Moderate Fluid Percussion Injury Research Articles

Elovanoids, a Novel Class of Lipid Mediators, Are Neuroprotective in a Traumatic Brain Injury Model in Rats.

In the United States, traumatic brain injury (TBI) contributes significantly to mortality and morbidity. Elovanoids (ELVs), a novel class of homeostatic lipid mediators we recently discovered and characterized, have demonstrated neuroprotection in experimental stroke models but have never been tested after TBI. A moderate fluid-percussion injury (FPI) model was used on male rats that were treated with ELVs by intravenous (IV) or intranasal (IN) delivery. In addition, using liquid chromatography-mass spectrometry (LC-MS/MS), we examined whether ELVs could be detected in brain tissue after IN delivery. ELVs administered intravenously 1 h after FPI improved behavior on days 2, 3, 7, and 14 by 20, 23, 31, and 34%, respectively, and preserved hippocampal CA3 and dentate gyrus (DG) volume loss compared to the vehicle. Whole-brain tractography revealed that ELV-IV treatment increased corpus callosum white matter fibers at the injury site. In comparison to treatment with saline on days 2, 3, 7, and 14, ELVs administered intranasally at 1 h and 24 h after FPI showed improved neurological scores by 37, 45, 41, and 41%. T2-weighted imaging (T2WI) abnormalities, such as enlarged ventricles and cortical thinning, were reduced in rats treated by ELV-IN delivery compared to the vehicle. On day 3, ELVs were detected in the striatum and ipsilateral cortex of ELV-IN-treated rats. We have demonstrated that both ELV-IN and ELV-IV administration offer high-grade neuroprotection that can be selectively supplied to the brain. This discovery may lead to innovative therapeutic targets for secondary injury cascade prevention following TBI.

The Effects of Cathepsin B Inhibition in the Face of Diffuse Traumatic Brain Injury and Secondary Intracranial Pressure Elevation.

Traumatic brain injury (TBI) affects millions of people each year. Previous studies using the central fluid percussion injury (CFPI) model in adult male rats indicated that elevated intracranial pressure (ICP) was associated with long-term effects, including neuronal cell loss and increased sensory sensitivity post-injury and secondary ICP elevation, which were not seen following injury alone. Investigations also indicated that cathepsin B (Cath B), a lysosomal cysteine protease, may play a role in the pathological progression of neuronal membrane disruption; however, the specific impact of Cath B inhibition following CFPI remained unknown. Thus, the focus of this study was to evaluate the effects of Cath B inhibition via the intracerebroventricular infusion of the Cath B inhibitor to the CA-074 methyl ester (CA-074Me) 2w following injury with or without secondary ICP elevation. This was accomplished using adult male rats continuously infused with CA-074Me or 10% DMSO as a vehicle control for 2w following either sham injury, CFPI only, or CFPI with subsequent ICP elevation to 20 mmHg. We assessed Cath B activity and evaluated the protein levels of Cath B and Cath B-binding partners AIF, Bcl-XL, and Bak. We also conducted histological analyses of the total cell counts to assess for cell loss, membrane disruption, and Cath B localization. Finally, we investigated somatosensory changes with the whisker nuisance task. Overall, this study demonstrated that Cath B is not a direct driver of membrane disruption; however, the administration of CA-074Me alters Cath B localization and reduces hypersensitivity, emphasizing Cath B as an important component in late secondary pathologies.

Targeting of nanoparticles to the cerebral vasculature after traumatic brain injury.

Traumatic brain injury has faced numerous challenges in drug development, primarily due to the difficulty of effectively delivering drugs to the brain. However, there is a potential solution in targeted drug delivery methods involving antibody-drug conjugates or nanocarriers conjugated with targeting antibodies. Following a TBI, the blood-brain barrier (BBB) becomes permeable, which can last for years and allow the leakage of harmful plasma proteins. Consequently, an appealing approach for TBI treatment involves using drug delivery systems that utilize targeting antibodies and nanocarriers to help restore BBB integrity. In our investigation of this strategy, we examined the efficacy of free antibodies and nanocarriers targeting a specific endothelial surface marker called vascular cell adhesion molecule-1 (VCAM-1), which is known to be upregulated during inflammation. In a mouse model of TBI utilizing central fluid percussion injury, free VCAM-1 antibody did not demonstrate superior targeting when comparing sham vs. TBI brain. However, the administration of VCAM-1-targeted nanocarriers (liposomes) exhibited a 10-fold higher targeting specificity in TBI brain than in sham control. Flow cytometry and confocal microscopy analysis confirmed that VCAM-1 liposomes were primarily taken up by brain endothelial cells post-TBI. Consequently, VCAM-1 liposomes represent a promising platform for the targeted delivery of therapeutics to the brain following traumatic brain injury.

