Increase in blood-brain barrier permeability, oxidative stress, and activated microglia in a rat model of blast-induced traumatic brain injury

Differences in postinjury auditory system pathophysiology after mild blast and nonblast acute acoustic trauma

Hearing difficulties are the most commonly reported disabilities among veterans. Blast exposures during explosive events likely play a role, given their propensity to directly damage both peripheral (PAS) and central auditory system (CAS) components. Postblast PAS pathophysiology has been well documented in both clinical case reports and laboratory investigations. In contrast, blast-induced CAS dysfunction remains understudied but has been hypothesized to contribute to an array of common veteran behavioral complaints, including learning, memory, communication, and emotional regulation. This investigation compared the effects of acute blast and nonblast acoustic impulse trauma in adult male Sprague-Dawley rats. An array of audiometric tests were utilized, including distortion product otoacoustic emissions (DPOAE), auditory brain stem responses (ABR), middle latency responses (MLR), and envelope following responses (EFRs). Generally, more severe and persistent postinjury central auditory processing (CAP) deficits were observed in blast-exposed animals throughout the auditory neuraxis, spanning from the cochlea to the cortex. DPOAE and ABR results captured cochlear and auditory nerve/brain stem deficits, respectively. EFRs demonstrated temporal processing impairments suggestive of functional damage to regions in the auditory brain stem and the inferior colliculus. MLRs captured thalamocortical transmission and cortical activation impairments. Taken together, the results suggest blast-induced CAS dysfunction may play a complementary pathophysiological role to maladaptive neuroplasticity of PAS origin. Even mild blasts can produce lasting hearing impairments that can be assessed with noninvasive electrophysiology, allowing these measurements to serve as simple, effective diagnostics.NEW & NOTEWORTHY Blasts exposures often produce hearing difficulties. Although cochlear damage typically occurs, the downstream effects on central auditory processing are less clear. Moreover, outcomes were compared between individuals exposed to the blast pressure wave vs. those who experienced the blast noise without the pressure wave. It was found that a single blast exposure produced changes at all stages of the ascending auditory path at least 4 wk postblast, whereas blast noise alone produced largely transient changes.

Defective methionine metabolism in the brain after repeated blast exposures might contribute to increased oxidative stress

Blast-induced traumatic brain injury (bTBI) is one of the major disabilities in Service Members returning from recent military operations. The neurobiological underpinnings of bTBI, which are associated with acute and chronic neuropathological and neurobehavioral deficits, are uncertain. Increased oxidative stress in the brain is reported to play a significant role promoting neuronal damage associated with both brain injury and neurodegenerative disorders. In this study, brains of rats exposed to repeated blasts in a shock tube underwent untargeted profiling of primary metabolism by automatic linear exchange/cold injection GC-TOF mass spectrometry and revealed acute and sub-acute disruptions in the metabolism of the essential amino acid methionine and associated antioxidants. Methionine sulfoxide, the oxidized metabolite of methionine, showed a sustained increase in the brain after blast exposure which was associated with a significant decrease in cysteine, the amino acid derived from methionine. Glutathione, the antioxidant synthesized from cysteine, also concomitantly decreased as did the antioxidant ascorbic acid. Reductions in ascorbic acid were accompanied by increased levels of its oxidized metabolite, dehydroascorbic acid and other metabolites such as threonic acid, isothreonic acid, glycolic acid and oxalic acid. Fluorometric analysis of the brains showed acute and sub-acute increase in total reactive oxygen species. In view of the fundamental importance of glutathione in the brain as an antioxidant, including its role in the reduction of dehydroascorbic acid to ascorbic acid, the disruptions in methionine metabolism elicited by blast exposure might prominently contribute to neuronal injury by promoting increased and sustained oxidative stress.

Antioxidants reduce neurodegeneration and accumulation of pathologic Tau proteins in the auditory system after blast exposure

Cochlear neurodegeneration commonly accompanies hair cell loss resulting from aging, ototoxicity, or exposures to intense noise or blast overpressures. However, the precise pathophysiological mechanisms that drive this degenerative response have not been fully elucidated. Our laboratory previously demonstrated that non-transgenic rats exposed to blast overpressures exhibited marked somatic accumulation of neurotoxic variants of the microtubule-associated protein, Tau, in the hippocampus. In the present study, we extended these analyses to examine neurodegeneration and pathologic Tau accumulation in the auditory system in response to blast exposure and evaluated the potential therapeutic efficacy of antioxidants on short-circuiting this pathological process. Blast injury induced ribbon synapse loss and retrograde neurodegeneration in the cochlea in untreated animals. An accompanying perikaryal accumulation of neurofilament light chain and pathologic Tau oligomers were observed in neurons from both the peripheral and central auditory system, spanning from the spiral ganglion to the auditory cortex. Due to its coincident accumulation pattern and well-documented neurotoxicity, our results suggest that the accumulation of pathologic Tau oligomers may actively contribute to blast-induced cochlear neurodegeneration. Therapeutic intervention with a combinatorial regimen of 2,4-disulfonyl α-phenyl tertiary butyl nitrone (HPN-07) and N-acetylcysteine (NAC) significantly reduced both pathologic Tau accumulation and indications of ongoing neurodegeneration in the cochlea and the auditory cortex. These results demonstrate that a combination of HPN-07 and NAC administrated shortly after a blast exposure can serve as a potential therapeutic strategy for preserving auditory function among military personnel or civilians with blast-induced traumatic brain injuries.

Characterization of Differences in Functional Connectivity Associated with Close-Range Blast Exposure

Despite the prevalence of blast injuries in recent overseas conflicts, knowledge of their impact on neural health is lacking. We have recently published work demonstrating differences in functional magnetic resonance imaging (fMRI) connectivity that were specific to close-range blast exposure (CBE), as opposed to other prevalent military-related factors. Here, we replicate this finding in an independent sample of 135 veterans, again finding that CBE, regardless of concussion, is predictive of persistent changes in brain physiology. Although there was weak overlap anatomically, in both samples, the group differences could be described as spreading of anticorrelation. Using the combined sample, we now seek to identify likely mechanisms that could bring about this effect. We compared participants with (n = 116) and without (n = 153) CBE by analyzing two networks through group difference maps and correlation distributions to assess spatially homogenous and heterogeneous effects. As boundaries between positive and negative correlations in fcMRI are determined by noise covariates, we compared analyses with and without global signal regression. We found evidence of widespread altered connectivity that was spatially heterogeneous across participants, and that the role of global signal regression was network dependent. These findings are not consistent with expected results from damaged white matter or impaired neural function. Rather, potential biological interpretations include disrupted cerebral blood flow or impaired neurovascular coupling, which have each been observed in animal models of blast exposure. Further targeted work will be necessary to distinguish the contribution of each of these mechanisms to producing changes in brain function associated with CBE.

Glibenclamide pretreatment protects against chronic memory dysfunction and glial activation in rat cranial blast traumatic brain injury

Blast traumatic brain injury (bTBI) affects both military and civilian populations, and often results in chronic deficits in cognition and memory. Chronic glial activation after bTBI has been linked with cognitive decline. Pharmacological inhibition of sulfonylurea receptor 1 (SUR1) with glibenclamide was shown previously to reduce glial activation and improve cognition in contusive models of CNS trauma, but has not been examined in bTBI. We postulated that glibenclamide would reduce chronic glial activation and improve long-term memory function after bTBI. Using a rat direct cranial model of bTBI (dc-bTBI), we evaluated the efficacy of two glibenclamide treatment paradigms: glibenclamide prophylaxis (pre-treatment), and treatment with glibenclamide starting after dc-bTBI (post-treatment). Our results show that dc-bTBI caused hippocampal astrocyte and microglial/macrophage activation that was associated with hippocampal memory dysfunction (rapid place learning paradigm) at 28days, and that glibenclamide pre-treatment, but not post-treatment, effectively protected against glial activation and memory dysfunction. We also report that a brief transient time-window of blood-brain barrier (BBB) disruption occurs after dc-bTBI, and we speculate that glibenclamide, which is mostly protein bound and does not normally traverse the intact BBB, can undergo CNS delivery only during this brief transient opening of the BBB. Together, our findings indicate that prophylactic glibenclamide treatment may help to protect against chronic cognitive sequelae of bTBI in warfighters and other at-risk populations.

