The spectrum of traumatic axonal injury

Glycolytic preconditioning in astrocytes mitigates trauma-induced neurodegeneration

Concussion is associated with a myriad of deleterious immediate and long-term consequences. Yet the molecular mechanisms and genetic targets promoting the selective vulnerability of different neural subtypes to dysfunction and degeneration remain unclear. Translating experimental models of blunt force trauma in C. elegans to concussion in mice, we identify a conserved neuroprotective mechanism in which reduction of mitochondrial electron flux through complex IV suppresses trauma-induced degeneration of the highly vulnerable dopaminergic neurons. Reducing cytochrome C oxidase function elevates mitochondrial-derived reactive oxygen species, which signal through the cytosolic hypoxia inducing transcription factor, Hif1a, to promote hyperphosphorylation and inactivation of the pyruvate dehydrogenase, PDHE1α. This critical enzyme initiates the Warburg shunt, which drives energetic reallocation from mitochondrial respiration to astrocyte-mediated glycolysis in a neuroprotective manner. These studies demonstrate a conserved process in which glycolytic preconditioning suppresses Parkinson-like hypersensitivity of dopaminergic neurons to trauma-induced degeneration via redox signaling and the Warburg effect.

Concussion is a type of traumatic brain injury that results from a sudden blow or jolt to the head. Symptoms can include a passing headache, dizziness, confusion or sensitivity to light, but experiencing multiple concussions can have drastic repercussions in later life.

Studies of professional athletes have shown that those who experience one or more concussions are prone to developing Alzheimer’s and Parkinson’s disease, two well-known neurodegenerative diseases. Both conditions involve the progressive loss or breakdown of nerve cells, called neurons. But exactly how this so-called neurodegeneration of brain cells stems from the original, physical injury remains unclear.

Head trauma may cause damage to the structural support of a cell or disrupt the flow of electrical impulses through neurons. Energy use and production in damaged cells could shift into overdrive to repair the damage. The chemical properties of different types of brain cells could also make some more vulnerable to trauma than others. Besides neurons, star-shaped support cells in the brain called astrocytes, which may have some protective ability, could also be affected.

To investigate which cells may be more susceptible to traumatic injuries, Solano Fonseca et al. modelled the impacts of concussion-like head trauma in roundworms (C. elegans) and mice. In both animals, one type of neuron was extremely vulnerable to cell death after trauma. Neurons that release dopamine, a chemical involved in cell-to-cell communication and the brain’s reward system, showed signs of cell damage and deteriorated after injury. Dopaminergic cells, as these cells are called, are involved in motor coordination, and the loss of dopaminergic cells has been linked to both Alzheimer’s and Parkinson’s disease.

Astrocytes, however, had a role in reducing the death of dopaminergic neurons after trauma. In experiments, astrocytes appeared to restore the balance of energy production to meet the increased energy demands of impacted neurons. Single-cell analyses showed that genes involved in metabolism were switched on in astrocytes to produce energy via an alternative pathway. This energetic shift facilitated via astrocytes may help mitigate against some damage to dopamine-producing neurons after trauma, reducing cell death.

This work furthers our understanding of cellular changes in the concussed brain. More research will be required to better characterise how this immediate trauma to cells, and the subsequent loss of dopaminergic neurons, impacts brain health long-term. Efforts to design effective therapies to slow or reverse these changes could then follow.

Semiquantitation of Axonal Injury in Traumatically Damaged Brains Using Color Deconvolution

INTRODUCTION

In traumatic brain injury biomechanics, macroscale biomechanical events need to be correlated with microscale neuropathologic changes and improved quantitation of microscopic axonal injury is an essential component of lesion evaluation.

OBJECTIVES

To develop a novel technique for automatically identifying injured amyloid precursor protein immunopositive axons and aggregating these observations over a macroscopic brain dissection.

METHODS

A color deconvolution method was adapted into Matlab to identify clusters of pixels with colors typical of amyloid precursor protein positive tissue from large-scale brain dissection.

RESULTS

The methodology is demonstrated in the brain of a sheep subjected to a controlled cortical indentation.

CONCLUSIONS

The technique will be of interest to pathologists and bioengineers seeking to quantitate brain injury over macroscales.

Erythropoietin attenuates axonal injury after middle cerebral artery occlusion in mice

OBJECTIVE

Erythropoietin (EPO) confers potent neuroprotection against ischemic injury through a variety of mechanisms. However, the protective effect of EPO on axons after cerebral ischemia in adult mice is rarely covered. The purpose of this study was to investigate the potential neuroprotective effects of EPO on axons in mice after cerebral ischemia.

METHODS

A total of 30 adult male C57 BL/6 mice were treated with EPO (5000 IU/kg) or vehicle after transient middle cerebral artery occlusion (MCAO). The mortality rate of each experimental group was calculated. Neurological function was assessed by Rota-rod test. Frozen sections from each mouse brain at 14 days after reperfusion were used to evaluate the fluorescent intensity of myelin basic protein (MBP) and neurofilament 200 (NF-200). Immunofluorescence staining and Western blotting were used to assess the protein level of β-amyloid precursor protein (β-APP) and glial fibrillary acidic protein (GFAP), a marker of mature astrocytes. The protein levels of the myelin-derived growth inhibitory proteins, neurite growth inhibitor-A (Nogo-A), myelin-associated glycoprotein (MAG) and oligodendrocyte-myelin glycoprotein (OMG) were also examined by Western blot after MCAO.

RESULTS

The survival rate of the vehicle group 14 days after cerebral ischemia-reperfusion was 50%, which increased to 80% after EPO treatment at the start of reperfusion. EPO improved neurobehavioral outcomes at days 3 and 7 after MCAO was compared with the vehicle group (P < 0.05). Furthermore, EPO ameliorated demyelination, demonstrated by upregulation of the MBP/NF-200 ratio. Meanwhile, increased levels of β-APP, GFAP, Nogo-A, and MAG after MCAO were reduced by EPO treatment (P < 0.05).

CONCLUSION

EPO treatment attenuates axonal injury and improves neurological function after cerebral ischemia in adult mice.

