Severe Axonal Injury Research Articles

Tumor microenvironment (Part I): Tissue integrity in a rat model of peripheral neural cancer

ICAM–1 (intercellular adhesion molecule 1) and MPZ (myelin protein zero) are thought to be a factor in the integrity of nerve tissues. In this report, we attempted to trace the expression of ICAM–1, responsible for cell-to-cell adhesion, and of MPZ, the main constituent of myelin sheath, in malignant tissues of the sciatic nerve (SN) in inbred male Copenhagen rats. AT–1 Cells (anaplastic tumor 1) were injected in the perineurial sheath, and tissues of the SNs were collected after 7, 14 and 21 days and compared to a sham-operated group of rats (n = 6 each). Tissues were sectioned and histologically examined, under light microscope, and stained for measuring the immunoreactivity of ICAM–1 and MPZ under laser scanning microscope. The cancer model was established, and the tumor growth was confirmed. ICAM–1 showed severe decreases, proportional to the growing anaplastic cells, as compared to the sham group. MPZ revealed, however, a distinct defensive pattern before substantially decreasing in a comparison with sham. These results support the notion that malignancies damage peripheral nerves and cause severe axonal injury and loss of neuronal integrity, and clearly define the role of ICAM–1 and MPZ in safeguarding the nerve tissues.

Role of integrin and its potential as a novel postmortem biomarker in traumatic axonal injury.

Traumatic axonal injury (TAI) accounts for a large proportion of the mortality of traumatic brain injury (TBI). The diagnosis of TAI is currently of limited use for medicolegal purposes. It is known that axons in TAI are diffusely damaged by secondary processes other than direct head injury. However, the physiopathological mechanism of TAI is still elusive. The present study used RGD peptide, an antagonist of the mechanotransduction protein integrin, to explore the role of integrin-transmitted mechanical signalling in the pathogenesis of rat TAI. The rats were subjected to a linearly accelerating load, and changes in beta-amyloid precursor protein (β-APP) expression, skeleton ultrastructure, skeleton protein neurofilament light (NF-L), and α-tubulin in the brainstem were observed, indicating that RGD could relieve the severity of axonal injury in TAI rats. In addition, the expression of β-integrin was stronger and centralized in the brainstem of the deceased died from TAI compared to other nonviolent causes. This study examined the pathophysiology and biomechanics of TAI and assessed the role of integrin in the injury of microtubules and neurofilaments in TAI. Thus, we propose that integrin-mediated cytoskeletal injury plays an important role in TAI and that integrin has the potential as a biomarker for TAI.

Very low peroneal nerve compound muscle action potential amplitude predicts poor outcome in patients with Guillain-Barré syndrome: a prospective cohort.

Twenty percent of patients with Guillain-Barré syndrome (GBS) have poor outcomes despite proper management. The aim of the study was to characterize electrophysiological factors related to poor outcome in patients with GBS. We conducted an observational study from a prospective cohort of 91 patients with GBS in a tertiary healthcare center in Mexico, from 2017 to 2019. Demographics and nerve conduction studies were performed on admission, and a 3-month follow-up for GBS disability score was ensued, allocating patients in good (GBS disability score ≤ 2) and poor outcome (GBS disability score ≥ 3) groups. A logistic regression analysis for independent walk at 3months was performed. Kaplan-Meier estimator curves for independent walk in very low (< 20% LLN) and low-normal ( ≥20% LLN) peroneal nerve CMAPs are presented. From the 91 GBS patients included, 37 (40.6%) did not regain independent walk at 3months. Axonal variants were more common in the poor outcome group (31.4% vs 59.4%, p = 0.01) as well as AIDP variants with motor conduction block (6.6% vs 42.4%, p = 0.018). Univariable analysis was statistically significant for very low median, ulnar, tibial, and peroneal CMAP amplitudes in poor outcome patients; however, multivariable analysis was only significant for very low peroneal nerve CMAP amplitude (OR 3.6 [1.1-11.5, p = 0.024]). Conversely, a greater proportion of GBS patients with low-normal CMAPs recovered independent walk at 90days (75% vs 30%, p < 0.001). Severe axonal injury of the peroneal nerve, axonal, and AIDP with motor conduction block variants predicts worse functional outcome regarding independent walk at 3months.

