A Comprehensive Review of Experimental Rodent Models of Repeated Blast TBI

Additive effects of mild head trauma, blast exposure, and aging within white matter tracts: A novel Diffusion Tensor Imaging analysis approach

Existing diffusion tensor imaging (DTI) studies of neurological injury following high-level blast exposure (hlBE) in military personnel have produced widely variable results. This is potentially due to prior studies often not considering the quantity and/or recency of hlBE, as well as co-morbidity with non-blast head trauma (nbHT). Herein, we compare commonly used DTI metrics: fractional anisotropy and mean, axial, and radial diffusivity, in Veterans with and without history of hlBE and/or nbHT. We use both the traditional method of dividing participants into 2 equally weighted groups and an alternative method wherein each participant is weighted by quantity and recency of hlBE and/or nbHT. While no differences were detected using the traditional method, the alternative method revealed diffuse and extensive changes in all DTI metrics. These effects were quantified within 43 anatomically defined white matter tracts, which identified the forceps minor, middle corpus callosum, acoustic and optic radiations, fornix, uncinate, inferior fronto-occipital and inferior longitudinal fasciculi, and cingulum, as the pathways most affected by hlBE and nbHT. Moreover, additive effects of aging were present in many of the same tracts suggesting that these neuroanatomical effects may compound with age.

Effect of blast orientation, multi-point blasts, and repetitive blasts on brain injury

Explosions in the battlefield can result in brain damage. Research on the effects of shock waves on brain tissue mainly focuses on the effects of single-orientation blast waves, while there have been few studies on the dynamic response of the human brain to directional explosions in different planes, multi-point explosions and repetitive explosions. Therefore, the brain tissue response and the intracranial pressure (ICP) caused by different blast loadings were numerically simulated using the CONWEP method. In the study of the blast in different directions, the lateral explosion blast wave was found to cause greater ICP than did blasts from other directions. When multi-point explosions occurred in the sagittal plane simultaneously, the ICP in the temporal lobe increased by 37.8 % and the ICP in the parietal lobe decreased by 17.6 %. When multi-point explosions occurred in the horizontal plane, the ICP in the frontal lobe increased by 61.8 % and the ICP in the temporal lobe increased by 12.2 %. In a study of repetitive explosions, the maximum ICP of the second blast increased by 40.6 % over that of the first blast, and that of the third blast increased by 61.2 % over that of the second blast. The ICP on the brain tissue from repetitive blasts can exceed 200 % of that of a single explosion blast wave.

Sleep, inflammation, and hemodynamics in rodent models of traumatic brain injury

Traumatic brain injury (TBI) can induce dysregulation of sleep. Sleep disturbances include hypersomnia and hyposomnia, sleep fragmentation, difficulty falling asleep, and altered electroencephalograms. TBI results in inflammation and altered hemodynamics, such as changes in blood brain barrier permeability and cerebral blood flow. Both inflammation and altered hemodynamics, which are known sleep regulators, contribute to sleep impairments post-TBI. TBIs are heterogenous in cause and biomechanics, which leads to different molecular and symptomatic outcomes. Animal models of TBI have been developed to model the heterogeneity of TBIs observed in the clinic. This review discusses the intricate relationship between sleep, inflammation, and hemodynamics in pre-clinical rodent models of TBI.

Late chronic local inflammation, synaptic alterations, vascular remodeling and arteriovenous malformations in the brains of male rats exposed to repetitive low-level blast overpressures

In the course of military operations in modern war theaters, blast exposures are associated with the development of a variety of mental health disorders associated with a post-traumatic stress disorder-related features, including anxiety, impulsivity, insomnia, suicidality, depression, and cognitive decline. Several lines of evidence indicate that acute and chronic cerebral vascular alterations are involved in the development of these blast-induced neuropsychiatric changes. In the present study, we investigated late occurring neuropathological events associated with cerebrovascular alterations in a rat model of repetitive low-level blast-exposures (3 × 74.5 kPa). The observed events included hippocampal hypoperfusion associated with late-onset inflammation, vascular extracellular matrix degeneration, synaptic structural changes and neuronal loss. We also demonstrate that arteriovenous malformations in exposed animals are a direct consequence of blast-induced tissue tears. Overall, our results further identify the cerebral vasculature as a main target for blast-induced damage and support the urgent need to develop early therapeutic approaches for the prevention of blast-induced late-onset neurovascular degenerative processes.