Diffuse Axonal Injury: An Important Form of Traumatic Brain Damage

Diffuse axonal injury (DAI) is a frequent form of traumatic brain injury in which a clinical spectrum of in creasing injury severity is paralleled by progressively increasing amounts of axonal damage in the brain. When less severe, DAI is associated with concussive syndromes; when most severe, it causes prolonged traumatic coma that is not related to mass lesions, increased intracranial pressure, or ischemia. Pathological investigations of DAI demonstrate widespread but heterogeneous microscopic damage to axons throughout the white matter of the cerebral and cerebellar hemispheres and brainstem. There is a propensity for injury to occur in the central third of the brain, and the corpus callosum and brain stem are especially prone to injury. In these locations, traumatic axonal damage can occur in several degrees of severity, ranging from transient disturbances of ionic homeostasis to swelling, impairment of axoplasmic transport with secondary (delayed) axotomy and primary axotomy (tearing). A more detailed understanding of the processes involved in axonal damage is crucial to the development of effective treatment for the clinical syndromes of DAI. NEUROSCIENTIST 4:202-215, 1998

Diffuse Axonal Injury-A Distinct Clinicopathological Entity in Closed Head Injuries

The knowledge about the diffuse axonal injury (DAI) as a clinicopathological entity has matured in the last 30 years. It has been defined clinically (immediate and prolonged unconsciousness leading to death or severe disability) and pathologically (the triad of DAI specific changes). In terms of its biomechanics, DAI is occurring as a result of acceleration forces of longer duration and has been fully reproduced experimentally.In the process of diagnosing DAI, the performance of a complete forensic neuropathological examination is essential and the immunohistochemistry method using antibodies against β-amyloid precursor protein (β-APP) has been proved to be highly sensitive and specific, selectively targeting the damaged axons.In this review, we are pointing to the significant characteristics of DAI as a distinct clinicopathological entity that can cause severe impairment of the brain function, and in the forensic medicine setting, it can be found as the concrete cause of death. We are discussing not only its pathological feature, its mechanism of occurrence, and the events on a cellular level but also the dilemmas about DAI that still exist in science: (1) regarding the strict criteria for its diagnosis and (2) regarding its biomechanical significance, which can be of a big medicolegal importance.

Autophagy Modulation by Lanthionine Ketimine Ethyl Ester Improves Long-Term Outcome after Central Fluid Percussion Injury in the Mouse

Diffuse axonal injury is recognized as a progressive and long-term consequence of traumatic brain injury. Axonal injury can have sustained negative consequences on neuronal functions such as anterograde and retrograde transport and cellular processes such as autophagy that depend on cytoarchitecture and axon integrity. These changes can lead to somatic atrophy and an inability to repair and promote plasticity. Obstruction of the autophagic process has been noted after brain injury, and rapamycin, a drug used to stimulate autophagy, has demonstrated positive effects in brain injury models. The optimization of drugs to promote beneficial autophagy without negative side effects could be used to attenuate traumatic brain injury and promote improved outcome. Lanthionine ketimine ethyl ester, a bioavailable derivative of a natural sulfur amino acid metabolite, has demonstrated effects on autophagy both in vitro and in vivo. Thirty minutes after a moderate central fluid percussion injury and throughout the survival period, lanthionine ketimine ethyl ester was administered, and mice were subsequently evaluated for learning and memory impairments and biochemical and histological changes over a 5-week period. Lanthionine ketimine ethyl ester, which we have shown previously to modulate autophagy markers and alleviate pathology and slow cognitive decline in the 3 × TgAD mouse model, spared cognition and pathology after central fluid percussion injury through a mechanism involving autophagy modulation.

Forensic Pathology of Traumatic Brain Injury

Traumatic brain injury constitutes a significant proportion of cases requiring forensic examination, and it encompasses (1) blunt, nonmissile head injury, especially involving motor vehicle accidents, and (2) penetrating, missile injury produced by a range of high- and lower-velocity projectiles. This review examines the complex pathophysiology and biomechanics of both types of neurotrauma and assesses the macroscopic and histologic features of component lesions, which may be used to determine the cause and manner of death resulting from an intentional assault or accident. Estimation of the survival time postinjury by pathologic examination is also important where malicious head injury is suspected, in an attempt to ascertain a time at which the traumatic event might have been committed, thereby evaluating the authenticity of statements made by the alleged perpetrator.

Effect of stab injury in the rat cerebral cortex on temporal pattern of expression of neuronal cytoskeletal proteins: an immunohistochemical study

Compelling evidence now points to the critical role of the cytoskeleton in neurodegeneration. In the present study, using an immunohistochemical approach, we have shown that cortical stab injury (CSI) in adult Wistar rats significantly affects temporal pattern of expression of neurofilament proteins (NFs), a major cytoskeleton components of neurons, and microtubule-associated proteins (MAP2). At 3 days post-injury (dpi) most of the NFs immunoreactivity was found in pyknotic neurons and in fragmentized axonal processes in the perilesioned cortex. These cytoskeletal alterations became more pronounced by 10dpi. At the subcellular level CSI also showed significant impact on NFs and MAP-2 expression. Thus, at 3dpi most of the dendrites disappeared, while large neuronal somata appeared like open circles pointing to membrane disintegration. Conversely, at 10dpi neuronal perikarya and a few new apical dendrites were strongly labeled. Since aberrant NF phosphorylation is a pathological hallmark of many human neurodegenerative disorders, as well as is found after stressor stimuli, the present results shed light into the expression of neurofilaments after the stab brain injury.

Considerations for return to work following traumatic brain injury

Population-based studies have demonstrated that a history positive for traumatic brain injury (TBI) can result in cognitive impairment, behavioral alterations, and pain. These outcomes can and do influence occupational function, can affect others in the workplace, and raise concerns about workplace safety upon re-entry to the workplace. Risk for long-term impairment and disability can in some cases be mitigated by assessment of capabilities relative to job duties, conservative return-to-work schedules, and, in some cases, interventions to support that return. For those in occupations at high risk for brain injury, including first responders, soldiers, and construction workers, the long-term risk of brain injury as a risk factor for neurodegenerative disease must and should inform increased concern for those with repeated injuries to the brain over the course of their lifetime and career. This chapter reviews the risks of TBI, considers factors that optimize functional recovery, and discusses potential interventions and factors that aid in return to the workplace.