Science, Medicine, and the Anesthesiologist

Science, Medicine, and the Anesthesiologist

Intracellular Recordings of Postsynaptic Voltage Responses at the Drosophila Neuromuscular Junction.

Axonal damage can cause a loss of neural control of target peripheral muscles and other organs. The hallmark of complete recovery from severe axonal injury is a successful return of function. To assay the degree of functional loss or recovery from injury, a measurement of electrical communication at the nerve-target junction can be used. Drosophila larval neuromuscular junction (NMJ) provides a genetically tractable and easily accessible model to measure the electrophysiological properties of the synapse. To study the functional consequences of injuries to the peripheral nerve, we describe the procedure to measure the spontaneous and evoked response to neurotransmitter release at the NMJ.

Laquinimod Supports Remyelination in Non-Supportive Environments.

Inflammatory demyelination, which is a characteristic of multiple sclerosis lesions, leads to acute functional deficits and, in the long term, to progressive axonal degeneration. While remyelination is believed to protect axons, the endogenous-regenerative processes are often incomplete or even completely fail in many multiple sclerosis patients. Although it is currently unknown why remyelination fails, recurrent demyelination of previously demyelinated white matter areas is one contributing factor. In this study, we investigated whether laquinimod, which has demonstrated protective effects in active multiple sclerosis patients, protects against recurrent demyelination. To address this, male mice were intoxicated with cuprizone for up to eight weeks and treated with either a vehicle solution or laquinimod at the beginning of week 5, where remyelination was ongoing. The brains were harvested and analyzed by immunohistochemistry. At the time-point of laquinimod treatment initiation, oligodendrocyte progenitor cells proliferated and maturated despite ongoing demyelination activity. In the following weeks, myelination recovered in the laquinimod- but not vehicle-treated mice, despite continued cuprizone intoxication. Myelin recovery was paralleled by less severe microgliosis and acute axonal injury. In this study, we were able to demonstrate that laquinimod, which has previously been shown to protect against cuprizone-induced oligodendrocyte degeneration, exerts protective effects during oligodendrocyte progenitor differentiation as well. By this mechanism, laquinimod allows remyelination in non-supportive environments. These results should encourage further clinical studies in progressive multiple sclerosis patients.

Tau progression in single severe frontal traumatic brain injury in human brains

The neuropathological features of chronic traumatic encephalopathy (CTE), caused by repeated traumatic brain injury (TBI), include abnormal accumulations of hyper-phosphorylated tau (p-tau) protein in neurons, neurites and astrocytes, considered to progress via neuronal circuits in brains. Some previous reports suggest that a single severe TBI (sTBI) can also induce CTE and p-tau accumulation, but it is not clear whether the pathology is the same as that of repetitive TBI (rTBI). Since prefrontal leucotomy could be regarded as a model of sTBI, in this study we evaluated two autopsied schizophrenia with this procedure. Histopathologically, gliosis and neuronal loss were found not only in the primary ablated prefrontal region, but also in secondary affected areas, i.e., cingulate gyrus, medial nucleus of the thalamus, and nucleus accumbens, which are connected to prefrontal areas. Accumulation of p-tau was mostly seen in neurons, neurites and glias around small blood vessels in the leucotomized prefrontal region. In addition, secondary regions showed some p-tau-positive neurons/glias, as well as many axonal spheroids. Regions of neuronal/glial p-tau pathology showed immunoreactivity to both 3R/4R tau antibodies. Immunoblot analyses of sarkosyl-insoluble tau from frozen brains showed an AD-type tau banding pattern with strong immunoreactivities. sTBI patients showed limited comorbidities, such as TDP-43, alpha-synuclein or AD pathology, whereas rTBI patients have high frequencies of them. The findings suggest that p-tau in the primary affected lesion might progress to connected regions via neuronal circuits over time, and a single severe axonal injury might lead to CTE pathology different from that caused by rTBI.

