Extent of impaired axoplasmic transport and neurofilament compaction in traumatically injured axon at various strains and strain rates

Studying the Effects of Shoulder Dystocia and Neonate-Focused Delivery Maneuvers on Brachial Plexus Strain: A Computational Study

The purpose of this computational study was to investigate the effects of neonate-focused clinical delivery maneuvers on brachial plexus (BP) during shoulder dystocia. During shoulder dystocia, the anterior shoulder of the neonate is obstructed behind the symphysis pubis of the maternal pelvis, postdelivery of the neonate's head. This is managed by a series of clinical delivery maneuvers. The goal of this study was to simulate these delivery maneuvers and study their effects on neonatal BP strain. Using madymo models of a maternal pelvis and a 90th-percentile neonate, various delivery maneuvers and positions were simulated including the lithotomy position alone of the maternal pelvis, delivery with the application of various suprapubic pressures (SPPs), neonate in an oblique position, and during posterior arm delivery maneuver. The resulting BP strain (%) along with the required maternal delivery force was reported in these independently simulated scenarios. The lithotomy position alone served as the baseline. Each of the successive maneuvers reported a decrease in the required delivery force and resulting neonatal BP strain. As the applied SPP force increased (three scenarios simulated), the required maternal delivery force and neonatal BP strain decreased. A further decrease in both delivery force and neonatal BP strain was observed in the oblique position, with the lowest delivery force and neonatal BP strain reported during the posterior arm delivery maneuver. Data obtained from the improved computational models in this study enhance our understanding of the effects of clinical maneuvers on neonatal BP strain during complicated birthing scenarios such as shoulder dystocia.

In vivo biomechanical responses of neonatal brachial plexus when subjected to stretch

Neonatal brachial plexus palsy (NBPP) results from over-stretching of the neonatal brachial plexus during complicated birthing scenarios. The lack of information on the biomechanical response of the neonatal brachial plexus complex when subjected to stretch limits our understanding of the NBPP injury mechanism. This study aims to fill that critical gap by using a neonatal piglet animal model and providing the in vivo biomechanical properties of the neonatal brachial plexus complex when subjected to stretch. Forty-seven brachial plexus levels (identified by the four brachial plexus terminal nerve branches namely musculocutaneous, median, ulnar, and radial), obtained from 16 neonatal Yorkshire piglets (3-5 days old), were subjected to stretch-induced failure. The average maximum load and corresponding strain were reported to be 16.6 ± 1.3 N and 36.1 ± 1.6%, respectively. Maximum loads reported at the musculocutaneous level were significantly lower than the median and radial levels. No differences in strains at failure were reported at all four tested levels. Proximal or distal failure locations were reported in 83% of the tests with 17% mid-length ruptures that were primarily reported at the bifurcation of the median and ulnar brachial plexus levels. Histological studies reported an overall loss of wavy pattern of the nerve fibers, an increase in nerve spacing, fiber disruptions, and blood vessel ruptures in the stretched tissue. This in vivo piglet animal study offers insight into the NBPP mechanism by reporting biomechanical, injury location, and structural damage responses in neonatal brachial plexus when subjected to stretch.

Axons-on-a-chip for mimicking non-disruptive diffuse axonal injury underlying traumatic brain injury

Diffuse axonal injury (DAI) is the most severe pathological feature of traumatic brain injury (TBI). However, how primary axonal injury is induced by transient mechanical impacts remains unknown, mainly due to the low temporal and spatial resolution of medical imaging approaches. Here we established an axon-on-a-chip (AoC) model for mimicking DAI and monitoring instant cellular responses. Integrating computational fluid dynamics and microfluidic techniques, DAI was induced by injecting a precisely controlled micro-flux in the transverse direction. The clear correlation between the flow speed of injecting flux and the severity of DAI was elucidated. We next used the AoC to investigate the instant intracellular responses underlying DAI and found that the dynamic formation of focal axonal swellings (FAS) accompanied by Ca²⁺ surge occurs during the flux. Surprisingly, periodic axonal cytoskeleton disruption also occurs rapidly after the flux. These instant injury responses are spatially restricted to the fluxed axon, not affecting the overall viability of the neuron in the acute stage. Compatible with high-resolution live microscopy, the AoC provides a versatile system to identify early mechanisms underlying DAI, offering a platform for screening effective treatments to alleviate TBI.

