Biomechanical simulation of traumatic brain injury in the rat

An atlas of the heterogeneous viscoelastic brain with local power-law attenuation synthesised using Prony-series

This review addresses the acute need to acknowledge the mechanical heterogeneity of brain matter and to accurately calibrate its local viscoelastic material properties accordingly. Specifically, it is important to compile the existing and disparate literature on attenuation power-laws and dispersion to make progress in wave physics of brain matter, a field of research that has the potential to explain the mechanisms at play in diffuse axonal injury and mild traumatic brain injury in general. Currently, viscous effects in the brain are modelled using Prony-series, i.e., a sum of decaying exponentials at different relaxation times. Here we collect and synthesise the Prony-series coefficients appearing in the literature for twelve regions: brainstem, basal ganglia, cerebellum, corona radiata, corpus callosum, cortex, dentate gyrus, hippocampus, thalamus, grey matter, white matter, homogeneous brain, and for eight different mammals: pig, rat, human, mouse, cow, sheep, monkey and dog. Using this data, we compute the fractional-exponent attenuation power-laws for different tissues of the brain, the corresponding dispersion laws resulting from causality, and the averaged Prony-series coefficients. STATEMENT OF SIGNIFICANCE: Traumatic brain injuries are considered a silent epidemic and finite element methods (FEMs) are used in modelling brain deformation, requiring access to viscoelastic properties of brain. To the best of our knowledge, this work presents 1) the first multi-frequency viscoelastic atlas of the heterogeneous brain, 2) the first review focusing on viscoelastic modelling in both FEMs and experimental works, 3) the first attempt to conglomerate the disparate existing literature on the viscoelastic modelling of the brain and 4) the largest collection of viscoelastic parameters for the brain (212 different Prony-series spanning 12 different tissues and 8 different animal surrogates). Furthermore, this work presents the first brain atlas of attenuation power-laws essential for modelling shear waves in brain.

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.

Cranial Bone Changes Induced by Mild Traumatic Brain Injuries: A Neglected Player in Concussion Outcomes?

Mild traumatic brain injuries (TBIs), particularly when repetitive in nature, are increasingly recognized to have a range of significant negative implications for brain health. Much of the ongoing research in the field is focused on the neurological consequences of these injuries and the relationship between TBIs and long-term neurodegenerative conditions such as chronic traumatic encephalopathy and Alzheimer's disease. However, our understanding of the complex relationship between applied mechanical force at impact, brain pathophysiology, and neurological function remains incomplete. Past research has shown that mild TBIs, even below the threshold that results in cranial fracture, induce changes in cranial bone structure and morphology. These structural and physiological changes likely have implications for the transmission of mechanical force into the underlying brain parenchyma. Here, we review this evidence in the context of the current understanding of bone mechanosensitivity and the consequences of TBIs or concussions. We postulate that heterogeneity of the calvarium, including differing bone thickness attributable to past impacts, age, or individual variability, may be a modulator of outcomes after subsequent TBIs. We advocate for greater consideration of cranial responses to TBI in both experimental and computer modeling of impact biomechanics, and raise the hypothesis that calvarial bone thickness represents a novel biomarker of brain injury vulnerability post-TBI.

"The Most Gentle of Lethal Methods": The Question of Retained Consciousness Following Decapitation

Since the development of the infamous guillotine in the French Revolution, physicians have debated how long consciousness persists in decapitated heads. Fueled by anecdotes of severed heads that blink, blush, and appear to retain intelligence, numerous experiments have investigated this macabre subject for nearly 250 years. In this paper, we examine the evidence, both historical and modern, and ultimately conclude that, while the truth may never be fully known, all evidence appears to indicate that loss of consciousness appears to occur within seconds of decapitation. The rumors that circulated through the European consciousness during the Terror of the French Revolution appear to be just that - curious urban legends from an awed and terrified public.

