Craniotomy: true sham for traumatic brain injury, or a sham of a sham?

Activity of a Novel Anti-Inflammatory Agent F-3,6'-dithiopomalidomide as a Treatment for Traumatic Brain Injury

Traumatic brain injury (TBI) is a major risk factor for several neurodegenerative disorders, including Parkinson's disease (PD) and Alzheimer's disease (AD). Neuroinflammation is a cause of later secondary cell death following TBI, has the potential to aggravate the initial impact, and provides a therapeutic target, albeit that has failed to translate into clinical trial success. Thalidomide-like compounds have neuroinflammation reduction properties across cellular and animal models of TBI and neurodegenerative disorders. They lower the generation of proinflammatory cytokines, particularly TNF-α which is pivotal in microglial cell activation. Unfortunately, thalidomide-like drugs possess adverse effects in humans before achieving anti-inflammatory drug levels. We developed F-3,6'-dithiopomalidomide (F-3,6'-DP) as a novel thalidomide-like compound to ameliorate inflammation. F-3,6'-DP binds to cereblon but does not efficiently trigger the degradation of the transcription factors (SALL4, Ikaros, and Aiolos) associated with the teratogenic and anti-proliferative responses of thalidomide-like drugs. We utilized a phenotypic drug discovery approach that employed cellular and animal models in the selection and development of F-3,6'-DP. F-3,6'-DP significantly mitigated LPS-induced inflammatory markers in RAW 264.7 cells, and lowered proinflammatory cytokine/chemokine levels in the plasma and brain of rats challenged with systemic LPS. We subsequently examined immunohistochemical, biochemical, and behavioral measures following controlled cortical impact (CCI) in mice, a model of moderate TBI known to induce inflammation. F-3,6'-DP decreased CCI-induced neuroinflammation, neuronal loss, and behavioral deficits when administered after TBI. F-3,6'-DP represents a novel class of thalidomide-like drugs that do not lower classical cereblon-associated transcription factors but retain anti-inflammatory actions and possess efficacy in the treatment of TBI and potentially longer-term neurodegenerative disorders.

Electromagnetic Controlled Closed-Head Model of Mild Traumatic Brain Injury in Mice

Highly reproducible animal models of traumatic brain injury (TBI), with well-defined pathologies, are needed for testing therapeutic interventions and understanding the mechanisms of how a TBI alters brain function. The availability of multiple animal models of TBI is necessary to model the different aspects and severities of TBI seen in people. This manuscript describes the use of a midline closed head injury (CHI) to develop a mouse model of mild TBI. The model is considered mild because it does not produce structural brain lesions based on neuroimaging or gross neuronal loss. However, a single impact creates enough pathology that cognitive impairment is measurable at least 1 month after injury. A step-by-step protocol to induce a CHI in mice using a stereotaxically guided electromagnetic impactor is defined in the paper. The benefits of the mild midline CHI model include the reproducibility of the injury-induced changes with low mortality. The model has been temporally characterized up to 1 year after the injury for neuroimaging, neurochemical, neuropathological, and behavioral changes. The model is complementary to open skull models of controlled cortical impact using the same impactor device. Thus, labs can model both mild diffuse TBI and focal moderate-to-severe TBI with the same impactor.

A Focal Impact Model of Traumatic Brain Injury in Xenopus Tadpoles Reveals Behavioral Alterations, Neuroinflammation, and an Astroglial Response

Traumatic Brain Injury (TBI) is a global driver of disability, and we currently lack effective therapies to promote neural repair and recovery. TBI is characterized by an initial insult, followed by a secondary injury cascade, including inflammation, excitotoxicity, and glial cellular response. This cascade incorporates molecular mechanisms that represent potential targets of therapeutic intervention. In this study, we investigate the response to focal impact injury to the optic tectum of Xenopus laevis tadpoles. This injury disrupts the blood-brain barrier, causing edema, and produces deficits in visually-driven behaviors which are resolved within one week. Within 3 h, injured brains show a dramatic transcriptional activation of inflammatory cytokines, upregulation of genes associated with inflammation, and recruitment of microglia to the injury site and surrounding tissue. Shortly afterward, astrocytes undergo morphological alterations and accumulate near the injury site, and these changes persist for at least 48 h following injury. Genes associated with astrocyte reactivity and neuroprotective functions also show elevated levels of expression following injury. Since our results demonstrate that the response to focal impact injury in Xenopus resembles the cellular alterations observed in rodents and other mammalian models, the Xenopus tadpole offers a new, scalable vertebrate model for TBI.

Evidence of traumatic brain injury in headbutting bovids

Traumatic brain injury (TBI) is a leading cause of neurologic impairment and death that remains poorly understood. Rodent models have yet to produce clinical therapies, and the exploration of larger and more diverse models remains relatively scarce. We investigated the potential for brain injury after headbutting in two combative bovid species by assessing neuromorphology and neuropathology through immunohistochemistry and stereological quantification. Postmortem brains of muskoxen (Ovibos moschatus, n = 3) and bighorn sheep (Ovis canadensis, n = 4) were analyzed by high-resolution MRI and processed histologically for evidence of TBI. Exploratory histological protocols investigated potential abnormalities in neurons, microglia, and astrocytes in the prefrontal and parietal cortex. Phosphorylated tau protein, a TBI biomarker found in the cerebrospinal fluid and in neurodegenerative lesions, was used to detect possible cellular consequences of chronic or acute TBI. MRI revealed no abnormal neuropathological changes; however, high amounts of tau-immunoreactive neuritic thread clusters, neurites, and neurons were concentrated in the superficial layers of the neocortex, preferentially at the bottom of the sulci in the muskoxen and occasionally around blood vessels. Tau-immunoreactive lesions were rare in the bighorn sheep. Additionally, microglia and astrocytes showed no grouping around tau-immunoreactive cells in either species. Our preliminary findings indicate that muskoxen and possibly other headbutting bovids suffer from chronic or acute brain trauma and that the males' thicker skulls may protect them to a certain extent.

Progress Toward a Multiomic Understanding of Traumatic Brain Injury: A Review

Traumatic brain injury (TBI) is not a single disease state but describes an array of conditions associated with insult or injury to the brain. While some individuals with TBI recover within a few days or months, others present with persistent symptoms that can cause disability, neuropsychological trauma, and even death. Understanding, diagnosing, and treating TBI is extremely complex for many reasons, including the variable biomechanics of head impact, differences in severity and location of injury, and individual patient characteristics. Because of these confounding factors, the development of reliable diagnostics and targeted treatments for brain injury remains elusive. We argue that the development of effective diagnostic and therapeutic strategies for TBI requires a deep understanding of human neurophysiology at the molecular level and that the framework of multiomics may provide some effective solutions for the diagnosis and treatment of this challenging condition. To this end, we present here a comprehensive review of TBI biomarker candidates from across the multiomic disciplines and compare them with known signatures associated with other neuropsychological conditions, including Alzheimer’s disease and Parkinson’s disease. We believe that this integrated view will facilitate a deeper understanding of the pathophysiology of TBI and its potential links to other neurological diseases.

Implantable Micro-Light-Emitting Diode (µLED)-based optogenetic interfaces toward human applications

Optogenetics has received wide attention in biomedical fields because of itsadvantages in temporal precision and spatial resolution. Beyond contributions to important advances in fundamental research, optogenetics is inspiring a shift towards new methods of improving human well-being and treating diseases. Soft, flexible and biocompatible systems using µLEDs as a light source have been introduced to realize brain-compatible optogenetic implants, but there are still many technical challenges to overcome before their human applications. In this review, we address progress in the development of implantable µLED probes and recent achievements in (i) device engineering design, (ii) driving power, (iii) multifunctionality and (iv) closed-loop systems. (v) Expanded optogenetic applications based on remarkable advances in µLED implants will also be discussed.

Time dependent analysis of rat microglial surface markers in traumatic brain injury reveals dynamics of distinct cell subpopulations

Traumatic brain injury (TBI) results in a cascade of cellular responses, which produce neuroinflammation, partly due to the activation of microglia. Accurate identification of microglial populations is key to understanding therapeutic approaches that modify microglial responses to TBI and improve long-term outcome measures. Notably, previous studies often utilized an outdated convention to describe microglial phenotypes. We conducted a temporal analysis of the response to controlled cortical impact (CCI) in rat microglia between ipsilateral and contralateral hemispheres across seven time points, identified microglia through expression of activation markers including CD45, CD11b/c, and p2y12 receptor and evaluated their activation state using additional markers of CD32, CD86, RT1B, CD200R, and CD163. We identified unique sub-populations of microglial cells that express individual or combination of activation markers across time points. We further portrayed how the size of these sub-populations changes through time, corresponding to stages in TBI response. We described longitudinal changes in microglial population after CCI in two different locations using activation markers, showing clear separation into cellular sub-populations that feature different temporal patterns of markers after injury. These changes may aid in understanding the symptomatic progression following TBI and help define microglial subpopulations beyond the outdated M1/M2 paradigm.