Effects of Prestretch on Neonatal Peripheral Nerve: An In Vitro Study

Background  Characterizing the biomechanical failure responses of neonatal peripheral nerves is critical in understanding stretch-related peripheral nerve injury mechanisms in neonates. Objective  This in vitro study investigated the effects of prestretch magnitude and duration on the biomechanical failure behavior of neonatal piglet brachial plexus (BP) and tibial nerves. Methods  BP and tibial nerves from 32 neonatal piglets were harvested and prestretched to 0, 10, or 20% strain for 90 or 300 seconds. These prestretched samples were then subjected to tensile loading until failure. Failure stress and strain were calculated from the obtained load-displacement data. Results  Prestretch magnitude significantly affected failure stress but not the failure strain. BP nerves prestretched to 10 or 20% strain, exhibiting significantly lower failure stress than those prestretched to 0% strain for both prestretch durations (90 and 300 seconds). Likewise, tibial nerves prestretched to 10 or 20% strain for 300 seconds, exhibiting significantly lower failure stress than the 0% prestretch group. An effect of prestretch duration on failure stress was also observed in the BP nerves when subjected to 20% prestretch strain such that the failure stress was significantly lower for 300 seconds group than 90 seconds group. No significant differences in the failure strains were observed. When comparing BP and tibial nerve failure responses, significantly higher failure stress was reported in tibial nerve prestretched to 20% strain for 300 seconds than BP nerve. Conclusion  These data suggest that neonatal peripheral nerves exhibit lower injury thresholds with increasing prestretch magnitude and duration while exhibiting regional differences.

Calpain Inhibitors as Potential Therapeutic Modulators in Neurodegenerative Diseases

It is considered a significant challenge to understand the neuronal cell death mechanisms with a suitable cure for neurodegenerative disorders in the coming years. Calpains are one of the best-considered "cysteine proteases activated" in brain disorders. Calpain is an important marker and mediator in the pathophysiology of neurodegeneration. Calpain activation being the essential neurodegenerative factor causing apoptotic machinery activation, it is crucial to develop reliable and effective approaches to prevent calpain-mediated apoptosis in degenerating neurons. It has been recently seen that the "inhibition of calpain activation" has appeared as a possible therapeutic target for managing neurodegenerative diseases. A systematic literature review of PubMed, Medline, Bentham, Scopus, and EMBASE (Elsevier) databases was conducted. The present article reviews the basic pathobiology and role of selective calpain inhibitors used in various neurodegenerative diseases as a therapeutic target.

A Systematic Review of the Tensile Biomechanical Properties of the Neonatal Brachial Plexus

Brachial plexus (BP) birth injury has a reported incidence of 1 to 4 per 1000 live births. During complicated deliveries, neonatal, maternal, and other birth-related factors can cause over-stretching or avulsion of the neonatal brachial plexus leading to injury. Understanding biomechanical responses of the neonate brachial plexus when subjected to stretch can offer insight into the injury outcomes while guiding the development of preventative maneuvers that can help reduce the occurrence of neonatal brachial plexus injuries. This review article aims to offer a comprehensive overview of existing literature reporting biomechanical responses of the brachial plexus, in both adults and neonates, when subjected to stretch. Despite the discrepancies in the reported biomechanical properties of the brachial plexus, available studies confirm the loading rate and loading direction dependency of the brachial plexus tissue. Future studies, possibly in vivo, that utilize clinically relevant neonatal large animal models can provide translational failure values of the biomechanical parameters for the neonatal brachial plexus when subjected to stretch.