Repeated Low Intensity Blast Exposure Is Associated with Damaged Endothelial Glycocalyx and Downstream Behavioral Deficits

Current clinical research into mild traumatic brain injury (mTBI) has focused on white matter changes as identified by advanced MRI based imaging techniques. However, perivascular tau accumulation in the brains of individuals diagnosed with mTBI suggests that the vasculature plays a key role in the pathology. This study used a rat model to examine whether the endothelial glycocalyx, a layer of the vasculature responsible for sensing luminal shear forces, is damaged by exposure to repeated low intensity blast, and whether this layer is associated with observed behavioral deficits. The blast exposure used consisted of 12, 40 kPa blast exposures conducted with a minimum of 24 h between blasts. We found that repeated blast exposure reduced glycocalyx length and density in various brain regions indicating damage. This blast exposure paradigm was associated with a mild performance decrement in the Morris water maze (MWM) which assesses learning and memory. Administration of hyaluronidase, an enzyme that binds to and degrades hyaluronan (a major structural component of the glycocalyx) prior to blast exposure reduced the observed behavioral deficits and induced a thickening of the glycocalyx layer. Taken together these findings demonstrate that the endothelial glycocalyx degradation following repeated blast is associated with behavioral decrements which can be prevented by treatment with hyaluronidase.

Protective Effect of N-Acetylcysteine Amide on Blast-Induced Increase in Intracranial Pressure in Rats

Blast-induced traumatic brain injury is associated with acute and possibly chronic elevation of intracranial pressure (ICP). The outcome after TBI is dependent on the progression of complex processes which are mediated by oxidative stress. So far, no effective pharmacological protection against TBI exists. In this study, rats were exposed to a single or repetitive blast overpressure (BOP) at moderate intensities of 72 or 110 kPa in a compressed air-driven shock tube. The degree and duration of the increase in ICP were proportional to the intensity and frequency of the blast exposure(s). In most cases, a single dose of antioxidant N-acetylcysteine amide (NACA) (500 mg/kg) administered intravenously 2 h after exposure to BOP significantly attenuated blast-induced increase in ICP. A single dose of NACA was not effective in improving the outcome in the group of animals that were subjected to repetitive blast exposures at 110 kPa on the same day. In this group, two treatments with NACA at 2 and 4 h post-BOP exposure resulted in significant attenuation of elevated ICP. Treatment with NACA prior to BOP exposure completely prevented the elevation of ICP. The findings indicate that oxidative stress plays an important role in blast-induced elevated ICP as treatment with NACA-ameliorated ICP increase, which is frequently related to poor functional recovery after TBI.

Does Normobaric Hyperoxia Cause Oxidative Stress in the Injured Brain? A Microdialysis Study Using 8-Iso-Prostaglandin F2α as a Biomarker

Significant controversy exists regarding the potential clinical benefit of normobaric hyperoxia (NBO) in patients with traumatic brain injury (TBI). This study consisted of two aims: 1) to assess whether NBO improves brain oxygenation and metabolism and 2) to determine whether this therapy may increase the risk of oxidative stress (OxS), using 8-iso-Prostaglandin F2α (PGF2α) as a biomarker. Thirty-one patients with a median admission Glasgow Coma Scale score of 4 (min: 3, max: 12) were monitored with cerebral microdialysis and brain tissue oxygen sensors and treated with fraction of inspired oxygen (FiO₂) of 1.0 for 4 h. Patients were divided into two groups according to the area monitored by the probes: normal injured brain and traumatic penumbra/traumatic core. NBO maintained for 4 h did not induce OxS in patients without preOxS at baseline, except in one case. However, for patients in whom OxS was detected at baseline, NBO induced a significant increase in 8-iso-PGF2α. The results of our study showed that NBO did not change energy metabolism in the whole group of patients. In the five patients with brain lactate concentration ([Lac]_brain) > 3.5 mmol/L at baseline, NBO induced a marked reduction in both [Lac]_brain and lactate-to-pyruvate ratio. Although these differences were not statistically significant, together with the results of our previous study, they suggest that TBI patients would benefit from receiving NBO when they show indications of disturbed brain metabolism. These findings, in combination with increasing evidence that TBI metabolic crises are common without brain ischemia, open new possibilities for the use of this accessible therapeutic strategy in TBI patients.

Protection against Blast-Induced Traumatic Brain Injury by Increase in Brain Volume

Blast-induced traumatic brain injury (bTBI) is a leading cause of injuries in recent military conflicts and it is responsible for an increased number of civilian casualties by terrorist attacks. bTBI includes a variety of neuropathological changes depending on the intensity of blast overpressure (BOP) such as brain edema, neuronal degeneration, diffuse axonal damage, and vascular dysfunction with neurological manifestations of psychological and cognitive abnormalities. Internal jugular vein (IJV) compression is known to reduce intracranial compliance by causing an increase in brain volume and was shown to reduce brain damage during closed impact-induced TBI. We investigated whether IJV compression can attenuate signs of TBI in rats after exposure to BOP. Animals were exposed to three 110 ± 5 kPa BOPs separated by 30 min intervals. Exposure to BOP resulted in a significant decrease of neuronal nuclei (NeuN) together with upregulation of aquaporin-4 (AQP-4), 3-nitrotyrosine (3-NT), and endothelin 1 receptor A (ETRA) expression in frontal cortex and hippocampus one day following exposures. IJV compression attenuated this BOP-induced increase in 3-NT in cortex and ameliorated the upregulation of AQP-4 in hippocampus. These results suggest that elevated intracranial pressure and intracerebral volume have neuroprotective potential in blast-induced TBI.

Blast Scaling Parameters: Transitioning from Lung to Skull Base Metrics

Neurotrauma from blast exposure is one of the single most characteristic injuries of modern warfare. Understanding blast traumatic brain injury is critical for developing new treatment options for warfighters and civilians exposed to improvised explosive devices. Unfortunately, the pre-clinical models that are widely utilized to investigate blast exposure are based on archaic lung based parameters developed in the early 20th century. Improvised explosive devices produce a different type of injury paradigm than the typical mortar explosion. Protective equipment for the chest cavity has also improved over the past 100 years. In order to improve treatments, it is imperative to develop models that are based more on skull-based parameters. In this mini-review, we discuss the important anatomical and biochemical features necessary to develop a skull-based model.

Vascular impairment as a pathological mechanism underlying long-lasting cognitive dysfunction after pediatric traumatic brain injury

Traumatic brain injury (TBI) is the leading cause of death and disability in children. Indeed, the acute mechanical injury often evolves to a chronic brain disorder with long-term cognitive, emotional and social dysfunction even in the case of mild TBI. Contrary to the commonly held idea that children show better recovery from injuries than adults, pediatric TBI patients actually have worse outcome than adults for the same injury severity. Acute trauma to the young brain likely interferes with the fine-tuned developmental processes and may give rise to long-lasting consequences on brain's function. This review will focus on cerebrovascular dysfunction as an important early event that may lead to long-term phenotypic changes in the brain after pediatric TBI. These, in turn may be associated with accelerated brain aging and cognitive dysfunction. Finally, since no effective treatments are currently available, understanding the unique pathophysiological mechanisms of pediatric TBI is crucial for the development of new therapeutic options.

Distinguishing the Unique Neuropathological Profile of Blast Polytrauma

Traumatic brain injury sustained after blast exposure (blast-induced TBI) has recently been documented as a growing issue for military personnel. Incidence of injury to organs such as the lungs has decreased, though current epidemiology still causes a great public health burden. In addition, unprotected civilians sustain primary blast lung injury (PBLI) at alarming rates. Often, mild-to-moderate cases of PBLI are survivable with medical intervention, which creates a growing population of survivors of blast-induced polytrauma (BPT) with symptoms from blast-induced mild TBI (mTBI). Currently, there is a lack of preclinical models simulating BPT, which is crucial to identifying unique injury mechanisms of BPT and its management. To meet this need, our group characterized a rodent model of BPT and compared results to a blast-induced mTBI model. Open field (OF) performance trials were performed on rodents at 7 days after injury. Immunohistochemistry was performed to evaluate cellular outcome at day seven following BPT. Levels of reactive astrocytes (GFAP), apoptosis (cleaved caspase-3 expression), and vascular damage (SMI-71) were significantly elevated in BPT compared to blast-induced mTBI. Downstream markers of hypoxia (HIF-1α and VEGF) were higher only after BPT. This study highlights the need for unique therapeutics and prehospital management when handling BPT.