Phosphatidylethanolamine Deficiency and Triglyceride Overload in Perilesional Cortex Contribute to Non-Goal-Directed Hyperactivity after Traumatic Brain Injury in Mice

Traumatic brain injury (TBI) is often complicated by long-lasting disabilities, including headache, fatigue, insomnia, hyperactivity, and cognitive deficits. In a previous study in mice, we showed that persistent non-goal-directed hyperactivity is a characteristic post-TBI behavior that was associated with low levels of endocannabinoids in the perilesional cortex. We now analyzed lipidome patterns in the brain and plasma in TBI versus sham mice in association with key behavioral parameters and endocannabinoids. Lipidome profiles in the plasma and subcortical ipsilateral and contralateral brain were astonishingly equal in sham and TBI mice, but the ipsilateral perilesional cortex revealed a strong increase in neutral lipids represented by 30 species of triacylglycerols (TGs) of different chain lengths and saturation. The accumulation of TG was localized predominantly to perilesional border cells as revealed by Oil Red O staining. In addition, hexosylceramides (HexCer) and phosphatidylethanolamines (PE and ether-linked PE-O) were reduced. They are precursors of gangliosides and endocannabinoids, respectively. High TG, low HexCer, and low PE/PE-O showed a linear association with non-goal-directed nighttime hyperactivity but not with the loss of avoidance memory. The analyses suggest that TG overload and HexCer and PE deficiencies contributed to behavioral dimensions of post-TBI psychopathology.

Progranulin deficiency promotes persistent neuroinflammation and causes regional pathology in the hippocampus following traumatic brain injury

Traumatic brain injury (TBI) can be progressive and can lead to the development of a long-term complication termed chronic traumatic encephalopathy. The mechanisms underlying the progressive changes are still unknown; however, studies have suggested that microglia-mediated neuroinflammation in response to TBI may play a fundamental role. This study aimed to determine whether progranulin (PGRN), a major modulator of microglial activity, plays a role in the progressive damage following TBI. PGRN-deficient and wild-type mice were subjected to controlled cortical impact and were observed neuropathologically after 3 days, 7 days, and 5 months. Compared to sham and wild-type mice, the PGRN-deficient mice showed overall stronger microgliosis and astrocytosis. The astrocytosis involved broader areas than the microgliosis and was more prominent in the basal ganglia, hippocampus, and internal capsule in PGRN-deficient mice. Ongoing neuronal death was uniquely observed in the hippocampal CA3 region of PGRN-deficient mice at 5 months after TBI, accompanying the regional chronic microgliosis and astrocytosis involving the CA3 commissural pathway. In addition, there was M1 microglial polarization in the pericontusional area with activated TLR4/MyD88/NF-κB signaling; however, the hippocampus showed only mild M1 polarization 7 days after TBI. Lastly, Morris water maze tests showed PGRN-deficient mice had poorer spatial learning and memory 5 months after TBI than wild-type or sham mice. The data indicated the PGRN deficiency caused TBI progression by promoting persistent microgliosis with microglial polarization and astrocytosis, as well as regional pathology in the hippocampus. The study suggests that PGRN should be evaluated as a potential therapy for TBI.

Determining Sex-Based Differences in Inflammatory Response in an Experimental Traumatic Brain Injury Model

Introduction

Traumatic brain injury is a leading cause of injury-related death and morbidity. Multiple clinical and pre-clinical studies have reported various results regarding sex-based differences in TBI. Our accepted rodent model of traumatic brain injury was used to identify sex-based differences in the pathological features of TBI.

Methods

Male and female Sprague-Dawley rats were subjected to either controlled-cortical impact (CCI) or sham injury; brain tissue was harvested at different time intervals depending on the specific study. Blood-brain barrier (BBB) analysis was performed using infrared imaging to measure fluorescence dye extravasation. Microglia and splenocytes were characterized with traditional flow cytometry; microglia markers such as CD45, P2Y12, CD32, and CD163 were analyzed with t-distributed stochastic neighbor embedding (t-SNE). Flow cytometry was used to study tissue cytokine levels, and supplemented with ELISAs of TNF-⍺, IL-17, and IL-1β of the ipsilateral hemisphere tissue.

Results

CCI groups of both sexes recorded a higher BBB permeability at 72 hours post-injury than their respective sham groups. There was significant difference in the integrated density value of BBB permeability between the male CCI group and the female CCI group (female CCI mean = 3.08 x 108 ± 2.83 x 107, male CCI mean = 2.20 x 108 ± 4.05 x 106, p = 0.0210), but otherwise no differences were observed. Traditional flow cytometry did not distinguish any sex-based difference in regards to splenocyte cell population after CCI. t-SNE did not reveal any significant difference between the male and female injury groups in the activation of microglia. Cytokine analysis after injury by flow cytometry and ELISA was limited in differences at the time point of 6 hours post-injury.

Conclusion

In our rodent model of traumatic brain injury, sex-based differences in pathology and neuroinflammation at specified time points are limited, and only noted in one specific analysis of BBB permeability.

Increased Brain-Derived Neurotrophic Factor Levels in Cerebrospinal Fluid During the Acute Phase in TBI-Induced Mechanical Allodynia in the Rat Model

Background

The present study aimed to develop a rat model for mechanical allodynia after traumatic brain injury (TBI) and to investigate the expression of brain-derived neurotrophic factor (BDNF) in the cerebrospinal fluid (CSF) using this model.

Methods

A total of 180 rats were randomly allocated into three groups: a control group (group C), a sham-operated group (group S), and a controlled cortical impact induced TBI group (group T), 60 in each group. Von Frey test was performed to evaluate mechanical withdrawal thresholds. An enzyme-linked immunosorbent assay was performed to quantify BDNF level in CSF.

Results

The 50% withdrawal thresholds of group T were lower than those of group C and group S at all measuring points except for the preoperative period (P = 0.026, <0.001, and <0.001 for POD1, POD7, and POD14, respectively). The BDNF level of group T was higher than those of group C and group S at POD1 (P = 0.005).

Conclusion

Upregulation of the BDNF expression in CSF was observed in rats who developed mechanical allodynia on the day after TBI. Based on our findings, to elucidate the relationship between TBI-induced neuropathic pain and BDNF expression in CSF, further research should be carried out through a multifaceted approach to a broad spectrum of pain behavior models.

Longitudinal cortex-wide monitoring of cerebral hemodynamics and oxygen metabolism in awake mice using multi-parametric photoacoustic microscopy

Multi-parametric photoacoustic microscopy (PAM) has emerged as a promising new technique for high-resolution quantification of hemodynamics and oxygen metabolism in the mouse brain. In this work, we have extended the scope of multi-parametric PAM to longitudinal, cortex-wide, awake-brain imaging with the use of a long-lifetime (24 weeks), wide-field (5 × 7 mm²), light-weight (2 g), dual-transparency (i.e., light and ultrasound) cranial window. Cerebrovascular responses to the window installation were examined in vivo, showing a complete recovery in 18 days. In the 22-week monitoring after the recovery, no dura thickening, skull regrowth, or changes in cerebrovascular structure and function were observed. The promise of this technique was demonstrated by monitoring vascular and metabolic responses of the awake mouse brain to ischemic stroke throughout the acute, subacute, and chronic stages. Side-by-side comparison of the responses in the ipsilateral (injury) and contralateral (control) cortices shows that despite an early recovery of cerebral blood flow and an increase in microvessel density, a long-lasting deficit in cerebral oxygen metabolism was observed throughout the chronic stage in the injured cortex, part of which proceeded to infarction. This longitudinal, functional-metabolic imaging technique opens new opportunities to study the chronic progression and therapeutic responses of neurovascular diseases.

Targeting Oxidative Stress with Antioxidant Duotherapy after Experimental Traumatic Brain Injury

We assessed the effect of antioxidant therapy using the Food and Drug Administration-approved respiratory drug N-acetylcysteine (NAC) or sulforaphane (SFN) as monotherapies or duotherapy in vitro in neuron-BV2 microglial co-cultures and validated the results in a lateral fluid-percussion model of TBI in rats. As in vitro measures, we assessed neuronal viability by microtubule-associated-protein 2 immunostaining, neuroinflammation by monitoring tumor necrosis factor (TNF) levels, and neurotoxicity by measuring nitrite levels. In vitro, duotherapy with NAC and SFN reduced nitrite levels to 40% (p < 0.001) and neuroinflammation to -29% (p < 0.001) compared with untreated culture. The treatment also improved neuronal viability up to 72% of that in a positive control (p < 0.001). The effect of NAC was negligible, however, compared with SFN. In vivo, antioxidant duotherapy slightly improved performance in the beam walking test. Interestingly, duotherapy treatment decreased the plasma interleukin-6 and TNF levels in sham-operated controls (p < 0.05). After TBI, no treatment effect on HMGB1 or plasma cytokine levels was detected. Also, no treatment effects on the composite neuroscore or cortical lesion area were detected. The robust favorable effect of duotherapy on neuroprotection, neuroinflammation, and oxidative stress in neuron-BV2 microglial co-cultures translated to modest favorable in vivo effects in a severe TBI model.

