Enduring cognitive, neurobehavioral and histopathological changes persist for up to one year following severe experimental brain injury in rats

Temporal-Specific Sex and Injury-Dependent Changes on Neurogranin-Associated Synaptic Signaling After Controlled Cortical Impact in Rats

Extensive effort has been made to study the role of synaptic deficits in cognitive impairment after traumatic brain injury (TBI). Neurogranin (Ng) is a calcium-sensitive calmodulin (CaM)-binding protein essential for Ca2+/CaM-dependent kinase II (CaMKII) autophosphorylation which subsequently modulates synaptic plasticity. Given the loss of Ng expression after injury, additional research is warranted to discern changes in hippocampal post-synaptic signaling after TBI. Under isoflurane anesthesia, adult, male and female Sprague-Dawley rats received a sham/control or controlled cortical impact (CCI) injury. Ipsilateral hippocampal synaptosomes were isolated at 24 h and 1, 2, and 4 weeks post-injury, and western blot was used to evaluate protein expression of Ng-associated signaling proteins. Non-parametric Mann-Whitney tests were used to determine significance of injury for each sex at each time point. There were significant changes in the hippocampal synaptic expression of Ng and associated synaptic proteins such as phosphorylated Ng, CaMKII, and CaM up to 4 weeks post-CCI, demonstrating TBI alters hippocampal post-synaptic signaling. This study furthers our understanding of mechanisms of cognitive dysfunction within the synapse sub-acutely after TBI.

Molecular Pathway Changes Associated with Different Post-Conditioning Exercise Interventions After Experimental TBI

Traumatic brain injury (TBI) causes complex, time-dependent molecular and cellular responses, which include adaptive changes that promote repair and recovery, as well as maladaptive processes such as chronic inflammation that contribute to chronic neurodegeneration and neurological dysfunction. Hormesis is a well-established biological phenomenon in which exposure to low-dose toxins or stressors results in protective responses to subsequent higher-level stressors or insults. Hormetic stimuli show a characteristic U-shaped or inverted J-shaped dose-response curve, as well as being time and exposure-frequency dependent, similar to pre-conditioning and post-conditioning actions. Voluntary exercise interventions, before or after injury, appear to follow these general hormetic principles. But the molecular alterations associated with exercise interventions or more general hormetic responses have received only limited attention. In this study, we used a well-characterized mouse TBI model to assess the effects of different post-conditioning exercise-intervention paradigms on diverse molecular pathways, including neuroinflammation regulators, and post-traumatic neurological deficits. We generated high-throughput gene expression data and associated molecular pathway analyses to assess the potential molecular mechanisms associated with time- and duration-dependent voluntary exercise intervention, as well as time after treatment. Importantly, we also used newer analytical methods to more broadly assess the impact of exercise on diverse molecular pathways. TBI caused long-term changes in multiple neuroinflammation markers and chronic cognitive dysfunction. Notably, all delayed, post-conditioning exercise interventions reduced post-traumatic neuroinflammation and/or attenuated the related cognitive changes, albeit with different pathway specificity and effects magnitude. Exercise comprehensively reversed injury-associated effects in the hippocampus across both activated inflammatory and inhibited neuronal pathways, consistent with a return toward the noninjured, homeostatic state. In contrast, the cortex showed a less consistent pattern with more limited attenuation of inflammatory pathway activation and an amplification in the injury-dependent inhibition of select noninflammatory pathways, indicating less effective and potentially detrimental responses to exercise. Exercise intervention beginning 2 weeks after injury and lasting 2 weeks was less effective than exercise continuing for 4 weeks. Exercise initiated at a more delayed timepoint of 6 weeks after injury and continuing for 4 weeks was more effective than that during the acute phase. The delayed paradigm was also more effective than exercise initiated at 10 weeks after injury and continuing for 8 weeks, consistent with hormetic responses in other models and species. Overall, our study delineates regional and interventional parameters, as well as related molecular pathway changes, associated with post-conditioning exercise treatment, which may help inform future translational interventional strategies.

White Matter Organization and Cortical Thickness Differ Among Active Duty Service Members With Chronic Mild, Moderate, and Severe Traumatic Brain Injury

Abstract This study compared findings from whole-brain diffusion tensor imaging (DTI) and volumetric magnetic resonance imaging (MRI) among 90 Active Duty Service Members with chronic mild traumatic brain injury (TBI; n = 52), chronic moderate-to-severe TBI (n = 17), and TBI-negative controls (n = 21). Data were collected on a Philips Ingenia 3T MRI with DTI in 32 directions. Results demonstrated that history of TBI was associated with differences in white matter microstructure, white matter volume, and cortical thickness in both mild TBI and moderate-to-severe TBI groups relative to controls. However, the presence, pattern, and distribution of these findings varied substantially depending on the injury severity. Spatially-defined forms of DTI fractional anisotropy (FA) analyses identified altered white matter organization within the chronic moderate-to-severe TBI group, but they did not provide clear evidence of abnormalities within the chronic mild TBI group. In contrast, DTI FA "pothole" analyses identified widely distributed areas of decreased FA throughout the white matter in both the chronic mild TBI and chronic moderate-to-severe TBI groups. Additionally, decreased white matter volume was found in several brain regions for the chronic moderate-to-severe TBI group compared with the other groups. Greater number of DTI FA potholes and reduced cortical thickness were also related to greater severity of self-reported symptoms. In sum, this study expands upon a growing body of literature using advanced imaging techniques to identify potential effects of brain injury in military Service Members. These findings may differ from work in other TBI populations due to varying mechanisms and frequency of injury, as well as a potentially higher level of functioning in the current sample related to the ability to maintain continued Active Duty status after injury. In conclusion, this study provides DTI and volumetric MRI findings across the spectrum of TBI severity. These results provide support for the use of DTI and volumetric MRI to identify differences in white matter microstructure and volume related to TBI. In particular, DTI FA pothole analysis may provide greater sensitivity for detecting subtle forms of white matter injury than conventional DTI FA analyses.

Lateral fluid percussion injury: A rat model of experimental traumatic brain injury

Traumatic brain injury (TBI) represents one of the leading causes of disability and death worldwide. The annual economic impact of TBI-including direct and indirect costs-is high, particularly impacting low- and middle-income countries. Despite extensive research, a comprehensive understanding of the primary and secondary TBI pathophysiology, followed by the development of promising therapeutic approaches, remains limited. These fundamental caveats in knowledge have motivated the development of various experimental models to explore the molecular mechanisms underpinning the pathogenesis of TBI. In this context, the Lateral Fluid Percussion Injury (LFPI) model produces a brain injury that mimics most of the neurological and systemic aspects observed in human TBI. Moreover, its high reproducibility makes the LFPI model one of the most widely used rodent-based TBI models. In this chapter, we provide a detailed surgical protocol of the LFPI model used to induce TBI in adult Wistar rats. We further highlight the neuroscore test as a valuable tool for the evaluation of TBI-induced sensorimotor consequences and their severity in rats. Lastly, we briefly summarize the current knowledge on the pathological aspects and functional outcomes observed in the LFPI-induced TBI model in rodents.

Overexpress miR-132 in the Brain Parenchyma by a Non-invasive Way Improves Tissue Repairment and Releases Memory Impairment After Traumatic Brain Injury

Traumatic brain injury (TBI) is a serious public health problem worldwide, which could lead to an extremely high percentage of mortality and disability. Current treatment strategies mainly concentrate on neuronal protection and reconstruction, among them, exogenous neural stem cell (NSC) transplantation has long been regarded as the most effective curative treatment. However, due to secondary trauma, transplant rejection, and increased incidence of brain malignant tumor, a non-invasive therapy that enhanced endogenous neurogenesis was more suitable for TBI treatment. Our previous work has shown that miR-132 overexpression could improve neuronal differentiation of NSCs in vitro and in vivo. So, we engineered a new kind of AAV vector named AAV-PHP.eB which can transfect brain parenchyma through intravenous injection to overexpress miR-132 in brain after TBI. We found that miR-132 overexpression could reduce impact volume, promote neurogenesis in the dentate gyrus (DG), accelerate neuroblast migrating into the impact cortex, ameliorate microglia-mediated inflammatory reaction, and ultimately restore learning memory function. Our results revealed that AAV-PHP.eB-based miR-132 overexpression could improve endogenous tissue repairment and release clinical symptoms after traumatic brain injury. This work would provide a new therapeutic strategy for TBI treatment and other neurological disorders characterized by markable neuronal loss and memory impairment. miR-132 overexpression accelerates endogenous neurogenesis and releases TBI-induced tissue repairment and memory impairment. Controlled cortical impact onto the cortex would induce serious cortical injury and microglia accumulation in both cortex and hippocampus. Moreover, endogenous neuroblast could migrate around the injury core. miR-132 overexpression could accelerate neuroblast migration toward the injury core and decreased microglia accumulation in the ipsilateral cortex and hippocampus. miR-132 could be a suitable target on neuroprotective therapy after TBI.