Noninvasive Quantification of Axonal Loss in the Presence of Tissue Swelling in Traumatic Spinal Cord Injury Mice

Neuroimaging plays an important role in assessing axonal pathology after traumatic spinal cord injury. However, coexisting inflammation confounds imaging assessment of the severity of axonal injury. Herein, we applied diffusion basis spectrum imaging (DBSI) to quantitatively differentiate and quantify underlying pathologies in traumatic spinal cord injury at 3 days post-injury. Results reveal that DBSI was capable of detecting and differentiating axonal injury, demyelination, and inflammation-associated edema and cell infiltration in contusion-injured spinal cords. DBSI was able to detect and quantify axonal loss in the presence of white matter tract swelling. The DBSI-defined apparent axonal volume correlated with the corresponding histological markers. DBSI-derived pathological metrics could serve as neuroimaging biomarkers to differentiate and quantify coexisting white matter pathologies in spinal cord injury, providing potential surrogate outcome measures to assess spinal cord injury progression and response to therapies.

Localized cortical chronic traumatic encephalopathy pathology after single, severe axonal injury in human brain

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with repetitive mild impact traumatic brain injury from contact sports. Recently, a consensus panel defined the pathognomonic lesion for CTE as accumulations of abnormally hyperphosphorylated tau (p-tau) in neurons (neurofibrillary tangles), astrocytes and cell processes distributed around small blood vessels at sulcal depths in irregular patterns within the cortex. The pathophysiological mechanism for this lesion is unknown. Moreover, a subset of CTE cases harbors cortical β-amyloid plaques. In this study, we analyzed postmortem brain tissues from five institutionalized patients with schizophrenia and history of surgical leucotomy with subsequent survival of at least another 40 years. Because leucotomy involves severing axons bilaterally in prefrontal cortex, this surgical procedure represents a human model of single traumatic brain injury with severe axonal damage and no external impact. We examined cortical tissues at the leucotomy site and at both prefrontal cortex rostral and frontal cortex caudal to the leucotomy site. For comparison, we analyzed brain tissues at equivalent neuroanatomical sites from non-leucotomized patients with schizophrenia, matched in age and gender. All five leucotomy cases revealed severe white matter damage with dense astrogliosis at the axotomy site and also neurofibrillary tangles and p-tau immunoreactive neurites in the overlying gray matter. Four cases displayed p-tau immunoreactivity in neurons, astrocytes and cell processes encompassing blood vessels at cortical sulcal depths in irregular patterns, similar to CTE. The three cases with apolipoprotein E ε4 haplotype showed scattered β-amyloid plaques in the overlying gray matter, but not the two cases with apolipoprotein E ε3/3 genotype. Brain tissue samples from prefrontal cortex rostral and frontal cortex caudal to the leucotomy site, and all cortical samples from the non-leucotomized patients, showed minimal p-tau and β-amyloid pathology. These findings suggest that chronic axonal damage contributes to the unique pathology of CTE over time.

Future treatment for Guillain–Barré syndrome

AbstractPlasma exchange and intravenous immunoglobulin were established to be effective treatments for Guillain–Barré syndrome (GBS) in the 1980s and 1990s, respectively. However, even when treated with the currently best therapy available, the mortality rate is still approximately 5%, and approximately 20% of patients cannot walk unaided 6 months after onset. Therefore, many GBS patients still develop severe weakness and have a long disease course, often with pain and fatigue as a result of persistent axonal loss. A better treatment is required. A clinical trial of a second immunoglobulin is ongoing. Eculizumab, a humanized monoclonal antibody against complement C5, is a promising novel agent, and phase 1/2 trials are ongoing in Japan (Japanese Eculizumab Trial for GBS) and Scotland (Inhibition of Compliment Activation for GBS). Immunoglobulin G‐degrading enzyme of Streptococcus pyogenes is another promising agent, and a phase 2 trial is planned. Prevention of severe axonal injury with new treatments early in the course of this disease remains a major focus, because axonal degeneration is an important limiting factor in achieving a good outcome.