Pathology of traumatic brain injury

Although traumatic brain injury (TBI) is frequently encountered in veterinary practice in companion animals, livestock and horses, inflicted head injury is a common method of euthanasia in domestic livestock, and malicious head trauma can lead to forensic investigation, the pathology of TBI has generally received little attention in the veterinary literature. This review highlights the pathology and pathogenesis of cerebral lesions produced by blunt, non-missile and penetrating, missile head injuries as an aid to the more accurate diagnosis of neurotrauma cases. If more cases of TBI in animals that result in fatality or euthanasia are subjected to rigorous neuropathological examination, this will lead to a better understanding of the nature and development of brain lesions in these species, rather than extrapolating data from human studies.

Cytoskeletal protein α-II spectrin degradation in the brain of repeated blast exposed mice

Repeated blast exposures commonly induce traumatic brain injury (TBI) characterized by diffuse axonal injury (DAI). We hypothesized that degradation of cytoskeletal proteins in the brain can lead to DAI, and evaluated α-II spectrin degradation in the pathophysiology of blast-induced TBI using the tightly-coupled three repetitive blast exposure mice model with a 1-30 min window in between exposures. Degradation of α-II spectrin and the expression profiles of caspase-3 and calpain-2, the major enzymes involved in the degradation were analyzed in the frontal cortex and cerebellum using Western blotting with specific antibodies. DAI at different brain regions was evaluated by neuropathology with silver staining. Repeated blast exposures resulted in significant increases in the α-II spectrin degradation products in the frontal cortex and cerebellum compared to sham controls. Expression of active caspase-3, which degrades α-II spectrin, showed significant increase in the frontal cortex after blast exposure at all the time points studied, while cerebellum showed an acute increase which was normalized over time. The expression of another α-II spectrin degrading enzyme, calpain-2, showed a rapid increase in the frontal cortex after blast exposure and it was significantly higher in the cerebellum at later time points. Neuropathological analysis showed significant levels of DAI at the frontal cortex and cerebellum at multiple time points after repeated blast injury. In summary, repeated blast exposure results in specific degradation of α-II spectrin in the brain along with differential expression of caspase-3/calpain-2 suggesting cytoskeletal breakdown as a possible contributor of DAI after repeated blast exposure.

Analysis of functional pathways altered after mild traumatic brain injury

Concussive injury (or mild traumatic brain injury; mTBI) can exhibit features of focal or diffuse injury patterns. We compared and contrasted the cellular and molecular responses after mild controlled cortical impact (mCCI; a focal injury) or fluid percussion injury (FPI; a diffuse injury) in rats. The rationale for this comparative analysis was to investigate the brain's response to mild diffuse versus mild focal injury to identify common molecular changes triggered by these injury modalities and to determine the functional pathways altered after injury that may provide novel targets for therapeutic intervention. Microarrays containing probes against 21,792 unique messenger RNAs (mRNAs) were used to investigate the changes in cortical mRNA expression levels at 3 and 24 h postinjury. Of the 354 mRNAs with significantly altered expression levels after mCCI, over 89% (316 mRNAs) were also contained within the mild FPI (mFPI) data set. However, mFPI initiated a more widespread molecular response, with over 2300 mRNAs differentially expressed. Bioinformatic analysis of annotated gene ontology molecular function and biological pathway terms showed a significant overrepresentation of genes belonging to inflammation, stress, and signaling categories in both data sets. We therefore examined changes in the protein levels of a panel of 23 cytokines and chemokines in cortical extracts using a Luminex-based bead immunoassay and detected significant increases in macrophage inflammatory protein (MIP)-1α (CCL3), GRO-KC (CXCL1), interleukin (IL)-1α, IL-1β, and IL-6. Immunohistochemical localization of MIP-1α and IL-1β showed marked increases at 3 h postinjury in the cortical vasculature and microglia, respectively, that were largely resolved by 24 h postinjury. Our findings demonstrate that both focal and diffuse mTBI trigger many shared pathobiological processes (e.g., inflammatory responses) that could be targeted for mechanism-based therapeutic interventions.

Differential effects of FK506 on structural and functional axonal deficits after diffuse brain injury in the immature rat

Diffuse axonal injury is a major component of traumatic brain injury in children and correlates with long-term cognitive impairment. Traumatic brain injury in adult rodents has been linked to a decrease in compound action potential (CAP) in the corpus callosum, but information on trauma-associated diffuse axonal injury in immature rodents is limited. We investigated the effects of closed head injury on CAP in the corpus callosum of 17-day-old rats. The injury resulted in CAP deficits of both myelinated and unmyelinated fibers in the corpus callosum between 1 and 14 days postinjury (dpi). These deficits were accompanied by intra-axonal dephosphorylation of the 200-kDa neurofilament subunit (NF200) at 1 and 3 dpi, a decrease in total NF200 at 3 dpi and axonal degeneration at 3 and 7 dpi. Although total phosphatase activity decreased at 1 dpi, calcineurin activity was unchanged. The calcineurin inhibitor, FK506, significantly attenuated the injury-induced NF200 dephosphorylation of NF200 at 3 dpi and axonal degeneration at 3 and 7 dpi but did not affect the decrease in NF200 protein levels or impaired axonal transport. FK506 had no effect on CAP deficits at 3 dpi but exacerbated the deficit in only the myelinated fibers at 7 dpi. Thus, in contrast to adult animals, FK506 treatment did not improve axonal function in brain-injured immature animals, suggesting that calcineurin may not contribute to impaired axonal function.

Comparative approach to understanding traumatic injury in the immature, postnatal brain of domestic animals

Traumatic brain injury (TBI) is a frequent occurrence in veterinary medicine, but the mechanisms leading to brain damage after a head impact are incompletely understood, particularly in the postnatal immature and still developing nervous system. This paper reviews neurotrauma studies, largely in paediatric humans and experimental animal models, in order to outline the pathophysiological and biomechanical events likely to be operative in head trauma involving domestic animal species in the postnatal period, as there is almost no other information available in the veterinary literature. Predicting the outcome of TBI is particularly difficult at this developmental time, in large part because recovery is influenced by the stage of brain maturation and neuroplasticity. An important part of the clinical management of TBI is the differentiation of primary brain damage, which occurs at the moment of head impact and is largely refractory to treatment, from the cascade of secondary events, which evolve over time and are potentially preventable and amenable to therapeutic intervention. An understanding of the causes and consequences of secondary brain damage such as hypoxia-ischaemia, brain swelling, elevated intracranial pressure, and infection is critical to limiting the resulting brain injury.

