Update of neuropathology and neurological recovery after traumatic brain injury

Persistent extreme regressive behavior in severe traumatic brain injury patients: a rare neurological phenomenon

Regressive behavior is a known sequela after severe traumatic brain injury (TBI). However, prolonged "infantile-like" behavior has received little attention in the literature, suggesting that this is a rare phenomenon. It is typically characterized by long-lasting childish, extremely dependent, and sometimes aggressive behavior, which is distinguished from the expected recovery process. The relevant theoretical framework lies in the field of disorders called "Neuropathologies of the self" (NPS). We report three cases of young adults who, following a severe TBI, developed continual regressive behavior. The Disability Rating Scale (DRS) was used to assess possible change in their condition. First, while admitted, which was performed in retrospect, and again 6 years later at the time stated. Inter-rater reliability for the scale items showed adequate correlation. Results showed no significant difference in patients' scores, indicating persistent functional difficulties. We conclude that this "regressive syndrome" presents an unusual form of behavior that is stable over time. It seems to be in line with other NPS disorders, and may stem from an interaction of organic factors and primary mental complexity. Nevertheless, further research is required to examine the factors affecting the emergence and recovery from this phenomenon.

The persistent influence of concussive injuries on cognitive control and neuroelectric function

CONTEXT

Increasing attention is being paid to the deleterious effects of sport-related concussion on cognitive and brain health.

OBJECTIVE

To evaluate the influence of concussion incurred during early life on the cognitive control and neuroelectric function of young adults.

DESIGN

Cross-sectional study.

SETTING

Research laboratory.

PATIENTS OR OTHER PARTICIPANTS

Forty young adults were separated into groups according to concussive history (0 or 1+). Participants incurred all injuries during sport and recreation before the age of 18 years and were an average of 7.1 ± 4.0 years from injury at the time of the study.

INTERVENTION(S)

All participants completed a 3-stimulus oddball task, a numeric switch task, and a modified flanker task during which event-related potentials and behavioral measures were collected.

MAIN OUTCOME MEASURE(S)

Reaction time, response accuracy, and electroencephalographic activity.

RESULTS

Compared with control participants, the concussion group exhibited decreased P3 amplitude during target detection within the oddball task and during the heterogeneous condition of the switch task. The concussion group also displayed increased N2 amplitude during the heterogeneous version of the switch task. Concussion history was associated with response accuracy during the flanker task.

CONCLUSIONS

People with a history of concussion may demonstrate persistent decrements in neurocognitive function, as evidenced by decreased response accuracy, deficits in the allocation of attentional resources, and increased stimulus-response conflict during tasks requiring variable amounts of cognitive control. Neuroelectric measures of cognitive control may be uniquely sensitive to the persistent and selective decrements of concussion.

Role of calpains in the injury-induced dysfunction and degeneration of the mammalian axon

Axonal injury and degeneration, whether primary or secondary, contribute to the morbidity and mortality seen in many acquired and inherited central nervous system (CNS) and peripheral nervous system (PNS) disorders, such as traumatic brain injury, spinal cord injury, cerebral ischemia, neurodegenerative diseases, and peripheral neuropathies. The calpain family of proteases has been mechanistically linked to the dysfunction and degeneration of axons. While the direct mechanisms by which transection, mechanical strain, ischemia, or complement activation trigger intra-axonal calpain activity are likely different, the downstream effects of unregulated calpain activity may be similar in seemingly disparate diseases. In this review, a brief examination of axonal structure is followed by a focused overview of the calpain family. Finally, the mechanisms by which calpains may disrupt the axonal cytoskeleton, transport, and specialized domains (axon initial segment, nodes, and terminals) are discussed.

A prospective study of gray matter abnormalities in mild traumatic brain injury

OBJECTIVE

To examine the underlying pathophysiology of mild traumatic brain injury through changes in gray matter diffusion and atrophy during the semiacute stage.

METHODS

Fifty patients and 50 sex-, age-, and education-matched controls were evaluated with a clinical and neuroimaging battery approximately 14 days postinjury, with 26 patients returning for follow-up 4 months postinjury. Clinical measures included tests of attention, processing speed, executive function, working memory, memory, and self-reported postconcussive symptoms. Measures of diffusion (fractional anisotropy [FA], mean diffusivity) and atrophy were obtained for cortical and subcortical structures to characterize effects of injury as a function of time.

RESULTS

Patients reported more cognitive, somatic, and emotional complaints during the semiacute injury phase, which were significantly reduced 4 months postinjury. Patients showed evidence of increased FA in the bilateral superior frontal cortex during the semiacute phase, with the left superior frontal cortex remaining elevated 4 months postinjury. There were no significant differences between patients and matched controls on neuropsychological testing or measures of gray matter atrophy/mean diffusivity at either time point.

CONCLUSIONS

Increased cortical FA is largely consistent with an emerging animal literature of gray matter abnormalities after neuronal injury. Potential mechanistic explanations for increased FA include cytotoxic edema or reactive gliosis. In contrast, there was no evidence of cortical or subcortical atrophy in the current study, suggesting that frank neuronal or neuropil loss does not occur early in the chronic disease course for patients with typical mild traumatic brain injury.

Traumatic brain injury and chronic traumatic encephalopathy: a forensic neuropsychiatric perspective

Recent scientific reports and popular press describing chronic traumatic encephalopathy (CTE) collectively link this condition to a broad array of neuropsychiatric symptoms, including extremely rare and multi-determined behaviors such as murder-suicide. These reports are difficult to reconcile with several decades of research on the science of traumatic brain injury (TBI) and its consequences, especially the natural history and prognosis of mild TBI. This article attempts to reconcile these sources by reviewing the state of the science on CTE, with particular attention to case definitions and neuropathological criteria for this diagnosis. The evidence for links between TBI, CTE, and catastrophic clinical events is explored, and the complexity of attributing rare frequency behavioral events to CTE is highlighted. The clinical and medicolegal implications of the best available evidence are discussed, concluding with a cautionary note against prematurely generalizing current findings on CTE to entire populations of persons with, or at risk for, concussion exposures.

Effect of alcohol on diffuse axonal injury in rat brainstem: diffusion tensor imaging and aquaporin-4 expression study

The aim of this study is to assess the effects of alcohol on traumatic brain injury by using diffusion tensor imaging (DTI) and evaluate aquaporin-4(AQP4) expression changes in rat brainstems following acute alcohol intoxication with diffuse axonal injury (DAI). We further investigated the correlation between the AQP4 expression and DTI in the brain edema. Eighty-five rats were imaged before and after injury at various stages. DTI was used to measure brainstem apparent diffusion coefficient (ADC) and fractional anisotropy (FA), with immunostaining being used to determine AQP4 expression. After acute alcoholism with DAI, ADC values of the brainstem first decreased within 6 h and then elevated. FA values began to decline by 1 h, reaching a minimum at 24 h after trauma. There was a negative correlation between ADC values and brainstem AQP4 expression at 6 h and positive correlation at 6 h to 24 h. Changes of ADC and FA values in DAI with acute alcoholism indicate the effects of ethanol on brain edema and the severity of axonal injury. The correlations between ADC values and the brainstem AQP4 expression at different time points suggest that AQP4 expression follows an adaptative profile to the severity of brain edema.