Assessment of single-vessel cerebral blood velocity by phase contrast fMRI

Current approaches to high-field functional MRI (fMRI) provide 2 means to map hemodynamics at the level of single vessels in the brain. One is through changes in deoxyhemoglobin in venules, i.e., blood oxygenation level-dependent (BOLD) fMRI, while the second is through changes in arteriole diameter, i.e., cerebral blood volume (CBV) fMRI. Here, we introduce cerebral blood flow-related velocity-based fMRI, denoted CBFv-fMRI, which uses high-resolution phase contrast (PC) MRI to form velocity measurements of flow. We use CBFv-fMRI in measure changes in blood velocity in single penetrating microvessels across rat parietal cortex. In contrast to the venule-dominated BOLD and arteriole-dominated CBV fMRI signals, CBFv-fMRI is comparable from both arterioles and venules. A single fMRI platform is used to map changes in blood pO2 (BOLD), volume (CBV), and velocity (CBFv). This combined high-resolution single-vessel fMRI mapping scheme enables vessel-specific hemodynamic mapping in animal models of normal and diseased states and further has translational potential to map vascular dementia in diseased or injured human brains with ultra-high-field fMRI.

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.

Coordinated expression of the renin-angiotensin genes in the lumbar spinal cord: Lateralization and effects of unilateral brain injury

In spite of its apparent symmetry, the spinal cord is asymmetric in its reflexes and gene expression patterns including leftward expression bias of the opioid and glutamate genes. To examine whether this is a general phenomenon for neurotransmitter and neurohormonal genes, we here characterized expression and co-expression (transcriptionally coordinated) patterns of genes of the renin-angiotensin system (RAS) that is involved in neuroprotection and pathological neuroplasticity in the left and right lumbar spinal cord. We also tested whether the RAS expression patterns were affected by unilateral brain injury (UBI) that rewired lumbar spinal neurocircuits. The left and right halves of the lumbar spinal cord were analysed in intact rats, and rats with left- or right-sided unilateral cortical injury, and left- or right-sided sham surgery. The findings were (i) lateralized expression of the RAS genes Ace, Agtr2 and Ren with higher levels on the left side; (ii) the asymmetry in coordination of the RAS gene expression that was stronger on the right side; (iii) the decay in coordination of co-expression of the RAS and neuroplasticity-related genes induced by the right-side but not left-side sham surgery and UBI; and (iv) the UBI-induced shift to negative regulatory interactions between RAS and neuroplasticity-related genes on the contralesional spinal side. Thus, the RAS genes may be a part of lateralized gene co-expression networks and have a role in a side-specific regulation of spinal neurocircuits.

Location Matters: Navigating Regional Heterogeneity of the Neurovascular Unit

The neurovascular unit (NVU) of the brain is composed of multiple cell types that act synergistically to modify blood flow to locally match the energy demand of neural activity, as well as to maintain the integrity of the blood-brain barrier (BBB). It is becoming increasingly recognized that the functional specialization, as well as the cellular composition of the NVU varies spatially. This heterogeneity is encountered as variations in vascular and perivascular cells along the arteriole-capillary-venule axis, as well as through differences in NVU composition throughout anatomical regions of the brain. Given the wide variations in metabolic demands between brain regions, especially those of gray vs. white matter, the spatial heterogeneity of the NVU is critical to brain function. Here we review recent evidence demonstrating regional specialization of the NVU between brain regions, by focusing on the heterogeneity of its individual cellular components and briefly discussing novel approaches to investigate NVU diversity.

A minimally invasive flexible electrode array for simultaneous recording of ECoG signals from multiple brain regions

The minimal invasiveness of electrocorticography (ECoG) enabled its widespread use in clinical areas as well as in neuroscience research. However, most existing ECoG arrays require that the entire surface area of the brain that is to be recorded be exposed through a large craniotomy. We propose a device that overcomes this limitation, i.e., a minimally invasive, polyimide-based flexible array of electrodes that can enable the recording of ECoG signals in multiple regions of the brain with minimal exposure of the surface of the brain. Magnetic force-assisted positioning of a flexible electrode array enables recording from distant brain regions with a small cranial window. Also, a biodegradable organic compound used for attaching a magnet on the electrodes allows simple retrieval of the magnet. We demonstrate with an in vivo chronic recording that an implanted ECoG electrode array can record ECoG signals from the visual cortex and the motor cortex during a rat's free behavior. Our results indicate that the proposed device induced minimal damage to the animal. We expect the proposed device to be utilized for experiments for large-scale brain circuit analyses as well as clinical applications for intra-operative monitoring of epileptic activity.

Single intracerebroventricular progranulin injection adversely affects the blood-brain barrier in experimental traumatic brain injury

Progranulin (PGRN) is a neurotrophic and anti-inflammatory factor with protective effects in animal models of ischemic stroke, subarachnoid hemorrhage, and traumatic brain injury (TBI). Administration of recombinant (r) PGRN prevents exaggerated brain pathology after TBI in Grn-deficient mice, suggesting that local injection of recombinant progranulin (rPGRN) provides therapeutic benefit in the acute phase of TBI. To test this hypothesis, we subjected adult male C57Bl/6N mice to the controlled cortical impact model of TBI, administered a single dose of rPGRN intracerebroventricularly (ICV) shortly before the injury, and examined behavioral and biological effects up to 5 days post injury (dpi). The anti-inflammatory bioactivity of rPGRN was confirmed by its capability to inhibit the inflammation-induced hypertrophy of murine primary microglia and astrocytes in vitro. In C57Bl/6N mice, however, ICV administration of rPGRN failed to attenuate behavioral deficits over the 5-day observation period. (Immuno)histological gene and protein expression analyses at 5 dpi did not reveal a therapeutic benefit in terms of brain injury size, brain inflammation, glia activation, cell numbers in neurogenic niches, and neuronal damage. Instead, we observed a failure of TBI-induced mRNA upregulation of the tight junction protein occludin and increased extravasation of serum immunoglobulin G into the brain parenchyma at 5 dpi. In conclusion, single ICV administration of rPGRN had not the expected protective effects in the acute phase of murine TBI, but appeared to cause an aggravation of blood-brain barrier disruption. The data raise questions about putative PGRN-boosting approaches in other types of brain injuries and disease.

Complement mediates neuroinflammation and cognitive decline at extended chronic time points after traumatic brain injury

Traumatic brain injury (TBI) can result in progressive cognitive decline occurring for years after the initial insult, and for which there is currently no pharmacological treatment. An ongoing chronic inflammatory response after TBI is thought to be an important factor in driving this cognitive decline. Here, we investigate the role of complement in neuroinflammation and cognitive decline for up to 6 months after murine TBI. Male C57BL/6 mice were subjected to open head injury using a controlled cortical impact device. At 2 months post TBI, mice were moved to large cages with an enriched environment to simulate rehabilitation therapy, and assigned to one of three treatment groups: 1. vehicle (PBS), 2. CR2Crry (3 doses over 1 week), 3. CR2Crry (continuous weekly dose until the end of the study). The study was terminated at 6 months post-TBI for all groups. Motor and cognitive function was analyzed, with histopathological analysis of brain tissue. Measured at 6 months after TBI, neither of the complement inhibition paradigms improved motor performance. However, mice receiving continuous CR2Crry treatment showed improved spatial learning and memory compared to both mice receiving only 3 doses and to mice receiving vehicle control. Analysis of brain sections at 6 months after injury revealed ongoing complement activation in the control group, with reduced complement activation and C3 deposition in the continuous CR2Crry treatment group. The ipsilateral hemisphere of continuously treated animals also showed a decrease in microglia/macrophage and astrocyte activation compared to vehicle. There was also increased astrocytosis in the contralateral hippocampus of vehicle treated vs. naïve mice, which was reduced in mice continuously treated with CR2Crry. This study demonstrates continued complement mediated neuroinflammation at extended chronic time points after TBI, and extends the potential treatment window for complement inhibition, which has previously been shown to improve outcomes after murine TBI.