Characteristics of an explosive blast-induced brain injury in an experimental model

Mild traumatic brain injury resulting from exposure to an explosive blast is associated with significant neurobehavioral outcomes in soldiers. Little is known about the neuropathologic consequences of such an insult to the human brain. This study is an attempt to understand the effects of an explosive blast in a large animal gyrencephalic brain blast injury model. Anesthetized Yorkshire swine were exposed to measured explosive blast levels in 3 operationally relevant scenarios: simulated free field (blast tube), high-mobility multipurpose wheeled vehicle surrogate, and building (4-walled structure). Histologic changes in exposed animals up to 2 weeks after blast were compared to a group of naive and sham controls. The overall pathologic changes in all 3 blast scenarios were limited, with very little neuronal injury, fiber tract demyelination, or intracranial hemorrhage observed. However, there were 2 distinct neuropathologic changes observed: increased astrocyte activation and proliferation and periventricular axonal injury detected with β-amyloid precursor protein immunohistochemistry. We postulate that the increased astrogliosis observed may have a longer-term potential for the exacerbation of brain injury and that the pattern of periventricular axonal injury may be related to a potential for cognitive and mood disorders.

Mild head injury and sympathetic arousal: investigating relationships with decision-making and neuropsychological performance in university students

SUMMARY

The purpose of this study was to examine the relationships between neuropsychological performance, physiological arousal and decision-making in university students who have or have not reported a history of mild head injury (MHI).

METHODS

Forty-four students, 18 (41%) reporting a history of MHI, performed a design fluency task and the Iowa Gambling Task (IGT) while electrodermal activity (EDA) was recorded.

RESULTS

General cognitive ability and overall choice outcomes did not differ between groups. However, self-reported MHI severity predicted decision-making performance such that the greater the neural indices of trauma, the more disadvantageous the choices made by participants. As expected, both groups exhibited similar base levels of autonomic arousal and physiological responses to reward and punishment outcomes; however, those reporting MHI produced significantly lower levels of EDA during the anticipatory stages of decision-making.

CONCLUSIONS

Overall, these findings encourage the acceptance of head injury as being on a continuum of brain injury severity, as MHI can emulate neurophysiological and neuropsychological features of more traumatic cases and may be impacting mechanisms which sustain adaptive social decision-making.

Diffusion tensor imaging and white matter lesions at the subacute stage in mild traumatic brain injury with persistent neurobehavioral impairment

Mild traumatic brain injury (mTBI) can induce long-term behavioral and cognitive disorders. Although the exact origin of these mTBI-related disorders is not known, they may be the consequence of diffuse axonal injury (DAI). Here, we investigated whether MRI at the subacute stage can detect lesions that are associated with poor functional outcome in mTBI by using anatomical images (T(1) ) and diffusion tensor imaging (DTI). Twenty-three patients with mTBI were investigated and compared with 23 healthy volunteers. All patients underwent an MRI investigation and clinical tests between 7 and 28 days (D15) and between 3 and 4 months (M3) after injury. Patients were divided in two groups of poor outcome (PO) and good outcome (GO), based on their complaints at M3. Groupwise differences in gray matter partial volume between PO patients, GO patients and controls were analyzed using Voxel-Based Morphometry (VBM) from T(1) data at D15. Differences in microstructural architecture were investigated using Tract-Based Spatial Statistics (TBSS) and the diffusion images obtained from DTI data at D15. Permutation-based non-parametric testing was used to assess cluster significance at p < 0.05, corrected for multiple comparisons. Twelve GO patients and 11 PO patients were identified on the basis of their complaints. In PO patients, gray matter partial volume was significantly lower in several cortical and subcortical regions compared with controls, but did not differ from that of GO patients. No difference in diffusion variables was found between GO and controls. PO patients showed significantly higher mean diffusivity values than both controls and GO patients in the corpus callosum, the right anterior thalamic radiations and the superior longitudinal fasciculus, the inferior longitudinal fasciculus and the fronto-occipital fasciculus bilaterally. In conclusion, PO patients differed from GO patients by the presence of diffusion changes in long association white matter fiber tracts but not by gray matter partial volume. These results suggest that DTI at the subacute stage may be a predictive marker of poor outcome in mTBI.

αII-spectrin breakdown products (SBDPs): diagnosis and outcome in severe traumatic brain injury patients

In this study we assessed the clinical utility of quantitative assessments of alphaII-spectrin breakdown products (SBDP145 produced by calpain, and SBDP120 produced by caspase-3) in cerebrospinal fluid (CSF) as markers of brain damage and outcome after severe traumatic brain injury (TBI). We analyzed 40 adult patients with severe TBI (Glasgow Coma Scale [GCS] score 6 ng/mL) and SBDP120 levels (>17.55 ng/mL) strongly predicted death (odds ratio 5.9 for SBDP145, and 18.34 for SBDP120). The time course of SBDPs in nonsurvivors also differed from that of survivors. These results suggest that CSF SBDP levels can predict injury severity and mortality after severe TBI, and can be useful complements to clinical assessment.

Thalamic integrity underlies executive dysfunction in traumatic brain injury

OBJECTIVE

To quantify the effects of traumatic brain injury on integrity of thalamocortical projection fibers and to evaluate whether damage to these fibers accounts for impairments in executive function in chronic traumatic brain injury.

METHODS

High-resolution (voxel size: 0.78 mm x 0.78 mm x 3 mm(3)) diffusion tensor MRI of the thalamus was conducted on 24 patients with a history of single, closed-head traumatic brain injury (TBI) (12 each of mild TBI and moderate to severe TBI) and 12 age- and education-matched controls. Detailed neuropsychological testing with an emphasis on executive function was also conducted. Fractional anisotropy was extracted from 12 regions of interest in cortical and corpus callosum structures and 7 subcortical regions of interest (anterior, ventral anterior, ventral lateral, dorsomedial, ventral posterior lateral, ventral posterior medial, and pulvinar thalamic nuclei).

RESULTS

Relative to controls, patients with a history of brain injury showed reductions in fractional anisotropy in both the anterior and posterior corona radiata, forceps major, the body of the corpus callosum, and fibers identified from seed voxels in the anterior and ventral anterior thalamic nuclei. Fractional anisotropy from cortico-cortico and corpus callosum regions of interest did not account for significant variance in neuropsychological function. However, fractional anisotropy from the thalamic seed voxels did account for variance in executive function, attention, and memory.

CONCLUSIONS

The data provide preliminary evidence that traumatic brain injury and resulting diffuse axonal injury results in damage to the thalamic projection fibers and is of clinical relevance to cognition.