Acute Treatment with the M-Channel (Kv7, KCNQ) Opener Retigabine Reduces the Long-Term Effects of Repetitive Blast Traumatic Brain Injuries

We investigated whether pharmacological increase of "M-type" (KCNQ, Kv7) K + channel currents by the M-channel opener, retigabine (RTG), acutely after repetitive traumatic brain injuries (rTBIs), prevents or reduces their long-term detrimental effects. rTBIs were studied using a blast shock air wave mouse model. Animals were monitored by video and electroencephalogram (EEG) records for nine months after the last injury to assess the occurrence of post-traumatic seizures (PTS), post-traumatic epilepsy (PTE), sleep-wake cycle architecture alterations, and the power of the EEG signals. We evaluated the development of long-term changes in the brain associated with various neurodegenerative diseases in mice by examining transactive response DNA-binding protein 43 (TDP-43) expression and nerve fiber damage ~ 2 years after the rTBIs. We observed acute RTG treatment to reduce the duration of PTS and impair the development of PTE. Acute RTG treatment also prevented post-injury hypersomnia, nerve fiber damage, and cortical TDP-43 accumulation and translocation from the nucleus to the cytoplasm. Mice that developed PTE displayed impaired rapid eye movement (REM) sleep, and there were significant correlations between seizure duration and time spent in the different stages of the sleep-wake cycle. We observed acute RTG treatment to impair injury-induced reduction of age-related increase in gamma frequency power of the EGG, which has been suggested to be necessary for a healthy aged brain. The data show that RTG, administered acutely post-TBI, is a promising, novel therapeutic option to blunt/prevent several long-term effects of rTBIs. Furthermore, our results show a direct relationship between sleep architecture and PTE.

Chronicity of repeated blast traumatic brain injury associated increase in oxycodone seeking in rats

Numerous epidemiological studies have found co-morbidity between non-severe traumatic brain injury (TBI) and substance misuse in both civilian and military populations. Preclinical studies have also identified this relationship for some misused substances. We have previously demonstrated that repeated blast traumatic brain injury (rbTBI) increased oxycodone seeking without increasing oxycodone self-administration, suggesting that the neurological sequelae of traumatic brain injury can elevate opioid misuse liability. Here, we determined the chronicity of this effect by testing different durations of time between injury and oxycodone self-administration and durations of abstinence. We found that the subchronic (four weeks), but not the acute (three days) or chronic (four months) duration between injury and oxycodone self-administration was associated with increased drug seeking and re-acquisition of self-administration following a 10-day abstinence. Examination of other abstinence durations (two days, four weeks, or four months) revealed no effect of rbTBI on drug seeking at any of the abstinence durations tested. Together, these data indicate that there is a window of vulnerability after TBI when oxycodone self-administration is associated with elevated drug seeking and relapse-related behaviors.

Double Blast Wave Primary Effect on Synaptic, Glymphatic, Myelin, Neuronal and Neurovascular Markers