Diffusion-Weighted Magnetic Resonance Imaging Characterization of White Matter Injury Produced by Axon-Sparing Demyelination and Severe Contusion Spinal Cord Injury in Rats.

Alterations in magnetic resonance imaging (MRI)-derived measurements of water diffusion parallel (D∥) and perpendicular (D⊥) to white matter tracts have been specifically attributed to pathology of axons and myelin, respectively. We test the hypothesis that directional diffusion measurements can distinguish between axon-sparing chemical demyelination and severe contusion spinal cord white matter injury. Adult rats received either unilateral ethidium bromide (EB) microinjections (chemical demyelination) into the lateral funiculus of the spinal cord at C5 or were subjected to unilateral severe contusion spinal cord injury (SCI). Diffusion MRI metrics in the lateral funiculus were analyzed at early and late time-points following injury and correlated with histology. Early EB-demyelination resulted in a significant elevation in D⊥ and significant reduction in D∥ at the injury epicenter, with histological evidence of uniform axon preservation. Alterations in D⊥ and D∥ at the epicenter of early EB-demyelination were not significantly different from those observed with severe contusion at the epicenter, where histology demonstrated severe combined axonal and myelin injury. Diffusion abnormalities away from the injury epicenter were seen with contusion injury, but not with EB-demyelination. Chronic EB lesions underwent endogenous remyelination with normalization of diffusion metrics, whereas chronic contusion resulted in persistently altered diffusivities. In the early setting, directional diffusion measurements at the injury epicenter associated with chemical demyelination are indistinguishable from those seen with severe contusive SCI, despite dramatic pathologic differences between injury models. Caution is advised in interpretation of diffusion metrics with respect to specific white matter structural alterations. Diffusion analysis should not be limited to the epicenter of focal spinal lesions as alterations marginal to the epicenter are useful for assessing the nature of focal white matter injury.

The back and forth of axonal injury and repair after stroke.

The axon plays a central role in both the injury and repair phases after stroke. This review highlights emerging principles in the study of axonal injury in stroke and the role of the axon in neural repair after stroke. Ischemic stroke produces a rapid and significant loss of axons in the acute phase. This early loss of axons results from a primary ischemic injury that triggers a wave of calcium signaling, activating proteolytic mechanisms and downstream signaling cascades. A second progressive phase of axonal injury occurs during the subacute period and damages axons that survive the initial ischemic insult but go on to experience a delayed axonal degeneration driven in part by changes in axoglial contact and axonal energy metabolism. Recovery from stroke is dependent on axonal sprouting and reconnection that occurs during a third degenerative/regenerative phase. Despite this central role played by the axon, comparatively little is understood about the molecular pathways that contribute to early and subacute axonal degeneration after stroke. Recent advances in axonal neurobiology and signaling suggest new targets that hold promise as potential molecular therapeutics including axonal calcium signaling, axoglial energy metabolism and cell adhesion as well as retrograde axonal mitogen-activated protein kinase pathways. These novel pathways must be modeled appropriately as the type and severity of axonal injury vary by stroke subtype. Stroke-induced injury to axons occurs in three distinct phases each with a unique molecular underpinning. A wealth of new data about the molecular organization and molecular signaling within axons is available but not yet robustly applied to the study of axonal injury after stroke. Identifying the spatiotemporal patterning of molecular pathways within the axon that contribute to injury and repair may offer new therapeutic strategies for the treatment of stroke.

Repetitive mild traumatic brain injury with impact acceleration in the mouse: Multifocal axonopathy, neuroinflammation, and neurodegeneration in the visual system