Neuronal Injury and Glial Changes Are Hallmarks of Open Field Blast Exposure in Swine Frontal Lobe

With the rapid increase in the number of blast induced traumatic brain injuries and associated neuropsychological consequences in veterans returning from the operations in Iraq and Afghanistan, the need to better understand the neuropathological sequelae following exposure to an open field blast exposure is still critical. Although a large body of experimental studies have attempted to address these pathological changes using shock tube models of blast injury, studies directed at understanding changes in a gyrencephalic brain exposed to a true open field blast are limited and thus forms the focus of this study. Anesthetized, male Yucatan swine were subjected to forward facing medium blast overpressure (peak side on overpressure 224-332 kPa; n = 7) or high blast overpressure (peak side on overpressure 350-403 kPa; n = 5) by detonating 3.6 kg of composition-4 charge. Sham animals (n = 5) were subjected to all the conditions without blast exposure. After a 3-day survival period, the brain was harvested and sections from the frontal lobes were processed for histological assessment of neuronal injury and glial reactivity changes. Significant neuronal injury in the form of beta amyloid precursor protein immunoreactive zones in the gray and white matter was observed in the frontal lobe sections from both the blast exposure groups. A significant increase in the number of astrocytes and microglia was also observed in the blast exposed sections compared to sham sections. We postulate that the observed acute injury changes may progress to chronic periods after blast and may contribute to short and long-term neuronal degeneration and glial mediated inflammation.

Elucidating the role of compression waves and impact duration for generating mild traumatic brain injury in rats

BACKGROUND

In total, 3.8 million concussions occur each year in the US leading to acute functional deficits, but the underlying histopathologic changes that occur are relatively unknown. In order to improve understanding of acute injury mechanisms, appropriately designed pre-clinical models must be utilized.

METHODS

The clinical relevance of compression wave injury models revolves around the ability to produce consistent histopathologic deficits. Mild traumatic brain injuries activate similar neuroinflammatory cascades, cell death markers and increases in amyloid precursor protein in both humans and rodents. Humans, however, infrequently succumb to mild traumatic brain injuries and, therefore, the intensity and magnitude of impacts must be inferred. Understanding compression wave properties and mechanical loading could help link the histopathologic deficits seen in rodents to what might be happening in human brains following concussions.

RESULTS

While the concept of linking duration and intensity of impact to subsequent histopathologic deficits makes sense, numerical modelling of compression waves has not been performed in this context. In this interdisciplinary work, numerical simulations were performed to study the creation of compression waves in an experimental model.

CONCLUSION

This work was conducted in conjunction with a repetitive compression wave injury paradigm in rats in order to better understand how the wave generation correlates with histopathologic deficits.

Regulatory T cells exhibit neuroprotective effect in a mouse model of traumatic brain injury

Traumatic brain injury (TBI) is a major health and socioeconomic problem as it is associated with high rates of mortality and morbidity worldwide. Regulatory T cells (Tregs) have been reported to reduce inflammatory response in several diseases, including myasthenia gravis, viral myocarditis and cerebral infarction. The present study investigated the role of Tregs in mediating neuro‑protective effects in a mouse model of TBI. Initially, Treg levels were determined, and compared between the controlled cortical impact (CCI) model for moderate TBI and the sham group, by using flow cytometry and ELISA. Afterwards, the number of Tregs was upregulated (by injection) and downregulated (by depletion), respectively, to elucidate the effect of Tregs in the presence of an inflammatory reaction and a deficient neurological function and consequently, in the prognosis of TBI in the mouse. The expression of pro‑inflammatory cytokines [tumor necrosis factor (TNF)‑α, interleukin (IL)‑1β, IL‑6)] and anti‑inflammatory cytokines [IL‑10, transforming growth factor (TGF)‑β] in blood and brain tissues was also measured in the five groups: Μice receiving a saline injection, mice experiencing Treg depletion, small‑dose (SD Tregs, 1.25x105), and mice receiving different doses of Tregs: Moderate‑dose (MD Tregs, 2.5x105) and large‑dose (LD Tregs, 5x105), using ELISA and PCR. Co‑cultures of Tregs and microglia were performed to evaluate the expression of pro‑inflammatory cytokines and observe the interaction between the two types of cells. The regulation patterns in JNK‑NF‑κB pathway by Tregs were also evaluated by western blot analysis. Treg levels were significantly reduced in TBI mouse group on the 3rd day after TBI (P<0.05). In the mouse model of TBI, the expression of pro‑inflammatory cytokines (TNF‑α, IL‑1β, IL‑6) was enhanced, while the expression of anti‑inflammatory cytokines (IL‑10, TGF‑β) was reduced (P<0.05). Tregs exhibited a suppressive effect on inflammatory reactions. In the MD group, the activation of microglia cells was markedly inhibited, compared to the activation in SD and LD groups. The expression of ERK1/2, JNK1/2/3 and NK‑κB was significantly downregulated in the MD group. The results indicated that Tregs exhibited significant neuro‑protective effects, suppressing pro‑inflammatory responses and promoting tissue repair after TBI injury in the mouse, specifically by deactivating the JNK‑NF‑κB pathway. The results of the study show that Tregs potentially participates in neuro‑therapeutic approaches for TBI.

Imaging Evaluation of Acute Traumatic Brain Injury

Traumatic brain injury (TBI) is a major cause of morbidity and mortality worldwide. Imaging plays an important role in the evaluation, diagnosis, and triage of patients with TBI. Recent studies suggest that it also helps predict patient outcomes. TBI consists of multiple pathoanatomic entities. This article reviews the current state of TBI imaging including its indications, benefits and limitations of the modalities, imaging protocols, and imaging findings for each of these pathoanatomic entities. Also briefly surveyed are advanced imaging techniques, which include several promising areas of TBI research.

Primary blast injury causes cognitive impairments and hippocampal circuit alterations

Blast-induced traumatic brain injury (bTBI) and its long term consequences are a major health concern among veterans. Despite recent work enhancing our knowledge about bTBI, very little is known about the contribution of the blast wave alone to the observed sequelae. Herein, we isolated its contribution in a mouse model by constraining the animals' heads during exposure to a shockwave (primary blast). Our results show that exposure to primary blast alone results in changes in hippocampus-dependent behaviors that correspond with electrophysiological changes in area CA1 and are accompanied by reactive gliosis. Specifically, five days after exposure, behavior in an open field and performance in a spatial object recognition (SOR) task were significantly different from sham. Network electrophysiology, also performed five days after injury, demonstrated a significant decrease in excitability and increase in inhibitory tone. Immunohistochemistry for GFAP and Iba1 performed ten days after injury showed a significant increase in staining. Interestingly, a threefold increase in the impulse of the primary blast wave did not exacerbate these measures. However, we observed a significant reduction in the contribution of the NMDA receptors to the field EPSP at the highest blast exposure level. Our results emphasize the need to account for the effects of primary blast loading when studying the sequelae of bTBI.

Astrocyte Reactivity Following Blast Exposure Involves Aberrant Histone Acetylation

Blast induced neurotrauma (BINT) is a prevalent injury within military and civilian populations. The injury is characterized by persistent inflammation at the cellular level which manifests as a multitude of cognitive and functional impairments. Epigenetic regulation of transcription offers an important control mechanism for gene expression and cellular function which may underlie chronic inflammation and result in neurodegeneration. We hypothesize that altered histone acetylation patterns may be involved in blast induced inflammation and the chronic activation of glial cells. This study aimed to elucidate changes to histone acetylation occurring following injury and the roles these changes may have within the pathology. Sprague Dawley rats were subjected to either a 10 or 17 psi blast overpressure within an Advanced Blast Simulator (ABS). Sham animals underwent the same procedures without blast exposure. Memory impairments were measured using the Novel Object Recognition (NOR) test at 2 and 7 days post-injury. Tissues were collected at 7 days for Western blot and immunohistochemistry (IHC) analysis. Sham animals showed intact memory at each time point. The novel object discrimination decreased significantly between two and 7 days for each injury group (p < 0.05). This is indicative of the onset of memory impairment. Western blot analysis showed glial fibrillary acidic protein (GFAP), a known marker of activated astrocytes, was elevated in the prefrontal cortex (PFC) following blast exposure for both injury groups. Analysis of histone protein extract showed no changes in the level of any total histone proteins within the PFC. However, acetylation levels of histone H2b, H3, and H4 were decreased in both groups (p < 0.05). Co-localization immunofluorescence was used to further investigate any potential correlation between decreased histone acetylation and astrocyte activation. These experiments showed a similar decrease in H3 acetylation in astrocytes exposed to a 17 psi blast but not a 10 psi blast. Further investigation of gene expression by polymerase chain reaction (PCR) array, showed dysregulation of several cytokine and cytokine receptors that are involved in neuroinflammatory processes. We have shown aberrant histone acetylation patterns involved in blast induced astrogliosis and cognitive impairments. Further understanding of their role in the injury progression may lead to novel therapeutic targets.