Explosive blasts are associated with neurological consequences as a result of blast waves impact on the brain. Yet, the neuropathologic and molecular consequences due to blast waves vs. blunt-TBI are not fully understood. An explosive-driven blast-generating system was used to reproduce blast wave exposure and examine pathological and molecular changes generated by primary wave effects of blast exposure. We assessed if pre- and post-synaptic (synaptophysin, PSD-95, spinophilin, GAP-43), neuronal (NF-L), glymphatic (LYVE1, podoplanin), myelin (MBP), neurovascular (AQP4, S100β, PDGF) and genomic (DNA polymerase-β, RNA polymerase II) markers could be altered across different brain regions of double blast vs. sham animals. Twelve male rats exposed to two consecutive blasts were compared to 12 control/sham rats. Western blot, ELISA, and immunofluorescence analyses were performed across the frontal cortex, hippocampus, cerebellum, and brainstem. The results showed altered levels of AQP4, S100β, DNA-polymerase-β, PDGF, synaptophysin and PSD-95 in double blast vs. sham animals in most of the examined regions. These data indicate that blast-generated changes are preferentially associated with neurovascular, glymphatic, and DNA repair markers, especially in the brainstem. Moreover, these changes were not accompanied by behavioral changes and corroborate the hypothesis for which an asymptomatic altered status is caused by repeated blast exposures.

A biomechanical-based approach to scale blast-induced molecular changes in the brain

Animal studies provide valuable insights on how the interaction of blast waves with the head may injure the brain. However, there is no acceptable methodology to scale the findings from animals to humans. Here, we propose an experimental/computational approach to project observed blast-induced molecular changes in the rat brain to the human brain. Using a shock tube, we exposed rats to a range of blast overpressures (BOPs) and used a high-fidelity computational model of a rat head to correlate predicted biomechanical responses with measured changes in glial fibrillary acidic protein (GFAP) in rat brain tissues. Our analyses revealed correlates between model-predicted strain rate and measured GFAP changes in three brain regions. Using these correlates and a high-fidelity computational model of a human head, we determined the equivalent BOPs in rats and in humans that induced similar strain rates across the two species. We used the equivalent BOPs to project the measured GFAP changes in the rat brain to the human. Our results suggest that, relative to the rat, the human requires an exposure to a blast wave of a higher magnitude to elicit similar brain-tissue responses. Our proposed methodology could assist in the development of safety guidelines for blast exposure.

A companion to the preclinical common data elements for rodent models of pediatric acquired epilepsy: A report of the TASK3-WG1B, Pediatric and Genetic Models Working Group of the ILAE/AES Joint Translational Task Force

Epilepsy syndromes during the early years of life may be attributed to an acquired insult, such as hypoxic-ischemic injury, infection, status epilepticus, or brain trauma. These conditions are frequently modeled in experimental rodents to delineate mechanisms of epileptogenesis and investigate novel therapeutic strategies. However, heterogeneity and subsequent lack of reproducibility of such models across laboratories is an ongoing challenge to maintain scientific rigor and knowledge advancement. To address this, as part of the TASK3-WG1B Working Group of the International League Against Epilepsy/American Epilepsy Society Joint Translational Task Force, we have developed a series of case report forms (CRFs) to describe common data elements for pediatric acquired epilepsy models in rodents. The "Rodent Models of Pediatric Acquired Epilepsy" Core CRF was designed to capture cohort-general information; while two Specific CRFs encompass physical induction models and chemical induction models, respectively. This companion manuscript describes the key elements of these models and why they are important to be considered and reported consistently. Together, these CRFs provide investigators with the tools to systematically record critical information regarding their chosen model of acquired epilepsy during early life, for improved standardization and transparency across laboratories. These outcomes will support the ultimate goal of such research; that is, to understand the childhood onset-specific biology of epileptogenesis after acquired insults, and translate this knowledge into therapeutics to improve pediatric patient outcomes and minimize the lifetime burden of epilepsy.