Repetitive mild traumatic brain injury (mTBI) is implicated in chronic neurological illness. The development of animal models of repetitive mTBI in mice is essential for exploring mechanisms of these chronic diseases, including genetic vulnerability by using transgenic backgrounds. In this study, the rat model of impact acceleration (IA) was redesigned for the mouse cranium and used in two clinically relevant repetitive mTBI paradigms. We first determined, by using increments of weight dropped from 1m that the 40g weight was most representative of mTBI and was not associated with fractures, brain contusions, anoxic–ischemic injury, mortality, or significant neurological impairments. Quantitative evaluation of traumatic axonal injury (TAI) in the optic nerve/tract, cerebellum and corpus callosum confirmed that weight increase produced a graded injury. We next evaluated two novel repetitive mTBI paradigms (1 time per day or 3 times per day at days 0, 1, 3, and 7) and compared the resulting TAI, neuronal cell death, and neuroinflammation to single hit mTBI at sub-acute (7days) and chronic time points (10weeks) post-injury. Both single and repetitive mTBI caused TAI in the optic nerve/tract, cerebellum, corticospinal tract, lateral lemniscus and corpus callosum. Reactive microglia with phagocytic phenotypes were present at injury sites. Severity of axonal injury corresponded to impact load and frequency in the optic nerve/tract and cerebellum. Both single and repeat injury protocols were associated with retinal ganglion cell loss and optic nerve degeneration; these outcomes correlated with impact load and number/frequency. No phosphorylated tau immunoreactivity was detected in the brains of animals subjected to repetitive mTBI. Our findings establish a new model of repetitive mTBI model featured by TAI in discrete CNS tracts, especially the visual system and cerebellum. Injury in retina and optic nerve provides a sensitive measure of severity of mTBI, thus enabling further studies on mechanisms and experimental therapeutics. Our model can also be useful in exploring mechanisms of chronic neurological disease caused by repetitive mTBI in wild-type and transgenic mice.

LUMBAR PLEXUS LESION ASSOCIATED WITH SPINAL MANIPULATION: A CASE REPORT

This is the first report of a lumbar plexus injury as a result of spinal manipulation. The 39-year-old female patient reported right lower limb pain after receiving a deep massage and spinal manipulation. The manipulation including back hyperextension had been done in a prone position 4 months before our visit. At that time she felt sudden onset pain in the low back radiating to the posteromedial side of right knee. The patient had numbness in the medial side of the knee and leg. Muscle force of hip flexion and knee extension as well as the muscle stretch reflex of right patella were reduced. Lumbosacral X-ray and MRI were normal. However, electrodiagnostic study revealed unobtainable sensory response of right sapheneus and lateral femoral cutaneous nerve as well as decreased amplitude of right quadriceps motor response. Needle electromyography revealed denervation potential in the vastus medialis, adductor longus and illiopsoas muscles compatible with severe partial axonal type right lumbar plexus injury. Considering potentially serious complications of manipulation and massage, these techniques should be performed only by expert hands.

Severe Diffuse Axon Injury in Chronic Alcoholic Rat Medulla Oblongata Following a Concussion Blow

We investigated the axonal morphological changes and expression of both tau protein and β-APP following concussion to the medulla oblongata, in a rat model of chronic alcoholism. Fifty-nine male Sprague-Dawley rats were randomly divided into EtOH, EtOH-TBI and control groups (water group, water-TBI group). To establish chronic alcoholic rats, rats were intragastrically given edible spirituous liquor twice daily. Rats also received a blow on the occipital tuberosity with an iron pendulum. Morphological changes and expression of tau and β-APP proteins in the medulla oblongata were examined. (a) Nerve fibre thickening and twisting were observed in alcoholic rats, with nerve fibre changes becoming more significant following a concussion blow, which leads to some nerve fibres fracturing. (b) Transmission electron microscopy revealed that the nerve fibre myelin became loosened and displayed lamellar separation, which became more significant following concussion. (c) The integral optical density (IOD) sum value of β-APP of the EtOH-TBI group was lower than that in the EtOH group (P < 0.05); the Tau IOD sum value of the EtOH-TBI group was higher than that in the EtOH group (P < 0.05). (a) Chronic alcoholism caused nerve fibre and neuronal morphology damage in the rat medulla oblongata, with structural damage becoming more significant following concussion. (b) Concussion changed the expression of β-APP and tau protein in chronic alcoholic rat medulla oblongata, suggesting that chronic alcoholism can lead to severe axonal injury following a concussion blow. (c) The effect of chronic alcoholism may be synergistic the concussion blow to promote animal injury and death.

