Search

Primary blast exposure is a predominant cause of mild traumatic brain injury (mTBI) among veterans and active-duty military personnel, and affected individuals may develop long-lasting behavioral disturbances that interfere with quality of life. Our prior research with the "Missouri Blast" model demonstrated behavioral changes relevant to deficits in cognitive and affective domains after exposure to low-intensity blast (LIB). In this study, behavioral evaluations were extended to 3 months post-LIB injury using multifaceted conventional and advanced behavioral paradigms. C57BL/6J male mice, aged 2 months old, were subjected to a non-inertial primary LIB-induced mTBI by detonating 350 g of C-4 at a 3-m distance on 1-m-tall platforms. Three months after injury, mice were evaluated using the open-field test (OFT), social interaction test, and advanced Erasmus Ladder paradigm. With OFT, no apparent anxiety-like changes were detected with the LIB-exposed mice and sham controls, and both groups displayed similar center-zone activities. Although no social interaction parameters reached significance, a majority of LIB-exposed mice initiated less than 50% of interactions compared with their interaction partners, suggesting decreased sociability. With the Erasmus Ladder test to assess motor functions, associative learning, and stimulus response, LIB-exposed mice appeared to display increased instances of leaving before the cue, reminiscent of "escape behavior," indicative of anxiety-related activity different from that OFT detected. Overall, these results revealed subtle multifaceted long-lasting anxiety-relevant effects following LIB exposure. The "Missouri Blast" platform offers a basis for future research to investigate the underlying biological mechanism(s) leading to domain-specific behavioral changes., (© The Author(s) 2024. Published by Mary Ann Liebert, Inc.)

Mild traumatic brain injury (mTBI) resulting from low-intensity blast (LIB) exposure in military and civilian individuals is linked to enduring behavioral and cognitive abnormalities. These injuries can serve as confounding risk factors for the development of neurodegenerative disorders, including Alzheimer's disease-related dementias (ADRD). Recent animal studies have demonstrated LIB-induced brain damage at the molecular and nanoscale levels. Nevertheless, the mechanisms linking these damages to cognitive abnormalities are unresolved. Challenges preventing the translation of preclinical studies into meaningful findings in "real-world clinics" encompass the heterogeneity observed between different species and strains, variable time durations of the tests, quantification of dosing effects and differing approaches to data analysis. Moreover, while behavioral tests in most pre-clinical studies are conducted at the group level, clinical tests are predominantly assessed on an individual basis. In this investigation, we advanced a high-resolution and sensitive method utilizing the CognitionWall test system and applying reversal learning data to the Boltzmann fitting curves. A flow chart was developed that enable categorizing individual mouse to different levels of learning deficits and patterns. In this study, rTg4510 mice, which represent a neuropathology model due to elevated levels of tau P301L, together with the non-carrier genotype were exposed to LIB. Results revealed distinct and intricate patterns of learning deficits and patterns within each group and in relation to blast exposure. With the current findings, it is possible to establish connections between mice with specific cognitive deficits to molecular changes. This approach can enhance the translational value of preclinical findings and also allow for future development of a precision clinical treatment plan for ameliorating neurologic damage of individuals with mTBI., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (Copyright © 2024 Zuckerman, Siedhoff, Balderrama, Li, Sun, Cifu, Cernak, Cui and Gu.)

Blast-induced neurotrauma (BINT) is a pressing concern for veterans and civilians exposed to explosive devices. Affected personnel may have increased risk for long-term cognitive decline and developing tauopathies including Alzheimer's disease-related disorders (ADRD) or frontal-temporal dementia (FTD). The goal of this study was to identify the effect of BINT on molecular networks and their modulation by mutant tau in transgenic (Tg) mice overexpressing the human tau P301L mutation (rTg4510) linked to FTD or non-carriers. The primary focus was on the phosphoproteome because of the prominent role of hyperphosphorylation in neurological disorders. Discrimination learning was assessed following injury in the subsequent 6 weeks, using the automated home-cage monitoring CognitionWall platform. At 40 days post injury, label-free phosphoproteomics was used to evaluate molecular networks in the frontal cortex of mice. Utilizing a weighted peptide co-expression network analysis (WpCNA) approach, we identified phosphopeptide networks tied to associative learning and mossy-fiber pathways and those which predicted learning outcomes. Phosphorylation levels in these networks were inversely related to learning and linked to synaptic dysfunction, cognitive decline, and dementia including Atp6v1a and Itsn1. Low-intensity blast (LIB) selectively increased pSer262tau in rTg4510, a site implicated in initiating tauopathy. Additionally, individual and group level analyses identified the Arhgap33 phosphopeptide as an indicator of BINT-induced cognitive impairment predominantly in rTg4510 mice. This study unveils novel interactions between ADRD genetic susceptibility, BINT, and cognitive decline, thus identifying dysregulated pathways as targets in potential precision-medicine focused therapeutics to alleviate the disease burden among those affected by BINT.