Mechanical membrane injury induces axonal beading through localized activation of calpain

Diffuse axonal injury (DAI), a major component of traumatic brain injury, is characterized by a sequence of neurochemical reactions initiated at the time of trauma and resulting in axonal degeneration and cell death. Calcium influx through mechanically induced axolemmal pores and subsequent activation of calpains are thought to be responsible for the cytoskeletal damage leading to impaired axonal transport. Focal disruption of cytoskeleton accompanied by the accumulation of transported membranous cargo leads to axonal beading which is the characteristic morphology of DAI. By applying fluid shear stress injury on cultured primary neurons, acute calcium (Ca(2+)) and calpain responses of axons to mechanical trauma were investigated. Intracellular Ca(2+) concentration ([Ca(2+)](i)) shows a steady increase following injury that can be blocked by sealing membrane pores with Poloxamer 188 and by chelating intra- or extracellular Ca(2+). Calpain activity increases in response to mechanical injury and this increase depends on Ca(2+) availability and on axolemmal permeability. Both the [Ca(2+)](i) increase and calpain activity exhibit focal peaks along the axons which co-localize with mitochondria and predict future axonal bead locations. These findings suggest that mechanoporation may be the initiating mechanism resulting in ensuing calcium fluxes and subsequent calpain activity and that post-injury membrane repair may be a valid therapeutic approach for acute intervention in DAI.

Cumulative effects of concussion in amateur athletes

PRIMARY OBJECTIVE

To examine the possibility that athletes with multiple concussions show cumulative effects of injury.

METHODS AND PROCEDURES

Amateur athletes with a history of three or more concussions were carefully matched (gender, age, education and sport) with athletes with no prior concussions. All completed a computerized neuropsychological test battery at preseason (ImPACT) and then within 5 days of sustaining a concussion (mean = 1.7 days).

MAIN OUTCOMES AND RESULTS

There were differences between groups in symptom reporting and memory performance. At baseline (i.e. preseason), athletes with multiple concussions reported more symptoms than athletes with no history of concussion. At approximately 2 days post-injury, athletes with multiple concussions scored significantly lower on memory testing than athletes with a single concussion. Athletes with multiple concussions were 7.7 times more likely to demonstrate a major drop in memory perfomance than athletes with no previous concussions.

CONCLUSIONS

This study provides preliminary evidence to suggest that athletes with multiple concussions might have cumulative effects.

Impaired axonal transport and neurofilament compaction occur in separate populations of injured axons following diffuse brain injury in the immature rat

Diffuse brain injury is a leading cause of mortality in infants and children under 4 years of age and results in cognitive deficits in survivors. The anatomic basis for these behavioral deficits may be traumatic axonal injury (TAI), which manifests as impaired axonal transport (IAT) and neurofilament compaction (NFC), and may occur as a result of glutamate receptor activation. The extent of IAT and NFC was evaluated at 6, 24 and 72 h following non-contusive brain trauma in the 17 day-old rat to examine the causal relationship between these two pathologic entities; in addition, the effect of antagonists to the ionotropic glutamate receptors on TAI was evaluated. At 6 h post-injury, NFC was observed primarily in the cingulum, and appeared as swollen axons and terminal bulbs. By 24 h, swollen axons were additionally present in the corpus callosum and lateral white matter tracts, and appeared to increase in diameter. At 72 h, the extent of axonal swellings exhibiting compacted neurofilaments appeared to decrease, and was accompanied by punctate immunoreactivity within axon tracts suggestive of axonal degeneration. Although NFC was present in the same anatomical locations where axonal accumulation of amyloid precursor protein (APP) has been observed, double-label immunohistochemistry revealed no evidence of colocalization of compacted neurofilament and APP. Pre-injury treatment with either the NMDA receptor antagonist, ifenprodil, or the AMPA receptor antagonist, NBQX, had no significant effect on the extent of TAI, suggesting that excitotoxicity may not be a primary mechanism underlying TAI. Importantly, these data are indicative of the heterogeneity of mechanisms underlying TAI in the traumatically-injured immature brain.

Potential for head injuries in infants from low-height falls

OBJECT

Falls are the most common accident scenario in young children as well as the most common history provided in child abuse cases. Understanding the biomechanics of falls provides clinicians with objective data to aid in their diagnosis of accidental or inflicted trauma. The objective of this study was to determine impact forces and angular accelerations associated with low-height falls in infants.

METHODS

An instrumented anthropomorphic infant surrogate was created to measure the forces and 3D angular accelerations associated with falls from low heights (0.3-0.9 m) onto a mattress, carpet pad, or concrete.

RESULTS

Although height significantly increased peak angular acceleration (alpha(p)), change in peak-to-peak angular velocity, time duration associated with the change in velocity, and peak impact force (F(p)) for head-first drops onto a carpet pad or concrete, none of these variables were significantly affected by height when dropped onto a mattress. The alpha(p) was not significantly different for drops onto a carpet pad and concrete from 0.6 or 0.9 m due to compression of the carpet pad. Surprisingly, sagittal alpha(p) was equaled or surpassed by axial alpha(p).

CONCLUSIONS

These are the first 3D angular acceleration and impact force data available for head impact in infants from low-height falls. A future study involving a computational model of the infant head will use the loads measured in this study to predict the probability of occipital skull fracture on impact from head-first low-height falls. Together, these studies will provide data that will aid clinicians in the evaluation of accidental and inflicted head injuries, and will contribute to the design of safer environments for children.

Congenital and acquired brain injury. 1. Epidemiology, pathophysiology, prognostication, innovative treatments, and prevention

This self-directed learning module reviews the current epidemiology of traumatic brain injury (TBI), its pathophysiology, prognostication after injury, currently available innovative early approaches to diagnosis and treatment, and effective methods of prevention. It is intended to provide the rehabilitation clinician with current knowledge to accurately inform patients, families, significant others, referring physicians, and payers and to aid in clinical decision making while caring for patients after TBI.

OVERALL ARTICLE OBJECTIVE

To describe current knowledge in traumatic brain injury epidemiology, pathophysiology, prognostication, acute treatment, and prevention.