Localization of the hydrogen sulfide and oxytocin systems at the depth of the sulci in a porcine model of acute subdural hematoma

In the porcine model discussed in this review, the acute subdural hematoma was induced by subdural injection of autologous blood over the left parietal cortex, which led to a transient elevation of the intracerebral pressure, measured by bilateral neuromonitoring. The hematoma-induced brain injury was associated with albumin extravasation, oxidative stress, reactive astrogliosis and microglial activation in the ipsilateral hemisphere. Further proteins and injury markers were validated to be used for immunohistochemistry of porcine brain tissue. The cerebral expression patterns of oxytocin, oxytocin receptor, cystathionine-γ-lyase and cystathionine-β-synthase were particularly interesting: these four proteins all co-localized at the base of the sulci, where pressure-induced brain injury elicits maximum stress. In this context, the pig is a very relevant translational model in contrast to the rodent brain. The structure of the porcine brain is very similar to the human: the presence of gyri and sulci (gyrencephalic brain), white matter to grey matter proportion and tentorium cerebelli. Thus, pressure-induced injury in the porcine brain, unlike in the rodent brain, is reflective of the human pathophysiology.

Measuring Anxiety-Like Behaviors in Rodent Models of Traumatic Brain Injury

Anxiety is a common complaint following acquired traumatic brain injury (TBI). However, the measurement of dysfunctional anxiety behavioral states following experimental TBI in rodents is complex. Some studies report increased anxiety after TBI, whereas others find a decreased anxiety-like state, often described as increased risk-taking behavior or impulsivity. These inconsistencies may reflect a lack of standardization of experimental injury models or of behavioral testing techniques. Here, we review the most commonly employed unconditioned tests of anxiety and discuss them in a context of experimental TBI. Special attention is given to the effects of repeated testing, and consideration of potential sensory and motor confounds in injured rodents. The use of multiple tests and alternative data analysis methods are discussed, as well as the potential for the application of common data elements (CDEs) as a means of providing a format for documentation of experimental details and procedures of each published research report. CDEs may improve the rigor, reproducibility, as well as endpoint for better relating findings with clinical TBI phenotypes and the final goal of translation. While this may not resolve all incongruities in findings across laboratories, it is seen as a way forward for standardized and universal data collection for improvement of data quality and sharing, and advance therapies for neuropsychiatric symptoms that often present for decades following TBI.

Low-level blast exposure induces chronic vascular remodeling, perivascular astrocytic degeneration and vascular-associated neuroinflammation

Cerebral vascular injury as a consequence of blast-induced traumatic brain injury is primarily the result of blast wave-induced mechanical disruptions within the neurovascular unit. In rodent models of blast-induced traumatic brain injury, chronic vascular degenerative processes are associated with the development of an age-dependent post-traumatic stress disorder-like phenotype. To investigate the evolution of blast-induced chronic vascular degenerative changes, Long-Evans rats were blast-exposed (3 × 74.5 kPa) and their brains analyzed at different times post-exposure by X-ray microcomputed tomography, immunohistochemistry and electron microscopy. On microcomputed tomography scans, regional cerebral vascular attenuation or occlusion was observed as early as 48 h post-blast, and cerebral vascular disorganization was visible at 6 weeks and more accentuated at 13 months post-blast. Progression of the late-onset pathology was characterized by detachment of the endothelial and smooth muscle cellular elements from the neuropil due to degeneration and loss of arteriolar perivascular astrocytes. Development of this pathology was associated with vascular remodeling and neuroinflammation as increased levels of matrix metalloproteinases (MMP-2 and MMP-9), collagen type IV loss, and microglial activation were observed in the affected vasculature. Blast-induced chronic alterations within the neurovascular unit should affect cerebral blood circulation, glymphatic flow and intramural periarterial drainage, all of which may contribute to development of the blast-induced behavioral phenotype. Our results also identify astrocytic degeneration as a potential target for the development of therapies to treat blast-induced brain injury.