Dissecting the microvascular contributions to diffuse correlation spectroscopy measurements of cerebral hemodynamics using optical coherence tomography angiography

Significance: Diffuse correlation spectroscopy (DCS) is an emerging noninvasive, diffuse optical modality that purportedly enables direct measurements of microvasculature blood flow. Functional optical coherence tomography angiography (OCT-A) can resolve blood flow in vessels as fine as capillaries and thus has the capability to validate key attributes of the DCS signal. Aim: To characterize activity in cortical vasculature within the spatial volume that is probed by DCS and to identify populations of blood vessels that are most representative of the DCS signals. Approach: We performed simultaneous measurements of somatosensory-evoked cerebral blood flow in mice in vivo using both DCS and OCT-A. Results: We resolved sensory-evoked blood flow in the somatosensory cortex with both modalities. Vessels with diameters smaller than 10    μ m featured higher peak flow rates during the initial poststimulus positive increase in flow, whereas larger vessels exhibited considerably larger magnitude of the subsequent undershoot. The simultaneously recorded DCS waveforms correlated most highly with flow in the smallest vessels, yet featured a more prominent undershoot. Conclusions: Our direct, multiscale, multimodal cross-validation measurements of functional blood flow support the assertion that the DCS signal preferentially represents flow in microvasculature. The significantly greater undershoot in DCS, however, suggests a more spatially complex relationship to flow in cortical vasculature during functional activation.

Transcriptomic Analysis of Mouse Brain After Traumatic Brain Injury Reveals That the Angiotensin Receptor Blocker Candesartan Acts Through Novel Pathways

Traumatic brain injury (TBI) results in complex pathological reactions, where the initial lesion is followed by secondary inflammation and edema. Our laboratory and others have reported that angiotensin receptor blockers (ARBs) have efficacy in improving recovery from traumatic brain injury in mice. Treatment of mice with a subhypotensive dose of the ARB candesartan results in improved functional recovery, and reduced pathology (lesion volume, inflammation and gliosis). In order to gain a better understanding of the molecular mechanisms through which candesartan improves recovery after controlled cortical impact injury (CCI), we performed transcriptomic profiling on brain regions after injury and drug treatment. We examined RNA expression in the ipsilateral hippocampus, thalamus and hypothalamus at 3 or 29 days post injury (dpi) treated with either candesartan (0.1 mg/kg) or vehicle. RNA was isolated and analyzed by bulk mRNA-seq. Gene expression in injured and/or candesartan treated brain region was compared to that in sham vehicle treated mice in the same brain region to identify genes that were differentially expressed (DEGs) between groups. The most DEGs were expressed in the hippocampus at 3 dpi, and the number of DEGs reduced with distance and time from the lesion. Among pathways that were differentially expressed at 3 dpi after CCI, candesartan treatment altered genes involved in angiogenesis, interferon signaling, extracellular matrix regulation including integrins and chromosome maintenance and DNA replication. At 29 dpi, candesartan treatment reduced the expression of genes involved in the inflammatory response. Some changes in gene expression were confirmed in a separate cohort of animals by qPCR. Fewer DEGs were found in the thalamus, and only one in the hypothalamus at 3 dpi. Additionally, in the hippocampi of sham injured mice, 3 days of candesartan treatment led to the differential expression of 384 genes showing that candesartan in the absence of injury had a powerful impact on gene expression specifically in the hippocampus. Our results suggest that candesartan has broad actions in the brain after injury and affects different processes at acute and chronic times after injury. These data should assist in elucidating the beneficial effect of candesartan on recovery from TBI.

Pharmacologic Inhibition of ADAM10 Attenuates Brain Tissue Loss, Axonal Injury and Pro-inflammatory Gene Expression Following Traumatic Brain Injury in Mice

The α-secretase A disintegrin and metalloprotease 10 (ADAM10) regulates various physiological and pathophysiological processes. Despite its broad functional implications during development, plasticity, and disease, no pharmacological approaches to inhibit ADAM10 in acute brain injury have been reported. Here, we examined the effects of the ADAM10 inhibitor GI254023X on the neurological and histopathological outcome after experimental traumatic brain injury (TBI). C57BL/6N mice were subjected to the controlled cortical impact (CCI) model of TBI or sham procedure and received GI254023X or vehicle during the acute phase of injury (n = 40, 100 mg/kg, 25% DMSO, 0.1 M Na2CO3, intraperitoneal, 30 min and 24 h after TBI). GI254023X treatment did not improve neurological deficits from 1 to 7 days post-injury (dpi) but animals treated with GI254023X exhibited smaller brain lesions compared to vehicle treatment. Determination of brain mRNA expression by quantitative PCR showed that TBI-induced up-regulation of Adam10 and Adam17 was not influenced by GI254023X but the up-regulation of the matrix metalloproteinase genes Mmp2 and Mmp9 was attenuated. GI254023X treatment further increased the T cell marker Cd247 but did not affect blood brain barrier integrity, as assessed by Occludin mRNA expression and IgG brain extravasation. However, in agreement with neuroprotective effects of ADAM10 inhibition, GI254023X treatment attenuated axonal injury, as indicated by decreased generation of spectrin breakdown products (SBDPs) and decreased immunostaining using anti-non-phosphorylated neurofilament (SMI-32). Interestingly, reduced axonal injury in GI254023X-treated animals coincided with subtle mRNA dysregulation in the glutamate receptor subunit genes Gria1 and Grin2b. Quantitative PCR also revealed that GI254023X mitigated up-regulation of the pro-inflammatory markers Il6, Tnfa, and Lcn2 but not the up-regulation of the pan-microglia marker Aif1, the M2 microglia marker Arg1 and the reactive astrocyte marker Gfap. Taken together, the ADAM10 inhibitor GI254023X attenuates brain tissue loss, axonal injury and pro-inflammatory gene expression in the CCI model of TBI. These results suggest that ADAM10 may represent a therapeutic target in the acute phase of TBI.

Delayed voluntary physical exercise restores "when" and "where" object recognition memory after traumatic brain injury

Physical exercise has been associated with improved cognition and may even reduce memory deficits after brain injuries. The aims of this work were to: 1) assess whether voluntary physical exercise can reduce the deficits associated with traumatic brain injury (TBI) in two different components of episodic-like memory based on object recognition, temporal order memory ("when"), and object location memory ("where"); and 2) determine whether changes in levels of brain-derived neurotrophic factor (BDNF) in the hippocampus and prefrontal cortex, as well as alterations in hippocampal cytokines, insulin-like growth factor-1 (IGF-1) and vascular endothelial growth factor (VEGF), may influence the effects exercise has on either or both tasks. The rats were distributed into a sham group, a TBI group that remained sedentary (TBI-sed), and a TBI group that had access to a running wheel for a 25-day period from post-injury day 11 (TBI-exe). The rats were sacrificed after the "where" memory task, at post-injury day 37. Physical exercise restored the "when" and "where" memories, which had been impaired by the TBI, and increased the concentration of BDNF in the hippocampus, but not the prefrontal cortex. Neither TBI nor exercise were found to significantly affect hippocampal cytokines, IGF-1 or VEGF at this time post-injury. BDNF levels showed significant positive correlations with exercise, and with "when" (but not "where") memory. These results indicate that post-injury physical exercise restores "when" and "where" object recognition memory tasks after TBI, and that increased BDNF seems to be involved in this effect, particularly with regard to "when" memory.

Plasma miR-9-3p and miR-136-3p as Potential Novel Diagnostic Biomarkers for Experimental and Human Mild Traumatic Brain Injury

Noninvasive, affordable circulating biomarkers for difficult-to-diagnose mild traumatic brain injury (mTBI) are an unmet medical need. Although blood microRNA (miRNA) levels are reportedly altered after traumatic brain injury (TBI), their diagnostic potential for mTBI remains inconclusive. We hypothesized that acutely altered plasma miRNAs could serve as diagnostic biomarkers both in the lateral fluid percussion injury (FPI) model and clinical mTBI. We performed plasma small RNA-sequencing from adult male Sprague-Dawley rats (n = 31) at 2 days post-TBI, followed by polymerase chain reaction (PCR)-based validation of selected candidates. miR-9a-3p, miR-136-3p, and miR-434-3p were identified as the most promising candidates at 2 days after lateral FPI. Digital droplet PCR (ddPCR) revealed 4.2-, 2.8-, and 4.6-fold elevations in miR-9a-3p, miR-136-3p, and miR-434-3p levels (p < 0.01 for all), respectively, distinguishing rats with mTBI from naïve rats with 100% sensitivity and specificity. DdPCR further identified a subpopulation of mTBI patients with plasma miR-9-3p (n = 7/15) and miR-136-3p (n = 5/15) levels higher than one standard deviation above the control mean at <2 days postinjury. In sTBI patients, plasma miR-9-3p levels were 6.5- and 9.2-fold in comparison to the mTBI and control groups, respectively. Thus, plasma miR-9-3p and miR-136-3p were identified as promising biomarker candidates for mTBI requiring further evaluation in a larger patient population.