Temporal profiles of cytoskeletal protein loss following traumatic axonal injury in mice

To examine the time course and relative extent of proteolysis of neurofilament and tubulin proteins after traumatic axonal injury (TAI), anesthetized mice were subjected to optic nerve stretch injury. Immunohistochemistry confirmed neurofilament accumulation within axonal swellings at 4, 24, and 72 h postinjury (n = 4 injured and 2 sham per time point). Immunoblotting of optic nerve homogenates (n = 5 injured and 1 sham at 0.5, 4, 24 or 72 h) revealed calpain-mediated spectrin proteolytic fragments after injury. Protein levels for NF68 progressively decreased from 0.5 h to 24 h postinjury, while NF200 and alpha-tubulin levels decreased acutely (0.5-4 h), with a secondary decline at 72 h postinjury. These data demonstrate that diffusely distributed TAI is associated not only with a localized accumulation of neurofilament proteins, but also significant decreases in total cytoskeletal protein levels which may be mediated, in part, by calpains. Protection of the axonal cytoskeleton represents a potential therapeutic target for axonal damage associated with injury or neurodegenerative diseases.

Predicting Unconsciousness from a Pediatric Brain Injury Threshold

The objective of this study was to utilize tissue deformation thresholds associated with acute axonal injury in the immature brain to predict the duration of unconsciousness. Ten anesthetized 3- to 5-day-old piglets were subjected to nonimpact axial rotations (110-260 rad/s) producing graded injury, with periods of unconsciousness from 0 to 80 min. Coronal sections of the perfusion-fixed brain were immunostained with neurofilament antibody (NF-68) and examined microscopically to identify regions of swollen axons and terminal retraction balls. Each experiment was simulated with a finite element computational model of the piglet brain and the recorded head velocity traces to estimate the local tissue deformation (strain), the strain rate and their product. Using thresholds associated with 50, 80 and 90% probability of axonal injury, white matter regions experiencing suprathreshold responses were determined and expressed as a fraction of the total white matter volume. These volume fractions were then correlated with the duration of unconsciousness, assuming a linear relationship. The thresholds for 80 and 90% probability of predicting injury were found to correlate better with injury severity than those for 50%, and the product of strain and strain rate was the best predictor of injury severity (p=0.02). Predictive capacity of the linear relationship was confirmed with additional (n=13) animal experiments. We conclude that the suprathreshold injured volume can provide a satisfactory prediction of injury severity in the immature brain.

Transgenic mice that overexpress the anti-apoptotic Bcl-2 protein have improved histological outcome but unchanged behavioral outcome after traumatic brain injury

Increasing evidence suggests that apoptosis is a contributing factor to neuronal cell death in traumatic brain injury (TBI). There is increased expression, cleavage and activation of caspases as well as other proteins known to regulate apoptosis in neurons after TBI. These proteins include the proto-oncogene Bcl-2 which belongs to a family of proteins with both pro- and anti-apoptotic properties. To investigate the role of apoptosis in TBI and the importance of Bcl-2 protein on the severity and outcome of injury, Bcl-2 overexpressing transgenic and wild-type control mice were subjected to the controlled cortical impact model of TBI. There was no significant difference in the cleavage of caspase-3 or caspase-9 detected by Western blotting of hippocampal samples from transgenic or wild-type mice after TBI. Bcl-2 transgenic mice had smaller contusion volumes and increased numbers of surviving neurons in CA2 but not other regions of hippocampus compared to wild-type controls. By contrast, there was no difference in motor function determined by the round beam balance and wire grip tests between transgenic and wild-type mice after TBI. Cognitive function assessed by the Morris water maze was also not different between groups. These results suggest that overexpression of Bcl-2 is only partially neuroprotective and other members of this protein family may prove to be more important in protecting neurons from cell death.

Traumatic brain injury in the elderly: diagnostic and treatment challenges

The purpose of this review is to introduce geriatric practitioners to issues and challenges presented in the elderly after onset of traumatic brain injury (TBI). Issues discussed include the magnitude of TBI in the elderly, mechanisms of onset, issues specific to both acute and rehabilitation care for the elderly with TBI, and specific physical and behavioral manifestations of TBI that may need to be addressed on an inpatient or outpatient basis. General guidelines are provided for the diagnosis and treatment of older individuals who have TBI, with specific clinical scenarios illustrating key points.

Delayed inhibition of Nogo-A does not alter injury-induced axonal sprouting but enhances recovery of cognitive function following experimental traumatic brain injury in rats

Traumatic brain injury causes long-term neurological motor and cognitive deficits, often with limited recovery. The inability of CNS axons to regenerate following traumatic brain injury may be due, in part, to inhibitory molecules associated with myelin. One of these myelin-associated proteins, Nogo-A, inhibits neurite outgrowth in vitro, and inhibition of Nogo-A in vivo enhances axonal outgrowth and sprouting and improves outcome following experimental CNS insults. However, the involvement of Nogo-A in the neurobehavioral deficits observed in experimental traumatic brain injury remains unknown and was evaluated in the present study using the 11C7 monoclonal antibody against Nogo-A. Anesthetized, male Sprague-Dawley rats were subjected to either lateral fluid percussion brain injury of moderate severity (2.5-2.6 atm) or sham injury. Beginning 24 h post-injury, monoclonal antibody 11C7 (n=17 injured, n=6 shams included) or control Ab (IgG) (n=16 injured, n=5 shams included) was infused at a rate of 5 microl/h over 14 days into the ipsilateral ventricle using osmotic minipumps connected to an implanted cannula. Rats were assessed up to 4 weeks post-injury using tests for neurological motor function (composite neuroscore, and sensorimotor test of adhesive paper removal) and, at 4 weeks, cognition was assessed using the Morris water maze. Hippocampal CA3 pyramidal neuron damage and corticospinal tract sprouting, using an anterograde tracer (biotinylated dextran amine), were also evaluated. Brain injury significantly increased sprouting from the uninjured corticospinal tract but treatment with monoclonal antibody 11C7 did not further increase the extent of sprouting nor did it alter the extent of CA3 cell damage. Animals treated with 11C7 showed no improvement in neurologic motor deficits but did show significantly improved cognitive function at 4 weeks post-injury when compared with brain-injured, IgG-treated animals. To our knowledge, the present findings are the first to suggest that (1) traumatic brain injury induces axonal sprouting in the corticospinal tract and this sprouting may be independent of myelin-associated inhibitory factors and (2) that post-traumatic inhibition of Nogo-A may promote cognitive recovery unrelated to sprouting in the corticospinal tract or neuroprotective effects on hippocampal cell loss following experimental traumatic brain injury.

