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Communication in the central nervous system (CNS) occurs through initiation and propagation of action potentials at excitable domains along axons. Action potentials generated at the axon initial segment (AIS) are regenerated at nodes of Ranvier through the process of saltatory conduction. Proper formation and maintenance of the molecular structure at the AIS and nodes are required for sustaining conduction fidelity. In myelinated CNS axons, paranodal junctions between the axolemma and myelinating oligodendrocytes delineate nodes of Ranvier and regulate the distribution and localization of specialized functional elements, such as voltage-gated sodium channels and mitochondria. Disruption of excitable domains and altered distribution of functional elements in CNS axons is associated with demyelinating diseases such as multiple sclerosis, and is likely a mechanism common to other neurological disorders. This review will provide a brief overview of the molecular structure of the AIS and nodes of Ranvier, as well as the distribution of mitochondria in myelinated axons. In addition, this review highlights important structural and functional changes within myelinated CNS axons that are associated with neurological dysfunction., (Copyright © 2016 Elsevier Ireland Ltd and Japan Neuroscience Society. All rights reserved.)

In some anti-ganglioside antibody-mediated neuropathies, human and experimental data suggest a common pathogenic mechanism of dysfunction/disruption at the node of Ranvier resulting in a pathophysiologic continuum from transitory nerve conduction failure to axonal degeneration. The traditional classification of polyneuropathies into demyelinating or axonal may generate some confusion in the electrophysiological diagnosis of Guillain-Barré syndrome subtypes associated with anti-ganglioside antibodies. The axonal forms show, besides axonal degeneration, promptly reversible nerve conduction failure. This may be interpreted, by a single electrophysiological study, as demyelinating conduction block or distal axonal degeneration leading to errors in classification and in establishing prognosis. Moreover the term axonal may be misleading as it is commonly associated to axonal degeneration and not to a transitory, promptly reversible, dysfunction of the excitable axolemma. To focus on the site of nerve injury and overcome the classification difficulties, we propose the new category of nodo-paranodopathy which seems appropriate to various acute and chronic neuropathies associated with anti-ganglioside antibodies and we think better systematizes the neuropathies characterized by an autoimmune attack targeting the nodal region., (Copyright © 2013 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)

Action potential propagation along myelinated nerve fibers requires high-density protein complexes that include voltage-gated Na(+) channels at the nodes of Ranvier. Several complementary mechanisms may be involved in node assembly including: (1) interaction of nodal cell adhesion molecules with the extracellular matrix; (2) restriction of membrane protein mobility by paranodal junctions; and (3) stabilization of ion channel clusters by axonal cytoskeletal scaffolds. In the peripheral nervous system, a secreted glial protein at the nodal extracellular matrix interacts with axonal cell adhesion molecules to initiate node formation. In the central nervous system, both glial soluble factors and paranodal axoglial junctions may function in a complementary manner to contribute to node formation.

Whereas paralysis is the hallmark for paralytic rabies, the precise pathological basis of paralysis is not known. It is unclear whether weakness results from involvement of anterior horn cells or of motor nerve fibers. There is also no conclusive data on the cause of the neuropathic pain which occurs at the bitten region, although it has been presumed to be related to sensory ganglionopathy. In this study, six laboratory-proven rabies patients (three paralytic and three furious) were assessed clinically and electrophysiologically. Our data suggests that peripheral nerve dysfunction, most likely demyelination, contributes to the weakness in paralytic rabies. In furious rabies, progressive focal denervation, starting at the bitten segment, was evident even in the absence of demonstrable weakness and the electrophysiologic study suggested anterior horn cell dysfunction. In two paralytic and one furious rabies patients who had severe paresthesias as a prodrome, electrophysiologic studies suggested dorsal root ganglionopathy. Postmortem studies in two paralytic and one furious rabies patients, who had local neuropathic pain, showed severe dorsal root ganglionitis. Intense inflammation of the spinal nerve roots was observed more in paralytic rabies patients. Inflammation was mainly noted in the spinal cord segment corresponding to the bite in all cases; however, central chromatolysis of the anterior horn cells could be demonstrated only in furious rabies patient. We conclude that differential sites of neural involvement and possibly different neuropathogenetic mechanisms may explain the clinical diversity in human rabies.