Moderate-severe traumatic brain injury causes delayed loss of white matter integrity: evidence of fornix deterioration in the chronic stage of injury

OBJECTIVES

To examine structural integrity loss in the fornix from 5-30 months after moderate and severe traumatic brain injury (TBI) using diffusion tensor imaging.

METHODS

MRIs were prospectively undertaken in 29 adults with moderate and severe TBI at two time points. Fractional anisotropy (FA) was calculated for the fornix (column/body, right crux and left crux) at 5 and 30 months post-injury.

RESULTS

Paired t-tests revealed significant FA reductions with large effect sizes across time in the column/body, p < 0.001, right crux, p < 0.001 and left crux, p < 0.001.

CONCLUSIONS

These data contribute to the growing body of evidence that loss of white matter continues in moderate and severe TBI even after the acute neurological effects of TBI have resolved. As the fornix plays a critical role in memory, this may be a contributing factor to the poor clinical outcomes observed in these patients.

Thalamic atrophy in antero-medial and dorsal nuclei correlates with six-month outcome after severe brain injury

The primary and secondary damage to neural tissue inflicted by traumatic brain injury is a leading cause of death and disability. The secondary processes, in particular, are of great clinical interest because of their potential susceptibility to intervention. We address the dynamics of tissue degeneration in cortico-subcortical circuits after severe brain injury by assessing volume change in individual thalamic nuclei over the first six-months post-injury in a sample of 25 moderate to severe traumatic brain injury patients. Using tensor-based morphometry, we observed significant localized thalamic atrophy over the six-month period in antero-dorsal limbic nuclei as well as in medio-dorsal association nuclei. Importantly, the degree of atrophy in these nuclei was predictive, even after controlling for full-brain volume change, of behavioral outcome at six-months post-injury. Furthermore, employing a data-driven decision tree model, we found that physiological measures, namely the extent of atrophy in the anterior thalamic nucleus, were the most predictive variables of whether patients had regained consciousness by six-months, followed by behavioral measures. Overall, these findings suggest that the secondary non-mechanical degenerative processes triggered by severe brain injury are still ongoing after the first week post-trauma and target specifically antero-medial and dorsal thalamic nuclei. This result therefore offers a potential window of intervention, and a specific target region, in agreement with the view that specific cortico-thalamo-cortical circuits are crucial to the maintenance of large-scale network neural activity and thereby the restoration of cognitive function after severe brain injury.

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Performed acute and chronic structural MRI in 25 severe TBI patients

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Tensor brain morphometry (TBM) shows localized thalamic acute-to-chronic atrophy.

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Anterior, medio- and lateral-dorsal nuclei are the most significant.

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Atrophy in these nuclei predicts 6-month outcome scores (GOSe).

Axonal pathology in traumatic brain injury

Over the past 70years, diffuse axonal injury (DAI) has emerged as one of the most common and important pathological features of traumatic brain injury (TBI). Axons in the white matter appear to be especially vulnerable to injury due to the mechanical loading of the brain during TBI. As such, DAI has been found in all severities of TBI and may represent a key pathologic substrate of mild TBI (concussion). Pathologically, DAI encompasses a spectrum of abnormalities from primary mechanical breaking of the axonal cytoskeleton, to transport interruption, swelling and proteolysis, through secondary physiological changes. Depending on the severity and extent of injury, these changes can manifest acutely as immediate loss of consciousness or confusion and persist as coma and/or cognitive dysfunction. In addition, recent evidence suggests that TBI may induce long-term neurodegenerative processes, such as insidiously progressive axonal pathology. Indeed, axonal degeneration has been found to continue even years after injury in humans, and appears to play a role in the development of Alzheimer's disease-like pathological changes. Here we review the current understanding of DAI as a uniquely mechanical injury, its histopathological identification, and its acute and chronic pathogenesis following TBI.

Cortical endogenic neural regeneration of adult rat after traumatic brain injury

Focal and diffuse neuronal loss happened after traumatic brain injury (TBI). With little in the way of effective repair, recent interest has focused on endogenic neural progenitor cells (NPCs) as a potential method for regeneration. Whether endogenic neural regeneration happened in the cortex of adult rat after TBI remains to be determined. In this study, rats were divided into a sham group and a TBI group, and the rat model of medium TBI was induced by controlled cortical impact. Rats were injected with BrdU at 1 to 7 days post-injury (dpi) to allow identification of differentiated cells and sacrificed at 1, 3, 7, 14 and 28 dpi for immunofluorescence. Results showed nestin(+)/sox-2(+) NPCs and GFAP(+)/sox-2(+) radial glial (RG)-like cells emerged in peri-injured cortex at 1, 3, 7, 14 dpi and peaked at 3 dpi. The number of GFAP(+)/sox-2(+) cells was less than that of nestin(+)/sox-2(+) cells. Nestin(+)/sox-2(+) cells from posterior periventricle (pPV) immigrated into peri-injured cortex through corpus callosum (CC) were found. DCX(+)/BrdU(+) newborn immature neurons in peri-injured cortex were found only at 3, 7, 14 dpi. A few MAP-2(+)/BrdU(+) newborn neurons in peri-injured cortex were found only at 7 and 14 dpi. NeuN(+)/BrdU(+) mature neurons were not found in peri-injured cortex at 1, 3, 7, 14 and 28 dpi. While GFAP(+)/BrdU(+) astrocytes emerged in peri-injured cortex at 1, 3, 7, 14, 28 dpi and peaked at 7 dpi then kept in a stable state. In the corresponding time point, the percentage of GFAP(+)/BrdU(+) astrocytes in BrdU(+) cells was more than that of NPCs or newborn neurons. No CNP(+)/BrdU(+) oligodendrocytes were found in peri-injured cortex. These findings suggest that NPCs from pPV and reactive RG-like cells emerge in peri-injured cortex of adult rats after TBI. It can differentiate into immature neurons and astrocytes, but the former fail to grow up to mature neurons.