Mild traumatic brain injury (mTBI) induced by low-intensity blast (LIB) is a serious health problem affecting military service members and veterans. Our previous reports using a single open-field LIB mouse model showed the absence of gross microscopic damage or necrosis in the brain, while transmission electron microscopy (TEM) identified ultrastructural abnormalities of myelin sheaths, mitochondria, and synapses. The neurovascular unit (NVU), an anatomical and functional system with multiple components, is vital for the regulation of cerebral blood flow and cellular interactions. In this study, we delineated ultrastructural abnormalities affecting the NVU in mice with LIB exposure quantitatively and qualitatively. Luminal constrictive irregularities were identified at 7 days post-injury (DPI) followed by dilation at 30 DPI along with degeneration of pericytes. Quantitative proteomic analysis identified significantly altered vasomotor-related proteins at 24 h post-injury. Endothelial cell, basement membrane and astrocyte end-foot swellings, as well as vacuole formations, occurred in LIB-exposed mice, indicating cellular edema. Structural abnormalities of tight junctions and astrocyte end-foot detachment from basement membranes were also noted. These ultrastructural findings demonstrate that LIB induces multiple-component NVU damage. Prevention of NVU damage may aid in identifying therapeutic targets to mitigate the effects of primary brain blast injury., (© 2023. BioMed Central Ltd., part of Springer Nature.)

Neurocognitive consequences of blast-induced traumatic brain injury (bTBI) pose significant concerns for military service members and veterans with the majority of "invisible injury." However, the underlying mechanism of such mild bTBI by low-intensity blast (LIB) exposure for long-term cognitive and mental deficits remains elusive. Our previous studies have shown that mice exposed to LIB result in nanoscale ultrastructural abnormalities in the absence of gross or apparent cellular damage in the brain. Here we tested the hypothesis that glutamatergic hyperexcitability may contribute to long-term learning deficits. Using brain slice electrophysiological recordings, we found an increase in averaged frequencies with a burst pattern of miniature excitatory postsynaptic currents (mEPSCs) in hippocampal CA3 neurons in LIB-exposed mice at 1- and 7-days post injury, which was blocked by a specific NMDA receptor antagonist AP5. In addition, cognitive function assessed at 3-months post LIB exposure by automated home-cage monitoring showed deficits in dynamic patterns of discrimination learning and cognitive flexibility in LIB-exposed mice. Collected hippocampal tissue was further processed for quantitative global-proteomic analysis. Advanced data-independent acquisition for quantitative tandem mass spectrometry analysis identified altered expression of proteins involved in synaptic plasticity and serine protease inhibitors in LIB-exposed mice. Some were correlated with the ability of discrimination learning and cognitive flexibility. These findings show that acute glutamatergic hyperexcitability in the hippocampus induced by LIB may contribute to long-term cognitive dysfunction and protein alterations. Studies using this military-relevant mouse model of mild bTBI provide valuable insights into developing a potential therapeutic strategy to ameliorate hyperexcitability-modulated LIB injuries., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Most traumatic brain injuries (TBIs) during military deployment or training are clinically "mild" and frequently caused by non-impact blast exposures. Experimental models were developed to reproduce the biological consequences of high-intensity blasts causing moderate to severe brain injuries. However, the pathophysiological mechanisms of low-intensity blast (LIB)-induced neurological deficits have been understudied. This review provides perspectives on primary blast-induced mild TBI models and discusses translational aspects of LIB exposures as defined by standardized physical parameters including overpressure, impulse, and shock wave velocity. Our mouse LIB-exposure model, which reproduces deployment-related scenarios of open-field blast (OFB), caused neurobehavioral changes, including reduced exploratory activities, elevated anxiety-like levels, impaired nesting behavior, and compromised spatial reference learning and memory. These functional impairments associate with subcellular and ultrastructural neuropathological changes, such as myelinated axonal damage, synaptic alterations, and mitochondrial abnormalities occurring in the absence of gross- or cellular damage. Biochemically, we observed dysfunctional mitochondrial pathways that led to elevated oxidative stress, impaired fission-fusion dynamics, diminished mitophagy, decreased oxidative phosphorylation, and compensated cell respiration-relevant enzyme activity. LIB also induced increased levels of total tau, phosphorylated tau, and amyloid β peptide, suggesting initiation of signaling cascades leading to neurodegeneration. We also compare translational aspects of OFB findings to alternative blast injury models. By scoping relevant recent research findings, we provide recommendations for future preclinical studies to better reflect military-operational and clinical realities. Overall, better alignment of preclinical models with clinical observations and experience related to military injuries will facilitate development of more precise diagnosis, clinical evaluation, treatment, and rehabilitation., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Siedhoff, Chen, Song, Cui, Cernak, Cifu, DePalma and Gu.)