Developmental Dysfunction of the Central Nervous System Lymphatics Modulates the Adaptive Neuro-Immune Response in the Perilesional Cortex in a Mouse Model of Traumatic Brain Injury

Rationale

The recently discovered meningeal lymphatic vessels (mLVs) have been proposed to be the missing link between the immune and the central nervous system. The role of mLVs in modulating the neuro-immune response following a traumatic brain injury (TBI), however, has not been analyzed. Parenchymal T lymphocyte infiltration has been previously reported as part of secondary events after TBI, suggestive of an adaptive neuro-immune response. The phenotype of these cells has remained mostly uncharacterized. In this study, we identified subpopulations of T cells infiltrating the perilesional areas 30 days post-injury (an early-chronic time point). Furthermore, we analyzed how the lack of mLVs affects the magnitude and the type of T cell response in the brain after TBI.

Methods

TBI was induced in K14-VEGFR3-Ig transgenic (TG) mice or in their littermate controls (WT; wild type), applying a controlled cortical impact (CCI). One month after TBI, T cells were isolated from cortical areas ipsilateral or contralateral to the trauma and from the spleen, then characterized by flow cytometry. Lesion size in each animal was evaluated by MRI.

Results

In both WT and TG-CCI mice, we found a prominent T cell infiltration in the brain confined to the perilesional cortex and hippocampus. The majority of infiltrating T cells were cytotoxic CD8+ expressing a CD44hiCD69+ phenotype, suggesting that these are effector resident memory T cells. K14-VEGFR3-Ig mice showed a significant reduction of infiltrating CD4+ T lymphocytes, suggesting that mLVs could be involved in establishing a proper neuro-immune response. Extension of the lesion (measured as lesion volume from MRI) did not differ between the genotypes. Finally, TBI did not relate to alterations in peripheral circulating T cells, as assessed one month after injury.

Conclusions

Our results are consistent with the hypothesis that mLVs are involved in the neuro-immune response after TBI. We also defined the resident memory CD8+ T cells as one of the main population activated within the brain after a traumatic injury.

Acute colitis during chronic experimental traumatic brain injury in mice induces dysautonomia and persistent extraintestinal, systemic, and CNS inflammation with exacerbated neurological deficits

BACKGROUND

Disruptions of brain-gut axis have been implicated in the progression of a variety of gastrointestinal (GI) disorders and central nervous system (CNS) diseases and injuries, including traumatic brain injury (TBI). TBI is a chronic disease process characterized by persistent secondary injury processes which can be exacerbated by subsequent challenges. Enteric pathogen infection during chronic TBI worsened cortical lesion volume; however, the pathophysiological mechanisms underlying the damaging effects of enteric challenge during chronic TBI remain unknown. This preclinical study examined the effect of intestinal inflammation during chronic TBI on associated neurobehavioral and neuropathological outcomes, systemic inflammation, and dysautonomia.

METHODS

Dextran sodium sulfate (DSS) was administered to adult male C57BL/6NCrl mice 28 days following craniotomy (Sham) or TBI for 7 days to induce intestinal inflammation, followed by a return to normal drinking water for an additional 7 to 28 days for recovery; uninjured animals (Naïve) served as an additional control group. Behavioral testing was carried out prior to, during, and following DSS administration to assess changes in motor and cognitive function, social behavior, and mood. Electrocardiography was performed to examine autonomic balance. Brains were collected for histological and molecular analyses of injury lesion, neurodegeneration, and neuroinflammation. Blood, colons, spleens, mesenteric lymph nodes (mLNs), and thymus were collected for morphometric analyses and/or immune characterization by flow cytometry.

RESULTS

Intestinal inflammation 28 days after craniotomy or TBI persistently induced, or exacerbated, respectively, deficits in fine motor coordination, cognition, social behavior, and anxiety-like behavior. Behavioral changes were associated with an induction, or exacerbation, of hippocampal neuronal cell loss and microglial activation in Sham and TBI mice administered DSS, respectively. Acute DSS administration resulted in a sustained systemic immune response with increases in myeloid cells in blood and spleen, as well as myeloid cells and lymphocytes in mesenteric lymph nodes. Dysautonomia was also induced in Sham and TBI mice administered DSS, with increased sympathetic tone beginning during DSS administration and persisting through the first recovery week.

CONCLUSION

Intestinal inflammation during chronic experimental TBI causes a sustained systemic immune response and altered autonomic balance that are associated with microglial activation, increased neurodegeneration, and persistent neurological deficits.

Therapeutic effects of eugenol in a rat model of traumatic brain injury: A behavioral, biochemical, and histological study

Background and aim

Traumatic brain injury (TBI) results in death or long term functional disabilities. Eugenol is demonstrated to be beneficial in a range of experimental models of neurological disorders via its anti-inflammatory and antioxidant properties. Thus, the present study was designed to investigate the neuroprotective effects of eugenol in a weight-drop induced rat model of TBI.

Experimental procedure

Rats were assigned into five groups; control and TBI groups pretreated with vehicle, and three TBI groups pretreated with different doses of eugenol (25, 50, and 100 mg/kg/day, p.o., seven consecutive days). Except for the control, all other groups were subjected to TBI using Marmarou’s weight-drop method. 24 h after TBI, locomotor functions and short term memory were evaluated. Lastly animals were scarified and the estimation of lipid peroxidation in brain tissue, blood-brain barrier (BBB) integrity, brain water content (brain edema) and histopathology of the brain tissue were performed.

Results

Weight-drop induced TBI caused functional disabilities in the rats as indicated by impairment in locomotor activities and short term memory. The TBI also resulted in augmented neuronal cell death designated by chromatolysis. The results also showed disruption in the BBB integrity, increased edema, and lipid peroxidation in the brain of the rats exposed to trauma. Pretreatment with eugenol (100 mg/kg) ameliorated histopathological, neurochemical, and behavioral consequences of trauma.

Conclusion

For the first time this study revealed that eugenol can be considered as a potential candidate for managing the functional disabilities associated with TBI because of its antioxidant activities.

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Eugenol pretreatment ameliorated the TBI induced disruption in the BBB integrity and increased brain edema in the rats.

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Eugenol pretreatment in rats mitigated the TBI induced increase in lipid peroxidation and chromatolysis.

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Eugenol pretreatment in rats reduced the TBI induced impairment in memory, locomotor activity, and motor coordination.

Sensorimotor dysfunction in a mild mouse model of cortical contusion injury without significant neuronal loss is associated with increases in inflammatory proteins with innate but not adaptive immune functions

Traumatic brain injury is a leading cause of mortality and morbidity in the United States. Acute trauma to the brain triggers chronic secondary injury mechanisms that contribute to long-term neurological impairment. We have developed a single, unilateral contusion injury model of sensorimotor dysfunction in adult mice. By targeting a topographically defined neurological circuit with a mild impact, we are able to track sustained behavioral deficits in sensorimotor function in the absence of tissue cavitation or neuronal loss in the contused cortex of these mice. Stereological histopathology and multiplex enzyme-linked immunosorbent assay proteomic screening confirm contusion resulted in chronic gliosis and the robust expression of innate immune cytokines and monocyte attractant chemokines IL-1β, IL-5, IL-6, TNFα, CXCL1, CXCL2, CXCL10, CCL2, and CCL3 in the contused cortex. In contrast, the expression of neuroinflammatory proteins with adaptive immune functions was not significantly modulated by injury. Our data support widespread activation of innate but not adaptive immune responses, confirming an association between sensorimotor dysfunction with innate immune activation in the absence of tissue or neuronal loss in our mice.

Mitochondrial-Protective Effects of R-Phenibut after Experimental Traumatic Brain Injury

Altered neuronal Ca²⁺ homeostasis and mitochondrial dysfunction play a central role in the pathogenesis of traumatic brain injury (TBI). R-Phenibut ((3R)-phenyl-4-aminobutyric acid) is an antagonist of the α₂δ subunit of voltage-dependent calcium channels (VDCC) and an agonist of gamma-aminobutyric acid B (GABA-B) receptors. The aim of this study was to evaluate the potential therapeutic effects of R-phenibut following the lateral fluid percussion injury (latFPI) model of TBI in mice and the impact of R- and S-phenibut on mitochondrial functionality in vitro. By determining the bioavailability of R-phenibut in the mouse brain tissue and plasma, we found that R-phenibut (50 mg/kg) reached the brain tissue 15 min after intraperitoneal (i.p.) and peroral (p.o.) injections. The maximal concentration of R-phenibut in the brain tissues was 0.6 μg/g and 0.2 μg/g tissue after i.p. and p.o. administration, respectively. Male Swiss-Webster mice received i.p. injections of R-phenibut at doses of 10 or 50 mg/kg 2 h after TBI and then once daily for 7 days. R-Phenibut treatment at the dose of 50 mg/kg significantly ameliorated functional deficits after TBI on postinjury days 1, 4, and 7. Seven days after TBI, the number of Nissl-stained dark neurons (N-DNs) and interleukin-1beta (IL-1β) expression in the cerebral neocortex in the area of cortical impact were reduced. Moreover, the addition of R- and S-phenibut at a concentration of 0.5 μg/ml inhibited calcium-induced mitochondrial swelling in the brain homogenate and prevented anoxia-reoxygenation-induced increases in mitochondrial H₂O₂ production and the H₂O₂/O ratio. Taken together, these results suggest that R-phenibut could serve as a neuroprotective agent and promising drug candidate for treating TBI.