Disconnection of the ascending arousal system in traumatic coma

Traumatic coma is associated with disruption of axonal pathways throughout the brain, but the specific pathways involved in humans are incompletely understood. In this study, we used high angular resolution diffusion imaging to map the connectivity of axonal pathways that mediate the 2 critical components of consciousness-arousal and awareness-in the postmortem brain of a 62-year-old woman with acute traumatic coma and in 2 control brains. High angular resolution diffusion imaging tractography guided tissue sampling in the neuropathologic analysis. High angular resolution diffusion imaging tractography demonstrated complete disruption of white matter pathways connecting brainstem arousal nuclei to the basal forebrain and thalamic intralaminar and reticular nuclei. In contrast, hemispheric arousal pathways connecting the thalamus and basal forebrain to the cerebral cortex were only partially disrupted, as were the cortical "awareness pathways." Neuropathologic examination, which used β-amyloid precursor protein and fractin immunomarkers, revealed axonal injury in the white matter of the brainstem and cerebral hemispheres that corresponded to sites of high angular resolution diffusion imaging tract disruption. Axonal injury was also present within the gray matter of the hypothalamus, thalamus, basal forebrain, and cerebral cortex. We propose that traumatic coma may be a subcortical disconnection syndrome related to the disconnection of specific brainstem arousal nuclei from the thalamus and basal forebrain.

Mild traumatic brain injury in the mouse induces axotomy primarily within the axon initial segment

Traumatic axonal injury (TAI) is a consistent component of traumatic brain injury (TBI), and is associated with much of its morbidity. Increasingly, it has also been recognized as a major pathology of mild TBI (mTBI). In terms of its pathogenesis, numerous studies have investigated the susceptibility of the nodes of Ranvier, the paranode and internodal regions to TAI. The nodes of Ranvier, with their unique composition and concentration of ion channels, have been suggested as the primary site of injury, initiating a cascade of abnormalities in the related paranodal and internodal domains that lead to local axonal swellings and detachment. No investigation, however, has determined the effect of TAI upon the axon initial segment (AIS), a segment critical to regulating polarity and excitability. The current study sought to identify the susceptibility of these different axon domains to TAI within the neocortex, where each axonal domain could be simultaneously assessed. Utilizing a mouse model of mTBI, a temporal and spatial heterogeneity of axonal injury was found within the neocortical gray matter. Although axonal swellings were found in all domains along myelinated neocortical axons, the majority of TAI occurred within the AIS, which progressed without overt structural disruption of the AIS itself. The finding of primary AIS involvement has important implications regarding neuronal polarity and the fate of axotomized processes, while also raising therapeutic implications, as the mechanisms underlying such axonal injury in the AIS may be distinct from those described for nodal/paranodal injury.

Soccer heading is associated with white matter microstructural and cognitive abnormalities

PURPOSE

To investigate the association of soccer heading with subclinical evidence of traumatic brain injury.

MATERIALS AND METHODS

With institutional review board approval and compliance with HIPAA guidelines, 37 amateur soccer players (mean age, 30.9 years; 78% [29] men, 22% [eight] women) gave written informed consent and completed a questionnaire to quantify heading in the prior 12 months and lifetime concussions. Diffusion-tensor magnetic resonance (MR) imaging at 3.0 T was performed (32 directions; b value, 800 sec/mm(2); 2 × 2 × 2-mm voxels). Cognitive function was measured by using a computerized battery of tests. Voxelwise linear regression (heading vs fractional anisotropy [FA]) was applied to identify significant regional associations. FA at each location and cognition were tested for a nonlinear relationship to heading by using an inverse logit model that incorporated demographic covariates and history of concussion.

RESULTS

Participants had headed 32-5400 times (median, 432 times) over the previous year. Heading was associated with lower FA at three locations in temporo-occipital white matter with a threshold that varied according to location (885-1550 headings per year) (P < .00001). Lower levels of FA were also associated with poorer memory scores (P < .00001), with a threshold of 1800 headings per year. Lifetime concussion history and demographic features were not significantly associated with either FA or cognitive performance.

CONCLUSION

Heading is associated with abnormal white matter microstructure and with poorer neurocognitive performance. This relationship is not explained by a history of concussion.

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.

Traumatic brain injury impairs small-world topology

OBJECTIVE

We test the hypothesis that brain networks associated with cognitive function shift away from a "small-world" organization following traumatic brain injury (TBI).

METHODS

We investigated 20 TBI patients and 21 age-matched controls. Resting-state functional MRI was used to study functional connectivity. Graph theoretical analysis was then applied to partial correlation matrices derived from these data. The presence of white matter damage was quantified using diffusion tensor imaging.

RESULTS

Patients showed characteristic cognitive impairments as well as evidence of damage to white matter tracts. Compared to controls, the graph analysis showed reduced overall connectivity, longer average path lengths, and reduced network efficiency. A particular impact of TBI is seen on a major network hub, the posterior cingulate cortex. Taken together, these results confirm that a network critical to cognitive function shows a shift away from small-world characteristics.

CONCLUSIONS

We provide evidence that key brain networks involved in supporting cognitive function become less small-world in their organization after TBI. This is likely to be the result of diffuse white matter damage, and may be an important factor in producing cognitive impairment after TBI.

Traumatic axonal injury in the mouse is accompanied by a dynamic inflammatory response, astroglial reactivity and complex behavioral changes

BACKGROUND

Diffuse traumatic axonal injury (TAI), a common consequence of traumatic brain injury, is associated with high morbidity and mortality. Inflammatory processes may play an important role in the pathophysiology of TAI. In the central fluid percussion injury (cFPI) TAI model in mice, the neuroinflammatory and astroglial response and behavioral changes are unknown.

METHODS

Twenty cFPI-injured and nine sham-injured mice were used, and the neuroinflammatory and astroglial response was evaluated by immunohistochemistry at 1, 3 and 7 days post-injury. The multivariate concentric square field test (MCSF) was used to compare complex behavioral changes in mice subjected to cFPI (n = 16) or sham injury (n = 10). Data was analyzed using non-parametric statistics and principal component analysis (MCSF data).

RESULTS

At all post-injury time points, β-amyloid precursor protein (β-APP) immunoreactivity revealed widespread bilateral axonal injury and IgG immunostaining showed increased blood-brain barrier permeability. Using vimentin and glial fibrillary acidic protein (GFAP) immunohistochemistry, glial cell reactivity was observed in cortical regions and important white matter tracts peaking at three days post-injury. Only vimentin was increased post-injury in the internal capsule and only GFAP in the thalamus. Compared to sham-injured controls, an increased number of activated microglia (MAC-2), infiltrating neutrophils (GR-1) and T-cells (CD3) appearing one day after TAI (P<0.05 for all cell types) was observed in subcortical white matter. In the MCSF, the behavioral patterns including general activity and exploratory behavior differed between cFPI mice and sham-injured controls.

CONCLUSIONS

Traumatic axonal injury TAI resulted in marked bilateral astroglial and neuroinflammatory responses and complex behavioral changes. The cFPI model in mice appears suitable for the study of injury mechanisms, including neuroinflammation, and the development of treatments targeting TAI.

Randomized controlled trials in adult traumatic brain injury

BACKGROUND

To optimize strategies for achieving the effectiveness of interdisciplinary interventions, this study conducted a comprehensive literature review of all Randomized Controlled Trials (RCT) in adults with traumatic brain injury (TBI) over the past 30 years.

