RESUMO
Neurofilaments(NFs) are the most abundant intermediate filaments that make up the inner volume of axon, with possible phosphorylation on their side arms, and their slow axonal transport by molecular motors along microtubule tracks in a "stop-and-go" manner with rapid, intermittent and bidirectional motion. The kinetics of NFs and morphology of axon are dramatically different between myelinate internode and unmyelinated node of Ranvier. The NFs in the node transport as 7.6 times faster as in the internode, and the distribution of NFs population in the internode is 7.6 folds as much as in the node of Ranvier. We hypothesize that the phosphorylation of NFs could reduce the on-track rate and slow down their transport velocity in the internode. By modifying the '6-state' model with (a) an extra phosphorylation kinetics to each six state and (b) construction a new '8-state' model in which NFs at off-track can be phosphorylated and have smaller on-track rate, our model and simulation demonstrate that the phosphorylation-induced decrease of on-track rate could slow down the NFs average velocity and increase the axonal caliber. The degree of phosphorylation may indicate the extent of velocity reduction. The Continuity equation used in our paper predicts that the ratio of NFs population is inverse proportional to the ratios of average velocity of NFs between node of Ranvier and internode. We speculate that the myelination of axon could increase the level of phosphorylation of NF side arms, and decrease the possibility of NFs to get on-track of microtubules, therefore slow down their transport velocity. In summary, our work provides a potential mechanism for understanding the phosphorylation kinetics of NFs in regulating their transport and morphology of axon in myelinated axons, and the different kinetics of NFs between node and internode.
Assuntos
Axônios/metabolismo , Filamentos Intermediários/metabolismo , Modelos Estatísticos , Fibras Nervosas Mielinizadas/metabolismo , Proteínas de Neurofilamentos/metabolismo , Nós Neurofibrosos/metabolismo , Animais , Transporte Axonal/fisiologia , Simulação por Computador , Humanos , Cinética , Microtúbulos/metabolismo , Método de Monte Carlo , FosforilaçãoRESUMO
BACKGROUND: Existing methods to predict recovery after severe traumatic brain injury lack accuracy. The aim of this study is to determine the prognostic value of quantitative diffusion tensor imaging (DTI). METHODS: In a multicenter study, the authors prospectively enrolled 105 patients who remained comatose at least 7 days after traumatic brain injury. Patients underwent brain magnetic resonance imaging, including DTI in 20 preselected white matter tracts. Patients were evaluated at 1 yr with a modified Glasgow Outcome Scale. A composite DTI score was constructed for outcome prognostication on this training database and then validated on an independent database (n=38). DTI score was compared with the International Mission for Prognosis and Analysis of Clinical Trials Score. RESULTS: Using the DTI score for prediction of unfavorable outcome on the training database, the area under the receiver operating characteristic curve was 0.84 (95% CI: 0.75-0.91). The DTI score had a sensitivity of 64% and a specificity of 95% for the prediction of unfavorable outcome. On the validation-independent database, the area under the receiver operating characteristic curve was 0.80 (95% CI: 0.54-0.94). On the training database, reclassification methods showed significant improvement of classification accuracy (P < 0.05) compared with the International Mission for Prognosis and Analysis of Clinical Trials score. Similar results were observed on the validation database. CONCLUSIONS: White matter assessment with quantitative DTI increases the accuracy of long-term outcome prediction compared with the available clinical/radiographic prognostic score.
Assuntos
Lesões Encefálicas/patologia , Fibras Nervosas Mielinizadas/patologia , Índice de Gravidade de Doença , Adolescente , Adulto , Idoso , Lesões Encefálicas/metabolismo , Lesões Encefálicas/terapia , Estudos de Coortes , Feminino , Seguimentos , Humanos , Imageamento por Ressonância Magnética/métodos , Masculino , Pessoa de Meia-Idade , Fibras Nervosas Mielinizadas/metabolismo , Estudos Prospectivos , Resultado do Tratamento , Adulto JovemRESUMO
Transplantation of neural stems cells (NSCs) could be a useful means to deliver biologic therapeutics for late-stage Alzheimer's disease (AD). In this study, we conducted a small preclinical investigation of whether NSCs could be modified to express metalloproteinase 9 (MMP9), a secreted protease reported to degrade aggregated Aß peptides that are the major constituents of the senile plaques. Our findings illuminated three issues with using NSCs as delivery vehicles for this particular application. First, transplanted NSCs generally failed to migrate to amyloid plaques, instead tending to colonize white matter tracts. Second, the final destination of these cells was highly influenced by how they were delivered. We found that our injection methods led to cells largely distributing to white matter tracts, which are anisotropic conduits for fluids that facilitate rapid distribution within the CNS. Third, with regard to MMP9 as a therapeutic to remove senile plaques, we observed high concentrations of endogenous metalloproteinases around amyloid plaques in the mouse models used for these preclinical tests with no evidence that the NSC-delivered enzymes elevated these activities or had any impact. Interestingly, MMP9-expressing NSCs formed substantially larger grafts. Overall, we observed long-term survival of NSCs in the brains of mice with high amyloid burden. Therefore, we conclude that such cells may have potential in therapeutic applications in AD but improved targeting of these cells to disease-specific lesions may be required to enhance efficacy.