Administration of all-trans retinoic acid after experimental traumatic brain injury is brain protective

BACKGROUND AND PURPOSE

All-trans retinoic acid (ATRA) is a vitamin A metabolite, important in the developing and mature brain. Pre-injury ATRA administration ameliorates ischaemic brain insults in rodents. This study examined the effects of post-traumatic ATRA treatment in experimental traumatic brain injury (TBI).

EXPERIMENTAL APPROACH

Male adult mice were subjected to the controlled cortical impact model of TBI or sham procedure and killed at 7 or 30 days post-injury (dpi). ATRA (10 mg kg-1, i.p.) was given immediately after the injury and 1, 2 and 3 dpi. Neurological function and sensorimotor coordination were evaluated. Brains were processed for (immuno-) histological, mRNA and protein analyses (qPCR and western blot).

KEY RESULTS

ATRA treatment reduced brain lesion size, reactive astrogliosis and axonal injury at 7 dpi, and hippocampal granule cell layer (GCL) integrity was protected at 7 and 30 dpi, independent of cell proliferation in neurogenic niches and blood-brain barrier damage. Neurological and motor deficits over time and the brain tissue loss at 30 dpi were not affected by ATRA treatment. ATRA decreased gene expression of markers for damage-associated molecular pattern (HMGB1), apoptosis (caspase-3 and Bax), activated microglia (TSPO), and reactive astrogliosis (GFAP, SerpinA3N) at 7 dpi and a subset of markers at 30 dpi (TSPO, GFAP).

CONCLUSION AND IMPLICATIONS

In experimental TBI, post-traumatic ATRA administration exerted brain protective effects, including long-term protection of GCL integrity, but did not affect neurological and motor deficits. Further investigations are required to optimize treatment regimens to enhance ATRA's brain protective effects and improve outcomes.

In Vivo Detection of Extracellular Adenosine Triphosphate in a Mouse Model of Traumatic Brain Injury

Traumatic brain injury (TBI) is traditionally characterized by primary and secondary injury phases, both contributing to pathological and morphological changes. The mechanisms of damage and chronic consequences of TBI remain to be fully elucidated, but synaptic homeostasis disturbances and impaired energy metabolism are proposed to be a major contributor. It has been proposed that an increase of extracellular (eATP) adenosine triphosphate (ATP) in the area immediately surrounding impact may play a pivotal role in this sequence of events. After tissue injury, rupture of cell membranes allows release of intracellular ATP into the extracellular space, triggering a cascade of toxic events and inflammation. ATP is a ubiquitous messenger; however, simple and reliable techniques to measure its concentration have proven elusive. Here, we integrate a sensitive bioluminescent eATP sensor known as pmeLUC, with a controlled cortical impact mouse model to monitor eATP changes in a living animal after injury. Using the pmeLUC probe, a rapid increase of eATP is observed proximal to the point of impact within minutes of the injury. This event is significantly attenuated when animals are pretreated with an ATP hydrolyzing agent (apyrase) before surgery, confirming the contribution of eATP. This new eATP reporter could be useful for understanding the role of eATP in the pathogenesis in TBI and may identify a window of opportunity for therapeutic intervention.

Progress in Brain-Compatible Interfaces with Soft Nanomaterials

Neural interfaces facilitating communication between the brain and machines must be compatible with the soft, curvilinear, and elastic tissues of the brain and yet yield enough power to read and write information across a wide range of brain areas through high-throughput recordings or optogenetics. Biocompatible-material engineering has facilitated the development of brain-compatible neural interfaces to support built-in modulation of neural circuits and neurological disorders. Recent developments in brain-compatible neural interfaces that use soft nanomaterials more suitable for complex neural circuit analysis and modulation are reviewed. Preclinical tests of the compatibility and specificity of these interfaces in animal models are also discussed.

Myeloid Pannexin-1 mediates acute leukocyte infiltration and leads to worse outcomes after brain trauma

Background

Neuroinflammation is a major component of secondary damage after traumatic brain injury (TBI). We recently reported that pharmacological inhibition of Pannexin-1 (Panx1) channels markedly reduced the inflammatory response after TBI. Panx1 channels have been shown to be important conduits for adenosine 5′-triphosphate (ATP) release and are associated with leukocyte infiltration and pyroptosis. Because Panx1 blockers significantly decrease ATP release and migration of activated microglia and other myeloid cells (such as monocyte-derived macrophages and dendritic cells) in vitro, we hypothesized that myeloid Panx1 channels play a specific role in immune cell infiltration promoting tissue damage following TBI.

Methods

The murine-controlled cortical impact (CCI) model was used on myeloid-specific Panx1 conditional knockout (Cx3cr1-Cre::Panx1^fl/fl) mice to determine whether myeloid Panx1 mediates neuroinflammation and brain damage. Immune cell infiltration was measured using flow cytometry. Locomotor and memory functions were measured using the rotarod and Barnes maze test, respectively. The levels of biomarkers for tissue damage and blood–brain barrier leakage were measured using western blot and magnetic resonance imaging. Panx1 channel activity was measured with ex vivo dye uptake assays, using flow cytometry and confocal microscopy.

Results

CCI-injured Cx3cr1-Cre::Panx1^fl/fl mice showed markedly reduced immune cell infiltration to the brain parenchyma compared with Panx1^fl/fl mice. As expected, Panx1 dependent activity, assessed by dye uptake, was markedly reduced only in myeloid cells from Cx3cr1-Cre::Panx1^fl/fl mice. The expression of biomarkers of tissue damage was significantly reduced in the CCI-injured Cx3cr1-Cre::Panx1^fl/fl mice compared with Panx1^fl/fl mice. In line with this, magnetic resonance imaging showed reduced blood–brain barrier leakage in CCI-injured Cx3cr1-Cre::Panx1^fl/fl mice. There was also a significant improvement in motor and memory function in Cx3cr1-Cre::Panx1^fl/fl mice when compared with Panx1^fl/fl mice within a week post-CCI injury.

Conclusion

Our data demonstrate that CCI-related outcomes correlate with Panx1 channel function in myeloid cells, indicating that activation of Panx1 channels in myeloid cells is a major contributor to acute brain inflammation following TBI. Importantly, our data indicate myeloid Panx1 channels could serve as an effective therapeutic target to improve outcome after TBI.

Depletion of gut microbiota is associated with improved neurologic outcome following traumatic brain injury

Signaling between intestinal microbiota and the brain influences neurologic outcome in multiple forms of brain injury. The impact of gut microbiota following traumatic brain injury (TBI) has not been well established. Our objective was to compare TBI outcomes in specific pathogen-free mice with or without depletion of intestinal bacteria. Adult male C57BL6/J SPF mice (n = 6/group) were randomized to standard drinking water or ampicillin (1 g/L), metronidazole (1 g/L), neomycin (1 g/L), and vancomycin (0.5 g/L) (AMNV) containing drinking water 14 days prior to controlled cortical impact (CCI) model of TBI. 16S rRNA gene sequencing of fecal pellets was performed and alpha and beta diversity determined. Hippocampal neuronal density and microglial activation was assessed 72 h post-injury by immunohistochemistry. In addition, mice (n = 8-12/group) were randomized to AMNV or no treatment initiated immediately after CCI and memory acquisition (fear conditioning) and lesion volume assessed. Mice receiving AMNV had significantly reduced alpha diversity (p < 0.05) and altered microbiota community composition compared to untreated mice (PERMANOVA: p < 0.01). Mice receiving AMNV prior to TBI had increased CA1 hippocampal neuronal density (15.2 ± 1.4 vs. 8.8 ± 2.1 cells/0.1 mm; p < 0.05) and a 26.6 ± 6.6% reduction in Iba-1 positive cells (p < 0.05) at 72 h. Mice randomized to AMNV immediately after CCI had attenuated associative learning deficit on fear conditioning test (%freeze Cue: 63.7 ± 2.7% vs. 41.0 ± 5.1%, p < 0.05) and decreased lesion volume (27.2 ± 0.8 vs. 24.6 ± 0.7 mm³, p < 0.05). In conclusion, depletion of intestinal microbiota was consistent with a neuroprotective effect whether initiated before or after injury in a murine model of TBI. Further investigations of the role of gut microbiota in TBI are warranted.