Neutralization of Interleukin 1-beta is associated with preservation of thalamic capillaries after experimental traumatic brain injury.

Traumatic brain injury to thalamo-cortical pathways is associated with posttraumatic morbidity. Diffuse mechanical forces to white matter tracts and deep grey matter regions induce an inflammatory response and vascular damage resulting in progressive neurodegeneration. Pro-inflammatory cytokines, including interleukin-1β (IL-1β), may contribute to the link between inflammation and the injured capillary network after TBI. This study investigates whether IL-1β is a key contributor to capillary alterations and changes in pericyte coverage in the thalamus and cortex after TBI. Animals were subjected to central fluid percussion injury (cFPI), a model of TBI causing widespread axonal and vascular pathology, or sham injury and randomized to receive a neutralizing anti-IL-1β or a control, anti-cyclosporin A antibody, at 30 min post-injury. Capillary length and pericyte coverage of cortex and thalamus were analyzed by immunohistochemistry at 2- and 7-days post-injury. Our results show that early post-injury attenuation of IL-1β dependent inflammatory signaling prevents capillary damage by increasing pericyte coverage in the thalamus.

Impaired oligodendrogenesis in the white matter of aged mice following diffuse traumatic brain injury.

Senescence is a negative prognostic factor for outcome and recovery following traumatic brain injury (TBI). TBI-induced white matter injury may be partially due to oligodendrocyte demise. We hypothesized that the regenerative capacity of oligodendrocyte precursor cells (OPCs) declines with age. To test this hypothesis, the regenerative capability of OPCs in young [(10 weeks ±2 (SD)] and aged [(62 weeks ±10 (SD)] mice was studied in mice subjected to central fluid percussion injury (cFPI), a TBI model causing widespread white matter injury. Proliferating OPCs were assessed by immunohistochemistry for the proliferating cell nuclear antigen (PCNA) marker and labeled by 5-ethynyl-2'-deoxyuridine (EdU) administered daily through intraperitoneal injections (50 mg/kg) from day 2 to day 6 after cFPI. Proliferating OPCs were quantified in the corpus callosum and external capsule on day 2 and 7 post-injury (dpi). The number of PCNA/Olig2-positive and EdU/Olig2-positive cells were increased at 2dpi (p < .01) and 7dpi (p < .01), respectively, in young mice subjected to cFPI, changes not observed in aged mice. Proliferating Olig2+/Nestin+ cells were less common (p < .05) in the white matter of brain-injured aged mice, without difference in proliferating Olig2+/PDGFRα+ cells, indicating a diminished proliferation of progenitors with different spatial origin. Following TBI, co-staining for EdU/CC1/Olig2 revealed a reduced number of newly generated mature oligodendrocytes in the white matter of aged mice when compared to the young, brain-injured mice (p < .05). We observed an age-related decline of oligodendrogenesis following experimental TBI that may contribute to the worse outcome of elderly patients following TBI.