Assuntos
Amiloidose/prevenção & controle , Encéfalo/patologia , Modelos Animais de Doenças , Metaloproteinase 9 da Matriz/metabolismo , Fibras Nervosas Mielinizadas/patologia , Células-Tronco Neurais/transplante , Placa Amiloide/prevenção & controle , Amiloide/metabolismo , Precursor de Proteína beta-Amiloide/genética , Precursor de Proteína beta-Amiloide/metabolismo , Amiloidose/enzimologia , Amiloidose/patologia , Animais , Encéfalo/metabolismo , Células Cultivadas , Técnicas Imunoenzimáticas , Lentivirus/genética , Camundongos , Fibras Nervosas Mielinizadas/metabolismo , Células-Tronco Neurais/citologia , Placa Amiloide/enzimologia , Placa Amiloide/patologiaRESUMO
Vascular endothelial growth factor (VEGF) is thought to provide neuroprotection to the traumatically injured spinal cord. We examined whether supplementing the injured environment with VEGF(165) via direct intraspinal injection into the lesion epicenter during the acute phase of spinal cord injury (SCI) results in improved outcome. The effect of treatment was investigated using longitudinal multi-modal magnetic resonance imaging (MRI), neurobehavioral assays, and end-point immunohistochemistry. We observed on MRI that rats treated with VEGF(165) after SCI had increased tissue sparing compared to vehicle-treated animals at the earlier time points. However, these favorable effects were not maintained into the chronic phase. Histology revealed that VEGF(165) treatment resulted in increased oligodendrogenesis and/or white matter sparing, and therefore may eventually lead to improved functional outcome. The increase in spared tissue as demonstrated by MRI, coupled with the possible remyelination and increased neurosensory sensitivity, suggests that VEGF(165) treatment may play a role in promoting plasticity in the sensory pathways following SCI. However, VEGF-treated animals also demonstrated an increased incidence of persistent allodynia, as indicated on the von Frey filament test.
Assuntos
Atividade Motora/efeitos dos fármacos , Recuperação de Função Fisiológica/efeitos dos fármacos , Traumatismos da Medula Espinal/terapia , Fator A de Crescimento do Endotélio Vascular/uso terapêutico , Animais , Axônios/efeitos dos fármacos , Axônios/metabolismo , Axônios/patologia , Diferenciação Celular/efeitos dos fármacos , Imuno-Histoquímica , Imageamento por Ressonância Magnética , Masculino , Atividade Motora/fisiologia , Fibras Nervosas Mielinizadas/efeitos dos fármacos , Fibras Nervosas Mielinizadas/metabolismo , Fibras Nervosas Mielinizadas/patologia , Oligodendroglia/efeitos dos fármacos , Oligodendroglia/metabolismo , Oligodendroglia/patologia , Ratos , Ratos Sprague-Dawley , Medula Espinal/efeitos dos fármacos , Medula Espinal/metabolismo , Medula Espinal/patologia , Traumatismos da Medula Espinal/metabolismo , Traumatismos da Medula Espinal/patologia , Fator A de Crescimento do Endotélio Vascular/farmacologiaRESUMO
Local brain tissue oxygen (ptiO2) monitoring is frequently applied in patients at risk for cerebral ischemia. To identify ischemic thresholds, the normal range of local brain tissue oxygen pressure (ptiO2) values needs to be established. Ideally, such normal values are determined in healthy and awake subjects, so as to eliminate the possible influences of anesthetics on cerebral physiology or ptiO2. Thus far, however, such measurements have not been conducted, and to fill this void, we determined the ptiO2 values in normal white matter of awake patients undergoing functional stereotactic brain surgery. In 25 otherwise healthy patients, who underwent functional neurosurgery for treatment of a refractory movement disorder under local anesthesia, the ptiO2 of white matter was recorded continuously using a polarographic Clark type electrode monitoring system. Preoperative screening ruled out cognitive dysfunction or structural cerebral lesions. Reliable intraoperative ptiO2 values were obtained in 22 patients. After an adaptation period of 118+/-35 min (range, 47-171 min), we found an average normal ptiO2 of 22.6+/-7.2 mm Hg in the frontal white matter. In 11 patients, ptiO2 measurements were continued postoperatively for 24 h. During this period, a similar normal ptiO2 value of 23.1+/-6.6 mm Hg was found. No iatrogenic complications occurred. In conclusion, the normal ptiO2 of cerebral white matter is most likely lower than previously assumed. Further, the long adaptation time renders this widely applied monitoring instrument unreliable in detecting ischemia early after insertion and limits its usefulness for intraoperative monitoring.