Identifying the Phenotypes of Diffuse Axonal Injury Following Traumatic Brain Injury

Diffuse axonal injury (DAI) is a significant feature of traumatic brain injury (TBI) across all injury severities and is driven by the primary mechanical insult and secondary biochemical injury phases. Axons comprise an outer cell membrane, the axolemma which is anchored to the cytoskeletal network with spectrin tetramers and actin rings. Neurofilaments act as space-filling structural polymers that surround the central core of microtubules, which facilitate axonal transport. TBI has differential effects on these cytoskeletal components, with axons in the same white matter tract showing a range of different cytoskeletal and axolemma alterations with different patterns of temporal evolution. These require different antibodies for detection in post-mortem tissue. Here, a comprehensive discussion of the evolution of axonal injury within different cytoskeletal elements is provided, alongside the most appropriate methods of detection and their temporal profiles. Accumulation of amyloid precursor protein (APP) as a result of disruption of axonal transport due to microtubule failure remains the most sensitive marker of axonal injury, both acutely and chronically. However, a subset of injured axons demonstrate different pathology, which cannot be detected via APP immunoreactivity, including degradation of spectrin and alterations in neurofilaments. Furthermore, recent work has highlighted the node of Ranvier and the axon initial segment as particularly vulnerable sites to axonal injury, with loss of sodium channels persisting beyond the acute phase post-injury in axons without APP pathology. Given the heterogenous response of axons to TBI, further characterization is required in the chronic phase to understand how axonal injury evolves temporally, which may help inform pharmacological interventions.

Gliptins normalize posttraumatic hippocampal neurogenesis and restore cognitive function after controlled cortical impact on sensorimotor cortex

Traumatic brain injury (TBI) often leads to long-term neurocognitive dysfunctions. Adult neurogenesis in the hippocampal dentate gyrus (DG) serves critical functions in cognition but can be disrupted by brain injury and insult in serval forms. In the present study, we explore the cellular and molecular targets of DPP-4 inhibitors (or gliptins) as related to hippocampal function and TBI cognitive sequelae. Two structurally different gliptins, sitagliptin and vildagliptin, were examined using a controlled cortical impact (CCI) model of moderate TBI in mice. Sensorimotor CCI, although distal from the hippocampus, impaired hippocampal-dependent cognition without obvious hippocampal tissue destruction. Neurogenic cell proliferation in the DG was increased accompanied by large numbers of reactive astrocyte. Increased numbers of immature granule cells with abnormal dendritic outgrowth were ectopically localized in the outer granule cell layer (GCL) and hilus. Long-term potentiation of dentate immature granule cells was also impaired. Both sitagliptin and vildagliptin attenuated the CCI-induced ectopic migration of doublecortin-positive immature neurons into the outer GCL and hilus, restored the normal dendritic branching pattern of the immature neurons and prevented astrocyte reactivation. Both gliptins prevented loss of normal synaptic integration in the DG after sensorimotor CCI and improved cognitive behavior. Sensorimotor cortical injury thus results in an abnormal neurogenesis pattern and astrocyte reactivation in the distal hippocampus which appears to contribute to the development of cognitive dysfunction after TBI. DPP-4 inhibitors prevent astrocyte reactivation, normalize the posttraumatic hippocampal neurogenesis and help to maintain normal electrophysiology in the DG with positive behavioral effect in a mouse model.

Repeated mild closed head injury in neonatal rats results in sustained cognitive deficits associated with chronic microglial activation and neurodegeneration

Abusive head trauma in infants is a consequence of multiple episodes of abuse and results in axonal injury, brain atrophy, and chronic cognitive deficits. Anesthetized 11-day-old rats, neurologically equivalent to infants, were subjected to 1 impact/day to the intact skull for 3 successive days. Repeated, but not single impact(s) resulted in spatial learning deficits (p < 0.05 compared to sham-injured animals) up to 5 weeks postinjury. In the first week following single or repetitive brain injury, axonal and neuronal degeneration, and microglial activation were observed in the cortex, white matter, thalamus, and subiculum; the extent of the histopathologic damage was significantly greater in the repetitive-injured animals compared to single-injured animals. At 40 days postinjury, loss of cortical, white matter and hippocampal tissue was evident only in the repetitive-injured animals, along with evidence of microglial activation in the white matter tracts and thalamus. Axonal injury and neurodegeneration were evident in the thalamus up to 40 days postinjury in the repetitive-injured rats. These data demonstrate that while single closed head injury in the neonate rat is associated with pathologic alterations in the acute post-traumatic period, repetitive closed head injury results in sustained behavioral and pathologic deficits reminiscent of infants with abusive head trauma.

Mechanical mechanism and indicator of diffuse axonal injury under blast-type acceleration

Diffuse axonal injury (DAI) caused by acceleration is one of the most prominent forms of blast-induced Traumatic Brain Injury. However, the mechanical mechanism and indicator of axonal deformation-induced injury under blast-type acceleration with high peak and short duration are unclear. This study constructed a multilayer head model that can reflect the response characteristics of translational and rotational acceleration (the peak time of which is within 0.5 ms). Based on von Mises stress, axonal strain and axonal strain rate indicators, the physical process of axonal injury is studied, and the vulnerable area under blast-type acceleration load is given. In the short term (within 1.75 ms), dominated by sagittal rotational acceleration peaks, the constraint of falx and tentorium rapidly imposes the inertial load on the brain tissue, resulting in a high-rate deformation of axons (axonal strain rate of which exceed 100 s-1). For a long term (after 1.75 ms), fixed-point rotation of the brain following the head causes excessive distortion of brain tissue (von Mises stress of which exceeds 15 kPa), resulting in a large axonal stretch strain where the main axonal orientation coincides with the principal strain direction. It is found that the axonal strain rate can better indicate the pathological axonal injury area and coincides with external inertial loading in the risk areas, which suggests that DAI under blast-type acceleration overload is mainly caused by the rapid axonal deformation instead of by the excessive axonal strain. The research in this paper helps understand and diagnose blast-induced DAI.

Chronic motor performance following different traumatic brain injury severity-A systematic review

Introduction

Traumatic brain injury (TBI) is now known to be a chronic disease, causing ongoing neurodegeneration and linked to increased risk of neurodegenerative motor diseases, such as Parkinson's disease and amyotrophic lateral sclerosis. While the presentation of motor deficits acutely following traumatic brain injury is well-documented, however, less is known about how these evolve in the long-term post-injury, or how the initial severity of injury affects these outcomes. The purpose of this review, therefore, was to examine objective assessment of chronic motor impairment across the spectrum of TBI in both preclinical and clinical models.

Methods

PubMed, Embase, Scopus, and PsycINFO databases were searched with a search strategy containing key search terms for TBI and motor function. Original research articles reporting chronic motor outcomes with a clearly defined TBI severity (mild, repeated mild, moderate, moderate-severe, and severe) in an adult population were included.

Results

A total of 97 studies met the inclusion criteria, incorporating 62 preclinical and 35 clinical studies. Motor domains examined included neuroscore, gait, fine-motor, balance, and locomotion for preclinical studies and neuroscore, fine-motor, posture, and gait for clinical studies. There was little consensus among the articles presented, with extensive differences both in assessment methodology of the tests and parameters reported. In general, an effect of severity was seen, with more severe injury leading to persistent motor deficits, although subtle fine motor deficits were also seen clinically following repeated injury. Only six clinical studies investigated motor outcomes beyond 10 years post-injury and two preclinical studies to 18-24 months post-injury, and, as such, the interaction between a previous TBI and aging on motor performance is yet to be comprehensively examined.

Conclusion

Further research is required to establish standardized motor assessment procedures to fully characterize chronic motor impairment across the spectrum of TBI with comprehensive outcomes and consistent protocols. Longitudinal studies investigating the same cohort over time are also a key for understanding the interaction between TBI and aging. This is particularly critical, given the risk of neurodegenerative motor disease development following TBI.