Enhancing cognitive function in chronic TBI: The Role of α7 nicotinic acetylcholine receptor modulation

Traumatic brain injury (TBI) results in several pathological changes within the hippocampus that result in adverse effects on learning and memory. Therapeutic strategies to enhance learning and memory after TBI are still in the early stages of clinical development. One strategy is to target the α7 nicotinic acetylcholine receptor (nAChR), which is highly expressed in the hippocampus and contributes to the formation of long-term memory. In our previous study, we found that AVL-3288, a positive allosteric modulator of the α7 nAChR, improved cognitive recovery in rats after moderate fluid-percussion injury (FPI). However, whether AVL-3288 improved cognitive recovery specifically through the α7 nAChR was not definitively determined. In this study we utilized Chrna7 knockout mice and compared their recovery to wild-type mice treated with AVL-3288 after TBI. We hypothesized that AVL-3288 treatment would improve learning and memory in wild-type mice, but not Chrna7−/− mice after TBI. Adult male C57BL/6 wild-type and Chrna7−/− mice received sham surgery or moderate controlled cortical impact (CCI) and recovered for 3 months. Mice were then treated with vehicle or AVL-3288 at 30 min prior to contextual fear conditioning. At 3 months after CCI, expression of α7 nAChR, choline acetyltransferase (ChAT), high-affinity choline transporter (ChT), and vesicular acetylcholine transporter (VAChT) were found to be significantly decreased in the hippocampus. Treatment of wild-type mice at 3 months after CCI with AVL-3288 significantly improved cue and contextual fear conditioning, whereas no beneficial effects were observed in Chrna7−/− mice. Parietal cortex and hippocampal atrophy were not improved with AVL-3288 treatment in either wild-type or Chrna7−/− mice. Our results indicate that AVL-3288 improves cognition during the chronic recovery phase of TBI through modulation of the α7 nAChR.

Concussive Head Trauma Deranges Axon Initial Segment Function in Axotomized and Intact Layer 5 Pyramidal Neurons.

The axon initial segment (AIS) is a critical locus of control of action potential (AP) generation and neuronal information synthesis. Concussive traumatic brain injury gives rise to diffuse axotomy, and the majority of neocortical axonal injury arises at the AIS. Consequently, concussive traumatic brain injury might profoundly disrupt the functional specialization of this region. To investigate this hypothesis, one and two days after mild central fluid percussion injury in Thy1-YFP-H mice, we recorded high-resolution APs from axotomized and adjacent intact layer 5 pyramidal neurons and applied a second derivative (2o) analysis to measure the AIS- and soma-regional contributions to the AP upstroke. All layer 5 pyramidal neurons recorded from sham animals manifested two stark 2o peaks separated by a negative intervening slope. In contrast, within injured mice, we discovered a subset of axotomized layer 5 pyramidal neurons in which the AIS-regional 2o peak was abolished, a functional perturbation associated with diminished excitability, axonal sprouting and distention of the AIS as assessed by staining for ankyrin-G. Our analysis revealed an additional subpopulation of both axotomized and intact layer 5 pyramidal neurons that manifested a melding together of the AIS- and soma-regional 2o peaks, suggesting a more subtle aberration of sodium channel function and/or translocation of the AIS initiation zone closer to the soma. When these experiments were repeated in animals in which cyclophilin-D was knocked out, these effects were ameliorated, suggesting that trauma-induced AIS functional perturbation is associated with mitochondrial calcium dysregulation.

Development and Application of a Novel Pressure System for Evaluating Trauma Severities Using a Physiological Approach After Traumatic Brain Injury in Rats

The fluid percussion injury (FPI) model is a surgical method for mimicking traumatic brain injury (TBI) models as it automatically and accurately measures peak impact pressure. Nevertheless, its elevated costs have led numerous researchers to develop more inexpensive alternative methods. Therefore, we used a copy of the classic FPI device to develop a novel method to evaluate the pressure pulse and determine injury severity with even more precision during the surgical procedure to induce an injury. The electronic components, algorithms, and hardware assembly were initially studied. Adult male Wistar rats received 2 different impact forces, and our novel system measured the pressure pulse in atmospheres to verify the differences between mild and moderate severity and the physiological alterations. The newly developed system was capable of detecting differences between mild and moderate severity, and severity parameters (e.g., apnea and unconsciousness) were more significant in animals with more moderate FPI than those with mild FPI. Additionally, electrocardiographic signals were modified 1day after TBI, and mild and moderate FPI decreased R-wave peak to R-wave peak intervals (increased heart rate) and high frequency (HF) index as well as increased low frequency (LF) and low frequency/high frequency ratio indices. All electrocardiographic parameters evaluated were more expressive in the more moderate FPI than in the mild one, corroborating clinical heart impairments after TBI. The method developed to evaluate pressure pulse in an FPI model proved capable of precisely determining different degrees of injury.

