Biomechanical analysis of fluid percussion model of brain injury

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

Introduction

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.

Methods

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.

Results and Conclusion

Our results show that early post-injury attenuation of IL-1β dependent inflammatory signaling prevents capillary damage by increasing pericyte coverage in the thalamus.

An Air-Filled Bicycle Helmet for Mitigating Traumatic Brain Injury

We created a novel air-filled bicycle helmet. The aims of this study were (i) to assess the head injury mitigation performance of the proposed helmet and (ii) to compare those performance results against the performance results of an expanded polystyrene (EPS) traditional bicycle helmet. Two bicycle helmet types were subjected to impacts in guided vertical drop tests onto a flat anvil: EPS helmets and air-filled helmets (Bumpair). The maximum acceleration value recorded during the test on the Bumpair helmet was 86.76 ± 3.06 g, while the acceleration during the first shock on the traditional helmets reached 207.85 ± 5.55 g (p < 0.001). For the traditional helmets, the acceleration increased steadily over the number of shocks. There was a strong correlation between the number of impacts and the response of the traditional helmet (cor = 0.94; p < 0.001), while the Bumpair helmets showed a less significant dependence over time (cor = 0.36; p = 0.048), meaning previous impacts had a lower consequence. The air-filled helmet significantly reduced the maximal linear acceleration when compared to an EPS traditional helmet, showing improvements in impact energy mitigation, as well as in resistance to repeated impacts. This novel helmet concept could improve head injury mitigation in cyclists.

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.

Diffuse traumatic injury in the mouse disrupts axon-myelin integrity in the cerebellum

Cerebellar dysfunction following 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 wide-spread 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, ankyrin G), and phosphorylated neurofilaments (SMI-31, SMI-312) in the cerebellum, remote from the impact, at 2, 7 and 30-day post-injury. When compared to sham-injured controls, cerebellar MBP and CNPase protein levels were decreased at 2 days post-injury (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. 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.

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.

Manifestations of Apprehension and Anxiety in a Sprague Dawley Cranial Defect Model

BACKGROUND

Syndrome of the trephined is a neurologic condition that commonly arises in patients who undergo craniectomy and have a prolonged cranial defect. Symptoms of this condition include headache, difficulties concentrating, diminished fine motor/dexterity skills, mood changes, and anxiety/apprehension. The authors hypothesize that an animal model demonstrating anxiety/apprehension in rats who undergo craniectomy is feasible utilizing standardized animal behavioral testing.

METHODS

Sprague Dawley rats were the stratified to 1 of 2 groups for comparison of neurobehavioral outcomes. Group #1 (closed cranial group) had their cranial trephination immediately closed with acrylic to restore normal cranial anatomy and Group #2 (open cranial group) had their cranial trephination enlarged to represent a decompressive hemicraniectomy immediately. Anxiety/apprehension was studied using a standardized rodent open field test. Statistical comparison of differences among the 2 groups was performed.

RESULTS

Ten rats were studied with 5 rats in each group. Standard rodent open field testing of anxiety demonstrated no difference among the 2 groups at 1 week. Rats in the "Open cranial group" demonstrated progressively more anxiety over the following 3-month period. Rats in the "Open cranial group" demonstrated increasing anxiety levels as compared with rats in the "Closed cranial group." At week 16, the "Open cranial group" anxiety levels were significantly greater than week 4 (t = 2.24, P = 0.04) demonstrating a significant linear trend over time (R = 0.99; P = 0.002). The "Closed cranial group" did not show this trend (R = 07; P = 0.74).

CONCLUSION

Our study demonstrates that anxiety and apprehension are more prevalent in rats with an open, prolonged cranial defect in comparison to those with a closed cranium. This correlates with similar finds in humans with syndrome of the trephined.

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

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

Initiators of Classical and Lectin Complement Pathways Are Differently Engaged after Traumatic Brain Injury-Time-Dependent Changes in the Cortex, Striatum, Thalamus and Hippocampus in a Mouse Model

The complement system is involved in promoting secondary injury after traumatic brain injury (TBI), but the roles of the classical and lectin pathways leading to complement activation need to be clarified. To this end, we aimed to determine the ability of the brain to activate the synthesis of classical and lectin pathway initiators in response to TBI and to examine their expression in primary microglial cell cultures. We have modeled TBI in mice by controlled cortical impact (CCI), a clinically relevant experimental model. Using Real-time quantitative polymerase chain reaction (RT-qPCR) we analyzed the expression of initiators of classical the complement component 1q, 1r and 1s (C1q, C1r, and C1s) and lectin (mannose binding lectin A, mannose binding lectin C, collectin 11, ficolin A, and ficolin B) complement pathways and other cellular markers in four brain areas (cortex, striatum, thalamus and hippocampus) of mice exposed to CCI from 24 h and up to 5 weeks. In all murine ipsilateral brain structures assessed, we detected long-lasting, time- and area-dependent significant increases in the mRNA levels of all classical (C1q, C1s, C1r) and some lectin (collectin 11, ficolin A, ficolin B) initiator molecules after TBI. In parallel, we observed significantly enhanced expression of cellular markers for neutrophils (Cd177), T cells (Cd8), astrocytes (glial fibrillary acidic protein—GFAP), microglia/macrophages (allograft inflammatory factor 1—IBA-1), and microglia (transmembrane protein 119—TMEM119); moreover, we detected astrocytes (GFAP) and microglia/macrophages (IBA-1) protein level strong upregulation in all analyzed brain areas. Further, the results obtained in primary microglial cell cultures suggested that these cells may be largely responsible for the biosynthesis of classical pathway initiators. However, microglia are unlikely to be responsible for the production of the lectin pathway initiators. Immunofluorescence analysis confirmed that at the site of brain injury, the C1q is localized in microglia/macrophages and neurons but not in astroglial cells. In sum, the brain strongly reacts to TBI by activating the local synthesis of classical and lectin complement pathway activators. Thus, the brain responds to TBI with a strong, widespread and persistent upregulation of complement components, the targeting of which may provide protection in TBI.

Overexpression of Astrocytes-Specific GJA1-20k Enhances the Viability and Recovery of the Neurons in a Rat Model of Traumatic Brain Injury

Traumatic brain injury (TBI) is a devastating actuality in clinics worldwide. It is estimated that approximately 10 million people among the world suffer from TBI each year, and a considerable number of patients will be temporarily or permanently disabled or even die due to this disease. Astrocytes play a very important role in the repair of brain tissue after TBI, including the formation of a neuroprotective barrier, inhibition of brain edema, and inhibition of normal nerve cell apoptosis. However, the detailed mechanism underlying this protective effect is still unclear. To investigate the regulatory factors of astrocytes to other neurons post-TBI, we established a TBI rat model and used the AAV to mediate the overexpression of GJA1-20k in astrocytes of rats. And functionally, the specific overexpression of GJA1-20k in astrocytes promoted the viability and recovery of neurons in TBI. Mechanistically, the astrocytes-specific upregulation of GJA1-20k protected the function of mitochondria in neurons of FPI rats, thus suppressing the apoptosis of the damaged neurons. We hereby reported that astrocytes-specific overexpression of GJA1-20k enhanced the viability and recovery of the neurons in TBI through regulating their mitochondrial function.