Investigation of the direct and indirect mechanisms of primary blast insult to the brain

The interaction of explosion-induced blast waves with the head (i.e., a direct mechanism) or with the torso (i.e., an indirect mechanism) presumably causes traumatic brain injury. However, the understanding of the potential role of each mechanism in causing this injury is still limited. To address this knowledge gap, we characterized the changes in the brain tissue of rats resulting from the direct and indirect mechanisms at 24 h following blast exposure. To this end, we conducted separate blast-wave exposures on rats in a shock tube at an incident overpressure of 130 kPa, while using whole-body, head-only, and torso-only configurations to delineate each mechanism. Then, we performed histopathological (silver staining) and immunohistochemical (GFAP, Iba-1, and NeuN staining) analyses to evaluate brain-tissue changes resulting from each mechanism. Compared to controls, our results showed no significant changes in torso-only-exposed rats. In contrast, we observed significant changes in whole-body-exposed (GFAP and silver staining) and head-only-exposed rats (silver staining). In addition, our analyses showed that a head-only exposure causes changes similar to those observed for a whole-body exposure, provided the exposure conditions are similar. In conclusion, our results suggest that the direct mechanism is the major contributor to blast-induced changes in brain tissues.

Insulin-like Growth Factors may be Markers of both Traumatic Brain Injury and Fear-Related Stress

Insulin-like growth factors (IGF) are potent neurotrophic and neurorepair factors that were recently proposed as biomarkers of traumatic brain injury (TBI) and associated psychiatric comorbidities, in particular post-traumatic stress disorder (PSTD). We tested the hypothesis that the IGF system is differentially deregulated in the acute and early chronic stages of TBI, and under acute stress. Plasma and brain IGF1 and IGF2 levels were evaluated in mice 3 weeks and 3 days after a controlled cortical impact (CCI)-induced mild-to-moderate TBI. The effects of conditioned fear on IGF levels and its interaction with TBI (TBI followed, 3 weeks later, by fear-inducing procedures) were also evaluated. In the plasma, IGF1 decreased 3 weeks post-TBI only (-9%), whereas IGF2 remained unaffected. In the brain, IGF1 increased only in the cortex and hippocampus at 3 weeks post-TBI (up to +650%). At 3 days, surpringly, this increase was more diffuse and more important in sham (craniotomized) animals. Additionally, IGF2 immunostaining in brain ventricles was reorganized in TBI animals at both post-TBI stages. Conditioned fear exposure did not influence the effects of early chronic TBI on plasma IGF1 levels, but reduced plasma IGF2 (-6%) levels. It also dampened the effects of TBI on brain IGF systems, but brain IGF1 level and IGF2 tissue distribution remained statistically different from controls under these conditions. In co-exposed animals, DNA methylation increased at the hippocampal Igf1 gene promoter. These results show that blood IGF1 and IGF2 are most reduced in the early chronic phase of TBI and after exposure to a stressful event, and that the brain IGF system is up-regulated after TBI, and more so in the acute phase.

Axonal damage and behavioral deficits in rats with repetitive exposure of the brain to laser-induced shock waves: Effects of inter-exposure time

Much attention has been given to effects of repeated exposure to a shock wave as a possible factor causing severe higher brain dysfunction and post-traumatic stress disorder (PTSD)-like symptoms in patients with mild to moderate blast-induced traumatic brain injury (bTBI). However, it is unclear how the repeated exposure and the inter-exposure time affect the brain. In this study, we topically applied low-impulse (∼54 Pa·s) laser-induced shock waves (LISWs; peak pressure, ∼75.7 MPa) to the rat brain once or twice with the different inter-exposure times (15 min, 1 h, 3 h, 24 h and 7 days) and examined anxiety-related behavior and motor dysfunction in the rats as well as expression of β-amyloid precursor protein (APP) as an axonal damage marker in the brains of the rats. The averaged APP expression scores for the rat brains doubly-exposed to LISWs with inter-exposure times from 15 min to 24 h were significantly higher than those for rats with a single exposure (P < 0.0001). The rats with double exposure to LISWs showed significantly more frequent anxiety-related behavior (P < 0.05) and poorer motor function (P < 0.01) than those of rats with a single exposure. When the inter-exposure time was extended to 7 days, however, the rats showed no significant differences either in axonal damage score or level of motor dysfunction. The results suggest that the cumulative effects of shock wave-related brain injury can be avoided with an appropriate inter-exposure time. However, clinical bTBI occurs in much more complex environments than those in our model. Further study considering other factors, such as the effects of acceleration, is needed to know the clinically-relevant, necessary inter-exposure time.