The Central Fluid Percussion Brain Injury in a Gyrencephalic Pig Brain: Scalable Diffuse Injury and Tissue Viability for Glial Cell Immunolabeling following Long-Term Refrigerated Storage.

Traumatic brain injury (TBI) affects millions of people annually; however, our knowledge of the diffuse pathologies associated with TBI is limited. As diffuse pathologies, including axonal injury and neuroinflammatory changes, are difficult to visualize in the clinical population, animal models are used. In the current study, we used the central fluid percussion injury (CFPI) model in a micro pig to study the potential scalability of these diffuse pathologies in a gyrencephalic brain of a species with inflammatory systems very similar to humans. We found that both axonal injury and microglia activation within the thalamus and corpus callosum are positively correlated with the weight-normalized pressure pulse, while subtle changes in blood gas and mean arterial blood pressure are not. We also found that the majority of tissue generated up to 10 years previously is viable for immunofluorescent labeling after long-term refrigeration storage. This study indicates that a micro pig CFPI model could allow for specific investigations of various degrees of diffuse pathological burdens following TBI.

Post-Injury Buprenorphine Administration Is Associated with Long-Term Region-Specific Glial Alterations in Rats.

Traumatic brain injury (TBI) is a major leading cause of death and disability. While previous studies regarding focal pathologies following TBI have been done, there is a lack of information concerning the role of analgesics and their influences on injury pathology. Buprenorphine (Bup), an opioid analgesic, is a commonly used analgesic in experimental TBI models. Our previous studies investigated the acute effects of Buprenorphine-sustained release-Lab (Bup-SR-Lab) on diffuse neuronal/glial pathology, neuroinflammation, cell damage, and systemic physiology. The current study investigated the longer-term chronic outcomes of Bup-SR-Lab treatment at 4 weeks following TBI utilizing a central fluid percussion injury (cFPI) model in adult male rats. Histological assessments of physiological changes, neuronal damage, cortical and thalamic cytokine expression, microglial and astrocyte morphological changes, and myelin alterations were done, as we had done in our acute study. In the current study the Whisker Nuisance Task (WNT) was also performed pre- and 4w post-injury to assess changes in somatosensory sensitivity following saline or Bup-SR-Lab treatment. Bup-SR-Lab treatment had no impact on overall physiology or neuronal damage at 4w post-injury regardless of region or injury, nor did it have any significant effects on somatosensory sensitivity. However, greater IL-4 cytokine expression with Bup-SR-Lab treatment was observed compared to saline treated animals. Microglia and astrocytes also demonstrated region-specific morphological alterations associated with Bup-SR-Lab treatment, in which cortical microglia and thalamic astrocytes were particularly vulnerable to Bup-mediated changes. There were discernable injury-specific and region-specific differences regarding myelin integrity and changes in specific myelin basic protein (MBP) isoform expression following Bup-SR-Lab treatment. This study indicates that use of Bup-SR-Lab could impact TBI-induced glial alterations in a region-specific manner 4w following diffuse brain injury.

Purkinje cell vulnerability induced by diffuse traumatic brain injury is linked to disruption of long-range neuronal circuits

Cerebellar dysfunction is commonly observed following traumatic brain injury (TBI). While direct impact to the cerebellum by TBI is rare, cerebellar pathology may be caused by indirect injury via cortico-cerebellar pathways. To address the hypothesis that degeneration of Purkinje cells (PCs), which constitute the sole output from the cerebellum, is linked to long-range axonal injury and demyelination, we used the central fluid percussion injury (cFPI) model of widespread traumatic axonal injury in mice. Compared to controls, TBI resulted in early PC loss accompanied by alterations in the size of pinceau synapses and levels of non-phosphorylated neurofilament in PCs. A combination of vDISCO tissue clearing technique and immunohistochemistry for vesicular glutamate transporter type 2 show that diffuse TBI decreased mossy and climbing fiber synapses on PCs. At 2 days post-injury, numerous axonal varicosities were found in the cerebellum supported by fractional anisotropy measurements using 9.4 T MRI. The disruption and demyelination of the cortico-cerebellar circuits was associated with poor performance of brain-injured mice in the beam-walk test. Despite a lack of direct input from the injury site to the cerebellum, these findings argue for novel long-range mechanisms causing Purkinje cell injury that likely contribute to cerebellar dysfunction after TBI.