Comparison between midline and lateral fluid percussion injury in mice reveals prolonged but divergent cortical neuroinflammation

Animal models are critical for determining the mechanisms mediating traumatic brain injury-induced (TBI) neuropathology. Fluid percussion injury (FPI) is a widely used model of brain injury typically applied either midline or parasagittally (lateral). Midline FPI induces a diffuse TBI, while lateral FPI induces both focal cortical injury (ipsilateral hemisphere) and diffuse injury (contralateral hemisphere). Nonetheless, discrete differences in neuroinflammation and neuropathology between these two versions of FPI remain unclear. The purpose of this study was to compare acute (4-72 h) and subacute (7 days) neuroinflammatory responses between midline and lateral FPI. Midline FPI resulted in longer righting reflex times than lateral FPI. At acute time points, the inflammatory responses to the two different injuries were similar. For instance, there was evidence of monocytes and cytokine mRNA expression in the brain with both injuries acutely. Midline FPI had the highest proportion of brain monocytes and highest IL-1β/TNFα mRNA expression 24 h later. NanoString nCounter analysis 7 days post-injury revealed robust and prolonged expression of inflammatory-related genes in the cortex after midline FPI compared to lateral FPI; however, Iba-1 cortical immunoreactivity was increased with lateral FPI. Thus, midline and lateral FPI caused similar cortical neuroinflammatory responses acutely and mRNA expression of inflammatory genes was detectable in the brain 7 days later. The primary divergence was that inflammatory gene expression was greater and more diverse subacutely after midline FPI. These results provide novel insight to variations between midline and lateral FPI, which may recapitulate unique temporal pathogenesis.

Non-Invasive Ultrasound Detection of Cerebrovascular Changes in a Mouse Model of Traumatic Brain Injury

Traumatic brain injury (TBI) can induce changes in vascular architecture. Although ultrasound metrics such as pulsatility index (PI) are sensitive to changes in hemodynamic resistance downstream from major arteries, these metrics depend on features unrelated to vessel architecture, such as blood pressure and heart rate. In contrast, input impedance and reflection coefficient that are derived from wave reflection theory seek to minimize the effects of altered cardiac output or heart rate. In this article, we investigate the use of ultrasound to assess changes in vascular impedance and wave reflection in the common carotid arteries of mice exposed to a controlled cortical impact. Focusing on the first harmonics of the reflected waves, the impedance phase was increased ipsilaterally in impacted mice compared with shams, whereas the magnitude of the impedance was unchanged. In contrast, PI was reduced bilaterally. Interestingly, PI and the first harmonic magnitude of input impedance in the carotid artery were correlated on the contralateral but not ipsilateral side. We investigated the use of these metrics to classify mice as sham or TBI, finding an area under the receiver operating characteristic curve ipsilaterally of 0.792 (confidence interval [CI]: 0.648-0.936) for correct classification with first harmonic impedance magnitude and phase as predictors and 0.716 (CI: 0.553-0.879) using carotid artery PI and diameter as predictors. Overall, the findings support the use of wave reflection analysis as a more specific measure of vascular changes following TBI and motivate the translation of this approach for monitoring vascular changes in humans affected by TBI.

Differential early effects of traumatic brain injury on spike-wave discharges in Sprague-Dawley rats

Unprovoked seizures in the late period of traumatic brain injury (TBI) occur in almost 20% of humans and experimental animals, psychiatric comorbidities being common in both situations. The aim of the study was to evaluate epileptiform activity in the early period of TBI induced by lateral fluid percussion brain injury in adult male Srague-Dawley rats and to reveal potential behavioral and pathomorphological correlates of early electrophysiological alterations. One week after TBI the group of animals was remarkably heterogeneous regarding the incidence of bifrontal 7-Hz spikes and spike-wave discharges (SWDs). It consisted of 3 typical groups: a) rats with low baseline and high post-craniotomy SWD level; b)with constantly low both baseline and post-craniotomy SWD levels; c) constantly high both baseline and post-craniotomy SWD levels. Rats with augmented SWD occurrence after TBI demonstrated freezing episodes accompanying SWDs as well as increased anxiety-like behavior (difficulty of choosing). The discharges were definitely associated with sleep phases. The incidence of SWDs positively correlated with the area of glial activation in the neocortex but not in the hippocampus.The translational potential of the data is revealing new pathophysiological links between epileptiform activity appearance, direct cortical and distant hippocampal damage and anxiety-like behavior, putative early predictors of late posttraumatic pathology.

Penetrating Traumatic Brain Injury Triggers Dysregulation of Cathepsin B Protein Levels Independent of Cysteine Protease Activity in Brain and Cerebral Spinal Fluid

Cathepsin B (CatB), a lysosomal cysteine protease, is important to brain function and may have dual utility as a peripheral biomarker of moderate-severe traumatic brain injury (TBI). The present study determined levels of pro- and mature (mat) CatB protein as well as cysteine protease activity within the frontal cortex (FC; proximal injury site), hippocampus (HC; distal injury site), and cerebral spinal fluid (CSF) collected 1-7 days after craniotomy and penetrating ballistic-like brain injury (PBBI) in rats. Values were compared with naïve controls. Further, the utility of CatB protein as a translational biomarker was determined in CSF derived from patients with severe TBI. Craniotomy increased matCatB levels in the FC and HC, and led to elevation of HC activity at day 7. PBBI caused an even greater elevation in matCatB within the FC and HC within 3-7 days. After PBBI, cysteine protease activity peaked at 3 days in the FC and was elevated at 1 day and 7 days, but not 3 days, in the HC. In rat CSF, proCatB, matCatB, and cysteine protease activity peaked at 3 days after craniotomy and PBBI. Addition of CA-074, a CatB-specific inhibitor, confirmed that protease activity was due to active matCatB in rat brain tissues and CSF at all time-points. In patients, CatB protein was detectable from 6 h through 10 days after TBI. Notably, CatB levels were significantly higher in CSF collected within 3 days after TBI compared with non-TBI controls. Collectively, this work indicates that CatB and its cysteine protease activity may serve as collective molecular signatures of TBI progression that differentially vary within both proximal and distal brain regions. CatB and its protease activity may have utility as a surrogate, translational biomarker of acute-subacute TBI.

Low-pressure fluid percussion minimally adds to the sham craniectomy-induced neurobehavioral changes: Implication for experimental traumatic brain injury model

Modeling experimental traumatic brain injury (TBI) in rodents is necessarily required to understand the pathophysiological and neurobehavioral consequences of neurotrauma. Numerous models have been developed to study experimental TBI. Fluid percussion injury (FPI) is the most extensively used model to represent clinical phenotypes. Nevertheless, the surgical 'sham' procedure (craniectomy), a prerequisite of FPI, is the impeding factor in experimental TBI. We hypothesized that if craniectomy causes substantial structural and functional changes in the brain, it might mimic the mild FPI-induced neurobehavioral dysfunctions. To understand the hypothesis, C57BL/6 mice were exposed to lateral FPI at 1.2 atm pressure and changes in the neuronal architecture, hippocampal neurogenesis, neuroinflammation, and behavioral functions were compared to the sham (craniectomy) and control mice at day 7 post-FPI. We observed that both the craniectomy and FPI significantly augmented the ipsilateral hippocampal neurogenesis as evaluated by DCX and Beta-III tubulin immunoreactivity. Similarly, a significant increase in GFAP and TMEM immunoreactivity in CA1 and CA3 regions showed that craniectomy mimics FPI-induced neuroinflammation. The additive damaging effect of craniectomy with FPI was also reported in the term of axonal and dendritic fragmentation, swelling and neuronal death using silver staining, Fluoro-jade, and MAP-2 immunoreactivity. Sham-exposed mice showed a significant functional decrease in grip strength. Our results indicate that sham craniectomy itself is enough to cause TBI like characteristics, and thus fluid percussion at mild pressure is minimally additive with craniectomy. Considering the method as a mixed (focal & diffused) injury model, the 'net neurotrauma severity' should be compared with naïve control instead of the sham as it is an outcome of cumulative damage due to fluid pressure and craniectomy. Nevertheless, to understand the long term consequences of neurotrauma, the extent of recovery in surgical sham may separately be quantified.