Routine and quantitative EEG in mild traumatic brain injury

This article reviews the pathophysiology of mild traumatic brain injury, and the findings from EEG and quantitative EEG (QEEG) testing after such an injury. Research on the clinical presentation and pathophysiology of mild traumatic brain injury is reviewed with an emphasis on details that may pertain to EEG or QEEG and their interpretation. Research reports on EEG and QEEG in mild traumatic brain injury are reviewed in this setting, and conclusions are drawn about general diagnostic results that can be determined using these tests. QEEG strengths and weaknesses are reviewed in the context of factors used to determine the clinical usefulness of proposed diagnostic tests. Clinical signs, symptoms, and the pathophysiologic axonal injury and cytotoxicity tend to clear over weeks or months after a mild head injury. Loss of consciousness might be similar to a non-convulsive seizure and accompanied subsequently by postictal-like symptoms. EEG shows slowing of the posterior dominant rhythm and increased diffuse theta slowing, which may revert to normal within hours or may clear more slowly over many weeks. There are no clear EEG or QEEG features unique to mild traumatic brain injury. Late after head injury, the correspondence is poor between electrophysiologic findings and clinical symptoms. Complicating factors are reviewed for the proposed commercial uses of QEEG as a diagnostic test for brain injury after concussion or mild traumatic brain injury. The pathophysiology, clinical symptoms and electrophysiological features tend to clear over time after mild traumatic brain injury. There are no proven pathognomonic signatures useful for identifying head injury as the cause of signs and symptoms, especially late after the injury.

Closed head injury-related information processing deficits: An event-related potential analysis

Event-related potentials (ERPs) can elucidate aspects of sensory and cognitive processing that have been compromised due to closed head injury. We present the results of two investigations, one previously unreported, in which we used ERPs to evaluate information processing in head-injury survivors. In the first study, we used visual and auditory reaction time tasks differing in attentional demands to assess processing after head trauma. We found numerous changes in auditory processing in survivors: longer reaction times (but normal accuracy), longer N200 and P300 latencies, and reduced N100 and N200 amplitudes. In contrast, on visual tasks, only reduced N200 amplitude distinguished survivors and controls. To increase attentional demands, in a second study, we administered the continuous performance test (CPT). Survivors performed with lower accuracy than controls on visual and auditory tasks, and their ERPs were characterized by smaller visual and auditory N200s and P300s and smaller auditory N100s. We also present a synthesis, derived from a review of the literature, of closed head-injury effects on ERPs. Our own findings are in agreement with that synthesis. Namely, cognitive ERP components are more sensitive than sensory components to the effects of trauma. Specifically, in survivors, the amplitudes of N200 and P300 are often reduced, and their latencies prolonged. In general, as compared with visual ERPs, auditory ERPs may be more susceptible to the effects of closed head injury, suggesting that the auditory processing system is more vulnerable than the visual system. We conclude by discussing the potential use of ERPs to monitor clinical course and recovery in survivors of closed head injury.

The impact of age on traumatic brain injury

Older individuals with TBI differ from younger adults with TBI in several ways, including their incidence rates, etiology of injury, nature of complications, lengths of hospitalization, functional outcomes, and mortality. Despite the greater likelihood of poorer functional outcomes, older adults with TBI often achieve good functional outcomes and can live in community settings after receiving appropriate rehabilitation services, although at higher costs and longer hospitalizations than younger individuals. The future of rehabilitation care for elderly patients after TBI is uncertain due to financial limitations associated with the implementation of the PPS payment system by CMS. Little is known regarding the long-term impact of TBI on individuals as they age, but this is an important issue as the population ages.

Axonal damage in multiple sclerosis: a complex issue in a complex disease

Multiple sclerosis is no longer considered to simply be an autoimmune demyelinating disease. Axonal destruction is another central pathological feature and a contributor to the accumulating disability of disease progression. The mechanism underlying axonal pathology has not been fully clarified but does not appear to be a simple one. The relationship between axonal damage and other components of the pathological features such as demyelination, inflammation and remyelination are under intense investigation. Experimental data suggest that therapeutic interventions such as the induction of rapid remyelination may lead to the protection of axons. In addition to immunomodulation, future strategies for neuroprotection may be of great importance.

The neurophysiology of brain injury

OBJECTIVE

This article reviews the mechanisms and pathophysiology of traumatic brain injury (TBI).

METHODS

Research on the pathophysiology of diffuse and focal TBI is reviewed with an emphasis on damage that occurs at the cellular level. The mechanisms of injury are discussed in detail including the factors and time course associated with mild to severe diffuse injury as well as the pathophysiology of focal injuries. Examples of electrophysiologic procedures consistent with recent theory and research evidence are presented.

RESULTS

Acceleration/deceleration (A/D) forces rarely cause shearing of nervous tissue, but instead, initiate a pathophysiologic process with a well defined temporal progression. The injury foci are considered to be diffuse trauma to white matter with damage occurring at the superficial layers of the brain, and extending inward as A/D forces increase. Focal injuries result in primary injuries to neurons and the surrounding cerebrovasculature, with secondary damage occurring due to ischemia and a cytotoxic cascade. A subset of electrophysiologic procedures consistent with current TBI research is briefly reviewed.

CONCLUSIONS

The pathophysiology of TBI occurs over time, in a pattern consistent with the physics of injury. The development of electrophysiologic procedures designed to detect specific patterns of change related to TBI may be of most use to the neurophysiologist.

SIGNIFICANCE

This article provides an up-to-date review of the mechanisms and pathophysiology of TBI and attempts to address misconceptions in the existing literature.

Real-time PCR quantitation of FE65 a beta-amyloid precursor protein-binding protein after traumatic brain injury in rats

In cases of traumatic brain injury (TBI) in which the patient survived for only a short period of time and was without macroscopic changes at autopsy, it is difficult to diagnose TBI. To detect early diagnostic markers of diffuse axonal injury (DAI), real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) in an experimental head trauma model of rat was chosen. The beta-amyloid precursor protein (beta-APP) is a well-known diagnostic marker of DAI which can be detected by immunolabeling as early as 1.5 h after injury. beta-APP has a binding protein, FE65, which is expressed in the brain of Alzheimer's disease patients along with beta-APP, but no involvement with brain injury has been reported. Neuron-specific enolase (NSE) is also a useful marker of DAI. We found that FE65 expression increased dramatically as early as 30 min after injury and decreased after peaking 1 h post-injury, although NSE showed no significant changes. These results suggest that real-time PCR of FE65 mRNA is useful for the diagnosis of DAI in forensic cases.