METHOD

Three major databases including Medline, PsycINFO and CINAHL were searched, yielding 1176 peer reviewed publications. One hundred RCTs were included, encompassing 55 pharmacologic and non-pharmacologic acute phase trials and 45 rehabilitation and pharmacologic post-acute trials.

RESULTS

The majority of acute phase pharmacologic or non-pharmacologic trials (40/55) showed either no effect or adverse effect on TBI outcomes. Several trials involving early nutritional therapy or pre-hospital rapid intubation demonstrated significant treatment effects. The effect of decompressive craniectomy, therapeutic hypothermia and osmotic therapy remained controversial. The majority of post-acute phase trials (36/45), consisting of cognitive rehabilitation, physical rehabilitation and pharmacotherapy, produced various beneficial treatment effects.

CONCLUSION

The data indicate that several active interventions during the acute phase of TBI are likely to be more effective than pharmacotherapy, whereas a comprehensive rehabilitation approach is preferred in post-acute phase TBI management. Great progress has been made in understanding the heterogeneous injury mechanisms as well as the complexity of medical management and rehabilitation following the recovery course of TBI.

White matter integrity following traumatic brain injury: the association with severity of injury and cognitive functioning

Traumatic brain injury (TBI) frequently results in impairments of memory, speed of information processing, and executive functions that may persist over many years. Diffuse axonal injury is one of the key pathologies following TBI, causing cognitive impairments due to the disruption of cortical white matter pathways. The current study examined the association between injury severity, cognition, and fractional anisotropy (FA) following TBI. Two diffusion tensor imaging techniques-region-of-interest tractography and tract-based spatial statistics-were used to assess the FA of white matter tracts. This study examined the comparability of these two approaches as they relate to injury severity and cognitive performance. Sixty-eight participants with mild-to-severe TBI, and 25 healthy controls, underwent diffusion tensor imaging analysis. A subsample of 36 individuals with TBI also completed cognitive assessment. Results showed reduction in FA values for those with moderate and severe TBI, compared to controls and individuals with mild TBI. Although FA tended to be lower for individuals with mild TBI no significant differences were found compared to controls. Information processing speed and executive abilities were most strongly associated with the FA of white matter tracts. The results highlight similarities and differences between region-of-interest tractography and tract-based spatial statistics approaches, and suggest that they may be used together to explore pathology following TBI.

Consequences of repeated blood-brain barrier disruption in football players

The acknowledgement of risks for traumatic brain injury in American football players has prompted studies for sideline concussion diagnosis and testing for neurological deficits. While concussions are recognized etiological factors for a spectrum of neurological sequelae, the consequences of sub-concussive events are unclear. We tested the hypothesis that blood-brain barrier disruption (BBBD) and the accompanying surge of the astrocytic protein S100B in blood may cause an immune response associated with production of auto-antibodies. We also wished to determine whether these events result in disrupted white matter on diffusion tensor imaging (DT) scans. Players from three college football teams were enrolled (total of 67 volunteers). None of the players experienced a concussion. Blood samples were collected before and after games (n = 57); the number of head hits in all players was monitored by movie review and post-game interviews. S100B serum levels and auto-antibodies against S100B were measured and correlated by direct and reverse immunoassays (n = 15 players; 5 games). A subset of players underwent DTI scans pre- and post-season and after a 6-month interval (n = 10). Cognitive and functional assessments were also performed. After a game, transient BBB damage measured by serum S100B was detected only in players experiencing the greatest number of sub-concussive head hits. Elevated levels of auto-antibodies against S100B were elevated only after repeated sub-concussive events characterized by BBBD. Serum levels of S100B auto-antibodies also predicted persistence of MRI-DTI abnormalities which in turn correlated with cognitive changes. Even in the absence of concussion, football players may experience repeated BBBD and serum surges of the potential auto-antigen S100B. The correlation of serum S100B, auto-antibodies and DTI changes support a link between repeated BBBD and future risk for cognitive changes.

Functional MRI in the investigation of blast-related traumatic brain injury

This review focuses on the application of functional magnetic resonance imaging (fMRI) to the investigation of blast-related traumatic brain injury (bTBI). Relatively little is known about the exact mechanisms of neurophysiological injury and pathological and functional sequelae of bTBI. Furthermore, in mild bTBI, standard anatomical imaging techniques (MRI and computed tomography) generally fail to show focal lesions and most of the symptoms present as subjective clinical functional deficits. Therefore, an objective test of brain functionality has great potential to aid in patient diagnosis and provide a sensitive measurement to monitor disease progression and treatment. The goal of this review is to highlight the relevant body of blast-related TBI literature and present suggestions and considerations in the development of fMRI studies for the investigation of bTBI. The review begins with a summary of recent bTBI publications followed by discussions of various elements of blast-related injury. Brief reviews of some fMRI techniques that focus on mental processes commonly disrupted by bTBI, including working memory, selective attention, and emotional processing, are presented in addition to a short review of resting state fMRI. Potential strengths and weaknesses of these approaches as regards bTBI are discussed. Finally, this review presents considerations that must be made when designing fMRI studies for bTBI populations, given the heterogeneous nature of bTBI and its high rate of comorbidity with other physical and psychological injuries.

Therapy development for diffuse axonal injury

Diffuse axonal injury (DAI) remains a prominent feature of human traumatic brain injury (TBI) and a major player in its subsequent morbidity. The importance of this widespread axonal damage has been confirmed by multiple approaches including routine postmortem neuropathology as well as advanced imaging, which is now capable of detecting the signatures of traumatically induced axonal injury across a spectrum of traumatically brain-injured persons. Despite the increased interest in DAI and its overall implications for brain-injured patients, many questions remain about this component of TBI and its potential therapeutic targeting. To address these deficiencies and to identify future directions needed to fill critical gaps in our understanding of this component of TBI, the National Institute of Neurological Disorders and Stroke hosted a workshop in May 2011. This workshop sought to determine what is known regarding the pathogenesis of DAI in animal models of injury as well as in the human clinical setting. The workshop also addressed new tools to aid in the identification of this axonal injury while also identifying more rational therapeutic targets linked to DAI for continued preclinical investigation and, ultimately, clinical translation. This report encapsulates the oral and written components of this workshop addressing key features regarding the pathobiology of DAI, the biomechanics implicated in its initiating pathology, and those experimental animal modeling considerations that bear relevance to the biomechanical features of human TBI. Parallel considerations of alternate forms of DAI detection including, but not limited to, advanced neuroimaging, electrophysiological, biomarker, and neurobehavioral evaluations are included, together with recommendations for how these technologies can be better used and integrated for a more comprehensive appreciation of the pathobiology of DAI and its overall structural and functional implications. Lastly, the document closes with a thorough review of the targets linked to the pathogenesis of DAI, while also presenting a detailed report of those target-based therapies that have been used, to date, with a consideration of their overall implications for future preclinical discovery and subsequent translation to the clinic. Although all participants realize that various research gaps remained in our understanding and treatment of this complex component of TBI, this workshop refines these issues providing, for the first time, a comprehensive appreciation of what has been done and what critical needs remain unfulfilled.