Inflammaging, cellular senescence, and cognitive aging after traumatic brain injury

Traumatic brain injury (TBI) is associated with mortality and morbidity worldwide. Accumulating pre-clinical and clinical data suggests TBI is the leading extrinsic cause of progressive neurodegeneration. Neurological deterioration after either a single moderate-severe TBI or repetitive mild TBI often resembles dementia in aged populations; however, no currently approved therapies adequately mitigate neurodegeneration. Inflammation correlates with neurodegenerative changes and cognitive dysfunction for years post-TBI, suggesting a potential association between immune activation and both age- and TBI-induced cognitive decline. Inflammaging, a chronic, low-grade sterile inflammation associated with natural aging, promotes cognitive decline. Cellular senescence and the subsequent development of a senescence associated secretory phenotype (SASP) promotes inflammaging and cognitive aging, although the functional association between senescent cells and neurodegeneration is poorly defined after TBI. In this mini-review, we provide an overview of the pre-clinical and clinical evidence linking cellular senescence with poor TBI outcomes. We also discuss the current knowledge and future potential for senotherapeutics, including senolytics and senomorphics, which kill and/or modulate senescent cells, as potential therapeutics after TBI.

Peg Forest Rehabilitation - A novel spatial navigation based cognitive rehabilitation paradigm for experimental neurotrauma

Traumatic brain injury (TBI) results from mechanical forces applied to the head. Ensuing cascades of complex pathophysiology transition the injury event into a disease process. The enduring constellation of emotional, somatic, and cognitive impairments degrade quality of life for the millions of TBI survivors suffering from long-term neurological symptoms. Rehabilitation strategies have reported mixed results, as most have not focused on specific symptomatology or explored cellular processes. The current experiments evaluated a novel cognitive rehabilitation paradigm for brain-injured and uninjured rats. The arena is a plastic floor with a cartesian grid of holes for plastic dowels to create new environments with the rearrangement of threaded pegs. Rats received either two weeks of Peg Forest rehabilitation (PFR) or open field exposure starting at 7 days post-injury; or one week starting at either day 7 or 14 post-injury; or served as caged controls. Cognitive performance was assessed on a battery of novel object tasks at 28 days post-injury. The results revealed that two weeks of PFR was required to prevent the onset of cognitive impairments, while one week of PFR was insufficient regardless of when rehabilitation was initiated after injury. Further assessment of the task showed that novel daily arrangements of the environment were required to impart the cognitive performance benefits, as exposure to a static arrangement of pegs for PFR each day did not improve cognitive performance. The results indicate that PFR prevents the onset of cognitive disorders following acquired a mild to moderate brain injury, and potentially other neurological conditions.

Diffusion MRI approaches for investigating microstructural complexity in a rat model of traumatic brain injury

Our study explores the potential of conventional and advanced diffusion MRI techniques including diffusion tensor imaging (DTI), and single-shell 3-tissue constrained spherical deconvolution (SS3T-CSD) to investigate complex microstructural changes following severe traumatic brain injury in rats at a chronic phase. Rat brains after sham-operation or lateral fluid percussion (LFP) injury were scanned ex vivo in a 9.4 T scanner. Our region-of-interest-based approach of tensor-, and SS3T-CSD derived fixel-, 3-tissue signal fraction maps were sensitive to changes in both white matter (WM) and grey matter (GM) areas. Tensor-based measures, such as fractional anisotropy (FA) and radial diffusivity (RD), detected more changes in WM and GM areas as compared to fixel-based measures including apparent fiber density (AFD), peak FOD amplitude and primary fiber bundle density, while 3-tissue signal fraction maps revealed distinct changes in WM, GM, and phosphate-buffered saline (PBS) fractions highlighting the complex tissue microstructural alterations post-trauma. Track-weighted imaging demonstrated changes in track morphology including reduced curvature and average pathlength distal from the primary lesion in severe TBI rats. In histological analysis, changes in the diffusion MRI measures could be associated to decreased myelin density, loss of myelinated axons, and increased cellularity, revealing progressive microstructural alterations in these brain areas five months after injury. Overall, this study highlights the use of combined conventional and advanced diffusion MRI measures to obtain more precise insights into the complex tissue microstructural alterations in chronic phase of severe brain injury.

Sex-Specific Alterations in Inflammatory MicroRNAs in Mouse Brain and Bone Marrow CD11b+ Cells Following Traumatic Brain Injury

Sex is a key biological variable in traumatic brain injury (TBI) and plays a significant role in neuroinflammatory responses. However, the molecular mechanisms contributing to this sexually dimorphic neuroinflammatory response remain elusive. Here we describe a significant and previously unreported tissue enrichment and sex-specific alteration of a set of inflammatory microRNAs (miRNAs) in CD11b+ cells of brain and bone marrow isolated from naïve mice as well as mice subjected to TBI. Our data from naïve mice demonstrated that expression levels of miR-146a-5p and miR-150-5p were relatively higher in brain CD11b+ cells, and that miR-155-5p and miR-223-3p were highly enriched in bone marrow CD11b+ cells. Furthermore, while miR-150-5p and miR-155-5p levels were higher in male brain CD11b+ cells, no significant sexual difference was observed for miR-146a-5p and miR-223-3p. However, TBI resulted in sex-specific differential responses of these miRNAs in brain CD11b+ cells. Specifically, miR-223-3p levels in brain CD11b+ cells were markedly elevated in both sexes in response to TBI at 3 and 24 h, with levels in females being significantly higher than males at 24 h. We then focused on analyzing several miR-223-3p targets and inflammation-related marker genes following injury. Corresponding to the greater elevation of miR-223-3p in females, the miR-223-3p targets, TRAF6 and FBXW7 were significantly reduced in females compared to males. Interestingly, anti-inflammatory genes ARG1 and IL4 were higher in females after TBI than in males. These observations suggest miR-223-3p and other inflammatory responsive miRNAs may play a key role in sex-specific neuroinflammatory response following TBI.

Plasma Neurofilament Light Chain (NF-L) Is a Prognostic Biomarker for Cortical Damage Evolution but Not for Cognitive Impairment or Epileptogenesis Following Experimental TBI

Plasma neurofilament light chain (NF-L) levels were assessed as a diagnostic biomarker for traumatic brain injury (TBI) and as a prognostic biomarker for somatomotor recovery, cognitive decline, and epileptogenesis. Rats with severe TBI induced by lateral fluid-percussion injury (n = 26, 13 with and 13 without epilepsy) or sham-operation (n = 8) were studied. During a 6-month follow-up, rats underwent magnetic resonance imaging (MRI) (day (D) 2, D7, and D21), composite neuroscore (D2, D6, and D14), Morris-water maze (D35−D39), and a 1-month-long video-electroencephalogram to detect unprovoked seizures during the 6th month. Plasma NF-L levels were assessed using a single-molecule assay at baseline (i.e., naïve animals) and on D2, D9, and D178 after TBI or a sham operation. Plasma NF-L levels were 483-fold higher on D2 (5072.0 ± 2007.0 pg/mL), 89-fold higher on D9 (930.3 ± 306.4 pg/mL), and 3-fold higher on D176 32.2 ± 8.9 pg/mL after TBI compared with baseline (10.5 ± 2.6 pg/mL; all p < 0.001). Plasma NF-L levels distinguished TBI rats from naïve animals at all time-points examined (area under the curve [AUC] 1.0, p < 0.001), and from sham-operated controls on D2 (AUC 1.0, p < 0.001). Plasma NF-L increases on D2 were associated with somatomotor impairment severity (ρ = −0.480, p < 0.05) and the cortical lesion extent in MRI (ρ = 0.401, p < 0.05). Plasma NF-L increases on D2 or D9 were associated with the cortical lesion extent in histologic sections at 6 months post-injury (ρ = 0.437 for D2; ρ = 0.393 for D9, p < 0.05). Plasma NF-L levels, however, did not predict somatomotor recovery, cognitive decline, or epileptogenesis (p > 0.05). Plasma NF-L levels represent a promising noninvasive translational diagnostic biomarker for acute TBI and a prognostic biomarker for post-injury somatomotor impairment and long-term structural brain damage.

Hydrogen sulfide prevents the vascular dysfunction induced by severe traumatic brain injury in rats by reducing reactive oxygen species and modulating eNOS and H2S-synthesizing enzyme expression

AIM

To assess the effects of subchronic administration with NaHS, an exogenous H₂S donor, on TBI-induced hypertension and vascular impairments.