Chronic Effects of Blast-Related TBI on Subcortical Functional Connectivity in Veterans

OBJECTIVES

Blast explosions are the most frequent mechanism of traumatic brain injury (TBI) in recent wars, but little is known about their long-term effects.

METHODS

Functional connectivity (FC) was measured in 17 veterans an average of 5.46 years after their most serious blast related TBI, and in 15 demographically similar veterans without TBI or blast exposure. Subcortical FC was measured in bilateral caudate, putamen, and globus pallidus. The default mode and fronto-parietal networks were also investigated.

RESULTS

In subcortical regions, between-groups t tests revealed altered FC from the right putamen and right globus pallidus. However, following analysis of covariance (ANCOVA) with age, depression (Center for Epidemiologic Studies Depression Scale), and posttraumatic stress disorder symptom (PTSD Checklist - Civilian version) measures, significant findings remained only for the right globus pallidus with anticorrelation in bilateral temporal occipital fusiform cortex, occipital fusiform gyrus, lingual gyrus, and cerebellum, as well as the right occipital pole. No group differences were found for the default mode network. Although reduced FC was found in the fronto-parietal network in the TBI group, between-group differences were nonsignificant after the ANCOVA.

CONCLUSIONS

FC of the globus pallidus is altered years after exposure to blast related TBI. Future studies are necessary to explore the trajectory of changes in FC in subcortical regions after blast TBI, the effects of isolated versus repetitive blast-related TBI, and the relation to long-term outcomes in veterans. (JINS, 2016, 22, 631-642).

Primary blast causes mild, moderate, severe and lethal TBI with increasing blast overpressures: Experimental rat injury model

Injury severity in blast induced Traumatic Brain Injury (bTBI) increases with blast overpressure (BOP) and impulse in dose-dependent manner. Pure primary blast waves were simulated in compressed gas shock-tubes in discrete increments. Present work demonstrates 24 hour survival of rats in 0–450 kPa (0–800 Pa∙s impulse) range at 10 discrete levels (60, 100, 130, 160, 190, 230, 250, 290, 350 and 420 kPa) and determines the mortality rate as a non-linear function of BOP. Using logistic regression model, predicted mortality rate (PMR) function was calculated, and used to establish TBI severities. We determined a BOP of 145 kPa as upper mild TBI threshold (5% PMR). Also we determined 146–220 kPa and 221–290 kPa levels as moderate and severe TBI based on 35%, and 70% PMR, respectively, while BOP above 290 kPa is lethal. Since there are no standards for animal bTBI injury severity, these thresholds need further refinements using histopathology, immunohistochemistry and behavior. Further, we specifically investigated mild TBI range (0–145 kPa) using physiological (heart rate), pathological (lung injury), immuno-histochemical (oxidative/nitrosative and blood-brain barrier markers) as well as blood borne biomarkers. With these additional data, we conclude that mild bTBI occurs in rats when the BOP is in the range of 85–145 kPa.

Eye-Directed Overpressure Airwave-Induced Trauma Causes Lasting Damage to the Anterior and Posterior Globe: A Model for Testing Cell-Based Therapies

PURPOSE

Characterization of the response of the Balb/c mouse to an eye-directed overpressure airwave, with the hypothesis that this mouse strain and model is useful for testing potential therapeutics for the treatment of traumatic eye injury.

METHODS

The left eyes of adult Balb/c mice were exposed to an eye-directed overpressure airwave. Intraocular pressure (IOP) was measured and eyes were inspected for gross pathology changes. Optical coherence tomography and histology were used to examine the structural integrity of the retina and optic nerve. Immunohistochemistry, in vivo molecular fluorophores, and a multiplex enzyme-linked immunosorbent assay were utilized to identify changes in cell death, neuroinflammation, and oxidative stress.

RESULTS

This model induced a transient increase in IOP, corneal injuries, infrequent large retinal detachments, retinal pigment epithelium (RPE) vacuolization, glial reactivity, and retinal cell death. Both the corneal damage and RPE vacuolization persisted with time. Optic nerve degeneration occurred as early as 7 days postinjury and persisted out to 60 days. Retinal cell death, increased levels of reactive oxygen species, and neuroinflammation were detected at 7 days postinjury.

CONCLUSIONS

The injury profile of the Balb/c mouse is consistent with commonly observed pathologies in blast-exposed patients. The damage is throughout the eye and persistent, making this mouse model useful for testing cell-based therapies.

Primary blast injury causes cognitive impairments and hippocampal circuit alterations

Blast-induced traumatic brain injury (bTBI) and its long term consequences are a major health concern among veterans. Despite recent work enhancing our knowledge about bTBI, very little is known about the contribution of the blast wave alone to the observed sequelae. Herein, we isolated its contribution in a mouse model by constraining the animals' heads during exposure to a shockwave (primary blast). Our results show that exposure to primary blast alone results in changes in hippocampus-dependent behaviors that correspond with electrophysiological changes in area CA1 and are accompanied by reactive gliosis. Specifically, five days after exposure, behavior in an open field and performance in a spatial object recognition (SOR) task were significantly different from sham. Network electrophysiology, also performed five days after injury, demonstrated a significant decrease in excitability and increase in inhibitory tone. Immunohistochemistry for GFAP and Iba1 performed ten days after injury showed a significant increase in staining. Interestingly, a threefold increase in the impulse of the primary blast wave did not exacerbate these measures. However, we observed a significant reduction in the contribution of the NMDA receptors to the field EPSP at the highest blast exposure level. Our results emphasize the need to account for the effects of primary blast loading when studying the sequelae of bTBI.

Subacute Oxidative Stress and Glial Reactivity in the Amygdala are Associated with Increased Anxiety Following Blast Neurotrauma

Behavioral symptoms, such as anxiety, are widely reported after blast overpressure (BOP) exposure. Amygdalar vulnerability to increasing magnitudes of BOP has not been investigated, and single exposures to blast have been limited to acute (<72 h) assessment. Rats were exposed to a single low, moderate, or high BOP (10, 14, or 24 psi) with an advanced blast simulator to test the susceptibility of the amygdala. Anxiety-like behavior was observed in the low- and moderate-pressure groups when subjected to the light/dark box assessment 7 days after the blast but not in high-pressure group. Immunohistochemistry was performed to measure apoptosis (cleaved caspase-3), neuronal loss (NeuN), reactive astrocytes (glial fibrillary acidic protein), microglia (Iba-1), and oxidative stress (CuZn superoxide dismutase). Slower progression of injury cascades was associated with a significant increase in anxiety, apoptosis, and astrogliosis in the low pressure group compared with others. A significant increase of CuZn superoxide dismutase in the low pressure group could be associated with neuroprotection from cell death caused by oxidative stress because neuronal loss was significant in the moderate- and high- but not the low-pressure group. Overall, this study demonstrated that overpressure as low as 10 psi can induce subacute anxiety, in addition to neuropathologic changes in the amygdala.