Diffusion abnormalities in pediatric mild traumatic brain injury

Pediatric mild traumatic brain injury (pmTBI) is the most prevalent neurological insult in children and is associated with both acute and chronic neurobehavioral sequelae. However, little is known about underlying pathophysiology and how injuries change as a function of recovery. Fractional anisotropy, axial diffusivity, and radial diffusivity were examined in 15 semi-acute pmTBI patients and 15 well-matched controls, with a subset of participants returning for a second visit. A novel analytic strategy was applied to capture spatially heterogeneous white matter injuries (lesions) in addition to standard analyses. Evidence of cognitive dysfunction after pmTBI was observed in the domains of attention (p = 0.02, d = -0.92) and processing speed (p = 0.05, d = -0.73) semi-acutely. Region of interest (ROI) and voxelwise analyses indicated increased anisotropic diffusion for pmTBI patients, with an elevated number of clusters with high anisotropy. Metrics of increased anisotropy were able to objectively classify pmTBI from healthy controls at 90% accuracy but were not associated with neuropsychological deficits. Little evidence of recovery in white matter abnormalities was observed over a 4-month interval in returning patients, indicating that physiological recovery may lag behind subjective reports of normality. Increased anisotropic diffusion has been previously linked with cytotoxic edema after TBI, and the magnitude and duration of these abnormalities appear to be greater in pediatric patients. Current findings suggest that developing white matter may be more susceptible to initial mechanical injury forces and that anisotropic diffusion provides an objective biomarker of pmTBI.

Methodological considerations in longitudinal morphometry of traumatic brain injury

Traumatic brain injury (TBI) has recently been reconceptualized as a chronic, evolving disease process. This new view necessitates quantitative assessment of post-injury changes in brain structure that may allow more accurate monitoring and prediction of recovery. In particular, TBI is known to trigger neurodegenerative processes and therefore quantifying progression of diffuse atrophy over time is currently of utmost interest. However, there are various methodological issues inherent to longitudinal morphometry in TBI. In this paper, we first overview several of these methodological challenges: lesion evolution, neurosurgical procedures, power, bias, and non-linearity. We then introduce a sensitive, reliable, and unbiased longitudinal multivariate analysis protocol that combines dimensionality reduction and region of interest approaches. This analysis pipeline is demonstrated using a small dataset consisting of four chronic TBI survivors.

Left temporopolar impairment in a case of posttraumatic hypersomnia

OBJECTIVE

We report a focal morphofunctional brain impairment within the left temporopolar cortex in a patient with a posttraumatic hypersomnia. This case may contribute to better understanding the possible pathophysiological mechanism for posttraumatic hypersomnia.

MRI evidence for altered venous drainage and intracranial compliance in mild traumatic brain injury

Purpose

To compare venous drainage patterns and associated intracranial hydrodynamics between subjects who experienced mild traumatic brain injury (mTBI) and age- and gender-matched controls.

Methods

Thirty adult subjects (15 with mTBI and 15 age- and gender-matched controls) were investigated using a 3T MR scanner. Time since trauma was 0.5 to 29 years (mean 11.4 years). A 2D-time-of-flight MR-venography of the upper neck was performed to visualize the cervical venous vasculature. Cerebral venous drainage through primary and secondary channels, and intracranial compliance index and pressure were derived using cine-phase contrast imaging of the cerebral arterial inflow, venous outflow, and the craniospinal CSF flow. The intracranial compliance index is the defined as the ratio of maximal intracranial volume and pressure changes during the cardiac cycle. MR estimated ICP was then obtained through the inverse relationship between compliance and ICP.

Results

Compared to the controls, subjects with mTBI demonstrated a significantly smaller percentage of venous outflow through internal jugular veins (60.9±21% vs. controls: 76.8±10%; p = 0.01) compensated by an increased drainage through secondary veins (12.3±10.9% vs. 5.5±3.3%; p<0.03). Mean intracranial compliance index was significantly lower in the mTBI cohort (5.8±1.4 vs. controls 8.4±1.9; p<0.0007). Consequently, MR estimate of intracranial pressure was significantly higher in the mTBI cohort (12.5±2.9 mmHg vs. 8.8±2.0 mmHg; p<0.0007).

Conclusions

mTBI is associated with increased venous drainage through secondary pathways. This reflects higher outflow impedance, which may explain the finding of reduced intracranial compliance. These results suggest that hemodynamic and hydrodynamic changes following mTBI persist even in the absence of clinical symptoms and abnormal findings in conventional MR imaging.

The use of stimulant medication to treat neurocognitive deficits in patients with pediatric cancer, traumatic brain injury, and sickle cell disease: a review

Several chronic health conditions of childhood, including pediatric cancers, traumatic brain injury (TBI), and sickle cell disease (SCD) are associated with significant neurocognitive impairments that can compromise educational attainment and future vocational opportunities. The prominence of attentional deficits as part of the neurocognitive sequelae associated with each of these conditions has led some researchers to draw parallels with another chronic condition that manifests in childhood, specifically the inattentive subtype of attention-deficit/hyperactivity disorder (ADHD). Because ADHD shares similar neurocognitive and symptomatological features with pediatric cancer, TBI, and SCD, stimulant medications may be indicated to treat associated deficits in each condition. However, relatively few studies have investigated the safety and effectiveness of stimulant medications in treating neurocognitive sequelae in children with cancer, TBI, or SCD. Thus, clinicians have received little guidance regarding a potentially useful treatment modality for ameliorating the neurocognitive deficits that can profoundly impact the educational, psychosocial, and vocational development of youth with these chronic health conditions. We provide a review of the literature and synthesize current developments in research regarding treatment with stimulant medication for children with cancer, TBI, and SCD, as well as discuss special considerations for each condition.

Quantitative brain electrical activity in the initial screening of mild traumatic brain injuries

Introduction:

The incidence of emergency department (ED) visits for Traumatic Brain Injury (TBI) in the United States exceeds 1,000,000 cases/year with the vast majority classified as mild (mTBI). Using existing computed tomography (CT) decision rules for selecting patients to be referred for CT, such as the New Orleans Criteria (NOC), approximately 70% of those scanned are found to have a negative CT. This study investigates the use of quantified brain electrical activity to assess its possible role in the initial screening of ED mTBI patients as compared to NOC.

Methods:

We studied 119 patients who reported to the ED with mTBI and received a CT. Using a hand-held electroencephalogram (EEG) acquisition device, we collected data from frontal leads to determine the likelihood of a positive CT. The brain electrical activity was processed off-line to generate an index (TBI-Index, biomarker). This index was previously derived using an independent population, and the value found to be sensitive for significant brain dysfunction in TBI patients. We compared this performance of the TBI-Index to the NOC for accuracy in prediction of positive CT findings.