Long-Term Effects of Moderate Concussive Brain Injury During Adolescence on Synaptic and Tonic GABA Currents in Dentate Granule Cells and Semilunar Granule Cells.

Progressive physiological changes in the hippocampal dentate gyrus circuits following traumatic brain injury (TBI) contribute to temporal evolution of neurological sequelae. Although early posttraumatic changes in dentate synaptic and extrasynaptic GABA currents have been reported, and whether they evolve over time and remain distinct between the two projection neuron classes, granule cells and semilunar granule cells, have not been evaluated. We examined long-term changes in tonic GABA currents and spontaneous inhibitory postsynaptic currents (sIPSCs) and in dentate projection neurons 3 months after moderate concussive fluid percussion injury (FPI) in adolescent rats. Granule cell tonic GABA current amplitude remained elevated up to 1 month after FPI, but decreased to levels comparable with age-matched controls by 3 months postinjury. Granule cell sIPSC frequency, which we previously reported to be increased 1 week after FPI, remained higher than in age-matched controls at 1 month and was significantly reduced 3 months after FPI. In semilunar granule cells, tonic GABA current amplitude and sIPSC frequency were not different from controls 3 months after FPI, which contrast with decreases observed 1 week after injury. The switch in granule cell inhibitory inputs from early increase to subsequent decrease could contribute to the delayed emergence of cognitive deficits and seizure susceptibility after brain injury.

Diffuse Traumatic Injury in the Mouse Disrupts Axon-Myelin Integrity in the Cerebellum.

Cerebellar dysfunction after traumatic brain injury (TBI) is commonly suspected based on clinical symptoms, although cerebellar pathology has rarely been investigated. To address the hypothesis that the cerebellar axon-myelin unit is altered by diffuse TBI, we used the central fluid percussion injury (cFPI) model in adult mice to create widespread axonal injury by delivering the impact to the forebrain. We specifically focused on changes in myelin components (myelin basic protein [MBP], 2',3'-cyclic nucleotide 3'-phosphodiesterase [CNPase], nodal/paranodal domains [neurofascin (Nfasc), ankyrin-G], and phosphorylated neurofilaments [SMI-31, SMI-312]) in the cerebellum, remote from the impact, at two, seven, and 30 days post-injury (dpi). When compared with sham-injured controls, cerebellar MBP and CNPase protein levels were decreased at 2 dpi that remained reduced up to 30 dpi. Diffuse TBI induced different effects on neuronal (Nfasc 186, Nfasc 140) and glial (Nfasc 155) neurofascin isoforms that play a key role in the assembly of the nodes of Ranvier. Expression of Nfasc 140 in the cerebellum increased at 7 dpi, in contrast to Nfasc 155 levels, which were decreased. Although neurofascin binding partner ankyrin-G protein levels decreased acutely after cFPI, its expression levels increased at 7 dpi and remained unchanged up to 30 dpi. The TBI-induced reduction in neurofilament phosphorylation (SMI-31) observed in the cerebellum was closely associated with decreased levels of the myelin proteins MBP and CNPase. This is the first evidence of temporal and spatial structural changes in the axon-myelin unit in the cerebellum, remote from the location of the impact site, in a diffuse TBI model in mice.

Age-At-Injury Influences the Glial Response to Traumatic Brain Injury in the Cortex of Male Juvenile Rats.