Assessing Quantitative Changes in Intrinsic Thalamic Networks in Blast and Nonblast Mild Traumatic Brain Injury: Implications for Mechanisms of Injury

In the global war on terror, the increased use of improvised explosive devices has resulted in increased incidence of blast-related mild traumatic brain injury (mTBI). Diagnosing mTBI is both challenging and controversial due to heterogeneity of injury location, trauma intensity, transient symptoms, and absence of focal biomarkers on standard clinical imaging modalities. The goal of this study is to identify a brain biomarker that is sensitive to mTBI injury. Research suggests the thalamus may be sensitive to changes induced by mTBI. A significant number of connections to and from various brain regions converge at the thalamus. In addition, the thalamus is involved in information processing, integration, and regulation of specific behaviors and mood. In this study, changes in task-free thalamic networks as quantified by graph theory measures in mTBI blast (N = 186), mTBI nonblast (N = 80), and controls (N = 21) were compared. Results show that the blast mTBI group had significant hyper-connectivity compared with the controls and nonblast mTBI group. However, after controlling for post-traumatic stress symptoms (PTSS), the blast mTBI group was not different from the controls, but the nonblast mTBI group showed significant hypo-connectivity. The results suggest that there are differences in the mechanisms of injury related to mTBI as reflected in the architecture of the thalamic networks. However, the effect of PTSS and its relationship to mTBI is difficult to distinguish and warrants more research.

Primary Blast Exposure Increases Hippocampal Vulnerability to Subsequent Exposure: Reducing Long-Term Potentiation

Up to 80% of injuries sustained by U.S. soldiers in Operation Enduring Freedom and Operation Iraqi Freedom were the result of blast exposure from improvised explosive devices. Some soldiers experience multiple blasts while on duty, and it has been suggested that symptoms of repetitive blast are similar to those that follow multiple non-blast concussions, such as sport-related concussion. Despite the interest in the effects of repetitive blast exposure, it remains unknown whether an initial blast renders the brain more vulnerable to subsequent exposure, resulting in a synergistic injury response. To investigate the effect of multiple primary blasts on the brain, organotypic hippocampal slice cultures were exposed to single or repetitive (two or three total) primary blasts of varying intensities. Long-term potentiation was significantly reduced following two Level 2 (92.7 kPa, 1.4 msec, 38.5 kPa·msec) blasts delivered 24 h apart without altering basal evoked response. This deficit persisted when the interval between injuries was increased to 72 h but not when the interval was extended to 144 h. The repeated blast exposure with a 24 h interval increased microglia staining and activation significantly but did not significantly increase cell death or damage axons, dendrites, or principal cell layers. Lack of overt structural damage and change in basal stimulated neuron response suggest that injury from repetitive primary blast exposure may specifically affect long-term potentiation. Our studies suggest repetitive primary blasts can exacerbate injury dependent on the injury severity and interval between exposures.

Noncontact Rotational Head Injury Produces Transient Cognitive Deficits but Lasting Neuropathological Changes

Traumatic brain injury (TBI) caused by improvised explosive devices (IEDs) is a growing problem in military settings, but modeling this disease in rodents to pre-clinically evaluate potential therapeutics has been challenging because of inconsistency between models. Although the effects of primary blast wave injury have been extensively studied, little is known regarding the effects of noncontact rotational TBIs independent of the blast wave. To model this type of injury, we generated an air cannon system that does not produce a blast wave, but generates enough air pressure to cause rotational TBI. Mice exposed to this type of injury showed deficits in cognitive and motor task acquisition within 1-2 weeks post-injury, but mice tested 7-8 weeks post-injury did not retain any deficits. This suggests that the effects of a single, noncontact rotational TBI are not long lasting. Despite the transient nature of the behavioral deficits, increased levels of phosphorylated tau were observed at 2 and 8 weeks post-injury; however, this tau did not adopt typical pathological structures that have been observed in other TBI models that incorporate blast waves. This was possibly attributed to the fact that this injury was insufficient to induce changes in microglial activation, which was not affected at 2 or 8 weeks post-injury. Taken together, these data suggest that exposure to noncontact, rotational head injury only produces transient cognitive anomalies, but elicits some minor lasting neuropathological changes.

Blast From the Past: A Retrospective Analysis of Blast-induced Head Injury

Because of the sharp increase in the number of military personnel exposed to explosive blasts in combat, research has been dedicated toward understanding the impact of explosions on the brain. It is important to consider that potential injuries that military personnel sustain may be both in the form of physical injury as well as "invisible" neuronal and psychological damage. Since the inception of the study of blast science in the Medieval and Renaissance eras, significant improvements have been made in the historical record keeping and biomedical analysis of blast injuries. This editorial comments on the evolution of blast science and the recognition of neurological sequelae from both the historical and scientific perspectives.

Blast exposure causes dynamic microglial/macrophage responses and microdomains of brain microvessel dysfunction

Exposure to blast overpressure (BOP) is associated with behavioral, cognitive, and neuroimaging abnormalities. We investigated the dynamic responses of cortical vasculature and its relation to microglia/macrophage activation in mice using intravital two-photon microscopy following mild blast exposure. We found that blast caused vascular dysfunction evidenced by microdomains of aberrant vascular permeability. Microglial/macrophage activation was specifically associated with these restricted microdomains, as evidenced by rapid microglial process retraction, increased ameboid morphology, and escape of blood-borne Q-dot tracers that were internalized in microglial/macrophage cell bodies and phagosome-like compartments. Microdomains of cortical vascular disruption and microglial/macrophage activation were also associated with aberrant tight junction morphology that was more prominent after repetitive (3×) blast exposure. Repetitive, but not single, BOPs also caused TNFα elevation two weeks post-blast. In addition, following a single BOP we found that aberrantly phosphorylated tau rapidly accumulated in perivascular domains, but cleared within four hours, suggesting it was removed from the perivascular area, degraded, and/or dephosphorylated. Taken together these findings argue that mild blast exposure causes an evolving CNS insult that is initiated by discrete disturbances of vascular function, thereby setting the stage for more protracted and more widespread neuroinflammatory responses.

Cellular Mechanisms and Behavioral Outcomes in Blast-Induced Neurotrauma: Comparing Experimental Setups

Blast-induced neurotrauma (BINT) has increased in incidence over the past decades and can result in cognitive issues that have debilitating consequences. The exact primary and secondary mechanisms of injury have not been elucidated and appearance of cellular injury can vary based on many factors, such as blast overpressure magnitude and duration. Many methodologies to study blast neurotrauma have been employed, ranging from open-field explosives to experimental shock tubes for producing free-field blast waves. While there are benefits to the various methods, certain specifications need to be accounted for in order to properly examine BINT. Primary cell injury mechanisms, occurring as a direct result of the blast wave, have been identified in several studies and include cerebral vascular damage, blood-brain barrier disruption, axonal injury, and cytoskeletal damage. Secondary cell injury mechanisms, triggered subsequent to the initial insult, result in the activation of several molecular cascades and can include, but are not limited to, neuroinflammation and oxidative stress. The collective result of these secondary injuries can lead to functional deficits. Behavioral measures examining motor function, anxiety traits, and cognition/memory problems have been utilized to determine the level of injury severity. While cellular injury mechanisms have been identified following blast exposure, the various experimental models present both concurrent and conflicting results. Furthermore, the temporal response and progression of pathology after blast exposure have yet to be detailed and remain unclear due to limited resemblance of methodologies. This chapter summarizes the current state of blast neuropathology and emphasizes the need for a standardized preclinical model of blast neurotrauma.

Ameliorative Effects of Antioxidants on the Hippocampal Accumulation of Pathologic Tau in a Rat Model of Blast-Induced Traumatic Brain Injury

Traumatic brain injury (TBI) can lead to early onset dementia and other related neurodegenerative diseases. We previously demonstrated that damage to the central auditory pathway resulting from blast-induced TBI (bTBI) could be significantly attenuated by a combinatorial antioxidant treatment regimen. In the current study, we examined the localization patterns of normal Tau and the potential blast-induced accumulation of neurotoxic variants of this microtubule-associated protein that are believed to potentiate the neurodegenerative effects associated with synaptic dysfunction in the hippocampus following three successive blast overpressure exposures in nontransgenic rats. We observed a marked increase in the number of both hyperphosphorylated and oligomeric Tau-positive hilar mossy cells and somatic accumulation of endogenous Tau in oligodendrocytes in the hippocampus. Remarkably, a combinatorial regimen of 2,4-disulfonyl α-phenyl tertiary butyl nitrone (HPN-07) and N-acetylcysteine (NAC) resulted in striking reductions in the numbers of both mossy cells and oligodendrocytes positively labeled for these pathological Tau immunoreactivity patterns in response to bTBI. This treatment strategy represents a promising therapeutic approach for simultaneously reducing or eliminating both primary auditory injury and nonauditory changes associated with bTBI-induced hippocampal neurodegeneration.