Results:

Both the brain electrical activity TBI-Index and the NOC had sensitivities, at 94.7% and 92.1% respectively. The specificity of the TBI-Index was more than twice that of NOC, 49.4% and 23.5% respectively. The positive predictive value, negative predictive value and the positive likelihood ratio were better with the TBI-Index. When either the TBI-Index or the NOC are positive (combining both indices) the sensitivity to detect a positive CT increases to 97%.

Conclusion:

The hand-held EEG device with a limited frontal montage is applicable to the ED environment and its performance was superior to that obtained using the New Orleans criteria. This study suggests a possible role for an index of brain function based on EEG to aid in the acute assessment of mTBI patients.

The effect of pediatric traumatic brain injury on behavioral outcomes: a systematic review

AIM

To review systematically the empirical evidence on traumatic brain injury (TBI) during childhood and subsequent behavioral problems.

METHOD

An initial literature search with keywords 'brain injury,''children,' and 'behavior' was conducted using Web of Knowledge and PubMed databases. Ancestry was also used. Original research studies published between 1990 and February 2012 focusing on behavioral outcomes of children sustaining TBI from ages 0 to 18 years were included.

RESULTS

Fifty studies, varying considerably in methodologies, were included in the review. Findings showed that up to 50% of brain-injured children are at risk for presenting with specific behavioral problems and disorders. These problems may emerge shortly or several years after injury and often persist and even worsen with time. These behavioral impairments appear to be moderated by the family environment.

INTERPRETATION

Survivors of childhood TBI are at risk for developing and sustaining behavioral impairments. Stronger research is needed to identify cognitive and environmental factors that contribute to the onset and maintenance of these problems. Healthcare providers should ensure adequate follow-up and assessment of a child's behavioral, social, and neurocognitive domains. Caregivers should be encouraged to provide positive environments and parenting styles, which may help reduce chronic behavioral problems after brain injury.

Inflammatory response following diffuse axonal injury

DAI is a leading cause of the patient's death or lasting vegetable state following severe TBI, and up to now the detailed mechanism of axonal injury after head trauma is still unclear. Inflammatory responses have been proved to be an important mechanism of neural injury after TBI. However, most of these studies are concerned with focal cerebral injury following head trauma. In contrast to focal injury, studies on the inflammatory reaction following DAI are only beginning. And in this article, we aimed to review such studies. From the studies reviewed, immune response cells would become reactive around the sites of axonal injury after DAI. Besides, the concentrations of several important inflammatory factors, such as IL-1 family, IL-6 and TNF-ɑ, increased after DAI as well, which implies the participation of inflammatory responses. It can be concluded that inflammatory responses probably participate in the neural injury in DAI, but at present the study of inflammatory responses following DAI is still limited and the clear effects of inflammatory response on axonal injury remain to be more explored.

Quantified MRI and cognition in TBI with diffuse and focal damage☆

In patients with chronic-phase traumatic brain injury (TBI), structural MRI is readily attainable and provides rich anatomical information, yet the relationship between whole-brain structural MRI measures and neurocognitive outcome is relatively unexplored and can be complicated by the presence of combined focal and diffuse injury. In this study, sixty-three patients spanning the full range of TBI severity received high-resolution structural MRI concurrent with neuropsychological testing. Multivariate statistical analysis assessed covariance patterns between volumes of grey matter, white matter, and sulcal/subdural and ventricular CSF across 38 brain regions and neuropsychological test performance. Patients with diffuse and diffuse + focal injury were analyzed both separately and together. Tests of speeded attention, working memory, and verbal learning and memory robustly covaried with a distributed pattern of volume loss over temporal, ventromedial prefrontal, right parietal regions, and cingulate regions. This pattern was modulated by the presence of large focal lesions, but held even when analyses were restricted to those with diffuse injury. Effects were most consistently observed within grey matter. Relative to regional brain volumetric data, clinically defined injury severity (depth of coma at time of injury) showed only weak relation to neuropsychological outcome. The results showed that neuropsychological test performance in patients with TBI is related to a distributed pattern of volume loss in regions mediating mnemonic and attentional processing. This relationship holds for patients with and without focal lesions, indicating that diffuse injury alone is sufficient to cause significant neuropsychological disability in relation to regional volume loss. Quantified structural brain imaging data provides a highly sensitive index of brain integrity that is related to cognitive functioning in chronic phase TBI.

Noninvasive brain stimulation in traumatic brain injury

OBJECTIVE

To review novel techniques of noninvasive brain stimulation (NBS), which may have value in assessment and treatment of traumatic brain injury (TBI).

METHODS

Review of the following techniques: transcranial magnetic stimulation, transcranial direct current stimulation, low-level laser therapy, and transcranial Doppler sonography. Furthermore, we provide a brief overview of TMS studies to date.

MAIN FINDINGS

We describe the rationale for the use of these techniques in TBI, discuss their possible mechanisms of action, and raise a number of considerations relevant to translation of these methods to clinical use. Depending on the stimulation parameters, NBS may enable suppression of the acute glutamatergic hyperexcitability following TBI and/or counter the excessive GABAergic effects in the subacute stage. In the chronic stage, brain stimulation coupled to rehabilitation may enhance behavioral recovery, learning of new skills, and cortical plasticity. Correlative animal models and comprehensive safety trials seem critical to establish the use of these modalities in TBI.

CONCLUSIONS

Different forms of NBS techniques harbor the promise of diagnostic and therapeutic utility, particularly to guide processes of cortical reorganization and enable functional restoration in TBI. Future lines of safety research and well-designed clinical trials in TBI are warranted to determine the capability of NBS to promote recovery and minimize disability.

White matter abnormalities in veterans with mild traumatic brain injury

OBJECTIVE

It has been estimated that 10%-20% of U.S. veterans of the wars in Iraq and Afghanistan experienced mild traumatic brain injury (TBI), mostly secondary to blast exposure. Diffusion tensor imaging (DTI) may detect subtle white matter changes in both the acute and chronic stages of mild TBI and thus has the potential to detect white matter damage in patients with TBI. The authors used DTI to examine white matter integrity in a relatively large group of veterans with a history of mild TBI.

METHOD

DTI images from 72 veterans of the wars in Iraq and Afghanistan who had mild TBI were compared with DTI images from 21 veterans with no exposure to TBI during deployment. Conventional voxel-based analysis as well as a method of identifying spatially heterogeneous areas of decreased fractional anisotropy ("potholes") were used. Veterans also underwent psychiatric and neuropsychological assessments.

RESULTS

Voxel-based analysis did not reveal differences in DTI parameters between the veterans with mild TBI and those with no TBI. However, the veterans with mild TBI had a significantly higher number of potholes than those without TBI. The difference in the number of potholes was not influenced by age, time since trauma, a history of mild TBI unrelated to deployment, or coexisting psychopathology. The number of potholes was correlated with the severity of TBI and with performance in executive functioning tasks.

