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Myelinated Nerve Fibers (myelinated + nerve_fiber)
Selected AbstractsMultiple functions of the paranodal junction of myelinated nerve fibers,JOURNAL OF NEUROSCIENCE RESEARCH, Issue 15 2009Jack Rosenbluth Abstract Myelin sheaths include an extraordinary structure, the "paranodal axoglial junction" (PNJ), which attaches the sheath to the axon at each end of each myelin segment. Its size is enormous and its structure unique. Here we review past and current studies showing that this junction can serve multiple functions in maintaining reliable saltatory conduction. The present evidence points to three functions in particular. 1) It seals the myelin sheath to the axon to prevent major shunting of nodal action currents beneath the myelin sheath while still leaving a narrow channel interconnecting the internodal periaxonal space with the perinodal space. This pathway represents a potential route through which juxtaparanodal and internodal channels can influence nodal activity and through which nutrients, such as glucose, and other metabolites can diffuse to and from the internodal periaxonal space. 2) It serves as a mechanism for maintaining discrete, differentiated axolemmal domains at and around the node of Ranvier by acting as a barrier to the lateral movement of ion channel complexes within the axolemma, thus concentrating voltage-gated sodium channels at the node and segregating fast voltage-gated potassium channels to the juxtaparanode under the myelin sheath. 3) It attaches the myelin sheath to the axon on either side of the node and can thus maintain nodal dimensions in the face of mechanical stresses associated with stretch or other local factors that might cause disjunction. It is therefore the likely means for maintaining constancy of nodal surface area and electrical parameters essential for consistency in conduction. © 2009 Wiley-Liss, Inc. [source] A simple protocol for paraffin-embedded myelin sheath staining with osmium tetroxide for light microscope observationMICROSCOPY RESEARCH AND TECHNIQUE, Issue 7 2008Federica Di Scipio Abstract Experimental investigation of peripheral nerve fiber regeneration is attracting more and more attention among both basic and clinical researchers. Assessment of myelinated nerve fiber morphology is a pillar of peripheral nerve regeneration research. The gold standard for light microscopic imaging of myelinated nerve fibers is toluidine blue staining of resin-embedded semithin sections. However, many researchers are unaware that the dark staining of myelin sheaths typically produced by this procedure is due to osmium tetroxide postfixation and not due to toluidine blue. In this article, we describe a simple pre-embedding protocol for staining myelin sheaths in paraffin-embedded nerve specimens using osmium tetroxide. The method involves immersing the specimen in 2% osmium tetroxide for 2 h after paraformaldeyde fixation, followed by routine dehydration and paraffin embedding. Sections can then be observed directly under the microscope or counterstained using routine histological methods. Particularly good results were obtained with Masson's trichrome counterstain, which permits the imaging of connective structures in nerves that are not detectable in toluidine blue-stained resin sections. Finally, we describe a simple protocol for osmium etching of sections, which makes further immunohistochemical analysis possible on the same specimens. Taken together, our results suggest that the protocol described in this article is a valid alternative to the conventional resin embedding-based protocol: it is much cheaper, can be adopted by any histological laboratory, and allows immunohistochemical analysis to be conducted. Microsc. Res. Tech., 2008. © 2008 Wiley-Liss, Inc. [source] Chronic demyelinating polyneuropathy in graft-versus-host disease following allogeneic bone marrow transplantationNEUROPATHOLOGY, Issue 1 2002Toshiko Nagashima In recent years a novel problem has arisen in organ transplantation medicine, namely GVHD. The nervous system has been involved mainly at the level of the CNS and this can lead to a serious outcome for the patient. In rare cases, peripheral nerves may be affected and show acute or chronic polyneuropathy. Here a case is reported of polyneuropathy associated with chronic GVHD. A 32-year-old man, suffering from chronic GVHD following an allogeneic bone marrow transplantation (BMT) for malignant lymphoma at the age of 25, developed a motor dominant polyneuropathy 5 years later. Electrophysiologic studies demonstrated the demyelinating