Isolated Primary Blast Inhibits Long-Term Potentiation in Organotypic Hippocampal Slice Cultures

Over the last 13 years, traumatic brain injury (TBI) has affected over 230,000 U.S. service members through the conflicts in Iraq and Afghanistan, mostly as a result of exposure to blast events. Blast-induced TBI (bTBI) is multi-phasic, with the penetrating and inertia-driven phases having been extensively studied. The effects of primary blast injury, caused by the shockwave interacting with the brain, remain unclear. Earlier in vivo studies in mice and rats have reported mixed results for primary blast effects on behavior and memory. Using a previously developed shock tube and in vitro sample receiver, we investigated the effect of isolated primary blast on the electrophysiological function of rat organotypic hippocampal slice cultures (OHSC). We found that pure primary blast exposure inhibited long-term potentiation (LTP), the electrophysiological correlate of memory, with a threshold between 9 and 39 kPa·ms impulse. This deficit occurred well below a previously identified threshold for cell death (184 kPa·ms), supporting our previously published finding that primary blast can cause changes in brain function in the absence of cell death. Other functional measures such as spontaneous activity, network synchronization, stimulus-response curves, and paired-pulse ratios (PPRs) were less affected by primary blast exposure, as compared with LTP. This is the first study to identify a tissue-level tolerance threshold for electrophysiological changes in neuronal function to isolated primary blast.

Effects of beta-hydroxybutyrate on brain vascular permeability in rats with traumatic brain injury

This study investigates the effect of beta-hydroxybutyrate (BHB) on blood-brain barrier (BBB) integrity during traumatic brain injury (TBI) in rats. Evans blue (EB) and horseradish peroxidase (HRP) were used as determinants of BBB permeability. Glutathione (GSH) and malondialdehyde (MDA) levels were estimated in the right (injury side) cerebral cortex of animals. The gene expression levels for occludin, glucose transporter (Glut)-1, aquaporin4 (AQP4) and nuclear factor-kappaB (NF-κB) were performed, and Glut-1 and NF-κB activities were analyzed. BHB treatment decreased GSH and MDA levels in intact animals and in those exposed to TBI (P<0.05). Glut-1 protein levels decreased in sham, BHB and TBI plus BHB groups (P<0.05). NF-κB protein levels increased in animals treated with BHB and/or exposed to TBI (P<0.05). The expression levels of occludin and AQP4 did not significantly change among experimental groups. Glut-1 expression levels increased in BHB treated and untreated animals exposed to TBI (P<0.05). While NF-κB expression levels increased in animals in TBI (P<0.01), a decrease was noticed in these animals upon BHB treatment (P<0.01). In animals exposed to TBI, EB extravasation was observed in the ipsilateral cortex regardless of BHB treatment. Ultrastructurally, BHB attenuated but did not prevent the presence of HRP in brain capillary endothelial cells of animals with TBI; moreover, the drug also led to the observation of the tracer when used in intact rats (P<0.01). Altogether, these results showed that BHB not only failed to provide overall protective effects on BBB in TBI but also led to BBB disruption in healthy animals.

The functional and structural changes in the basilar artery due to overpressure blast injury

Overpressure blast-wave induced brain injury (OBI) leads to progressive pathophysiologic changes resulting in a reduction in brain blood flow, blood brain barrier breakdown, edema, and cerebral ischemia. The aim of this study was to evaluate cerebral vascular function after single and repeated OBI. Male Sprague-Dawley rats were divided into three groups: Control (Naive), single OBI (30 psi peak pressure, 1 to 2 msec duration), and repeated (days 1, 4, and 7) OBI (r-OBI). Rats were killed 24 hours after injury and the basilar artery was isolated, cannulated, and pressurized (90 cm H2O). Vascular responses to potassium chloride (KCl) (30 to 100 mmol/L), endothelin-1 (10(-12) to 10(-7) mol/L), acetylcholine (ACh) (10(-10) to 10(-4) mol/L) and diethylamine-NONO-ate (DEA-NONO-ate) (10(-10) to 10(-4) mol/L) were evaluated. The OBI resulted in an increase in the contractile responses to endothelin and a decrease in the relaxant responses to ACh in both single and r-OBI groups. However, impaired DEA-NONO-ate-induced vasodilation and increased wall thickness to lumen ratio were observed only in the r-OBI group. The endothelin-1 type A (ET(A)) receptor and endothelial nitric oxide synthase (eNOS) immunoreactivity were significantly enhanced by OBI. These findings indicate that both single and r-OBI impairs cerebral vascular endothelium-dependent dilation, potentially a consequence of endothelial dysfunction and/or vascular remodelling in basilar arteries after OBI.

Bryostatin-1 Restores Blood Brain Barrier Integrity following Blast-Induced Traumatic Brain Injury

Recent wars in Iraq and Afghanistan have accounted for an estimated 270,000 blast exposures among military personnel. Blast traumatic brain injury (TBI) is the 'signature injury' of modern warfare. Blood brain barrier (BBB) disruption following blast TBI can lead to long-term and diffuse neuroinflammation. In this study, we investigate for the first time the role of bryostatin-1, a specific protein kinase C (PKC) modulator, in ameliorating BBB breakdown. Thirty seven Sprague-Dawley rats were used for this study. We utilized a clinically relevant and validated blast model to expose animals to moderate blast exposure. Groups included: control, single blast exposure, and single blast exposure + bryostatin-1. Bryostatin-1 was administered i.p. 2.5 mg/kg after blast exposure. Evan's blue, immunohistochemistry, and western blot analysis were performed to assess injury. Evan's blue binds to albumin and is a marker for BBB disruption. The single blast exposure caused an increase in permeability compared to control (t = 4.808, p < 0.05), and a reduction back toward control levels when bryostatin-1 was administered (t = 5.113, p < 0.01). Three important PKC isozymes, PKCα, PKCδ, and PKCε, were co-localized primarily with endothelial cells but not astrocytes. Bryostatin-1 administration reduced toxic PKCα levels back toward control levels (t = 4.559, p < 0.01) and increased the neuroprotective isozyme PKCε (t = 6.102, p < 0.01). Bryostatin-1 caused a significant increase in the tight junction proteins VE-cadherin, ZO-1, and occludin through modulation of PKC activity. Bryostatin-1 ultimately decreased BBB breakdown potentially due to modulation of PKC isozymes. Future work will examine the role of bryostatin-1 in preventing chronic neurodegeneration following repetitive neurotrauma.

A Wireless Intracranial Brain Deformation Sensing System for Blast-Induced Traumatic Brain Injury

Blast-induced traumatic brain injury (bTBI) has been linked to a multitude of delayed-onset neurodegenerative and neuropsychiatric disorders, but complete understanding of their pathogenesis remains elusive. To develop mechanistic relationships between bTBI and post-blast neurological sequelae, it is imperative to characterize the initiating traumatic mechanical events leading to eventual alterations of cell, tissue, and organ structure and function. This paper presents a wireless sensing system capable of monitoring the intracranial brain deformation in real-time during the event of a bTBI. The system consists of an implantable soft magnet and an external head-mounted magnetic sensor that is able to measure the field in three dimensions. The change in the relative position of the soft magnet WITH respect to the external sensor as the result of the blast wave induces changes in the magnetic field. The magnetic field data in turn is used to extract the temporal and spatial motion of the brain under the blast wave in real-time. The system has temporal and spatial resolutions of 5 μs and 10 μm. Following the characterization and validation of the sensor system, we measured brain deformations in a live rodent during a bTBI.

Time Course and Size of Blood-Brain Barrier Opening in a Mouse Model of Blast-Induced Traumatic Brain Injury

An increasing number of studies have reported blood-brain barrier (BBB) dysfunction after blast-induced traumatic brain injury (bTBI). Despite this evidence, there is limited quantitative understanding of the extent of BBB opening and the time course of damage after blast injury. In addition, many studies do not report kinematic parameters of head motion, making it difficult to separate contributions of primary and tertiary blast-loading. Detailed characterization of blast-induced BBB damage may hold important implications for serum constituents that may potentially cross the compromised barrier and contribute to neurotoxicity, neuroinflammation, and persistent neurologic deficits. Using an in vivo bTBI model, systemic administration of sodium fluorescein (NaFl; 376 Da), Evans blue (EB; 69 kDa when bound to serum albumin), and dextrans (3-500 kDa) was used to estimate the pore size of BBB opening and the time required for recovery. Exposure to blast with 272 ± 6 kPa peak overpressure, 0.69 ± 0.01 ms duration, and 65 ± 1 kPa*ms impulse resulted in significant acute extravasation of NaFl, 3 kDa dextran, and EB. However, there was no significant acute extravasation of 70 kDa or 500 kDa dextrans, and minimal to no extravasation of NaFl, dextrans, or EB 1 day after exposure. This study presents a detailed analysis of the time course and pore size of BBB opening after bTBI, supported by a characterization of kinematic parameters associated with blast-induced head motion.