Adenosine kinase inhibition promotes proliferation of neural stem cells after traumatic brain injury

Traumatic brain injury (TBI) is a major public health concern and remains a leading cause of disability and socio-economic burden. To date, there is no proven therapy that promotes brain repair following an injury to the brain. In this study, we explored the role of an isoform of adenosine kinase expressed in the cell nucleus (ADK-L) as a potential regulator of neural stem cell proliferation in the brain. The rationale for this hypothesis is based on coordinated expression changes of ADK-L during foetal and postnatal murine and human brain development indicating a role in the regulation of cell proliferation and plasticity in the brain. We first tested whether the genetic disruption of ADK-L would increase neural stem cell proliferation after TBI. Three days after TBI, modelled by a controlled cortical impact, transgenic mice, which lack ADK-L (ADK^Δneuron) in the dentate gyrus (DG) showed a significant increase in neural stem cell proliferation as evidenced by significant increases in doublecortin and Ki67-positive cells, whereas animals with transgenic overexpression of ADK-L in dorsal forebrain neurons (ADK-L^tg) showed an opposite effect of attenuated neural stem cell proliferation. Next, we translated those findings into a pharmacological approach to augment neural stem cell proliferation in the injured brain. Wild-type C57BL/6 mice were treated with the small molecule adenosine kinase inhibitor 5-iodotubercidin for 3 days after the induction of TBI. We demonstrate significantly enhanced neural stem cell proliferation in the DG of 5-iodotubercidin-treated mice compared to vehicle-treated injured animals. To rule out the possibility that blockade of ADK-L has any effects in non-injured animals, we quantified baseline neural stem cell proliferation in ADK^Δneuron mice, which was not altered, whereas baseline neural stem cell proliferation in ADK-L^tg mice was enhanced. Together these findings demonstrate a novel function of ADK-L involved in the regulation of neural stem cell proliferation after TBI.

Effects of controlled cortical impact and docosahexaenoic acid on rat pup fatty acid profiles

Traumatic brain injury (TBI) is the leading cause of acquired neurologic disability in children, particularly in those under four years old. During this period, rapid brain growth demands higher Docosahexaenoic Acid (DHA) intake. DHA is an essential fatty acid and brain cell component derived almost entirely from the diet. DHA improved neurologic outcomes and decreased inflammation after controlled cortical impact (CCI) in 17-day old (P17) rats, our established model of pediatric TBI. In adult rodents, TBI decreases brain DHA. We hypothesized that CCI would decrease rat brain DHA at post injury day (PID) 60, blunted by 0.1% DHA diet. We quantitated fatty acids using Gas Chromatography-Mass Spectrometry. We provided 0.1% DHA before CCI to ensure high DHA in dam milk. We compared brain DHA in rats after 60 days of regular (REG) or DHA diet to SHAM pups on REG diet. Brain DHA decreased in REGCCI, not in DHACCI, relative to SHAMREG. In a subsequent experiment, we gave rat pups DHA or vehicle intraperitoneally after CCI followed by DHA or REG diet for 60 days. REG increased brain Docosapentaenoic Acid (n-6 DPA, a brain DHA deficiency marker) relative to SHAMDHA and DHACCI pups (p < 0.001, diet effect). DHA diet nearly doubled DHA and decreased n-6 DPA in blood but did not increase brain DHA content (p < 0.0001, diet effect). We concluded that CCI or craniotomy alone induces a mild DHA deficit as shown by increased brain DPA.

Skull Fractures Induce Neuroinflammation and Worsen Outcomes after Closed Head Injury in Mice

The weight-drop model is used widely to replicate closed-head injuries in mice; however, the histopathological and functional outcomes may vary significantly between laboratories. Because skull fractures are reported to occur in this model, we aimed to evaluate whether these breaks may influence the variability of the weight-drop (WD) model. Male Swiss Webster mice underwent WD injury with either a 2 or 5 mm cone tip, and behavior was assessed at 2 h and 24 h thereafter using the neurological severity score. The expression of interleukin (IL)-6, IL-1β, tumor necrosis factor-α, matrix metalloproteinase-9, and tissue inhibitor of metalloproteinase-1 genes was measured at 12 h and 1, 3, and 14 days after injury. Before the injury, micro-computed tomography (micro-CT) was performed to quantify skull thickness at the impact site. With a conventional tip diameter of 2 mm, 33% of mice showed fractures of the parietal bone; the 5 mm tip produced only 10% fractures. Compared with mice without fractures, mice with fractures had a severity-dependent worse functional outcome and a more pronounced upregulation of inflammatory genes in the brain. Older mice were associated with thicker parietal bones and were less prone to skull fractures. In addition, mice that underwent traumatic brain injury (TBI) with skull fracture had macroscopic brain damage because of skull depression. Skull fractures explain a considerable proportion of the variability observed in the WD model in mice—i.e., mice with skull fractures have a much stronger inflammatory response than do mice without fractures. Using older mice with thicker skull bones and an impact cone with a larger diameter reduces the rate of skull fractures and the variability in this very useful closed-head TBI model.

Craniectomy Effects on Resting State Functional Connectivity and Cognitive Performance in Immature Rats

Experimental models have been proven to be valuable tools to understand downstream cellular mechanisms of Traumatic Brain Injury (TBI). The models allow for reduction of confounding variables and tighter control of varying parameters. It has been recently reported that craniectomy induces pro-inflammatory responses, which therefore needs to be properly addressed given the fact that craniectomy is often considered a control procedure for experimental TBI models. The current study aims to determine whether a craniectomy induces alterations in Resting State Network (RSN) in a developmental rodent model. Functional Magnetic Resonance Imaging (fMRI) data-driven RSN show clusters of peak differences (left caudate putamen, somatosensory cortex, amygdala and piriform cortex) between craniectomy and control group, four days post-craniectomy. In addition, the Novel Object Recognition (NOR) task revealed impaired working memory in the craniectomy group. This evidence supports craniectomy-induced neurological changes which need to be carefully addressed, considering the frequent use of craniectomy as a control procedure for experimental models of TBI.

Repeated mild traumatic brain injuries induce persistent changes in plasma protein and magnetic resonance imaging biomarkers in the rat

A single mild traumatic brain injury (mTBI) typically causes only transient symptoms, but repeated mTBI (RmTBI) is associated with cumulative and chronic neurological abnormalities. Clinical management of mTBI is challenging due to the heterogeneous, subjective and transient nature of symptoms, and thus would be aided by objective biomarkers. Promising biomarkers including advanced magnetic resonance imaging (MRI) and plasma levels of select proteins were examined here in a rat model of RmTBI. Rats received either two mild fluid percussion or sham injuries administered five days apart. Rats underwent MRI and behavioral testing 1, 3, 5, 7, and 30 days after the second injury and blood samples were collected on days 1, 7, and 30. Structural and diffusion-weighted MRI revealed that RmTBI rats had abnormalities in the cortex and corpus callosum. Proteomic analysis of plasma found that RmTBI rats had abnormalities in markers indicating axonal and vascular injury, metabolic and mitochondrial dysfunction, and glial reactivity. These changes occurred in the presence of ongoing cognitive and sensorimotor deficits in the RmTBI rats. Our findings demonstrate that RmTBI can result in chronic neurological abnormalities, provide insight into potential contributing pathophysiological mechanisms, and supports the use of MRI and plasma protein measures as RmTBI biomarkers.

Out of Control? Managing Baseline Variability in Experimental Studies with Control Groups

Control groups are expected to show what happens in the absence of the intervention of interest (negative control) or the effect of an intervention expected to have an effect (positive control). Although they usually give results we can anticipate, they are an essential component of all experiments, both in vitro and in vivo, and fulfil a number of important roles in any experimental design. Perhaps most importantly they help you understand the influence of variables that you cannot fully eliminate from your experiment and thus include them in your analysis of treatment effects. Because of this it is essential that they are treated as any other experimental group in terms of subjects, randomisation, blinding, etc. It also means that in almost all cases, contemporaneous control groups are required. Historical and baseline control groups serve a slightly different role and cannot fully replace control groups run as an integral part of the experiment. When used correctly, a good control group not only validates your experiment; it provides the basis for evaluating the effect of your treatments.

Exposure to uncertainty mediates the effects of traumatic brain injury on probabilistic decision-making in rats

Primary Objective: Traumatic brain injury (TBI) is associated with numerous psychiatric comorbidities, and subclinical psychiatric symptoms. While many symptoms have been replicated in animal models of brain injury, a vast majority of studies utilize naïve rats as subjects, which fail to mimic the complex learning history of human patients.Methods and Procedures: In the current study, we evaluated the effects of a brain injury in animals with early exposure to uncertainty on post-injury decision-making in a probabilistic task, the rodent gambling task (RGT).Main Outcomes and Results: Exposure to uncertainty resulted in a heterogeneous sample relative to prior publications, and brain-injured rats showed no deficits in choice behavior compared to shams which contrasts with large, pervasive deficits in previously published work. However, TBI increased impulsivity and caused transient changes in behavioral variables indicative of initial motivational deficits (pellets earned, omitted responses). Notably, effects of amphetamine were similar on this heterogeneous sample of rats relative to a number of other published reports, suggesting consistent effects of gross monoaminergic manipulations on choice behavior, independent of experience.Conclusions: Going forward, translational studies need to consider the heterogeneity that exists at the clinical level and account for these problems when modeling diseases in animals.