Neuroprotectin D1 Attenuates Blast Overpressure Induced Reactive Microglial Cells in the Cochlea

OBJECTIVE/HYPOTHESIS

We examined a neuroinflammatory response associated with glial activation in the cochlea exposed to blast overpressure and evaluated the potential therapeutic efficacy of specialized pro-resolving mediators such as neuroprotectin D1, NPD1; (10R, 17S-dihydroxy-4Z, 7Z, 11E, 13E, 15Z, 19Z-docosahexaenoic acid) in a rodent blast-induced auditory injury model.

STUDY DESIGN

Animal Research.

METHODS

A compressed-air driven shock tube was used to expose anesthetized adult male Long-Evan rats to shock waves simulating an open-field blast exposure. Approximately 30 minutes after blast exposure, rats were treated with NPD1 (100 ng/kg body wt.) or vehicle delivered intravenously via tail vein injection. Rats were then euthanized 48 hours after blast exposure. Unexposed rats were included as controls. Tissue sections containing both middle and inner ear were prepared with hematoxylin-eosin staining to elucidate histopathological changes associated with blast exposure. Cochlear tissues were evaluated for relative expression of ionized calcium-binding adaptor 1 (Iba1), as an indicator of microglial activation by immunohistochemistry and western blot analyses.

RESULTS

Our animal model resulted in an acute injury mechanism manifested by damage to the tympanic membrane, hemorrhage, infiltration of inflammatory cells, and increased expression of Iba1 protein. Moreover, therapeutic intervention with NPD1 significantly reduced Iba1 expression in the cochlea, suggesting a reduction of a neuroinflammatory response caused by blast overpressure.

CONCLUSIONS

Blast overpressure resulted in an increased expression of proteins involved in gliosis within the auditory system, which were reduced by NPD1. Treatment of NPD1 suggests an effective strategy to reduce or halt auditory microglial cell activation due to primary blast exposure.

LEVEL OF EVIDENCE

NA Laryngoscope, 131:E2018-E2025, 2021.

Links between thrombosis and inflammation in traumatic brain injury

Traumatic brain injury (TBI) continues to be a major healthcare problem and there is much to be explored regarding the secondary pathobiology to identify early predictive markers and new therapeutic targets. While documented changes in thrombosis and inflammation in major trauma have been well described, growing evidence suggests that isolated TBI also results in systemic alterations in these mechanisms. Here, we review recent experimental and clinical findings that demonstrate how blood-brain barrier dysfunction, systemic immune response, inflammation, platelet activation, and thrombosis contribute significantly to the pathogenesis of TBI. Despite advances in the links between thrombosis and inflammation, there is a lack of treatment options aimed at both processes and this could be crucial to treating vascular injury, local and systemic inflammation, and secondary ischemic events following TBI. With emerging evidence of newly-identified roles for platelets, leukocytes, the coagulation system and extracellular vesicles in processes of inflammation and thrombosis, there is a growing need to characterize these mechanisms within the context of TBI and whether these changes persist into the chronic phase of injury. Importantly, this review defines areas in need of further research to advance the field and presents a roadmap to identify new diagnostic and treatment options for TBI.

Sex as a Biological Variable in Preclinical Modeling of Blast-Related Traumatic Brain Injury

Approaches to furthering our understanding of the bioeffects, behavioral changes, and treatment options following exposure to blast are a worldwide priority. Of particular need is a more concerted effort to employ animal models to determine possible sex differences, which have been reported in the clinical literature. In this review, clinical and preclinical reports concerning blast injury effects are summarized in relation to sex as a biological variable (SABV). The review outlines approaches that explore the pertinent role of sex chromosomes and gonadal steroids for delineating sex as a biological independent variable. Next, underlying biological factors that need exploration for blast effects in light of SABV are outlined, including pituitary, autonomic, vascular, and inflammation factors that all have evidence as having important SABV relevance. A major second consideration for the study of SABV and preclinical blast effects is the notable lack of consistent model design—a wide range of devices have been employed with questionable relevance to real-life scenarios—as well as poor standardization for reporting of blast parameters. Hence, the review also provides current views regarding optimal design of shock tubes for approaching the problem of primary blast effects and sex differences and outlines a plan for the regularization of reporting. Standardization and clear description of blast parameters will provide greater comparability across models, as well as unify consensus for important sex difference bioeffects.