Assuntos
Encéfalo/metabolismo , Monitorização Intraoperatória/métodos , Procedimentos Neurocirúrgicos/métodos , Oxigênio/análise , Oxigênio/metabolismo , Polarografia/métodos , Adaptação Fisiológica/fisiologia , Adulto , Idoso , Encéfalo/cirurgia , Isquemia Encefálica/diagnóstico , Isquemia Encefálica/metabolismo , Isquemia Encefálica/prevenção & controle , Eletrodos/normas , Eletrofisiologia/instrumentação , Eletrofisiologia/métodos , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Monitorização Intraoperatória/instrumentação , Fibras Nervosas Mielinizadas/metabolismo , Consumo de Oxigênio/fisiologia , Polarografia/instrumentação , Valores de Referência , Técnicas EstereotáxicasRESUMO
The experimental investigation of nerve regeneration after microsurgical repair is usually carried out in rats, rather than mice, because of the larger sized peripheral nerves. Today however, the availability of genetically modified mice makes the use of this laboratory animal very intriguing for investigating nerve regeneration at a molecular level. In this study we aimed to provide a standardization of the experimental model based on microsurgical direct repair, by 12/0 suture, of the left median nerve in adult male mice. Postoperative recovery was regularly assessed by the grasping test. At day-75 postoperative, regenerated median nerve fibers were analyzed by design-based quantitative morphology and electron microscopy. Yet, sections were immuno-labelled using two axonal antibodies commonly employed for rat nerve fibers. Results indicated that functional recovery begun at day-15 and progressively increased reaching values not significantly different from normal by day-50. Quantitative morphology showed that, at day-75, the number of regenerated nerve fibers was not significantly different in comparison to controls. In contrast, differences were detected in fiber density, mean axon and fiber diameter and myelin thickness which were all significantly lower than controls. Immunohistochemistry showed that axonal markers commonly used for rat nerves studies are effective also for mouse nerves. Similar to the rat, the mouse median nerve model is superior to sciatic nerve model for the minimal impact on animal well-being and the effectiveness of the grasping test for motor function evaluation. The main limitation is the small nerve size which requires advanced microsurgical skills for performing 12/0 epineurial suturing.