MAIN METHODS

Animals underweministration does not prevent the body weight loss but slightly imnt a lateral fluid percussion injury, and the hemodynamic variables were measured in vivo by plethysmograph method. The vascular function in vitro, the ROS levels by the DCFH-DA method and the expression of H₂S-synthesizing enzymes and eNOS by Western blot were measured in isolated thoracic aortas at day 7 post-TBI. The effect of L-NAME on NaHS-induced effects in vascular function was evaluated. Brain water content was determined 7 days after trauma induction. Body weight was recorded throughout the experimental protocol, whereas the sensorimotor function was evaluated using the neuroscore test at days -1 (basal), 2, and 7 after the TBI induction.

KEY FINDINGS

TBI animals showed: 1) an increase in hemodynamic variables and ROS levels in aortas; 2) vascular dysfunction; 3) sensorimotor dysfunction; and 4) a decrease in body weight, the expression of H₂S-synthesizing enzymes, and eNOS phosphorylation. Interestingly, NaHS subchronic administration (3.1 mg/kg; i.p.; every 24 h for six days) prevented the development of hypertension, vascular dysfunction, and oxidative stress. L-NAME abolished NaHS-induced effects. Furthermore, NaHS treatment restored H₂S-synthesizing enzymes and eNOS phosphorylation with no effect on body weight, sensorimotor impairments, or brain water content.

SIGNIFICANCE

Taken together, these results demonstrate that H₂S prevents TBI-induced hypertension by restoring vascular function and modulating ROS levels, H₂S-synthesizing enzymes expression, and eNOS phosphorylation.

Acute Hippocampal Damage as a Prognostic Biomarker for Cognitive Decline but Not for Epileptogenesis after Experimental Traumatic Brain Injury

It is necessary to develop reliable biomarkers for epileptogenesis and cognitive impairment after traumatic brain injury when searching for novel antiepileptogenic and cognition-enhancing treatments. We hypothesized that a multiparametric magnetic resonance imaging (MRI) analysis along the septotemporal hippocampal axis could predict the development of post-traumatic epilepsy and cognitive impairment. We performed quantitative T2 and T2* MRIs at 2, 7 and 21 days, and diffusion tensor imaging at 7 and 21 days after lateral fluid-percussion injury in male rats. Morris water maze tests conducted between 35-39 days post-injury were used to diagnose cognitive impairment. One-month-long continuous video-electroencephalography monitoring during the 6th post-injury month was used to diagnose epilepsy. Single-parameter and regularized multiple linear regression models were able to differentiate between sham-operated and brain-injured rats. In the ipsilateral hippocampus, differentiation between the groups was achieved at most septotemporal locations (cross-validated area under the receiver operating characteristic curve (AUC) 1.0, 95% confidence interval 1.0-1.0). In the contralateral hippocampus, the highest differentiation was evident in the septal pole (AUC 0.92, 95% confidence interval 0.82-0.97). Logistic regression analysis of parameters imaged at 3.4 mm from the contralateral hippocampus's temporal end differentiated between the cognitively impaired rats and normal rats (AUC 0.72, 95% confidence interval 0.55-0.84). Neither single nor multiparametric approaches could identify the rats that would develop post-traumatic epilepsy. Multiparametric MRI analysis of the hippocampus can be used to identify cognitive impairment after an experimental traumatic brain injury. This information can be used to select subjects for preclinical trials of cognition-improving interventions.

Chronic Cognitive and Cerebrovascular Function after Mild Traumatic Brain Injury in Rats

Severe traumatic brain injury (TBI) results in cognitive dysfunction in part due to vascular perturbations. In contrast, the long-term vasculo-cognitive pathophysiology of mild TBI (mTBI) remains unknown. We evaluated mTBI effects on chronic cognitive and cerebrovascular function and assessed their interrelationships. Sprague-Dawley rats received midline fluid percussion injury (n = 20) or sham (n = 21). Cognitive function was assessed (3- and 6-month novel object recognition [NOR], novel object location [NOL], and temporal order object recognition [TOR]). Six-month cerebral blood flow (CBF) and cerebral blood volume (CBV) using contrast magnetic resonance imaging (MRI) and ex vivo circle of Willis artery endothelial and smooth muscle-dependent function were measured. mTBI rats showed significantly impaired NOR, with similar trends (non-significant) in NOL/TOR. Regional CBF and CBV were similar in sham and mTBI. NOR correlated with CBF in lateral hippocampus, medial hippocampus, and primary somatosensory barrel cortex, whereas it inversely correlated with arterial smooth muscle-dependent dilation. Six-month baseline endothelial and smooth muscle-dependent arterial function were similar among mTBI and sham, but post-angiotensin 2 stimulation, mTBI showed no change in smooth muscle-dependent dilation from baseline response, unlike the reduction in sham. mTBI led to chronic cognitive dysfunction and altered angiotensin 2-stimulated smooth muscle-dependent vasoreactivity. The findings of persistent pathophysiological consequences of mTBI in this animal model add to the broader understanding of chronic pathophysiological sequelae in human mild TBI.

Moderate traumatic brain injury triggers long-term risks for the development of peripheral pain sensitivity and depressive-like behavior in mice

As traumatic brain injury (TBI) is one of the major causes of permanent disability, there is increasing interest in the long-term outcome of TBI. While motor deficits, cognitive impairment and longer-term risks of neurodegenerative disease are well-established consequences in animal models of TBI, pain is discussed less often despite its high prevalence. The current study addresses the need to characterize the extent of chronic pain and long-term behavioral impairments induced by moderate lateral fluid percussion injury (latFPI) in mice up to 12 months post-TBI and evaluates the validity of the model. Adult male BALB/c mice were subjected to latFPI, and the results were compared with outcomes in sham-operated mice. Mouse behavior was assessed at 1 and 7 days and 1, 3, 6, 9, and 12 months post-injury using sensory-motor (neurological severity score, NSS), cold (acetone) and mechanical sensitivity (von Frey), depressive-like behavior (tail suspension), locomotor (open field), motor coordination (rotarod) and cognitive (Morris water maze, y-maze, passive avoidance) tests. Animals with TBI demonstrated significantly higher NSS than the sham-operated group for up to 9 months after the injury. Cold sensitization was significantly increased in the contralateral hind paw in the TBI group compared to that of the sham group at 3, 6, and 9 months after TBI. In the von Frey test, the withdrawal threshold of the contralateral and ipsilateral hind paws was reduced at 6 months after TBI and lasted for up to 12 months post-injury. latFPI induced progressive depressive-like behavior starting at 6 months post-injury. No significant deficits were observed in memory, motor coordination or locomotion over the 12-month assessment period. The present study demonstrates that moderate TBI in mice elicits long-lasting impairment of sensory-motor function, results in progressive depression and potentiates peripheral pain. Hence, the latFPI model provides a relevant preclinical setting for the study of the link between brain injury and chronic sequelae such as depression and peripheral pain.

The Emergence of Model Systems to Investigate the Link Between Traumatic Brain Injury and Alzheimer’s Disease

Numerous epidemiological studies have demonstrated that individuals who have sustained a traumatic brain injury (TBI) have an elevated risk for developing Alzheimer’s disease and Alzheimer’s-related dementias (AD/ADRD). Despite these connections, the underlying mechanisms by which TBI induces AD-related pathology, neuronal dysfunction, and cognitive decline have yet to be elucidated. In this review, we will discuss the various in vivo and in vitro models that are being employed to provide more definite mechanistic relationships between TBI-induced mechanical injury and AD-related phenotypes. In particular, we will highlight the strengths and weaknesses of each of these model systems as it relates to advancing the understanding of the mechanisms that lead to TBI-induced AD onset and progression as well as providing platforms to evaluate potential therapies. Finally, we will discuss how emerging methods including the use of human induced pluripotent stem cell (hiPSC)-derived cultures and genome engineering technologies can be employed to generate better models of TBI-induced AD.

Reductions in Synaptic Vesicle Glycoprotein 2 Isoforms in the Cortex and Hippocampus in a Rat Model of Traumatic Brain Injury

Traumatic brain injury (TBI) can produce lasting cognitive, emotional, and somatic difficulties that can impact quality of life for patients living with an injury. Impaired hippocampal function and synaptic alterations have been implicated in contributing to cognitive difficulties in experimental TBI models. In the synapse, neuronal communication is facilitated by the regulated release of neurotransmitters from docking presynaptic vesicles. The synaptic vesicle glycoprotein 2 (SV2) isoforms SV2A and SV2B play central roles in the maintenance of the readily releasable pool of vesicles and the coupling of calcium to the N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex responsible for vesicle docking. Recently, we reported the findings of TBI-induced reductions in presynaptic vesicle density and SNARE complex formation; however, the effect of TBI on SV2 is unknown. To investigate this, rats were subjected to controlled cortical impact (CCI) or sham control surgery. Abundance of SV2A and SV2B were assessed at 1, 3, 7, and 14 days post-injury by immunoblot. SV2A and SV2B were reduced in the cortex at several time points and in the hippocampus at every time point assessed. Immunohistochemical staining and quantitative intensity measurements completed at 14 days post-injury revealed reduced SV2A immunoreactivity in all hippocampal subregions and reduced SV2B immunoreactivity in the molecular layer after CCI. Reductions in SV2A abundance and immunoreactivity occurred concomitantly with motor dysfunction and spatial learning and memory impairments in the 2 weeks post-injury. These findings provide novel evidence for the effect of TBI on SV2 with implications for impaired neurotransmission neurobehavioral dysfunction after TBI.

