediatric TBI

Traumatic brain injury (TBI) and orthopedic injury (OI) patients are prone to anxiety and mood disorders. In the present study, we integrated anatomical and diffusion tensor neuroimaging to investigate structural properties of the amygdala and hippocampus, gray matter regions implicated in anxiety and mood disorders. Children and adolescents were evaluated during the late sub-acute phase of recovery following trauma resulting from either moderate to severe TBI or OI. Mean diffusivity (MD) of the amygdala and hippocampus was elevated following TBI. An interaction of hemisphere, structure, and group revealed that MD of the right amygdala was elevated in females with TBI. Self-reported anxiety scores were not related to either volume or microstructure of the hippocampus, or to volume or fractional anisotropy of the amygdala. Left amygdala MD in the TBI group accounted for 17.5% of variance in anxiety scores. Anxiety symptoms may be mediated by different mechanisms in patients with TBI or OI.

Guilty molecules, guilty minds? The conflicting roles of the innate immune response to traumatic brain injury

Traumatic brain injury (TBI) is a complex disease in the most complex organ of the body, whose victims endure lifelong debilitating physical, emotional, and psychosocial consequences. Despite advances in clinical care, there is no effective neuroprotective therapy for TBI, with almost every compound showing promise experimentally having disappointing results in the clinic. The complex and highly interrelated innate immune responses govern both the beneficial and deleterious molecular consequences of TBI and are present as an attractive therapeutic target. This paper discusses the positive, negative, and often conflicting roles of the innate immune response to TBI in both an experimental and clinical settings and highlights recent advances in the search for therapeutic candidates for the treatment of TBI.

Lesional accumulation of CD163+ macrophages/microglia in rat traumatic brain injury

A robust neuroinflammation, contributing to the development of secondary injury, is a common histopathological feature of traumatic brain injury (TBI). Characterization of leukocytic subpopulations contributing to the early infiltration of the damaged tissue might aid in further understanding of lesion development. Reactive macrophages/microglia can exert protective or damaging effects in TBI. CD163 is considered a marker of M2 (alternatively activated) macrophages. Therefore we investigated the accumulation of CD163(+) macrophages/microglia in the brain of TBI rats. TBI was induced in rats using an open skull weight-drop contusion model and the accumulation of CD163(+) cells was analyzed by immunohistochemistry. In normal rat brains, CD163 was expressed by meningeal, choroid plexus and perivascular macrophages. Significant parenchymal CD163(+) cell accumulation was observed two days post TBI and continuously increased in the investigated survival time. The accumulated CD163(+) cells were mainly distributed to the lesional areas and exhibited macrophage phenotypes with amoeboid morphologic characteristics but not activated microglial phenotypes with hypertrophic morphology and thick processes. Double-labeling experiments showed that most CD163(+) cells co-expressed heme oxygenase-1 (HO-1). In addition, in vitro incubating of macrophage RAW264.7 cells or primary peritoneal macrophages with hemoglobin- haptoglobin (Hb-Hp) complex suppressed LPS-induced inflammatory macrophages phenotype and induced CD163 and HO-1 upregulation, indicating that CD163(+) macrophages/microglia in TBI might have anti-inflammatory effects. And further study is necessary to identify functions of these cells in TBI.

Mild traumatic brain injury: is diffusion imaging ready for primetime in forensic medicine?

Mild traumatic brain injury (MTBI) is difficult to accurately assess with conventional imaging because such approaches usually fail to detect any evidence of brain damage. Recent studies of MTBI patients using diffusion-weighted imaging and diffusion tensor imaging suggest that these techniques have the potential to help grade tissue damage severity, track its development, and provide prognostic markers for clinical outcome. Although these results are promising and indicate that the forensic diagnosis of MTBI might eventually benefit from the use of diffusion-weighted imaging and diffusion tensor imaging, healthy skepticism and caution should be exercised with regard to interpreting their meaning because there is no consensus about which methods of data analysis to use and very few investigations have been conducted, of which most have been small in sample size and examined patients at only one time point after injury.

Postinjury treatment with rolipram increases hemorrhage after traumatic brain injury

The pathology caused by traumatic brain injury (TBI) is exacerbated by the inflammatory response of the injured brain. Two proinflammatory cytokines that contribute to inflammation after TBI are tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β). From previous studies using the parasagittal fluid-percussion brain injury model, we reported that the anti-inflammatory drug rolipram, a phosphodiesterase 4 inhibitor, reduced TNF-α and IL-1β levels and improved histopathological outcome when administered 30 min prior to injury. We now report that treatment with (±)-rolipram given 30 min after injury significantly reduced TNF-α levels in the cortex and hippocampus. However, postinjury administration of (±)-rolipram significantly increased cortical contusion volume and increased atrophy of the cortex compared with vehicle-treated animals at 10 days postinjury. Thus, despite the reduction in proinflammatory cytokine levels, histopathological outcome was worsened with post-TBI (±)-rolipram treatment. Further histological analysis of (±)-rolipram-treated TBI animals revealed significant hemorrhage in the contused brain. Given the well-known role of (±)-rolipram of increasing vasodilation, it is likely that (±)-rolipram worsened outcome after fluid-percussion brain injury by causing increased bleeding.

Substance P-induced changes in cell genesis following diffuse traumatic brain injury

Inhibition of substance P (SP) activity through the use of NK1 receptor antagonists has been shown to be a promising neuroprotective therapy following traumatic brain injury (TBI). Conversely, recent research has implicated SP in the stimulation of neurogenesis, suggesting that the neuropeptide has the potential to promote recovery following TBI. This study characterised the effects of SP and the NK1 antagonist, n-acetyl tryptophan (NAT), on cell proliferation following diffuse TBI. Adult male Sprague-Dawley rats were injured using the impact acceleration model of TBI and randomly assigned to one of five treatment groups: sham, vehicle control, NAT alone, SP alone or SP with NAT. Cellular proliferation was assessed with immunostaining for bromodeoxyuridine (BrdU) and cell-specific markers. Infusion of SP (±NAT) promoted cellular proliferation in the subventricular zone and dentate gyrus following TBI. This increase was largely associated with microglial proliferation and did not correspond with functional improvements. These results suggest that NAT treatment results in neuroprotection following TBI, mediated in part via inhibition of microglia.

Mechanisms and consequences of acquired brain injury during development

The brain of the infant and young child is a developing, dynamic, structure subject to functional remodelling under the influence of factors responsible for optimal neuronal development and synaptogenesis. It exhibits age dependent variation in metabolic rate, blood flow, and ability to tolerate oxidative stress. It is also characterized by an exuberance of neurotransmitter activity, particularly in the first few years of life. The dynamic evolution and adaptability of early brain function permits the organization of neuronal networks to be influenced by environmental stimulation, and, to reduce the functional impact of injury. However, these same processes may also exacerbate the harm sustained by the brain following an acquired brain injury (ABI). The developing neurons are susceptible to excitotoxicity, oxidative stress, and, inflammation, often leading to cellular necrosis and apoptosis. Despite being immunologically privileged via the blood brain barrier, the developing brain is susceptible to injury from systemic inflammation through alteration of normally protective cerebrovascular endothelial cell function. Finally, many of the therapeutic agents currently employed in post-ABI hospital care may also compromise ABI outcome via non-intended pharmacological effects. These agents include analgesic, sedative and anti-convulsant medications. This review emphasizes those physiological considerations in the developing brain which may impact the outcome after ABI, including, the cellular mechanisms of neuronal and cerebrovascular endothelial cell injury, ABI outcome and future therapeutic directions.