Mild traumatic brain injury induced by low-intensity blast (LIB) exposure poses concerns in military personnel. Using an open-field, non-inertial blast model and assessments by conventional behavioral tests, our previous studies revealed early-phase anxiety-like behaviors in LIB-exposed mice. However, the impact of LIB upon long-term anxiety-like behaviors requires clarification. This study applied a highly sensitive automated home-cage monitoring (HCM) system, which minimized human intervention and environmental changes, to assess anxiety-like responses in mice 3 months after LIB exposure. Initial assessment of 72-h spontaneous activities in a natural cage condition over multiple light and dark phases showed altered sheltering behaviors. LIB-exposed mice exhibited a subtle, but significantly decreased, duration of short shelter visits as compared to sham controls. Other measured responses between LIB-exposed mice and sham controls were insignificant. When behavioral assessments were performed in a challenged condition using an aversive spotlight, LIB-exposed mice demonstrated a significantly higher frequency of movements of shorter distance and duration per movement. Taken together, these findings demonstrated the presence of chronic anxiety-like behaviors assessed by the HCM system under both natural and challenged conditions in mice occurring post-LIB exposure. This model thus provides a platform to test for screening and interventions on anxiety disorders occurring after LIB non-inertial brain injury., Competing Interests: No competing financial interests exist., (© Heather R. Siedhoff et al., 2021; Published by Mary Ann Liebert, Inc.)

Spinal cord injury (SCI) is a deliberating disorder with impairments in locomotor deficits and incapacitating sensory abnormalities. Harpagophytum procumbens (Hp) is a botanical widely used for treating inflammation and pain related to various inflammatory and musculoskeletal conditions. Using a modified rodent contusion model of SCI, we explored the effects of this botanical on locomotor function and responses to mechanical stimuli, and examined possible neurochemical changes associated with SCI-induced allodynia. Following spinal cord contusion at T10 level, Hp (300 mg/kg, p.o.) or vehicle (water) was administered daily starting 24 h post-surgery, and behavioral measurements made every-other day until sacrifice (Day 21). Hp treatment markedly ameliorated the contusion-induced decrease in locomotor function and increased sensitivity to mechanical stimuli. Determination of Iba1 expression in spinal cord tissues indicated microglial infiltration starting 3 days post-injury. SCI results in increased levels of 4-hydroxynonenal, an oxidative stress product and proalgesic, which was diminished at 7 days by treatment with Hp. SCI also enhanced antioxidant heme oxygenase-1 (HO-1) expression. Concurrent studies of cultured murine BV-2 microglial cells revealed that Hp suppressed oxidative/nitrosative stress and inflammatory responses, including production of nitric oxide and reactive oxygen species, phosphorylation of cytosolic phospholipases A 2 , and upregulation of the antioxidative stress pathway involving the nuclear factor erythroid 2-related factor 2 and HO-1. These results support the use of Hp for management of allodynia by providing resilience against the neuroinflammation and pain associated with SCI and other neuropathological conditions.