Spinal root avulsion: an excellent model for studying motoneuron degeneration and regeneration after severe axonal injury

Spinal root avulsion: an excellent model for studying motoneuron degeneration and regeneration after severe axonal injury

Prognostication in Neurocritical Care: Just Crystal Ball Gazing?

Karina Melchior, a 19-year-old Danish girl, was driving her car when she came off the road and crashed. She sustained severe traumatic brain injury. She was admitted to the intensive care unit in the Aarhus University Hospital, Denmark in a comatose state. Three days after admission, the physician determines that there was no hope for recovery and even informed the relatives that the girl may become brain dead. The CT scan images showed severe traumatic brain injury. She asked the parents’ consent for organ donation. They consented, but Carina did not progress to brain dead. Then, the doctors decided that all life support should be withdrawn in order to let the young girl die. The ventriculotomy was removed, mechanical ventilation was stopped, and the endotracheal tube was removed. But, to the surprise of the parents, sister, and brother of the girl and the medical and nursing staff, the girl opened her eyes and started moving her arms and legs. In the following months, she made a good strides at a rehabilitation center. She has fully recovered; she walks, talks, is independent, rides her horse, and continued high school again. This all can be seen in the shocking documentary Piggen der ikke ville do (The girl who wouldn’t die) [1]. The documentary, that followed Carina’s family from the moment she was admitted in the hospital, sparked a public debate in Denmark about organ donation, brain death, and withdrawal of life-sustaining treatment in cases of severe brain injury. Over 500 registered donors withdrew their consent in fear of being declared dead too soon. To their credit, the doctors in the Aarhus Hospital have admitted that they made a grave error in prognostication. A similar situation occurred in 2002, 34-year-old Jesper Bendixen was also wrongly assessed brain dead in the same hospital, after he was admitted for a severe traumatic brain injury. His relatives were also asked for organ donation, but Jesper also recovered. This documentary was also broadcasted in many other european countries. What happened? Were there just incompetent doctors in Aarhus Hospital? Did they make a too early judgment? Is prognostication in neurocritical care still very difficult? The report by Edlow et al. shows some of the challenges [2] with the unexpected recovery of a 19-year-old man who sustained a severe traumatic brain injury. The early MRI findings, suggested a poor prognosis. Despite the presence of severe axonal injury on early MRI, he regained the ability to communicate and perform activities of daily living independently a year after his surgery. The authors conclude in their report that MRI data should be interpreted with caution when prognosticating for patients with traumatic brain injury. What if the staff, based on the MRI findings, had decided to withdraw all life-sustaining measures when the patient was still in critical condition and dependent on mechanical ventilation? Most probably, he would have died. And, as this was to be expected seeing the severity of the injury as judged from the MRI images, nobody would have doubted the decision to withdraw support. We now know that this was nothing more than a self-fulfilling prophecy. A self-fulfilling prophecy is a prediction that directly causes itself to become true, by the very terms of the prophecy itself. In critical care, predictions of poor prognosis may become self-fulfilling if life-sustaining measures as mechanical ventilation are withheld or withdrawn on the basis of that prediction. Patients are believed to have a high E. J. O. Kompanje (&) Department of Intensive Care Medicine, Erasmus MC University Medical Center, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands e-mail: e.j.o.kompanje@erasmusmc.nl

Unexpected Recovery of Function After Severe Traumatic Brain Injury: The Limits of Early Neuroimaging-Based Outcome Prediction

Prognostication in the early stage of traumatic coma is a common challenge in the neuro-intensive care unit. We report the unexpected recovery of functional milestones (i.e., consciousness, communication, and community reintegration) in a 19-year-old man who sustained a severe traumatic brain injury. The early magnetic resonance imaging (MRI) findings, at the time, suggested a poor prognosis. During the first year of the patient's recovery, MRI with diffusion tensor imaging and T2*-weighted imaging was performed on day 8 (coma), day 44 (minimally conscious state), day 198 (post-traumatic confusional state), and day 366 (community reintegration). Mean apparent diffusion coefficient (ADC) and fractional anisotropy values in the corpus callosum, cerebral hemispheric white matter, and thalamus were compared with clinical assessments using the Disability Rating Scale (DRS). Extensive diffusion restriction in the corpus callosum and bihemispheric white matter was observed on day 8, with ADC values in a range typically associated with neurotoxic injury (230-400 × 10(-6 )mm(2)/s). T2*-weighted MRI revealed widespread hemorrhagic axonal injury in the cerebral hemispheres, corpus callosum, and brainstem. Despite the presence of severe axonal injury on early MRI, the patient regained the ability to communicate and perform activities of daily living independently at 1 year post-injury (DRS = 8). MRI data should be interpreted with caution when prognosticating for patients in traumatic coma. Recovery of consciousness and community reintegration are possible even when extensive traumatic axonal injury is demonstrated by early MRI.