Embedded axonal fiber tracts improve finite element model predictions of traumatic brain injury

With the growing rate of traumatic brain injury (TBI), there is an increasing interest in validated tools to predict and prevent brain injuries. Finite element models (FEM) are valuable tools to estimate tissue responses, predict probability of TBI, and guide the development of safety equipment. In this study, we developed and validated an anisotropic pig brain multi-scale FEM by explicitly embedding the axonal tract structures and utilized the model to simulate experimental TBI in piglets undergoing dynamic head rotations. Binary logistic regression, survival analysis with Weibull distribution, and receiver operating characteristic curve analysis, coupled with repeated k-fold cross-validation technique, were used to examine 12 FEM-derived metrics related to axonal/brain tissue strain and strain rate for predicting the presence or absence of traumatic axonal injury (TAI). All 12 metrics performed well in predicting of TAI with prediction accuracy rate of 73-90%. The axonal-based metrics outperformed their rival brain tissue-based metrics in predicting TAI. The best predictors of TAI were maximum axonal strain times strain rate (MASxSR) and its corresponding optimal fraction-based metric (AF-MASxSR7.5) that represents the fraction of axonal fibers exceeding MASxSR of 7.5 s-1. The thresholds compare favorably with tissue tolerances found in in-vitro/in-vivo measurements in the literature. In addition, the damaged volume fractions (DVF) predicted using the axonal-based metrics, especially MASxSR (DVF = 0.05-4.5%), were closer to the actual DVF obtained from histopathology (AIV = 0.02-1.65%) in comparison with the DVF predicted using the brain-related metrics (DVF = 0.11-41.2%). The methods and the results from this study can be used to improve model prediction of TBI in humans.

Head Rotational Kinematics, Tissue Deformations, and Their Relationships to the Acute Traumatic Axonal Injury

Head rotational kinematics and tissue deformation metrics obtained from finite element models (FEM) have the potential to be used as traumatic axonal injury (TAI) assessment criteria and headgear evaluation standards. These metrics have been used to predict the likelihood of TAI occurrence; however, their ability in the assessment of the extent of TAI has not been explored. In this study, a pig model of TAI was used to examine a wide range of head loading conditions in two directions. The extent of TAI was quantified through histopathology and correlated to the FEM-derived tissue deformations and the head rotational kinematics. Peak angular acceleration and maximum strain rate of axonal fiber and brain tissue showed relatively good correlation to the volume of axonal injury, with similar correlation trends for both directions separately or combined. These rotational kinematics and tissue deformations can estimate the extent of acute TAI. The relationships between the head kinematics and the tissue strain, strain rate, and strain times strain rate were determined over the experimental range examined herein, and beyond that through parametric simulations. These relationships demonstrate that peak angular velocity and acceleration affect the underlying tissue deformations and the knowledge of both help to predict TAI risk. These relationships were combined with the injury thresholds, extracted from the TAI risk curves, and the kinematic-based risk curves representing overall axonal and brain tissue strain and strain rate were determined for predicting TAI. After scaling to humans, these curves can be used for real-time TAI assessment.

Apolipoprotein E Affects In Vitro Axonal Growth and Regeneration via the MAPK Signaling Pathway

Following central nervous system injury in mammals, failed axonal regeneration is closely related to dysneuria. Previous studies have shown that the obvious effects of apolipoprotein E (ApoE) on traumatic brain injury (TBI) were associated with an axonal mechanism. However, little information on the actions of ApoE and its isoforms on axonal regeneration following TBI was provided. In our study, the cerebral cortices of ApoE-deficient (ApoE^-/-) and wild-type (ApoE^+/+) mice were cultured in vitro, and an axonal transection model was established. Interventions included the conditioned medium of astrocytes, human recombinant ApoE2/3/4 isoforms and inhibitors of the JNK/ERK/p38 pathway. Axonal growth and regeneration were evaluated by measuring the maximum distance and area of the axons. The expression levels of β-tubulin III, MAP2, ApoE, p-JNK, p-ERK and p-p38 were detected by immunofluorescence and western blotting. The results showed that ApoE mRNA and protein were expressed in intact axons and regenerated axons. Axonal growth and regeneration were attenuated in ApoE^-/- mice but recovered by exogenous ApoE. Human recombinant ApoE3 positively influenced axonal growth and regeneration; these effects were mediated by the JNK/ERK/p38 pathway. These results suggest ApoE and its isoforms may have influenced axonal growth and regeneration via the MAPK signaling pathway in vitro.