Rodent models used in preclinical studies of deep brain stimulation to rescue memory deficits

Deep brain stimulation paradigms might be used to treat memory disorders in patients with stroke or traumatic brain injury. However, proof of concept studies in animal models are needed before clinical translation. We propose here a comprehensive review of rodent models for Traumatic Brain Injury and Stroke. We systematically review the histological, behavioral and electrophysiological features of each model and identify those that are the most relevant for translational research.

Roadmap for Advancing Pre-Clinical Science in Traumatic Brain Injury

Pre-clinical models of disease have long played important roles in the advancement of new treatments. However, in traumatic brain injury (TBI), despite the availability of numerous model systems, translation from bench to bedside remains elusive. Integrating clinical relevance into pre-clinical model development is a critical step toward advancing therapies for TBI patients across the spectrum of injury severity. Pre-clinical models include in vivo and ex vivo animal work-both small and large-and in vitro modeling. The wide range of pre-clinical models reflect substantial attempts to replicate multiple aspects of TBI sequelae in humans. Although these models reveal multiple putative mechanisms underlying TBI pathophysiology, failures to translate these findings into successful clinical trials call into question the clinical relevance and applicability of the models. Here, we address the promises and pitfalls of pre-clinical models with the goal of evolving frameworks that will advance translational TBI research across models, injury types, and the heterogenous etiology of pathology.

The neuroprotective effects of AMN082 on neuronal apoptosis in rats after traumatic brain injury

BACKGROUND

The aim of this study was to investigate whether AMN082 exerts its neuroprotective effect by attenuating glutamate receptor-associated neuronal apoptosis and improving functional outcomes after traumatic brain injury (TBI).

METHODS

Anesthetized male Sprague-Dawley rats were divided into the sham-operated, TBI + vehicle, and TBI + AMN082 groups. AMN082 (10 mg/kg) was intraperitoneally injected 0, 24, or 48 h after TBI. In the 120 min after TBI, heart rate, mean arterial pressure, intracranial pressure (ICP), and cerebral perfusion pressure (CPP) were continuously measured. Motor function, the infarct volume, neuronal nitrosative stress-associated apoptosis, and N-methyl-D-aspartate receptor 2A (NR2A) and NR2B expression in the pericontusional cortex were measured on the 3rd day after TBI.

RESULTS

The results showed that the AMN082-treated group had a lower ICP and higher CPP after TBI. TBI-induced motor deficits, the increase in infarct volume, neuronal apoptosis, and 3-nitrotyrosine and inducible nitric oxide synthase expression in the pericontusional cortex were significantly improved by AMN082 therapy. Simultaneously, AMN082 increased NR2A and NR2B expression in neuronal cells.

CONCLUSIONS

We concluded that intraperitoneal injection of AMN082 for 3 days may ameliorate TBI by attenuating glutamate receptor-associated nitrosative stress and neuronal apoptosis in the pericontusional cortex. We suggest that AMN082 administration in the acute stage may be a promising strategy for TBI.

Emerging Applications for Quantitative Susceptibility Mapping in the Detection of Traumatic Brain Injury Pathology

Traumatic brain injury (TBI) is a common but heterogeneous injury underpinned by numerous complex and interrelated pathophysiological mechanisms. An essential trace element, iron is abundant within the brain and involved in many fundamental neurobiological processes, including oxygen transportation, oxidative phosphorylation, myelin production and maintenance, as well as neurotransmitter synthesis and metabolism. Excessive levels of iron are neurotoxic and thus iron homeostasis is tightly regulated in the brain, however, many details about the mechanisms by which this is achieved are yet to be elucidated. A key mediator of oxidative stress, mitochondrial dysfunction and neuroinflammatory response, iron dysregulation is an important contributor to secondary injury in TBI. Advances in neuroimaging that leverage magnetic susceptibility properties have enabled increasingly comprehensive investigations into the distribution and behaviour of iron in the brain amongst healthy individuals as well as disease states such as TBI. Quantitative Susceptibility Mapping (QSM) is an advanced neuroimaging technique that promises quantitative estimation of local magnetic susceptibility at the voxel level. In this review, we provide an overview of brain iron and its homeostasis, describe recent advances enabling applications of QSM within the context of TBI and summarise the current state of the literature. Although limited, the emergent research suggests that QSM is a promising neuroimaging technique that can be used to investigate a host of pathophysiological changes that are associated with TBI.

Inflammation in Traumatic Brain Injury

There is an increasing evidence that inflammation contributes to clinical and functional outcomes in traumatic brain injury (TBI). Many successful target-engaging, lesion-reducing, symptom-alleviating, and function-improving interventions in animal models of TBI have failed to show efficacy in clinical trials. Timing and immunological context are paramount for the direction, quality, and intensity of immune responses to TBI and the resulting neuroanatomical, clinical, and functional course. We present components of the immune system implicated in TBI, potential immune targets, and target-engaging interventions. The main objective of our article is to point toward modifiable molecular and cellular mechanisms that may modify the outcomes in TBI, and contribute to increasing the translational value of interventions that have been identified in animal models of TBI.

Spatial Distribution of Neuropathology and Neuroinflammation Elucidate the Biomechanics of Fluid Percussion Injury

Diffuse brain injury is better described as multi-focal, where pathology can be found adjacent to seemingly uninjured neural tissue. In experimental diffuse brain injury, pathology and pathophysiology have been reported far more lateral than predicted by the impact site. We hypothesized that local thickening of the rodent skull at the temporal ridges serves to focus the intracranial mechanical forces experienced during brain injury and generate predictable pathology. We demonstrated local thickening of the skull at the temporal ridges using contour analysis on magnetic resonance imaging. After diffuse brain injury induced by midline fluid percussion injury (mFPI), pathological foci along the anterior-posterior length of cortex under the temporal ridges were evident acutely (1, 2, and 7 days) and chronically (28 days) post-injury by deposition of argyophilic reaction product. Area CA3 of the hippocampus and lateral nuclei of the thalamus showed pathological change, suggesting that mechanical forces to or from the temporal ridges shear subcortical regions. A proposed model of mFPI biomechanics suggests that injury force vectors reflect off the skull base and radiate toward the temporal ridge, thereby injuring ventral thalamus, dorsolateral hippocampus, and sensorimotor cortex. Surgically thinning the temporal ridge before injury reduced injury-induced inflammation in the sensorimotor cortex. These data build evidence for temporal ridges of the rodent skull to contribute to the observed pathology, whether by focusing extracranial forces to enter the cranium or intracranial forces to escape the cranium. Pre-clinical investigations can take advantage of the predicted pathology to explore injury mechanisms and treatment efficacy.

Quantitative susceptibility mapping of the rat brain after traumatic brain injury

The primary lesion arising from the initial insult after traumatic brain injury (TBI) triggers a cascade of secondary tissue damage, which may also progress to connected brain areas in the chronic phase. The aim of this study was, therefore, to investigate variations in the susceptibility distribution related to these secondary tissue changes in a rat model after severe lateral fluid percussion injury. We compared quantitative susceptibility mapping (QSM) and R₂ * measurements with histological analyses in white and grey matter areas outside the primary lesion but connected to the lesion site. We demonstrate that susceptibility variations in white and grey matter areas could be attributed to reduction in myelin, accumulation of iron and calcium, and gliosis. QSM showed quantitative changes attributed to secondary damage in areas located rostral to the lesion site that appeared normal in R₂ * maps. However, combination of QSM and R₂ * was informative in disentangling the underlying tissue changes such as iron accumulation, demyelination, or calcifications. Therefore, combining QSM with R₂ * measurement can provide a more detailed assessment of tissue changes and may pave the way for improved diagnosis of TBI, and several other complex neurodegenerative diseases.