Human Apolipoprotein E4 Worsens Acute Axonal Pathology but Not Amyloid-β Immunoreactivity After Traumatic Brain Injury in 3×TG-AD Mice

Apolipoprotein E4 (APOE4) genotype is a risk factor for poor outcome after traumatic brain injury (TBI), particularly in young patients, but the underlying mechanisms are not known. By analogy to effects of APOE4 on the risk of Alzheimer disease (AD), the APOE genotype may influence β-amyloid (Aβ) and tau deposition after TBI. To test this hypothesis, we crossed 3xTG-AD transgenic mice carrying 3 human familial AD mutations (PS1(M146V), tauP(301)L, and APP(SWE)) to human ApoE2-, ApoE3-, and ApoE4-targeted replacement mice. Six- to 8-month-old 3xTG-ApoE mice were assayed by quantitative immunohistochemistry for amyloid precursor protein (APP), Aβ(1-40) (Aβ40), Aβ(1-42) (Aβ42), total human tau, and phospho-serine 199 (pS199) tau at 24 hours after moderate controlled cortical impact. There were increased numbers of APP-immunoreactive axonal varicosities in 3xTG-ApoE4 mice versus the other genotypes. This finding was repeated in a separate cohort of ApoE4-targeted replacement mice without human transgenes compared with ApoE3 and ApoE2 mice. There were no differences between genotypes in the extent of intra-axonal Aβ40 and Aβ42; none of the mice had extracellular Aβ deposition. Regardless of injury status, 3xTG-ApoE4 mice had more total human tau accumulation in both somatodendritic and intra-axonal compartments than other genotypes. These results suggest that the APOE4 genotype may have a primary effect on the severity of axonal injury in acute TBI.

Chronic Alcoholism-Mediated Impairment in the Medulla Oblongata: A Mechanism of Alcohol-Related Mortality in Traumatic Brain Injury?

Alcohol-related traumatic brain injury (TBI) is a common condition in medical and forensic practice, and results in high prehospital mortality. We investigated the mechanism of chronic alcoholism-related mortality by examining the effects of alcohol on the synapses of the medulla oblongata in a rat model of TBI. Seventy adult male Sprague-Dawley rats were randomly assigned to either ethanol (EtOH) group, EtOH-TBI group, or control groups (water group, water-TBI group). To establish chronic alcoholism model, rats in the EtOH group were given EtOH twice daily (4 g/kg for 2 weeks and 6 g/kg for another 2 weeks). The rats also received a minor strike on the occipital tuberosity with an iron pendulum. Histopathologic and ultrastructure changes and the numerical density of the synapses in the medulla oblongata were examined. Expression of postsynaptic density-95 (PSD-95) in the medulla oblongata was measured by ELISA. Compared with rats in the control group, rats in the chronic alcoholism group showed: (1) minor axonal degeneration; (2) a significant decrease in the numerical density of synapses (p < 0.01); and (3) compensatory increase in PSD-95 expression (p < 0.01). Rats in the EtOH-TBI group showed: (1) high mortality (50%, p < 0.01); (2) inhibited respiration before death; (3) severe axonal injury; and (4) decrease in PSD-95 expression (p < 0.05). Chronic alcoholism induces significant synapse loss and axonal impairment in the medulla oblongata and renders the brain more susceptible to TBI. The combined effects of chronic alcoholism and TBI induce significant synapse and axon impairment and result in high mortality.