CONCLUSIONS

Veterans who had blast-related mild TBI showed evidence of multifocal white matter abnormalities that were associated with severity of the injury and with relevant functional measures. Overall, white matter potholes may constitute a sensitive biomarker of axonal injury that can be identified in mild TBI at acute and chronic stages of its clinical course.

Chronic stress, somatic and depressive symptoms following mild to moderate traumatic brain injury

Despite advances in research on symptoms, stress, and depression after traumatic brain injury, there has been limited focus on the collective relationships between neurocognitive performance, chronic stress, and somatic and depressive symptoms. Guided by our adaptation of the allostatic load theory, we examined relationships between chronic stress, somatic and depressive symptoms, and cognitive performance using the Immediate Postconcussion Assessment and Cognitive Testing cognitive battery. Only somatic symptoms and chronic stress explained variation in depressive symptoms (R(2) = .71, P < .0001), not neurocognitive performance, preinjury, or injury-specific variables. Our findings suggest that increased chronic stress and somatic symptoms can contribute significantly to depressive symptoms after mild to moderate traumatic brain injury.

Diffusion tensor imaging evidence of white matter disruption associated with loss versus alteration of consciousness in warfighters exposed to combat in Operations Enduring and Iraqi Freedom

The effects on the human brain of mild traumatic brain injury (mTBI), which is defined as a brief alteration (AOC) or loss of consciousness (LOC), are incompletely understood. Major psychiatric illnesses such as major depressive disorder (MDD) and posttraumatic stress disorder (PTSD) are common after mTBI. Prior research suggests that individuals who develop MDD after blast-related mTBI versus those who do not show significant white matter disruption and higher rates of LOC, suggesting that LOC might be uniquely associated with brain changes that increase the risk of developing mental illness after neurotrauma. Therefore, the objective of this study was to examine the effects of LOC, MDD, and PTSD on white matter integrity in individuals who reported experiencing mTBI during combat in Operations Enduring and Iraqi Freedom. We hypothesized that LOC would be associated with significant disruption of white matter, above and beyond putative effects of MDD and PTSD. To test this hypothesis, 46 individuals who experienced blast-related mTBI underwent a detailed clinical assessment and diffusion tensor imaging. As hypothesized, LOC versus AOC individuals displayed significantly lower fractional anisotropy (FA) in 14 regions, which included the superior longitudinal fasciculus and corpus callosum. No regions of significant FA difference were identified between individuals with and without PTSD, or between individuals with and without MDD. These preliminary results show that LOC is associated with detectable alterations in brain microstructure and may suggest a brain basis for psychiatric symptoms and mental illness after mTBI.

Robust detection of traumatic axonal injury in individual mild traumatic brain injury patients: intersubject variation, change over time and bidirectional changes in anisotropy

To identify and characterize otherwise occult inter-individual spatial variation of white matter abnormalities across mild traumatic brain injury (mTBI) patients. After informed consent and in compliance with Health Insurance Portability and Accountability Act (HIPAA), Diffusion tensor imaging (DTI) was performed on a 3.0 T MR scanner in 34 mTBI patients (19 women; 19-64 years old) and 30 healthy control subjects. The patients were imaged within 2 weeks of injury, 3 months after injury, and 6 months after injury. Fractional anisotropy (FA) images were analyzed in each patient. To examine white matter diffusion abnormalities across the entire brain of individual patients, we applied Enhanced Z-score Microstructural Assessment for Pathology (EZ-MAP), a voxelwise analysis optimized for the assessment of individual subjects. Our analysis revealed areas of abnormally low or high FA (voxel-wise P-value < 0.05, cluster-wise P-value < 0.01(corrected for multiple comparisons)). The spatial pattern of white matter FA abnormalities varied among patients. Areas of low FA were consistent with known patterns of traumatic axonal injury. Areas of high FA were most frequently detected in the deep and subcortical white matter of the frontal, parietal, and temporal lobes, and in the anterior portions of the corpus callosum. The number of both abnormally low and high FA voxels changed during follow up. Individual subject assessments reveal unique spatial patterns of white matter abnormalities in each patient, attributable to inter-individual differences in anatomy, vulnerability to injury and mechanism of injury. Implications of high FA remain unclear, but may evidence a compensatory mechanism or plasticity in response to injury, rather than a direct manifestation of brain injury.

Critical role of trkB receptors in reactive axonal sprouting and hyperexcitability after axonal injury

Traumatic brain injury (TBI) causes many long-term neurological complications. Some of these conditions, such as posttraumatic epilepsy, are characterized by increased excitability that typically arises after a latent period lasting from months to years, suggesting that slow injury-induced processes are critical. We tested the hypothesis that trkB activation promotes delayed injury-induced hyperexcitability in part by promoting reactive axonal sprouting. We modeled penetrative TBI with transection of the Schaffer collateral pathway in knock-in mice having an introduced mutation in the trkB receptor (trkB(F616A)) that renders it susceptible to inhibition by the novel small molecule 1NMPP1. We observed that trkB activation was increased in area CA3 1 day after injury and that expression of a marker of axonal growth, GAP43, was increased 7 days after lesion. Extracellular field potentials in stratum pyramidale of area CA3 in acute slices from sham-operated and lesioned mice were normal in control saline. Abnormal bursts of population spikes were observed under conditions that were mildly proconvulsive but only in slices taken from mice lesioned 7-21 days earlier and not in slices from control mice. trkB activation, GAP43 upregulation, and hyperexcitability were diminished by systemic administration of 1NMPP1 for 7 days after the lesion. Synaptic transmission from area CA3 to area CA1 recovered 7 days after lesion in untreated mice but not in mice treated with 1NMPP1. We conclude that trkB receptor activation and reactive axonal sprouting are critical factors in injury-induced hyperexcitability and may contribute to the neurological complications of TBI.

Rit GTPase signaling promotes immature hippocampal neuronal survival

The molecular mechanisms governing the spontaneous recovery seen following brain injury remain elusive, but recent studies indicate that injury-induced stimulation of hippocampal neurogenesis contributes to the repair process. The therapeutic potential of endogenous neurogenesis is tempered by the demonstration that traumatic brain injury (TBI) results in the selective death of adult-born immature neurons, compromising the cell population poised to compensate for trauma-induced neuronal loss. Here, we identify the Ras-related GTPase, Rit, as a critical player in the survival of immature hippocampal neurons following brain injury. While Rit knock-out (Rit(-/-)) did not alter hippocampal development, hippocampal neural cultures derived from Rit(-/-) mice display increased cell death and blunted MAPK cascade activation in response to oxidative stress, without affecting BDNF-dependent signaling. When compared with wild-type hippocampal cultures, Rit loss rendered immature (Dcx(+)) neurons susceptible to oxidative damage, without altering the survival of neural progenitor (Nestin(+)) cells. Oxidative stress is a major contributor to neuronal cell death following brain injury. Consistent with the enhanced vulnerability of cultured Rit(-/-) immature neurons, Rit(-/-) mice exhibited a significantly greater loss of adult-born immature neurons within the dentate gyrus after TBI. In addition, post-TBI neuronal remodeling was blunted. Together, these data identify a new and unexpected role for Rit in injury-induced neurogenesis, functioning as a selective survival mechanism for immature hippocampal neurons within the subgranular zone of the dentate gyrus following TBI.