Few translational studies have examined how age-at-injury affects the glial response to traumatic brain injury (TBI). We hypothesized that rats injured at post-natal day (PND) 17 would exhibit a greater glial response, that would persist into early adulthood, compared to rats injured at PND35. PND17 and PND35 rats (n = 75) received a mild to moderate midline fluid percussion injury or sham surgery. In three cortical regions [peri-injury, primary somatosensory barrel field (S1BF), perirhinal], we investigated the glial response relative to age-at-injury (PND17 or PND35), time post-injury (2 hours, 1 day, 7 days, 25 days, or 43 days), and post-natal age, such that rats injured at PND17 or PND35 were compared at the same post-natal-age (e.g., PND17 + 25D post-injury = PND42; PND35 + 7D post-injury = PND42). We measured Iba1 positive microglia cells (area, perimeter) and quantified their activation status using skeletal analysis (branch length/cell, mean processes/cell, cell abundance). GFAP expression was examined using immunohistochemistry and pixel analysis. Data were analyzed using Bayesian multivariate multi-level models. Independent of age-at-injury, TBI activated microglia (shorter branches, fewer processes) in the S1BF and perirhinal cortex with more microglia in all regions compared to uninjured shams. TBI-induced microglial activation (shorter branches) was sustained in the S1BF into early adulthood (PND60). Overall, PND17 injured rats had more microglial activation in the perirhinal cortex than PND35 injured rats. Activation was not confounded by age-dependent cell size changes, and microglial cell body sizes were similar between PND17 and PND35 rats. There were no differences in astrocyte GFAP expression. Increased microglial activation in PND17 brain-injured rats suggests that TBI upregulates the glial response at discrete stages of development. Age-at-injury and aging with an injury are translationally important because experiencing a TBI at an early age may trigger an exaggerated glial response.

Cathepsin B Relocalization in Late Membrane Disrupted Neurons Following Diffuse Brain Injury in Rats.

Traumatic brain injury (TBI) has consequences that last for years following injury. While TBI can precipitate a variety of diffuse pathologies, the mechanisms involved in injury-induced neuronal membrane disruption remain elusive. The lysosomal cysteine protease, Cathepsin B (Cath B), and specifically its redistribution into the cytosol has been implicated in cell death. Little is known about Cath B or neuronal membrane disruption chronically following diffuse TBI. Therefore, the current study evaluated Cath B and diffuse neuronal membrane disruption over a more chronic post-injury window (6 h–4 w). We evaluated Cath B in adult male Sprague-Dawley rats following central fluid percussion injury (CFPI). Expression of Cath B, as well as Cath B-associated pro (Bak and AIF) and anti-apoptotic (Bcl-xl) proteins, were assessed using western blot analysis. Cath B activity was also assessed. Localization of Cath B was evaluated in the membrane disrupted and non-disrupted population following CFPI using immunohistochemistry paired with quantitative image analysis and ultrastructural verification. There was no difference in expression or activity of Cath B or any of the associated proteins between sham and CFPI at any time post-injury. Immunohistological studies, however, showed a sub-cellular re-localization of Cath B at 2 w and 4 w post-injury in the membrane disrupted neuronal population as compared to the time-point matched non-disrupted neurons. Both membrane disruption and Cath B relocalization appear linked to neuronal atrophy. These observations are indicative of a late secondary pathology that represents an opportunity for therapeutic treatment of these neurons following diffuse TBI. Summary Statement Lysosomal cathepsin B relocalizes to the cytosol in neurons with disrupted plasmalemmal membranes weeks following diffuse brain injury. Both the membrane disrupted and cathepsin B relocalized neuronal subpopulations displayed smaller soma and nucleus size compared to non-pathological neurons, indicating atrophy.

Axonal injury following mild traumatic brain injury is exacerbated by repetitive insult and is linked to the delayed attenuation of NeuN expression without concomitant neuronal death in the mouse.