Methanolic extract of Fennel (Foeniculum vulgare) escalates functional restoration following a compression injury to the sciatic nerve in a mouse model

Peripheral nerve injury (PNI) is one of the major health concerns faced by the community at present. Till now, available therapeutic approaches are ineffective to fully heal a nerve injury and to assure the functional recovery entirely. Natural compounds can prove attractive and effective drug candidates to bridge up this gap. In this scenario, the present study was designed to explore the role of methanolic extract of Foeniculum vulgare (F. vulgare) seeds in accelerating the function regain following a sciatic nerve injury in a mouse model. For this purpose, 12 adult healthy albino mice (BALB/C), 8-10 weeks old, were grouped as control (Ctrl, n = 6) and treatment (Trt, n = 6). The treated group was given methanolic extract of F. vulgare (200 mg/kg per day) started from the day of nerve crush until the end of the study. The sensorimotor function regain assessed by hot plate test, grip strength, and SFI assessments was found significantly (p < .05) ameliorated in the F. vulgare-treated group. A prominent improvement in the muscle mass of the treated group further affirmed these effects. Furthermore, morphometric analysis of muscle fiber cross-sectional area of tibialis anterior muscle between groups revealed a noticeable improvement in muscle fibers' diameter of the treated group. Conclusively, these findings suggest that F. vulgare methanolic extract exhibits the potential to escalate functional recovery following a peripheral nerve injury. However, the real players of this extract and the mechanism involved in boosting functional restoration need to be dissected by further work.

Chemokine Receptors CC Chemokine Receptor 5 and C-X-C Motif Chemokine Receptor 4 Are New Therapeutic Targets for Brain Recovery after Traumatic Brain Injury

Recently, chemokine receptor CC chemokine receptor 5 (CCR5) was found to be a negative modulator of learning and memory. Its inhibition improved outcome after stroke and traumatic brain injury (TBI). To better understand its role after TBI and establish therapeutic strategies, we investigated the effect of reduced CCR5 signaling as a neuroprotective strategy and of the temporal changes of CCR5 expression after TBI in different brain cell types. To silence CCR5 expression, ccr5 short hairpin RNA (shRNA) or dsred shRNA (control) was injected into the cornu ammonis (CA) 1 and CA3 regions of the hippocampus 2 weeks before induction of closed-head injury in mice. Animals were then monitored for 32 days and euthanized at different time points to assess lesion area, inflammatory components of the glial response (immunohistochemistry; IHC), cytokine levels (enzyme-linked immunosorbent array), and extracellular signal-regulated kinase (ERK) phosphorylation (western blot). Fluorescence-activated cell sorting (FACS) analysis was performed to study post-injury temporal changes of CCR5 and C-X-C motif chemokine receptor 4 (CXCR4) expression in cortical and hippocampal cell populations (neurons, astrocytes, and microglia). Phosphorylation of the N-methyl-d-aspartate subunit 1 (NR1) subunit of N-methyl-d-aspartate (western blot) and cAMP-response-element-binding protein (CREB; IHC) were also assessed. The ccr5 shRNA mice displayed reduced lesion area, dynamic alterations in levels of inflammation-related CCR5 ligands and cytokines, and higher levels of phosphorylated ERK. The ccr5 shRNA also reduced astrocytosis in the lesioned and sublesioned cortex. FACS analysis revealed increased cortical CCR5 and CXCR4 expression in CD11b-positive cells, astrocytes, and neurons, which was most evident in cells expressing both receptors, at 3 and 11 days post-injury. The lowest levels of phosphorylated NR1 and phosphorylated CREB were found at day 3 post-injury, suggesting that this is the critical time point for therapeutic intervention.

Pharmacological blockers of CCR5 and CXCR4 improve recovery after traumatic brain injury

CCR5 and CXCR4 are structurally related chemokine receptors that belong to the superfamily of G-protein coupled receptors through which the HIV virus enters and infects cells. Both receptors are also related to HIV-associated neurocognitive disorders that include difficulties in concentration and memory, impaired executive functions, psychomotor slowing, depression and irritability, which are also hallmarks of the long-term sequelae of TBI. Moreover, A growing body of evidence attributes negative influences to CCR5 activation on cognition, particularly after stroke and traumatic brain injury (TBI). Here we investigated the effect of their blockage on motor and cognitive functions, on brain tissue loss and preservation and on some of the biochemical pathways involved. We examined the effect of maraviroc, a CCR5 antagonist used in HIV patients as a viral entry inhibitor, and of plerixafor (AMD3100), a CXCR4 antagonist used in cancer patients as an immune-modulator, on mice subjected to closed head injury (CHI). Mice were treated with maraviroc or plerixafor after CHI for the following 4 or 5 days, respectively. Neurobehavior was assessed according to the Neurological Severity Score; cognitive tests were performed by using the Y-maze, Barnes maze and the novel object recognition test; anxiety was evaluated with the open field test. The mice were sacrificed and brain tissues were collected for Western blot, pathological and immunohistochemical analyses. Both drugs enhanced tissue preservation in the cortex, hippocampus, periventricular areas, corpus callosum and striatum, and reduced astrogliosis)GFAP expression). They also increased the levels of synaptic cognition-related signaling molecules such as phosphorylated NR1 and CREB, and the synaptic plasticity protein PSD95. Both treatments also enhanced the expression of CCR5 and CXCR4 on different brain cell types. In summary, the beneficial effects of blocking CCR5 and CXCR4 after CHI suggest that the drugs used in this study, both FDA approved and in clinical use, should be considered for translational research in TBI patients.

Neural Markers of Vulnerability to Anxiety Outcomes after Traumatic Brain Injury

Anxiety outcomes after traumatic brain injury (TBI) are complex, and the underlying neural mechanisms are poorly understood. Here, we developed a multi-dimensional behavioral profiling approach to investigate anxiety-like outcomes in mice that takes into account individual variability. Departing from the tradition of comparing outcomes in TBI versus sham groups, we identified a subgroup within the TBI group that is vulnerable to anxiety dysfunction, and present increased exploration of the anxiogenic zone compared to sham controls or resilient injured animals, by applying dimensionality reduction, clustering, and post hoc validation to behavioral data obtained from multiple assays for anxiety at several post-injury time points. These vulnerable animals expressed distinct molecular profiles in the corticolimbic network, with downregulation in gamma-aminobutyric acid and glutamate and upregulation in neuropeptide Y markers. Indeed, among vulnerable animals, not resilient or sham controls, severity of anxiety-related outcomes correlated strongly with expression of molecular markers. Our results establish a foundational approach, with predictive power, for reliably identifying maladaptive anxiety outcomes after TBI and uncovering neural signatures of vulnerability to anxiety.

Sodium Cromoglycate Decreases Sensorimotor Impairment and Hippocampal Alterations Induced by Severe Traumatic Brain Injury in Rats

Severe traumatic brain injury (TBI) results in significant functional disturbances in the hippocampus. Studies support that sodium cromoglycate (CG) induces neuroprotective effects. This study focused on investigating the effects of post-TBI subchronic administration of CG on hippocampal hyperexcitability and damage as well as on sensorimotor impairment in rats. In contrast to the control group (Sham+SS group), animals undergoing severe TBI (TBI+SS group) showed sensorimotor dysfunction over the experimental post-TBI period (day 2, 55%, p < 0.001; day 23, 39.5%, p < 0.001; day 30, 38.6%, p < 0.01). On day 30 post-TBI, TBI+SS group showed neuronal hyperexcitability (63.3%, p < 0.01). The hippocampus ipsilateral to the injury showed volume reduction (14.4%, p < 0.001) with a volume of damage of 0.15 ± 0.09 mm³. These changes were associated with neuronal loss in the dentate gyrus (ipsilateral, 33%, p < 0.05); hilus (ipsilateral, 77%, p < 0.001; contralateral, 51%, p < 0.001); Cornu Ammonis (CA)1 (ipsilateral, 40%, p < 0.01), and CA3 (ipsilateral, 52%, p < 0.001; contralateral, 34%, p < 0.01). Animals receiving subchronic treatment with CG (50 mg/kg, s.c. daily for 10 days) after TBI (TBI+CG group) displayed a sensorimotor dysfunction less evident than that of the TBI+SS group (p < 0.001). Their hippocampal excitability was similar to that of the Sham+SS group (p = 0.21). The TBI+CG group presented hippocampal volume reduction (12.7%, p = 0.94) and damage (0.10 ± 0.03 mm³, p > 0.99) similar to the TBI+SS group. However, their hippocampal neuronal preservation was similar to that of the Sham+SS group. These results indicate that CG represents an appropriate and novel pharmacological strategy to reduce the long-term sensorimotor impairment and hippocampal damage and hyperexcitability that result as consequences of severe TBI.