Salidroside improves behavioral and histological outcomes and reduces apoptosis via PI3K/Akt signaling after experimental traumatic brain injury

Background

Traumatic brain injury (TBI) induces a complex sequence of apopototic cascades that contribute to secondary tissue damage. The aim of this study was to investigate the effects of salidroside, a phenolic glycoside with potent anti-apoptotic properties, on behavioral and histological outcomes, brain edema, and apoptosis following experimental TBI and the possible involvement of the phosphoinositide 3-kinase/protein kinase B (PI3K)/Akt signaling pathway.

Methodology/Principal Findings

Mice subjected to controlled cortical impact injury received intraperitoneal salidroside (20, or 50 mg/kg) or vehicle injection 10 min after injury. Behavioral studies, histology analysis and brain water content assessment were performed. Levels of PI3K/Akt signaling-related molecules, apoptosis-related proteins, cytochrome C (CytoC), and Smac/DIABLO were also analyzed. LY294002, a PI3K inhibitor, was administered to examine the mechanism of protection. The protective effect of salidroside was also investigated in primary cultured neurons subjected to stretch injury. Treatment with 20 mg/kg salidroside_significantly improved functional recovery and reduced brain tissue damage up to post-injury day 28. Salidroside_also significantly reduced neuronal death, apoptosis, and brain edema at day 1. These changes were associated with significant decreases in cleaved caspase-3, CytoC, and Smac/DIABLO at days 1 and 3. Salidroside increased phosphorylation of Akt on Ser473 and the mitochondrial Bcl-2/Bax ratio at day 1, and enhanced phosphorylation of Akt on Thr308 at day 3. This beneficial effect was abolished by pre-injection of LY294002. Moreover, delayed administration of salidroside at 3 or 6 h post-injury reduced neuronal damage at day 1. Salidroside treatment also decreased neuronal vulnerability to stretch-induced injury in vitro.

Conclusions/Significance

Post-injury salidroside improved long-term behavioral and histological outcomes and reduced brain edema and apoptosis following TBI, at least partially via the PI3K/Akt signaling pathway.

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.

A perfusion fMRI study of the neural correlates of sustained-attention and working-memory deficits in chronic traumatic brain injury

BACKGROUND

Given that traumatic brain injury (TBI) results in chronic alteration of baseline cerebral perfusion, a perfusion functional MRI (fMRI) method that dissociates resting- and task-related cerebral blood flow (CBF) changes can be useful in noninvasively investigating the neural correlates of cognitive dysfunction and recovery in TBI.

OBJECTIVE

The authors used continuous arterial spin-labeled (ASL) perfusion fMRI to characterize CBF at rest and during sustained-attention and working-memory tasks.

METHODS

A total of 18 to 21 individuals with moderate to severe TBI and 14 to 18 demographically matched healthy controls completed 3 continuous 6-minute perfusion fMRI scans (resting, visual sustained attention, and 2-back working memory).

RESULTS

For both tasks, TBI participants showed worse behavioral performance than controls. Voxelwise neuroimaging analysis of the 2-back task found that group differences in task-induced CBF changes were localized to bilateral superior occipital cortices and the left superior temporal cortex. Whereas controls deactivated these areas during task performance, TBI participants tended to activate these same areas. These regions were among those found to be disproportionately hypoperfused at rest after TBI. For both tasks, the control and TBI groups showed different patterns of correlation between performance and task-related CBF changes.

CONCLUSIONS

ASL perfusion fMRI demonstrated differences between individuals with TBI and healthy controls in resting perfusion and in task-evoked CBF changes as well as different patterns of performance-activation correlation. These results are consistent with the notion that sensory/attentional modulation deficits contribute to higher cognitive dysfunction in TBI.

Calpastatin overexpression protects axonal transport in an in vivo model of traumatic axonal injury

Traumatic brain injury (TBI) causes substantial morbidity and mortality worldwide. A key component of both mild and severe TBI is diffuse axonal injury. Except in cases of extreme mechanical strain, when axons are torn at the moment of trauma, axonal stretch injury is characterized by early cytoskeletal proteolysis, transport disruption, and secondary axotomy. Calpains, a family of Ca(2+)-dependent proteases, have been implicated in this pathologic cascade, but direct in vivo evidence is lacking. To test the hypothesis that calpains play a causal role in axonal stretch injury in vivo, we used our rat optic nerve stretch model following adeno-associated viral (AAV) vector-mediated overexpression of the endogenous calpain inhibitor calpastatin in optic nerve axons. AAV vectors were designed for optimal expression of human calpastatin (hCAST) in retinal ganglion cells (RGCs). Calpain inhibition by the expressed protein was then confirmed in primary cortical cultures. Finally, we performed bilateral intravitreal injections of AAV vectors expressing hCAST or the reporter protein ZsGreen 3 weeks prior to unilateral optic nerve stretch. Immediately after stretch injury, Fluoro-Gold was injected into the superior colliculi for assessment of retrograde axonal transport. Rats were euthanized 4 days after stretch injury. Both hCAST and ZsGreen were detected in axons throughout the optic nerve to the chiasm. Calpastatin overexpression partially preserved axonal transport after stretch injury (58.3±15.6% reduction in Fluoro-Gold labeling relative to uninjured contralateral controls in ZsGreen-expressing RGCs, versus 33.8±23.9% in hCAST-expressing RGCs; p=0.038). These results provide direct evidence that axonal calpains play a causal role in transport disruption after in vivo stretch injury.

Neuroimaging of structural pathology and connectomics in traumatic brain injury: Toward personalized outcome prediction

Recent contributions to the body of knowledge on traumatic brain injury (TBI) favor the view that multimodal neuroimaging using structural and functional magnetic resonance imaging (MRI and fMRI, respectively) as well as diffusion tensor imaging (DTI) has excellent potential to identify novel biomarkers and predictors of TBI outcome. This is particularly the case when such methods are appropriately combined with volumetric/morphometric analysis of brain structures and with the exploration of TBI-related changes in brain network properties at the level of the connectome. In this context, our present review summarizes recent developments on the roles of these two techniques in the search for novel structural neuroimaging biomarkers that have TBI outcome prognostication value. The themes being explored cover notable trends in this area of research, including (1) the role of advanced MRI processing methods in the analysis of structural pathology, (2) the use of brain connectomics and network analysis to identify outcome biomarkers, and (3) the application of multivariate statistics to predict outcome using neuroimaging metrics. The goal of the review is to draw the community's attention to these recent advances on TBI outcome prediction methods and to encourage the development of new methodologies whereby structural neuroimaging can be used to identify biomarkers of TBI outcome.