Inhibition of PDE10A-Rescued TBI-Induced Neuroinflammation and Apoptosis through the cAMP/PKA/NLRP3 Pathway

Phosphodiesterase 10A (PDE10A) is a dual-substrate phosphodiesterase that is highly expressed in the striatal complex. PDE10A is an important target for the treatment of ganglion dysfunction and neuroinflammation-related diseases, but its possible impact on traumatic brain injury (TBI) is still unclear. This study aims to investigate the protective effects of inhibiting PDE10A on neuroinflammation post-TBI injury and its possible molecular mechanism. The expression of PDE10A in rats and HT22 cells was determined by Western blotting. The neurological dysfunction of these rats was detected by Nissl staining, hematoxylin-eosin (HE) staining, and Morris water maze test. The activity of HT22 cells was measured by MTT. The findings of this study suggest that PDE10A is highly expressed in the brain tissue of TBI rats and HT22 cells induced by mechanical injury. Inhibition of PDE10A reduces the expression of interleukin-1β (IL-1β) and interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-α) in HT22 cells induced by mechanical injury to inhibit cell apoptosis. Simultaneously, inhibition of PDE10A in TBI rats reduces the time to find a visible platform in the same pool, while cAMP/PKA activator treatment alleviates all of the abovementioned phenomena. Additionally, it is further confirmed that inhibition of PDE10A activates the cAMP/PKA pathway and downregulates the expression of NRLP3. These findings demonstrate that inhibition of PDE10A exerts neuroprotection by inhibiting apoptosis and inflammation following TBI, at least partially by the cAMP/PKA/NLRP3 pathway.

Therapeutic effects of Lacosamide in a rat model of traumatic brain injury: A histological, biochemical and electroencephalography monitoring study

OBJECTIVE

Traumatic Brain Injury (TBI) is a major cause of death and disability worldwide, especially in children and young adults. TBI can be classified based on severity, mechanism or other features. Inflammation, apoptosis, oxidative stress, and ischemia are some of the important pathophys-iological mechanisms underlying neuronal loss after TBI. Lacosamide (LCM) is an anticonvulsant compound approved for the adjunctive treatment of partial-onset seizures and neuropathic pain. This study aimed to investigate possible neuroprotective effects of LCM in a rat model of TBI.

MATERIAL AND METHODS

Twenty-eight adult male, Wistar albino rats were used. The rats were divided into 4 groups. Group 1 was the control group (n=7). Group 2 was the trauma group (n=7) where rats were treated with 100 mg/kg saline intraperitoneally (IP) twice a day. Groups 3 and 4, rats were treated with 6 (group 3, n=7) or 20 (group 4, n=7) mg/kg Lacosamide IP twice a day. For each group, brain samples were collected 72 hours after injury. Brain samples and blood were evaluated with histopathological and biochemical methods. In addition, electroencephalograpy monitoring results were compared.

RESULTS

The immunoreactivity of both iNOS and eNOS (oxidative stress markers) were decreased with LCM treatment compared to trauma group. The results were statistically significant (***P<0.001). The treatments of low (56,17±9,69) and high-dose LCM (43,91±9,09) were decreased the distribution of HIF-1α compared to trauma group (P<0.01). The number of apoptotic cells were decreased with LCM treatment the difference between the trauma group and 20mg/kg LCM treated group (9,55±1,02) was statistically significant (***P<0.001). Malondialdehyde level was reduced with LCM treatment. MDA level was significantly higher in trauma group compared to LCM treated groups (***P<0.001). The level of Superoxide dismutase in the trauma group was 1,86 U/ml, whereas it was 36,85 U/ml in 20mg/kg LCM treated group (***P<0.001). Delta strength of EEG in 20mg/kg LCM treated group were similar to control group values after LCM treatment.

CONCLUSION

No existing study has produced results suggesting that different doses of LCM has therapeutic effect against TBI, using EEG recording in addition to histological and biochemical evaluations in rats.

Evidence of early vasogenic edema following minor head impact that can be reduced with a vasopressin V1a receptor antagonist

BACKGROUND

Does minor head impact without signs of structural brain damage cause short-term changes in vasogenic edema as measured by an increase apparent diffusion coefficient (ADC) using diffusion weighted imaging? If so, could the increase in vasogenic edema be treated with a vasopressin V1a receptor antagonist? We hypothesized that SRX251, a highly selective V1a antagonist, would reduce vasogenic edema in response to a single minor head impact.