Pre-Clinical Traumatic Brain Injury Common Data Elements: Toward a Common Language Across Laboratories

Traumatic brain injury (TBI) is a major public health issue exacting a substantial personal and economic burden globally. With the advent of "big data" approaches to understanding complex systems, there is the potential to greatly accelerate knowledge about mechanisms of injury and how to detect and modify them to improve patient outcomes. High quality, well-defined data are critical to the success of bioinformatics platforms, and a data dictionary of "common data elements" (CDEs), as well as "unique data elements" has been created for clinical TBI research. There is no data dictionary, however, for preclinical TBI research despite similar opportunities to accelerate knowledge. To address this gap, a committee of experts was tasked with creating a defined set of data elements to further collaboration across laboratories and enable the merging of data for meta-analysis. The CDEs were subdivided into a Core module for data elements relevant to most, if not all, studies, and Injury-Model-Specific modules for non-generalizable data elements. The purpose of this article is to provide both an overview of TBI models and the CDEs pertinent to these models to facilitate a common language for preclinical TBI research.

Blast induced neurotrauma causes overpressure dependent changes to the DNA methylation equilibrium

Traumatic brain injury (TBI) has a high prevalence in our society and often leads to morbidity and mortality. TBI also occurs frequently in a military setting where exposure to blast waves is common. Abnormal gene expression involved with oxidative stress, inflammation and neuronal apoptosis has been well documented following blast induced neurotrauma (BINT). Altered epigenetic transcriptional regulation through DNA methylation has been implicated in the pathology of the injury. Imbalance between DNA methylation and DNA demethylation may lead to altered methylation patterns and subsequent changes in gene transcription. DNA methyltransferase enzymes (DNMT1, DNMT3a, and DNMT3b) are responsible for the addition of methyl groups to DNA, DNA methylation. Whereas the combined function of ten-eleven translocation enzymes (TET1, TET2, and TET3) and thymine-DNA glycosylase (TDG) result in the removal of methyl groups from DNA, DNA demethylation. We used an established rodent model of BINT to assess changes in DNA methylation and demethylation enzymes following injury. Three different blast overpressures were investigated (10, 17 and 23psi). Gene expression was investigated in the prefrontal cortex and hippocampus two weeks following injury. We observed DNMT, TET and TDG expression changes between pressure groups and brain regions. The hippocampus was more vulnerable to enzyme expression changes than the prefrontal cortex, which correlated with aberrant DNA methylation. A significant negative correlation was found between global DNA methylation and the magnitude of blast overpressure exposure. Through transcriptional regulation, altered DNA methylation patterns may offer insight into the characteristic outcomes associated with the injury pathology including inflammation, oxidative stress and apoptosis. As such, these enzymes may be important targets to future therapeutic intervention strategies.

Dexamethasone potentiates in vitro blood-brain barrier recovery after primary blast injury by glucocorticoid receptor-mediated upregulation of ZO-1 tight junction protein

Owing to the frequent incidence of blast-induced traumatic brain injury (bTBI) in recent military conflicts, there is an urgent need to develop effective therapies for bTBI-related pathologies. Blood-brain barrier (BBB) breakdown has been reported to occur after primary blast exposure, making restoration of BBB function and integrity a promising therapeutic target. We tested the hypothesis that treatment with dexamethasone (DEX) after primary blast injury potentiates recovery of an in vitro BBB model consisting of mouse brain endothelial cells (bEnd.3). DEX treatment resulted in complete recovery of transendothelial electrical resistance and hydraulic conductivity 1 day after injury, compared with 3 days for vehicle-treated injured cultures. Administration of RU486 (mifepristone) inhibited effects of DEX, confirming that barrier restoration was mediated by glucocorticoid receptor signaling. Potentiated recovery with DEX treatment was accompanied by stronger zonula occludens (ZO)-1 tight junction immunostaining and expression, suggesting that increased ZO-1 expression was a structural correlate to BBB recovery after blast. Interestingly, augmented ZO-1 protein expression was associated with specific upregulation of the α(+) isoform but not the α(-) isoform. This is the first study to provide a mechanistic basis for potentiated functional recovery of an in vitro BBB model because of glucocorticoid treatment after primary blast injury.

Blast-Associated Shock Waves Result in Increased Brain Vascular Leakage and Elevated ROS Levels in a Rat Model of Traumatic Brain Injury

Blast-associated shock wave-induced traumatic brain injury (bTBI) remains a persistent risk for armed forces worldwide, yet its detailed pathophysiology remains to be fully investigated. In this study, we have designed and characterized a laboratory-scale shock tube to develop a rodent model of bTBI. Our blast tube, driven by a mixture of oxygen and acetylene, effectively generates blast overpressures of 20–130 psi, with pressure-time profiles similar to those of free-field blast waves. We tested our shock tube for brain injury response to various blast wave conditions in rats. The results show that blast waves cause diffuse vascular brain damage, as determined using a sensitive optical imaging method based on the fluorescence signal of Evans Blue dye extravasation developed in our laboratory. Vascular leakage increased with increasing blast overpressures and mapping of the brain slices for optical signal intensity indicated nonhomogeneous damage to the cerebral vasculature. We confirmed vascular leakage due to disruption in the blood-brain barrier (BBB) integrity following blast exposure. Reactive oxygen species (ROS) levels in the brain also increased with increasing blast pressures and with time post-blast wave exposure. Immunohistochemical analysis of the brain sections analyzed at different time points post blast exposure demonstrated astrocytosis and cell apoptosis, confirming sustained neuronal injury response. The main advantages of our shock-tube design are minimal jet effect and no requirement for specialized equipment or facilities, and effectively generate blast-associated shock waves that are relevant to battle-field conditions. Overall data suggest that increased oxidative stress and BBB disruption could be the crucial factors in the propagation and spread of neuronal degeneration following blast injury. Further studies are required to determine the interplay between increased ROS activity and BBB disruption to develop effective therapeutic strategies that can prevent the resulting cascade of neurodegeneration.

What's New in Traumatic Brain Injury: Update on Tracking, Monitoring and Treatment

Traumatic brain injury (TBI), defined as an alteration in brain functions caused by an external force, is responsible for high morbidity and mortality around the world. It is important to identify and treat TBI victims as early as possible. Tracking and monitoring TBI with neuroimaging technologies, including functional magnetic resonance imaging (fMRI), diffusion tensor imaging (DTI), positron emission tomography (PET), and high definition fiber tracking (HDFT) show increasing sensitivity and specificity. Classical electrophysiological monitoring, together with newly established brain-on-chip, cerebral microdialysis techniques, both benefit TBI. First generation molecular biomarkers, based on genomic and proteomic changes following TBI, have proven effective and economical. It is conceivable that TBI-specific biomarkers will be developed with the combination of systems biology and bioinformation strategies. Advances in treatment of TBI include stem cell-based and nanotechnology-based therapy, physical and pharmaceutical interventions and also new use in TBI for approved drugs which all present favorable promise in preventing and reversing TBI.