Propylparaben Reduces the Long-Term Consequences in Hippocampus Induced by Traumatic Brain Injury in Rats: Its Implications as Therapeutic Strategy to Prevent Neurodegenerative Diseases

BACKGROUND

Severe traumatic brain injury (TBI), an important risk factor for Alzheimer's disease, induces long-term hippocampal damage and hyperexcitability. On the other hand, studies support that propylparaben (PPB) induces hippocampal neuroprotection in neurodegenerative diseases.

OBJECTIVE

Experiments were designed to evaluate the effects of subchronic treatment with PPB on TBI-induced changes in the hippocampus of rats.

METHODS

Severe TBI was induced using the lateral fluid percussion model. Subsequently, rats received subchronic administration with PPB (178 mg/kg, TBI+PPB) or vehicle (TBI+PEG) daily for 5 days. The following changes were examined during the experimental procedure: sensorimotor dysfunction, changes in hippocampal excitability, as well as neuronal damage and volume.

RESULTS

TBI+PEG group showed sensorimotor dysfunction (p < 0.001), hyperexcitability (64.2%, p < 0.001), and low neuronal preservation ipsi- and contralateral to the trauma. Magnetic resonance imaging (MRI) analysis revealed lower volume (17.2%; p < 0.01) and great damage to the ipsilateral hippocampus. TBI+PPB group showed sensorimotor dysfunction that was partially reversed 30 days after trauma. This group showed hippocampal excitability and neuronal preservation similar to the control group. However, MRI analysis revealed lower hippocampal volume (p < 0.05) when compared with the control group.

CONCLUSION

The present study confirms that post-TBI subchronic administration with PPB reduces the long-term consequences of trauma in the hippocampus. Implications of PPB as a neuroprotective strategy to prevent the development of Alzheimer's disease as consequence of TBI are discussed.

Metabolomics Analysis of Hippocampus and Cortex in a Rat Model of Traumatic Brain Injury in the Subacute Phase

Traumatic brain injury (TBI) is a complex and serious disease as its multifaceted pathophysiological mechanisms remain vague. The molecular changes of hippocampal and cortical dysfunction in the process of TBI are poorly understood, especially their chronic effects on metabolic profiles. Here we utilize metabolomics-based liquid chromatography coupled with tandem mass spectrometry coupled with bioinformatics method to assess the perturbation of brain metabolism in rat hippocampus and cortex on day 7. The results revealed a signature panel which consisted of 13 identified metabolites to facilitate targeted interventions for subacute TBI discrimination. Purine metabolism change in cortical tissue and taurine and hypotaurine metabolism change in hippocampal tissue were detected. Furthermore, the associations between the metabolite markers and the perturbed pathways were analyzed based on databases: 64 enzyme and one pathway were evolved in TBI. The findings represented significant profiling changes and provided unique metabolite-protein information in a rat model of TBI following the subacute phase. This study may inspire scientists and doctors to further their studies and provide potential therapy targets for clinical interventions.

Traumatic Brain Injury Preserves Firing Rates But Disrupts Laminar Oscillatory Coupling and Neuronal Entrainment in Hippocampal CA1

While hippocampal-dependent learning and memory are particularly vulnerable to traumatic brain injury (TBI), the functional status of individual hippocampal neurons and their interactions with oscillations are unknown following injury. Using the most common rodent TBI model and laminar recordings in CA1, we found a significant reduction in oscillatory input into the radiatum layer of CA1 after TBI. Surprisingly, CA1 neurons maintained normal firing rates despite attenuated input, but did not maintain appropriate synchronization with this oscillatory input or with local high-frequency oscillations. Normal synchronization between these coordinating oscillations was also impaired. Simultaneous recordings of medial septal neurons known to participate in theta oscillations revealed increased GABAergic/glutamatergic firing rates postinjury under anesthesia, potentially because of a loss of modulating feedback from the hippocampus. These results suggest that TBI leads to a profound disruption of connectivity and oscillatory interactions, potentially disrupting the timing of CA1 neuronal ensembles that underlie aspects of learning and memory.

Proteomic analysis identifies plasma correlates of remote ischemic conditioning in the context of experimental traumatic brain injury

Remote ischemic conditioning (RIC), transient restriction and recirculation of blood flow to a limb after traumatic brain injury (TBI), can modify levels of pathology-associated circulating protein. This study sought to identify TBI-induced molecular alterations in plasma and whether RIC would modulate protein and metabolite levels at 24 h after diffuse TBI. Adult male C57BL/6 mice received diffuse TBI by midline fluid percussion or were sham-injured. Mice were assigned to treatment groups 1 h after recovery of righting reflex: sham, TBI, sham RIC, TBI RIC. Nine plasma metabolites were significantly lower post-TBI (six amino acids, two acylcarnitines, one carnosine). RIC intervention returned metabolites to sham levels. Using proteomics analysis, twenty-four putative protein markers for TBI and RIC were identified. After application of Benjamini–Hochberg correction, actin, alpha 1, skeletal muscle (ACTA1) was found to be significantly increased in TBI compared to both sham groups and TBI RIC. Thus, identified metabolites and proteins provide potential biomarkers for TBI and therapeutic RIC in order to monitor disease progression and therapeutic efficacy.

Early Increase in Cortical T2 Relaxation Is a Prognostic Biomarker for the Evolution of Severe Cortical Damage, but Not for Epileptogenesis, after Experimental Traumatic Brain Injury

Prognostic biomarkers for post-injury outcome are necessary for the development of neuroprotective and antiepileptogenic treatments for traumatic brain injury (TBI). We hypothesized that T₂ relaxation magnetic resonance imaging (MRI) predicts the progression of perilesional cortical pathology and epileptogenesis. The EPITARGET animal cohort used for MRI analysis included 120 adult male Sprague-Dawley rats with TBI induced by lateral fluid-percussion injury and 24 sham-operated controls. T₂ MRI was performed at days 2, 7, and 21 post-TBI. The lesioned cortex was outlined, and the T₂ value of each imaging voxel within the lesion area was scored using a five-grade pathology classification. Analysis of 1-month video-electroencephalography recordings initiated 5 months post-TBI indicated that 27% (31 of 114) of the animals with TBI developed epilepsy. Multiple linear regression analysis indicated that T₂-based classification of lesion volume at day 2 and day 7 post-TBI explained the necrotic lesion volume with greatly increased T₂ (>102 ms) at day 21 post-TBI (F_(13,103) = 52.5; p < 0.001; R² =  0.87; adjusted R² = 0.85). The volume of moderately increased (78-102 ms) T₂ at day 7 post-TBI predicted the evolution of large (>12 mm³) cortical lesions (area under the curve, 0.92; p < 0.001; cutoff, 1.9 mm³; false positive rate, 0.10; true positive rate, 0.62). Logistic regression analysis, however, showed that the different severities of T₂ lesion volumes at days 2, 7, and 21 post-TBI did not explain the development of epilepsy (χ²_(18,95) = 18.4; p = 0.427). In addition, the location of the T₂ abnormality within the cortex did not correlate with epileptogenesis. A single measurement of T₂ relaxation MRI in the acute post-TBI phase is useful for identifying post-TBI subjects at highest risk of developing large cortical lesions, and thus, in the greatest need of neuroprotective therapies after TBI, but not the development of post-traumatic epilepsy.

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.

Neuroprotective effect of lithium in cold- induced traumatic brain injury in mice

Apart from its well-established therapeutic activity on bipolar disorder and depression, lithium exerts neuroprotective activity upon neurodegenerative disorders, such as traumatic brain injury (TBI). However, the cellular signaling mechanisms mediating lithium's neuroprotective activity and long-term dose- and time-dependent effects on close and remote proximity are largely unknown. Herein, we tested prophylactic and acute effects of lithium (2 mmol/kg) after cold- induced TBI. In both conditions, treatments with lithium resulted in reduced infarct volume and apoptosis. Its acute treatment resulted in the increase of Akt, ERK-1/2 and GSK-3 α/β phosphoylations. Interestingly, its prophylactic treatment instead resulted in decreased phosphorylations of Akt, ERK-1/2, p38, JNK-1 moderately and GSK-3 α/β significantly. Then, we tested subacute (35-day follow-up) role of low (0.2 mmol/kg) and high dose (2 mmol/kg) lithium and revealed that high dose lithium group was the most mobile so the least depressed in the tail suspension test. Anxiety level was assessed by light-dark test, all groups' anxiety levels were decreased with time, but lithium had no effect on anxiety like behavior. When subacute effects of injury and drug treatment were evaluated on the defined brain regions, infarct volume was decreased in the high dose lithium group significantly. In contrast to other brain regions, hippocampal atrophies were observed in both lithium treatment groups, which were significant in the low dose lithium group in both hemispheres, which was associated with the reduced cell proliferation and neurogenesis. Our data demonstrate that lithium treatment protects neurons from TBI. However, long term particularly low-dose lithium causes hippocampal atrophy and decreased neurogenesis.