Improved blind tracheal intubation in rats: a simple and secure approach

Successful tracheal intubation is the prerequisite for open-chest models. Tracheal intubation in small animal such as the rat is often challenging due to the small size and special anatomy. We investigated whether endotracheal intubation can be performed safely and reliably in rats employing only gesture fixation and a catheter. Rats were randomly classified into three groups: Improved blind intubation (B group) was performed with gestures fixed intubation position. Transillumination intubation (T group) utilized light to locate the larynx. Incision intubation (I group) was intubated after trachea incision. The feasibility, difficulty, complications of the three groups were compared. B group was faster than the other two groups. Completion time of the operation was recorded as follows: B group: 35.00 ± 9.86 sec; T group: 57.12 ± 6.54 sec; I group: 184.33 ± 25.49 sec (P≤0.001). B group has fewer attempts than Group T (P=0.001). The operational success rates of all three groups (B group 14 (93.3%) vs. T group 12 (80.0%) vs. I group 13 (86.7%)) were similar (P>0.05). In terms of operation difficult and operational complications, the differences between the three groups were not significant. The rate of endometrial damage under microscope were no difference, too. The Improved blind endotracheal intubation is a simple method, with a comparable safety profile to that of the transillumination and incision intubaton.

The closed-head impact model of engineered rotational acceleration (CHIMERA) as an application for traumatic brain injury pre-clinical research: A status report

Closed-head traumatic brain injury (TBI) is a worldwide concern with increasing prevalence and cost to society. Rotational acceleration is a primary mechanism in TBI that results from tissue strains that give rise to diffuse axonal injury. The Closed-Head Impact Model of Engineered Rotational Acceleration (CHIMERA) was recently introduced as a method for the study of impact acceleration effects in pre-clinical TBI research. This review provides a survey of the published literature implementing the CHIMERA device and describes pathological, imaging, neurophysiological, and behavioral findings. Findings show CHIMERA inflicts damage in white matter tracts as a key area of injury. Behaviorally, repeated studies have shown motor deficits and more chronic cognitive effects after CHIMERA injury. Good progress with model application has been accomplished by investigators attending to what is required for model validation. However, the majority of CHIMERA studies only utilize adult male mice. To further establish this model, more work with female animals and various age groups need to be performed, as well as studies to further establish and standardize methodologies for validation of the models for clinical relevance. Common data elements to standardize the reporting methodology for the CHIMERA literature are suggested.

Blast exposure predisposes the brain to increased neurological deficits in a model of blast plus blunt traumatic brain injury

Soldiers are often exposed to more than one traumatic brain injury (TBI) over the course of their service. In recent years, more attention has been drawn to the increased risk of neurological deficits caused by the 'blast plus' polytrauma, which typically is a blast trauma combined with other forms of TBI. In this study, we investigated the behavioral and neuronal deficits resulting from a blast plus injury involving a mild-moderate blast followed by a mild blunt trauma using the fluid percussion injury model. We identified that the blast injury predisposed the brain to increased cognitive deficits, chronic ventricular enlargement, increased neurodegeneration at acute time points and chronic neuronal loss. Interestingly, a single blast and single blunt injury differed in their onset and manifestation of cognitive and regional neuronal loss. We also identified the presence of cleaved RIP1 from caspase 8 mediated apoptosis in the blunt injury while the blast injury did not activate immediate apoptosis but led to decreased hilar neuronal survival over time.