Disruption of caudate working memory activation in chronic blast-related traumatic brain injury

Mild to moderate traumatic brain injury (TBI) due to blast exposure is frequently diagnosed in veterans returning from the wars in Iraq and Afghanistan. However, it is unclear whether neural damage resulting from blast TBI differs from that found in TBI due to blunt-force trauma (e.g., falls and motor vehicle crashes). Little is also known about the effects of blast TBI on neural networks, particularly over the long term. Because impairment in working memory has been linked to blunt-force TBI, the present functional magnetic resonance imaging (fMRI) study sought to investigate whether brain activation in response to a working memory task would discriminate blunt-force from blast TBI. Twenty-five veterans (mean age = 29.8 years, standard deviation = 6.01 years, 1 female) who incurred TBI due to blast an average of 4.2 years prior to enrollment and 25 civilians (mean age = 27.4 years, standard deviation = 6.68 years, 4 females) with TBI due to blunt-force trauma performed the Sternberg Item Recognition Task while undergoing fMRI. The task involved encoding 1, 3, or 5 items in working memory. A group of 25 veterans (mean age = 29.9 years, standard deviation = 5.53 years, 0 females) and a group of 25 civilians (mean age = 27.3 years, standard deviation = 5.81 years, 0 females) without history of TBI underwent identical imaging procedures and served as controls. Results indicated that the civilian TBI group and both control groups demonstrated a monotonic relationship between working memory set size and activation in the right caudate during encoding, whereas the blast TBI group did not (p < 0.05, corrected for multiple comparisons using False Discovery Rate). Blast TBI was also associated with worse performance on the Sternberg Item Recognition Task relative to the other groups, although no other group differences were found on neuropsychological measures of episodic memory, inhibition, and general processing speed. These results could not be attributed to caudate atrophy or the presence of PTSD symptoms. Our results point to a specific vulnerability of the caudate to blast injury. Changes in activation during the Sternberg Item Recognition Task, and potentially other tasks that recruit the caudate, may serve as biomarkers for blast TBI.

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We investigated whether fMRI would discriminate blunt-force from blast mTBI.

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We used a working memory task with varying numbers of letters (set sizes).

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Blunt-force TBI showed a monotonic relation between set size and caudate activation.

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This relation was disrupted in the blast TBI group.

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Results point to a specific vulnerability of the caudate to blast injury

A novel rat model of blast-induced traumatic brain injury simulating different damage degree: implications for morphological, neurological, and biomarker changes

In current military conflicts and civilian terrorism, blast-induced traumatic brain injury (bTBI) is the primary cause of neurotrauma. However, the effects and mechanisms of bTBI are poorly understood. Although previous researchers have made significant contributions to establishing animal models for the simulation of bTBI, the precision and controllability of blast-induced injury in animal models must be improved. Therefore, we established a novel rat model to simulate blast-wave injury to the brain. To simulate different extents of bTBI injury, the animals were divided into moderate and severe injury groups. The miniature spherical explosives (pentaerythritol tetranitrate) used in each group were of different sizes (2.5 mm diameter in the moderate injury group and 3.0 mm diameter in the severe injury group). A specially designed apparatus was able to precisely adjust the positions of the miniature explosives and create eight rats with bTBI simultaneously, using a single electric detonator. Neurological functions, gross pathologies, histopathological changes and the expression levels of various biomarkers were examined after the explosion. Compared with the moderate injury group, there were significantly more neurological dysfunctions, cortical contusions, intraparenchymal hemorrhages, cortical expression of S-100β, myelin basic protein, neuron-specific enolase, IL-8, IL-10, inducible nitric oxide synthase, and HIF-1α in the severe injury group. These results demonstrate that we have created a reliable and reproducible bTBI model in rats. This model will be helpful for studying the mechanisms of bTBI and developing strategies for clinical bTBI treatment.

Characterization of traumatic brain injury in human brains reveals distinct cellular and molecular changes in contusion and pericontusion

Traumatic brain injury (TBI) contributes to fatalities and neurological disabilities worldwide. While primary injury causes immediate damage, secondary events contribute to long-term neurological defects. Contusions (Ct) are primary injuries correlated with poor clinical prognosis, and can expand leading to delayed neurological deterioration. Pericontusion (PC) (penumbra), the region surrounding Ct, can also expand with edema, increased intracranial pressure, ischemia, and poor clinical outcome. Analysis of Ct and PC can therefore assist in understanding the pathobiology of TBI and its management. This study on human TBI brains noted extensive neuronal, astroglial and inflammatory changes, alterations in mitochondrial, synaptic and oxidative markers, and associated proteomic profile, with distinct differences in Ct and PC. While Ct displayed petechial hemorrhages, thrombosis, inflammation, neuronal pyknosis, and astrogliosis, PC revealed edema, vacuolation of neuropil, axonal loss, and dystrophic changes. Proteomic analysis demonstrated altered immune response, synaptic, and mitochondrial dysfunction, among others, in Ct, while PC displayed altered regulation of neurogenesis and cytoskeletal architecture, among others. TBI brains displayed oxidative damage, glutathione depletion, mitochondrial dysfunction, and loss of synaptic proteins, with these changes being more profound in Ct. We suggest that analysis of markers specific to Ct and PC may be valuable in the evaluation of TBI pathobiology and therapeutics. We have characterized the primary injury in human traumatic brain injury (TBI). Contusions (Ct) - the injury core displayed hemorrhages, inflammation, and astrogliosis, while the surrounding pericontusion (PC) revealed edema, vacuolation, microglial activation, axonal loss, and dystrophy. Proteomic analysis demonstrated altered immune response, synaptic and mitochondrial dysfunction in Ct, and altered regulation of neurogenesis and cytoskeletal architecture in PC. Ct displayed more oxidative damage, mitochondrial, and synaptic dysfunction compared to PC.

Vascular and inflammatory factors in the pathophysiology of blast-induced brain injury

Blast-related traumatic brain injury (TBI) has received much recent attention because of its frequency in the conflicts in Iraq and Afghanistan. This renewed interest has led to a rapid expansion of clinical and animal studies related to blast. In humans, high-level blast exposure is associated with a prominent hemorrhagic component. In animal models, blast exerts a variety of effects on the nervous system including vascular and inflammatory effects that can be seen with even low-level blast exposures which produce minimal or no neuronal pathology. Acutely, blast exposure in animals causes prominent vasospasm and decreased cerebral blood flow along with blood-brain barrier breakdown and increased vascular permeability. Besides direct effects on the central nervous system, evidence supports a role for a thoracically mediated effect of blast; whereby, pressure waves transmitted through the systemic circulation damage the brain. Chronically, a vascular pathology has been observed that is associated with alterations of the vascular extracellular matrix. Sustained microglial and astroglial reactions occur after blast exposure. Markers of a central and peripheral inflammatory response are found for sustained periods after blast injury and include elevation of inflammatory cytokines and other inflammatory mediators. At low levels of blast exposure, a microvascular pathology has been observed in the presence of an otherwise normal brain parenchyma, suggesting that the vasculature may be selectively vulnerable to blast injury. Chronic immune activation in brain following vascular injury may lead to neurobehavioral changes in the absence of direct neuronal pathology. Strategies aimed at preventing or reversing vascular damage or modulating the immune response may improve the chronic neuropsychiatric symptoms associated with blast-related TBI.

Effects of blast overpressure on neurons and glial cells in rat organotypic hippocampal slice cultures

Due to recent involvement in military conflicts, and an increase in the use of explosives, there has been an escalation in the incidence of blast-induced traumatic brain injury (bTBI) among US military personnel. Having a better understanding of the cellular and molecular cascade of events in bTBI is prerequisite for the development of an effective therapy that currently is unavailable. The present study utilized organotypic hippocampal slice cultures (OHCs) exposed to blast overpressures of 150 kPa (low) and 280 kPa (high) as an in vitro bTBI model. Using this model, we further characterized the cellular effects of the blast injury. Blast-evoked cell death was visualized by a propidium iodide (PI) uptake assay as early as 2 h post-injury. Quantification of PI staining in the cornu Ammonis 1 and 3 (CA1 and CA3) and the dentate gyrus regions of the hippocampus at 2, 24, 48, and 72 h following blast exposure revealed significant time dependent effects. OHCs exposed to 150 kPa demonstrated a slow increase in cell death plateauing between 24 and 48 h, while OHCs from the high-blast group exhibited a rapid increase in cell death already at 2 h, peaking at ~24 h post-injury. Measurements of lactate dehydrogenase release into the culture medium also revealed a significant increase in cell lysis in both low- and high-blast groups compared to sham controls. OHCs were fixed at 72 h post-injury and immunostained for markers against neurons, astrocytes, and microglia. Labeling OHCs with PI, neuronal, and glial markers revealed that the blast-evoked extensive neuronal death and to a lesser extent loss of glial cells. Furthermore, our data demonstrated activation of astrocytes and microglial cells in low- and high-blasted OHCs, which reached a statistically significant difference in the high-blast group. These data confirmed that our in vitro bTBI model is a useful tool for studying cellular and molecular changes after blast exposure.