METHODS

Lightly anesthetized male rats were subjected to a sham procedure or a single hit to the forehead using a closed skull, momentum exchange model. Animals recovered in five min and were injected with saline vehicle (n = 8) or SRX251 (n = 8) at 15 min post head impact and again 7-8 hrs later. At 2 h, 6 h, and 24 h post injury, rats were anesthetized and scanned for increases in ADC, a neurological measure of vasogenic edema. Sham rats (n = 6) were exposed to anesthesia and scanned at all time points but were not hit or treated. Images were registered to and analyzed using a 3D MRI rat atlas providing site-specific data on 150 different brain areas. These brain areas were parsed into 11 major brain regions.

RESULTS

Untreated rats with brain injury showed a significant increase in global brain vasogenic edema as compared to sham and SRX251 treated rats. Edema peaked at 6 h in injured, untreated rats in three brain regions where changes in ADC were observed, but returned to sham levels by 24 h. There were regional variations in the time course of vasogenic edema and drug efficacy. Edema was significantly reduced in cerebellum and thalamus with SRX251 treatment while the basal ganglia did not show a response to treatment.

CONCLUSION

A single minor impact to the forehead causes regional increases in vasogenic edema that peak at 6 h but return to baseline within a day in a subset of brain regions. Treatment with a selective V1a receptor antagonist can reduce much of the edema.

A machine learning approach for magnetic resonance image-based mouse brain modeling and fast computation in controlled cortical impact

Computational modeling of the brain is crucial for the study of traumatic brain injury. An anatomically accurate model with refined details could provide the most accurate computational results. However, computational models with fine mesh details could take prolonged computation time that impedes the clinical translation of the models. Therefore, a way to construct a model with low computational cost while maintaining a computational accuracy comparable with that of the high-fidelity model is desired. In this study, we constructed magnetic resonance (MR) image-based finite element (FE) models of a mouse brain for simulations of controlled cortical impact. The anatomical details were kept by mapping each image voxel to a corresponding FE mesh element. We constructed a super-resolution neural network that could produce computational results of a refined FE model with a mesh size of 70 μm from a coarse FE model with a mesh size of 280 μm. The peak signal-to-noise ratio of the reconstructed results was 33.26 dB, while the computational speed was increased by 50-fold. This proof-of-concept study showed that using machine learning techniques, MR image-based computational modeling could be applied and evaluated in a timely fashion. This paved ways for fast FE modeling and computation based on MR images. Results also support the potential clinical applications of MR image-based computational modeling of the human brain in a variety of scenarios such as brain impact and intervention.Graphical abstract MR image-based FE models with different mesh sizes were generated for CCI. The training and testing data sets were computed with 5 different impact locations and 3 different impact velocities. High-resolution strain maps were estimated using a SR neural network with greatly reduced computational cost.

Improved voiding function by deep brain stimulation in traumatic brain-injured animals with bladder dysfunctions

OBJECTIVE

Traumatic brain injury (TBI) is a global scenario with high mortality and disability, which does not have an effectual and approved therapy till now. Bladder dysfunction is a major symptom after TBI, and this study deals with the alleviation of bladder function in TBI rats, with the aid of deep brain stimulations (DBS).

METHODS

TBI was induced by weight drop model (WDM) and standardized with the experimental subjects with variable heights for weight dropping. The rats survived after TBI were considered for bladder dysfunction observations. DBS with variable stimulation parameters like cystometric analysis and MRI studies were also performed.

RESULTS

After experimental studies, TBI 2-m-height crash was determined as suitable parameter due to minimal mortality rate and significant reduction in the voiding efficiency from 67 to 28%, whereas DBS significantly reversed the value of voiding efficiency to 65-84%. MRI studies revealed the severity of TBI impact and DBS localization.

CONCLUSION

The results showed profound therapeutic effect of PnO-DBS on voiding functions and bladder control on TBI rats.