Mild traumatic brain injury (mTBI) affects brain structure and function and can lead to persistent abnormalities. Repetitive mTBI exacerbates the acute phase response to injury. Nonetheless, its long‐term implications remain poorly understood, particularly in the context of traumatic axonal injury (TAI), a player in TBI morbidity via axonal disconnection, synaptic loss and retrograde neuronal perturbation. In contrast to the examination of these processes in the acute phase of injury, the chronic‐phase burden of TAI and/or its implications for retrograde neuronal perturbation or death have received little consideration. To critically assess this issue, murine neocortical tissue was investigated at acute (24‐h postinjury, 24hpi) and chronic time points (28‐days postinjury, 28dpi) after singular or repetitive mTBI induced by central fluid percussion injury (cFPI). Neurons were immunofluorescently labeled for NeuroTrace and NeuN (all neurons), p‐c‐Jun (axotomized neurons) and DRAQ5 (cell nuclei), imaged in 3D and quantified in automated manner. Single mTBI produced axotomy in 10% of neurons at 24hpi and the percentage increased after repetitive injury. The fraction of p‐c‐Jun+ neurons decreased at 28dpi but without neuronal loss (NeuroTrace), suggesting their reorganization and/or repair following TAI. In contrast, NeuN+ neurons decreased with repetitive injury at 24hpi while the corresponding fraction of NeuroTrace+ neurons decreased over 28dpi. Attenuated NeuN expression was linked exclusively to non‐axotomized neurons at 24hpi which extended to the axotomized at 28dpi, revealing a delayed response of the axotomized neurons. Collectively, we demonstrate an increased burden of TAI after repetitive mTBI, which is most striking in the acute phase response to the injury. Our finding of widespread axotomy in large fields of intact neurons contradicts the notion that repetitive mTBI elicits progressive neuronal death, rather, emphasizing the importance of axotomy‐mediated change.

Vascular Dysfunction after Modeled Traumatic Brain Injury Is Preserved with Administration of Umbilical Cord Derived Mesenchymal Stromal Cells and Is Associated with Modulation of the Angiogenic Response.

Vascular dysfunction arising from blood-brain barrier (BBB) breakdown after traumatic brain injury (TBI) can adversely affect neuronal health and behavioral outcome. Pericytes and endothelial cells of the neurovascular unit (NVU) function collectively to maintain strict regulation of the BBB through tight junctions. Secondary injury mechanisms, such as pro-angiogenic signals that contribute to pericyte loss, can prolong and exacerbate primary vascular injury. Human umbilical cord perivascular cells (HUCPVCs) are a source of mesenchymal stromal cells (MSCs) that have been shown to reduce vascular dysfunction after neurotrauma. We hypothesized that the perivascular properties of HUCPVCs can reduce vascular dysfunction after modeled TBI by preserving the pericyte-endothelial interactions. Rats were subjected to a moderate fluid percussion injury (FPI) and intravenously infused with 1,500,000 HUCPVCs post-injury. At acute time points (24 h and 48 h) quantitative polymerase chain reaction (qPCR) analysis demonstrated that the gene expression of angiopoietin-2 was increased with FPI and reduced with HUCPVCs. Immunofluorescent assessment of RECA-1 (endothelial cells) and platelet-derived growth factor receptors (PDGFR-β) (pericytes) revealed that capillary and pericyte densities as well as the co-localization of the two cells were decreased with FPI and preserved with HUCPVC administration. These acute HUCPVC-mediated protective effects were associated with less permeability to Evan's blue dye and increased expression of the tight junction occludin, suggesting less vascular leakage. Further, at 4 weeks post-injury, HUCPVC administration was associated with reduced anxiety and decreased β-amyloid precursor protein (β-APP) accumulation. In summary, HUCPVCs promoted pericyte-endothelial barrier function that was associated with improved long-term outcome.

Buprenorphine alters microglia and astrocytes acutely following diffuse traumatic brain injury