Pathology of head trauma

This article reviews the essential primary and secondary injuries attributable to traumatic brain injury (TBI) which causes one third of all injury deaths in the United States. Motor vehicle crashes, falls, assaults, guns, sports, and recreational activities are the major causes of TBI. Secondary peak incidences of TBI occur in infants and children and the elderly. Conditions that increase risk for accidents include alcoholism, prior head injury, prior meningitis, seizure disorders, mental retardation, and psychiatric disorders. However, gunshot wounds to the head are steadily increasing and since 1990 have caused more deaths each year than motor vehicle accidents. The incidence, severity, etiology, and specific types of injuries have been assessed in clinicopathologic studies of head injuries. The pathologic features of both the primary and secondary lesions attributed to TBI should be understood by anyone caring for head-injured patients. The computed tomography (CT) and magnetic resonance (MR) images mirror the pathologic abnormalities found in head trauma. Radiologists must accurately interpret the CT and MR images of injured patients. Forensic pathologists have long appreciated the characteristic focal lesions, such as coup and contracoup contusions, that occur in falls or vehicle accidents, but the understanding of diffuse injuries has been more elusive. Understanding the nature of the focal and diffuse injuries is critical to understanding the morbidity and mortality of brain injury.

The current status of electrophysiologic procedures for the assessment of mild traumatic brain injury

DESIGN

This review examines studies that used spontaneous electroencephalography (EEG), evoked potentials (EP), event-related potentials (ERP), and magnetoencephalography (MEG) to detect brain dysfunction in mild traumatic brain injured (MTBI) subjects.

CONCLUSIONS

The following conclusions are offered: (1) standard clinical EEG is not useful; however, newer analytical procedures may be proven valuable; (2) consistent with current theory of MTBI, cognitive ERPs seem to be more sensitive to injury than EPs; (3) development of an assessment battery that may include EEG, EPs, ERPs, and neuropsychologic testing is advocated.

Demyelination and axonal damage in a non-human primate model of multiple sclerosis

The demyelinating plaque is the paradigmatic lesion of multiple sclerosis (MS), but only recently attention has been given to axonal damage and to its role in the pathophysiology of disease. Albeit the possible relevance of axonal loss in MS and its experimental models, the amount and timing of axonal sufferance has been addressed only in experimental autoimmune encephalomyelitis (EAE) of rodents. In this report we observed that, in the marmoset model of EAE, axonal damage occurs early during the demyelinating process as assessed by immunoreactivity for amyloid precursor protein (APP) and non-phosphorylated neurofilaments (SMI-32 positive) detected mostly in early active lesions compared to late active and normal appearing white matter. The rare occurrence of morphological features of axonal transection, such as APP or SMI-32 positive spheroids and swellings, as well as an increase of neurofilament density in the demyelinated axons without accumulation of electron dense organelles or osmiophilic bodies, at electron microscopy, suggests that early axonal damage may be, at least in part, a reversible process. These findings are of relevance for the development of therapies, which can protect axons and enhance their function and survival.

Electrophysiological evidence for the cumulative effects of concussion

PURPOSE

A study was initiated with the intent of demonstrating the cumulative effects of concussion in junior hockey players using visual event-related potentials and post-concussion syndrome (PCS) self-reports.

METHODS

Players were assessed at the beginning of the season (pre-injury) and at various times post-injury.

RESULTS

The results suggest that players with three or more concussions differed significantly on the several cognitive PCS symptoms as well as for the latency of the P3 response compared to those with no concussion history.

DISCUSSION

Event-related potentials are useful indices of the cumulative damage that can occur following multiple concussions. These measures correlate significantly with cognitive self-reports of PCS symptoms.

CONCLUSIONS

This pattern of results is consistent with the position that each concussion potentially causes brain damage. Cumulative damage can be detected using electrophysiological measures of brain function.

Electrophysiological indices of persistent post-concussion symptoms

Mild head injuries (MHI) including concussion were once considered transient alterations of function that resulted in no long-term structural or functional effects. This opinion has changed somewhat in recent years, based on the scientific evidence and popular cases in the media that suggest MHI can result in damage that can, in some cases, lead to long-term cognitive sequelae.

PURPOSE AND METHODS

An EP/ERP assessment battery is presented as a method for detecting changes in brain function that form the organic basis of persistent post-concussion symptoms (PCS). The primary focus of the paper was directed towards using this battery to determine whether or not brain function in individuals with persistent PCS was different than responses of individuals that comprised a nomative database.

RESULTS

Visual and auditory ERPs and visual EPs were beyond a 2.5 standard deviation normal limit in young and older groups of individuals with persistent post-concussion symptoms.

CONCLUSIONS

Evidence of changes in brain function in individuals with persistent post-concussion symptoms is consistent with the position that the post-concussion syndrome has a substantial biological, as opposed to a psychological, basis.

Multiple sclerosis and chronic autoimmune encephalomyelitis: a comparative quantitative study of axonal injury in active, inactive, and remyelinated lesions

Recent magnetic resonance (MR) studies of multiple sclerosis lesions indicate that axonal injury is a major correlate of permanent clinical deficit. In the present study we systematically quantified acute axonal injury, defined by immunoreactivity for beta-amyloid-precursor-protein in dystrophic neurites, in the central nervous system of 22 multiple sclerosis patients and 18 rats with myelin-oligodendrocyte glycoprotein (MOG)-induced chronic autoimmune encephalomyelitis (EAE). The highest incidence of acute axonal injury was found during active demyelination, which was associated with axonal damage in periplaque and in the normal appearing white matter of actively demyelinating cases. In addition, low but significant axonal injury was also observed in inactive demyelinated plaques. In contrast, no significant axonal damage was found in remyelinated shadow plaques. The patterns of axonal pathology in chronic active EAE were qualitatively and quantitatively similar to those found in multiple sclerosis. Our studies confirm previous observations of axonal destruction in multiple sclerosis lesions during active demyelination, but also indicate that ongoing axonal damage in inactive lesions may significantly contribute to the clinical progression of the disease. The results further emphasize that MOG-induced EAE may serve as a suitable model for testing axon-protective therapies in inflammatory demyelinating conditions.