type of polyneuropathy. Biopsy specimens from skin and skeletal muscle disclosed perivascular lymphocytic infiltrates expressing T-cell markers. The sural nerve showed a loss of myelinated nerve fibers with epineurial fibrosis and rare occurrence of T cells, but without obvious vasculitic changes. The present case suggested that polyneuropathy could develop in association with chronic GVHD in some patients with a longstanding disease course. [source] Role of transverse bands in maintaining paranodal structure and axolemmal domain organization in myelinated nerve fibers: Effect on longevity in dysmyelinated mutant miceTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 14 2010Amanda J. Mierzwa Abstract The consequences of dysmyelination are poorly understood and vary widely in severity. The shaking mouse, a quaking allele, is characterized by severe central nervous system (CNS) dysmyelination and demyelination, a conspicuous action tremor, and seizures in ,25% of animals, but with normal muscle strength and a normal lifespan. In this study we compare this mutant with other dysmyelinated mutants including the ceramide sulfotransferase deficient (CST,/,) mouse, which are more severely affected behaviorally, to determine what might underlie the differences between them with respect to behavior and longevity. Examination of the paranodal junctional region of CNS myelinated fibers shows that "transverse bands," a component of the junction, are present in nearly all shaking paranodes but in only a minority of CST,/, paranodes. The number of terminal loops that have transverse bands within a paranode and the number of transverse bands per unit length are only moderately reduced in the shaking mutant, compared with controls, but markedly reduced in CST,/, mice. Immunofluorescence studies also show that although the nodes of the shaking mutant are somewhat longer than normal, Na+ and K+ channels remain separated, distinguishing this mutant from CST,/, mice and others that lack transverse bands. We conclude that the essential difference between the shaking mutant and others more severely affected is the presence of transverse bands, which serve to stabilize paranodal structure over time as well as the organization of the axolemmal domains, and that differences in the prevalence of transverse bands underlie the marked differences in progressive neurological impairment and longevity among dysmyelinated mouse mutants. J. Comp. Neurol. 518:2841,2853, 2010. © 2010 Wiley-Liss, Inc. [source] Disrupted myelin and axon loss in the anterior commissure of the aged rhesus monkeyTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 1 2003Julie H. Sandell Abstract This study assesses the effects of age on the composition of the anterior commissure of the rhesus monkey. The anterior commissures of nine young (5,10 years), five middle-aged (15,20 years), and eight old (25,35 years) monkeys were examined by light and electron microscopy. In all, 90,95% of the nerve fibers in the anterior commissure are myelinated. With age, the structure of the myelin sheaths of some nerve fibers is altered. Some of the axons also show signs of degeneration and this leads to a loss of nerve fibers. Thus, in young and the middle-aged monkeys the mean number of myelinated nerve fibers in the anterior commissure is 2.2 × 106, while in the old monkeys the mean is 1.2 × 106. Increasing age is correlated with a reduction in the number of myelinated nerve fibers in the anterior commissure, an increase in the frequency of structural alterations in myelin sheaths, and an increase in the frequency of occurrence of degenerating axons. However, the number of myelinated nerve fibers is the only variable that correlates with cognition: in monkeys 5,20 years of age the fewer the number of nerve fibers the poorer the cognitive performance, as measured by our Cognitive Impairment Index (CII). The most common neuroglial cells in the anterior commissure are oligodendrocytes. They account for 86% of all neuroglial cell profiles, while astrocytes account for 9%, and microglial cells for 5% of profiles. There is no apparent change with age in the total numbers of neuroglial cells, although as they age each of the neuroglial cell types acquires some inclusions in their cytoplasm. The data, together with those from previous studies, support the concept that in aging there is a ubiquitous loss of myelinated nerve fibers from the brain and that fiber loss is preceded by alterations in the structure of many of the myelin sheaths. J. Comp. Neurol. 466:14,30, 2003. © 2003 Wiley-Liss, Inc. [source] | |||||||||||||