Traumatic brain injury (TBI) is a common phenomenon, accounting for significant cost and adverse health effects. While there is information about focal pathologies following TBI, knowledge of more diffuse processes is lacking, particularly regarding how analgesics affect this pathology. As buprenorphine is the most commonly used analgesic in experimental TBI models, this study investigated the acute effects of the opioid analgesic buprenorphine (Bup-SR-Lab) on diffuse neuronal/glial pathology, neuroinflammation, cell damage, and systemic physiology. We utilized a model of central fluid percussion injury (CFPI) in adult male rats treated with a single subcutaneous bolus of Bup-SR-Lab or saline 15 min post-injury. Microscopic assessments were performed at 1 day post-injury. Cell impermeable dextran was infused intraventricularly prior to sacrifice to assess neuronal membrane disruption. Axonal injury was assessed by investigating labeling of the anterogradely transported amyloid precursor protein. Neuroinflammation was assessed by analyzing Iba-1 + microglial and GFAP + astrocyte histological/morphological features as well as cytokine levels in both regions of interest (ROIs). Myelin pathology was assessed by evaluating the expression of myelin basic protein (MBP) and the propensity of MBP + myelin debris. Acute physiologic data showed no difference between groups except for reduction in weight loss following cFPI in Bup treated animals compared to saline. There were no discernable differences in axonal injury or membrane disruption between treatment groups. Cytokine levels were consistent between Bup and saline treated animals, however, microglia and astrocytes revealed region specific histological changes at 1d following Bup treatment. Myelin integrity and overall MBP expression showed no differences between Bup and saline treated animals, but there were significant regional differences in MBP expression between the cortex and thalamus. These data suggest effects of Bup treatment on weight following CFPI and potential regional specificity of Bup-associated microglial and astrocyte alterations, but very little change in other acute pathology at 1-day post-injury. Overall, this preliminary study indicates that use of Bup-SR-Lab in preclinical work does have effects on acute glial pathology, however, longer term studies will be needed to assess potential effects of Bup treatment on more chronic pathological progressions.

Interleukin-1 Beta Neutralization Attenuates Traumatic Brain Injury-Induced Microglia Activation and Neuronal Changes in the Globus Pallidus.

Traumatic brain injury (TBI) increases the risk of delayed neurodegenerative processes, including Parkinson’s disease (PD). Interleukin-1beta (IL-1β), a key pro-inflammatory cytokine, may promote secondary injury development after TBI. Conversely, neutralizing IL-1β was found to improve functional recovery following experimental TBI. However, the mechanisms underlying the behavioral improvements observed by IL-1β neutralization are still poorly understood. The present study investigated the role of IL-1β on the microglia response and neuronal changes in the globus pallidus in response to diffuse TBI. Mice were subjected to sham injury or the central fluid percussion injury (cFPI) (a model of traumatic axonal injury), and were randomly administered an IL-1β neutralizing or a control antibody at 30 min post-injury. The animals were analyzed at 2, 7, or 14 days post-injury. When compared to controls, mice subjected to cFPI TBI had increased microglia activation and dopaminergic innervation in the globus pallidus, and a decreased number of parvalbumin (PV) positive interneurons in the globus pallidus. Neutralization of IL-1β attenuated the microglia activation, prevented the loss of PV+ interneurons and normalized dopaminergic fiber density in the globus pallidus of brain-injured animals. These findings argue for an important role for neuro-inflammation in the PD-like pathology observed in TBI.

Hemorrhage Associated Mechanisms of Neuroinflammation in Experimental Traumatic Brain Injury

Traumatic brain injury (TBI) is a major health problem for over 3.17 million people in the US, attracting increasing public attentions. Understanding the underlying mechanism of TBI is urgent for better diagnosis and treatment. Here, we examined the hypothesis that cerebral hemorrhagic coagulation and subsequent immune cells infiltration causes the progressive mechanisms of brain injury in moderate fluid percussion injury model. This represents a subdural hematoma and hemorrhagic head injury. We found increased hemorrhagic lesions and infarct volume in the injured brain with increment of pressure. The extent of hemorrhage was also validated by the bio-distribution of fluorescent tracer in cerebrospinal fluid (CSF) pathway after the injury. Bio-distribution of tracer was specifically diminished at the site of hemorrhage resulting from coagulation, which blocked the interstitial and CSF movement of the tracer. Increased expression of coagulation factor XII and necrotic cell death in and around the impact site confirmed the reason for this blockade. Different biomarkers, including immune cells accumulation and neuronal death showed that blood-brain barrier disruption played an important role for induction of neuroinflammation and neurodegeneration around the impact site. Our results suggest that instant hemorrhagic injury resulting from rupturing the brain blood vessels intertwined with coagulation causes onsite perivascular inflammation and neurodegeneration. Understanding of this sequential event should be valuable for development of therapeutic treatment in TBI. Graphical Abstract Underlying mechanisms in moderate/severe blunt TBI: hemorrhage following cerebrovascular disruption results in coagulation, thrombotic necrosis, and acute immune cell infiltration.