Interferon-β Plays a Detrimental Role in Experimental Traumatic Brain Injury by Enhancing Neuroinflammation That Drives Chronic Neurodegeneration

DNA damage and type I interferons (IFNs) contribute to inflammatory responses after traumatic brain injury (TBI). TBI-induced activation of microglia and peripherally-derived inflammatory macrophages may lead to tissue damage and neurological deficits. Here, we investigated the role of IFN-β in secondary injury after TBI using a controlled cortical impact model in adult male IFN-β-deficient (IFN-β^-/-) mice and assessed post-traumatic neuroinflammatory responses, neuropathology, and long-term functional recovery. TBI increased expression of DNA sensors cyclic GMP-AMP synthase and stimulator of interferon genes in wild-type (WT) mice. IFN-β and other IFN-related and neuroinflammatory genes were also upregulated early and persistently after TBI. TBI increased expression of proinflammatory mediators in the cortex and hippocampus of WT mice, whereas levels were mitigated in IFN-β^-/- mice. Moreover, long-term microglia activation, motor, and cognitive function impairments were decreased in IFN-β^-/- TBI mice compared with their injured WT counterparts; improved neurological recovery was associated with reduced lesion volume and hippocampal neurodegeneration in IFN-β^-/- mice. Continuous central administration of a neutralizing antibody to the IFN-α/β receptor (IFNAR) for 3 d, beginning 30 min post-injury, reversed early cognitive impairments in TBI mice and led to transient improvements in motor function. However, anti-IFNAR treatment did not improve long-term functional recovery or decrease TBI neuropathology at 28 d post-injury. In summary, TBI induces a robust neuroinflammatory response that is associated with increased expression of IFN-β and other IFN-related genes. Inhibition of IFN-β reduces post-traumatic neuroinflammation and neurodegeneration, resulting in improved neurological recovery. Thus, IFN-β may be a potential therapeutic target for TBI.SIGNIFICANCE STATEMENT TBI frequently causes long-term neurological and psychiatric changes in head injury patients. TBI-induced secondary injury processes including persistent neuroinflammation evolve over time and can contribute to chronic neurological impairments. The present study demonstrates that TBI is followed by robust activation of type I IFN pathways, which have been implicated in microglial-associated neuroinflammation and chronic neurodegeneration. We examined the effects of genetic or pharmacological inhibition of IFN-β, a key component of type I IFN mechanisms to address its role in TBI pathophysiology. Inhibition of IFN-β signaling resulted in reduced neuroinflammation, attenuated neurobehavioral deficits, and limited tissue loss long after TBI. These preclinical findings suggest that IFN-β may be a potential therapeutic target for TBI.

Histological and Behavioral Evaluation after Traumatic Brain Injury in Mice: A Ten Months Follow-Up Study

Traumatic brain injury (TBI) is a chronic pathology, inducing long-term deficits that remain understudied in pre-clinical studies. In this context, exploration, anxiety-like behavior, cognitive flexibility, and motor coordination were assessed until 5 and 10 months after an experimental TBI in the adult mouse, using two cohorts. In order to differentiate age, surgery, and remote gray and white matter lesions, three groups (unoperated, sham-operated, and TBI) were studied. TBI induced delayed motor coordination deficits at the pole test, 4.5 months after injury, that could be explained by gray and white matter damages in ipsilateral nigrostriatal structures (striatum, internal capsule) that were spreading to new structures between cohorts, at 5 versus 10 months after the injury. Further, TBI induced an enhanced exploratory behavior during stressful situations (active phase during actimetry test, object exploration in an open field), risk-taking behaviors in the elevated plus maze 5 months after injury, and a cognitive inflexibility in the Barnes maze that persisted until 9 months after the injury. These behavioral modifications could be related to the white and gray matter lesions observed in ipsi- and contralateral limbic structures (amygdala, hilus/cornu ammonis 4, hypothalamus, external capsule, corpus callosum, and cingular cortex) that were spreading to new structures between cohorts, at 5 months versus 10 months after the injury. The present study corroborates clinical findings on TBI and provides a relevant rodent chronic model which could help in validating pharmacological strategies against the chronic consequences of TBI.

Animal Models of Post-Traumatic Epilepsy

Traumatic brain injury is the leading cause of morbidity and mortality worldwide, with the incidence of post-traumatic epilepsy increasing with the severity of the head injury. Post-traumatic epilepsy (PTE) is defined as a recurrent seizure disorder secondary to trauma to the brain and has been described as one of the most devastating complications associated with TBI (Traumatic Brain Injury). The goal of this review is to characterize current animal models of PTE and provide succinct protocols for the development of each of the currently available animal models. The development of translational and effective animal models for post-traumatic epilepsy is critical in both elucidating the underlying pathophysiology associated with PTE and providing efficacious clinical breakthroughs in the management of PTE.

Neurogranin Protein Expression Is Reduced after Controlled Cortical Impact in Rats

Traumatic brain injury (TBI) is known to cause short- and long-term synaptic changes in the brain, possibly underlying downstream cognitive impairments. Neuronal levels of neurogranin, a calcium-sensitive calmodulin-binding protein essential for synaptic plasticity and postsynaptic signaling, are correlated with cognitive function. This study aims to understand the effect of TBI on neurogranin by characterizing changes in protein expression at various time points after injury. Adult, male rats were subjected to either controlled cortical impact (CCI) or control surgery. Expression of neurogranin and post-synaptic density 95 (PSD-95) were evaluated by Western blot in the cortex and hippocampus at 24 h and 1, 2, and 4 weeks post-injury. We hypothesized that CCI reduces neurogranin levels in the cortex and hippocampus, and demonstrate different expression patterns from PSD-95. Neurogranin levels were reduced in the ipsilateral cortex and hippocampus up to 2 weeks after injury but recovered to sham levels by 4 weeks. The contralateral cortex and hippocampus were relatively resistant to changes in neurogranin expression post-injury. Qualitative immunohistochemical assessment corroborated the immunoblot findings. Particularly, the pericontusional cortex and ipsilateral Cornu Ammonis (CA)3 region showed marked reduction in immunoreactivity. PSD-95 demonstrated similar expression patterns to neurogranin in the cortex; however, in the hippocampus, protein expression was increased compared with sham at the 2 and 4 week time points. Our results indicate that CCI lowers neurogranin expression with temporal and regional specificity and that this occurs independently of dendritic loss. Further understanding of the role of neurogranin in synaptic biology after TBI will elucidate pathological mechanisms contributing to cognitive dysfunction.

Greater neurodegeneration and behavioral deficits after single closed head traumatic brain injury in adolescent versus adult male mice

Traumatic brain injury (TBI) is a major public health concern affecting 2.8 million people per year in the United States, of whom about 1 million are children under 19 years old. Animal models of TBI have been developed and used in multiple ages of animals, but direct comparisons of adult and adolescent populations are rare. The current studies were undertaken to directly compare outcomes between adult and adolescent male mice, using a closed head, single-impact model of TBI. Six-week-old adolescent and 9-week-old adult male mice were subjected to mild-moderate TBI. Histological measures for neurodegeneration, gliosis, and microglial neuroinflammation, and behavioral tests of locomotion and memory were performed. Adolescent TBI mice have increased mortality (Χ²  = 20.72, p < 0.001) compared to adults. There is also evidence of hippocampal neurodegeneration in adolescents that is not present in adults. Hippocampal neurodegeneration correlates with histologic activation of microglia, but not with increased astrogliosis. Adults and adolescents have similar locomotion deficits after TBI that recover by 16 days postinjury. Adolescents have memory deficits as evidenced by impaired novel object recognition between 3-4 and 4-16 days postinjury (F_1,26  = 5.23, p = 0.031) while adults do not. In conclusion, adults and adolescents within a close age range (6-9 weeks) respond to TBI differently. Adolescents are more severely affected by mortality, neurodegeneration, and inflammation in the hippocampus compared to adults. Adolescents, but not adults, have worse memory performance after TBI that lasts at least 16 days postinjury.