A 37-year-old man developed an acute encephalitic condition after respiratory infection. His condition rapidly deteriorated, and he experienced ophthalmoplegia, tetraplegia, loss of brainstem reflexes and deep tendon reflexes, and deep coma. Electrophysiological evaluations indicated involvement of the peripheral nerve as well as the brainstem. Follow-up studies found acute progression of peripheral nerve damage. Serum anti-GQ1b IgG antibody was present. The initial condition was diagnosed as Bickerstaff's brainstem encephalitis, and subsequent overlapping of Guillain-Barré syndrome probably was responsible for the clinical deterioration. When unusual worsening is observed in clinically suspected encephalitis, neurologists must take into account the possibility of associated Guillain-Barré syndrome and related disorders.

Anti-ganglioside antibodies frequently are present in sera from patients with Guillain-Barré syndrome (GBS) during the acute phase, but no patients in whom anti-ganglioside antibodies were tested before the onset of the syndrome have been reported. We describe the first case of GBS subsequent to Campylobacter jejuni infection, in which longitudinal changes in anti-ganglioside antibody titers were measured before and after the onset of limb weakness. Serum antibody titers against GM1 (IgM/IgG), GM1b (IgM/IgG), GalNAc-GD1a (IgM/IgG), and GD1b (IgG) were highest on the day of onset, but negative before onset. Anti-C. jejuni IgG and IgA antibody titers paralleled those of the anti-ganglioside antibodies, indicative that C. jejuni infection triggered anti-ganglioside antibody production. Press et al. [J. Neurol. Sci. 190 (2001) 41] reported that anti-ganglioside antibody titers peaked during the recovery phase, but our findings are counter to theirs. We speculate that anti-ganglioside antibodies are the primary effectors of nerve damage in GBS.

We investigated the prevalence of anti-LM1 IgG antibody and its fine specificity in Guillain-Barré syndrome (GBS). Anti-LM1 IgG and IgM antibodies from sera of 47 patients with GBS--19 with acute inflammatory demyelinating polyneuropathy (AIDP), 27 with acute motor axonal neuropathy (AMAN), and 1 with acute motor-sensory axonal neuropathy (AMSAN)--were tested. Anti-LM1 IgG antibody was detected in only one patient with AIDP, whereas it was present in seven with AMAN and in one with AMSAN. Sera from the eight IgG anti-LM1-positive patients with AMAN/AMSAN also had IgG activity against the gangliosides GM1, GM1b, GD1a, GalNAc-GD1a, GD1b, or GQ1b. Anti-LM1 IgG antibodies from the AMAN/AMSAN patients cross-reacted with other gangliosides, whereas IgG antibody from the AIDP patient was monospecific against LM1. Anti-LM1 IgG antibody therefore, cannot be a marker of AIDP. In addition, whether monospecific anti-LM1 IgG antibody is associated with AIDP remains to be concluded. Larger studies are needed to verify whether monospecific anti-LM1 IgG antibody could be a marker of AIDP.

Anti-GQ1b IgG frequently is present in sera of patients with Miller Fisher syndrome (MFS), Guillain-Barré syndrome (GBS) with ophthalmoplegia, Bickerstaff's brainstem encephalitis (BBE), and acute ophthalmoparesis (AO) in the acute phase. Why various clinical signs develop under these conditions, however, has yet to be clarified. We investigated the fine specificity of anti-GQ1b IgG and its clinical correlation in sera from 82 patients: 56 with MFS, 11 with GBS, 13 with BBE, and 2 with AO. Anti-GQ1b IgG antibodies were absorbed by GT1a in 80 (98%) of the 82 sera, by GD1b in 11 (13%), and by the other b-series gangliosides GD3, GD2, or GT1b in 24 (29%). The most frequent pattern of fine specificity was the cross-reaction with GT1a alone, seen in 56 (68%) samples. Of the 11 patients with anti-GQ1b IgG, cross-reacting with GD1b, 6 (55%) had impaired deep sense, and the association was significant (p=0.02). This is the first study to show that the fine specificity of anti-GQ1b IgG is heterogeneous and that the difference is correlated with the presence of a particular clinical sign.