Assuntos
Nervo Mediano/cirurgia , Nervo Mediano/ultraestrutura , Regeneração Nervosa/fisiologia , Procedimentos Neurocirúrgicos/métodos , Animais , Axônios/metabolismo , Axônios/ultraestrutura , Bioensaio/métodos , Biomarcadores/análise , Biomarcadores/metabolismo , Modelos Animais de Doenças , Membro Anterior/inervação , Membro Anterior/fisiologia , Força da Mão/fisiologia , Imuno-Histoquímica , Masculino , Nervo Mediano/fisiologia , Camundongos , Músculo Esquelético/inervação , Músculo Esquelético/fisiopatologia , Fibras Nervosas Mielinizadas/metabolismo , Fibras Nervosas Mielinizadas/ultraestrutura , Proteínas do Tecido Nervoso/análise , Proteínas do Tecido Nervoso/metabolismo , Paralisia/diagnóstico , Paralisia/fisiopatologia , Recuperação de Função Fisiológica/fisiologia , Técnicas de Sutura/normasRESUMO
Diffusion tensor magnetic resonance imaging (DT-MRI) was applied for in vivo quantification of myelin loss and regeneration. A transgenic mouse line (Oligo-TTK) expressing a truncated form of the herpes simplex virus 1 thymidine kinase gene (hsv1-tk) in oligodendrocytes was studied along with two induced phenotypes of myelin pathology. Myelin loss and axonal abnormalities differentially affect values of DT-MRI parameters in the brain of transgenic mice. Changes in the anisotropy of the white matter were assessed by calculating and mapping the radial (D perpendicular) and axial (D parallel) water diffusion to axonal tracts and fractional anisotropy (FA). A significant increase in D perpendicular attributed to the lack of myelin was observed in all selected brain white matter tracts in dysmyelinated mice. Lower D parallel values were consistent with the histological observation of axonal modifications, including reduced axonal caliber and overexpression of neurofilaments and III beta-tubulin. We show clearly that myelination and axonal changes play a role in the degree of diffusion anisotropy, because FA was significantly decreased in dysmyelinated brain. Importantly, myelin reparation during brain postnatal development induced a decrease in the magnitude of D( perpendicular) and an increase in FA compared with the same brain before recovery. The progressive increase in D parallel values was attributed to the gain in normal axonal morphology. This regeneration was confirmed by the detection of enlarged oligodendrocyte population, newly formed myelin sheaths around additional axons, and a gradual increase in axonal caliber.
Assuntos
Encefalopatias/patologia , Doenças Desmielinizantes/patologia , Imagem de Difusão por Ressonância Magnética , Recuperação de Função Fisiológica/fisiologia , Animais , Animais Recém-Nascidos , Anisotropia , Antivirais/administração & dosagem , Encéfalo/citologia , Encéfalo/efeitos dos fármacos , Encéfalo/metabolismo , Encéfalo/patologia , Encéfalo/virologia , Encefalopatias/tratamento farmacológico , Encefalopatias/metabolismo , Encefalopatias/virologia , Mapeamento Encefálico , Doenças Desmielinizantes/tratamento farmacológico , Doenças Desmielinizantes/metabolismo , Doenças Desmielinizantes/virologia , Ganciclovir/administração & dosagem , Processamento de Imagem Assistida por Computador/métodos , Imuno-Histoquímica/métodos , Camundongos , Camundongos Transgênicos , Microscopia Eletrônica de Transmissão/métodos , Proteína Básica da Mielina/metabolismo , Fibras Nervosas Mielinizadas/metabolismo , Fibras Nervosas Mielinizadas/patologia , Fibras Nervosas Mielinizadas/ultraestrutura , Oligodendroglia/metabolismo , Oligodendroglia/patologia , Oligodendroglia/ultraestrutura , Proteínas Serina-Treonina Quinases/genética , Proteínas Tirosina Quinases/genética , Recuperação de Função Fisiológica/efeitos dos fármacos , Fatores de TempoRESUMO
The ability of putative neuroprotective compounds to protect against white matter injury remains poorly investigated due to the lack of suitable methods for assessing white matter injury. This study was therefore designed to investigate the utility of Tau 1 (oligodendrocytes/axons), myelin basic protein (MBP; myelin) and amyloid precursor protein (APP; axons) immunohistochemistry in assessing white matter injury at various times following middle cerebral artery occlusion (MCAO) in the rat. Focal cerebral, ischaemia was induced in halothane-anaesthetised rats using an intraluminal thread model. At 24 h, 1 and 2 weeks following MCAO, white matter injury was assessed using Tau 1, APP, MBP and Luxol-fast blue staining and neuronal injury with cresyl fast violet (CFV). In histologically normal tissue MBP immunoreactivity was detected in myelinated fibre tracts, while Tau 1 and APP were axonally located. At 24 h following permanent MCAO, MBP, and Tau 1 staining remained relatively unchanged within the myelin and axonal compartments of the ischaemic region. In contrast, increased Tau 1 staining was apparent in oligodendrocytes within ischaemic tissue, while APP accumulated in axons surrounding the lesion. At 1 and 2 weeks following transient MCAO, Tau 1 and APP staining was markedly decreased within ischaemic tissue. Marked reduction in MBP levels within ischaemic tissue were not detected until 2 weeks following MCAO. The area of axonal injury as assessed by reduced Tau 1 or APP staining correlated with the area of neuronal damage as assessed by CFV staining. This study shows that MBP, Tau 1 and APP immunohistochemistry can be utilised to assess myelin and axonal integrity following sustained ischaemia using standard image analysis techniques.