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Aerobic exercise training improves endothelial vasomotor function in the coronary circulation of patients with coronary artery disease (CAD), an effect that has been attributed to local repetitive increases in shear stress on the endothelium. To study the effects of exercise on endothelial function in the peripheral circulation, we used vascular ultrasound to examine flow-mediated dilation and nitroglycerin-mediated dilation in the brachial and posterior tibial arteries of 58 subjects with CAD. Studies were performed at baseline and after 10 weeks in 40 subjects (aged 59 +/- 10 years) who participated in a supervised cardiac rehabilitation program that predominantly involved moderate intensity leg exercise (three 30-minute sessions/week), and 18 matched patients who did not exercise and maintained a sedentary lifestyle. Exercise was associated with a 29% increase in functional capacity (7.3 +/- 2.2 vs 9.4 +/- 2.7 METs, p <0.001), and significant improvement in endothelium-dependent, flow-mediated dilation in a conduit artery of the leg, but not the arm. Nitroglycerin-mediated dilation in the upper arm and lower extremity was unaffected. These findings suggest that exercise improves endothelial function in peripheral conduit arteries of patients with CAD and that the beneficial effect may be more marked in the vascular beds of the exercised limbs. [ABSTRACT FROM AUTHOR]

Purpose: For the same reasons that rural telehealth has shown promise for enhancing the provision of care in underserved environments, social media recruitment may facilitate more inclusive research engagement in rural areas. However, little research has examined social media recruitment in the rural context, and few studies have evaluated the feasibility of using a free social media page to build a network of rural community members who may be interested in a research study. Here, we describe the rationale, process, and protocols of developing and implementing a social media approach to recruit rural residents to participate in an mHealth intervention., Methods: Informed by extensive formative research, we created a study Facebook page emphasizing community engagement in an mHealth behavioral intervention. We distributed the page to local networks and regularly posted recruitment and community messages. We collected data on the reach of the Facebook page, interaction with our messages, and initiations of our study intake survey., Findings: Over 21 weeks, our Facebook page gained 429 followers, and Facebook users interacted with our social media messages 3,080 times. Compared to messages that described desirable study features, messages that described community involvement resulted in higher levels of online interaction. Social media and other recruitment approaches resulted in 225 people initiating our in-take survey, 9 enrolling in our pilot study, and 26 placing their names on a waiting list., Conclusions: A standalone social media page highlighting community involvement shows promise for recruiting in rural areas., (© 2023 National Rural Health Association.)

In the brain’s gray matter, astrocytes regulate synapse properties, but their role is unclear for the white matter, where myelinated axons rapidly transmit information between gray matter areas. We found that in rodents, neuronal activity raised the intracellular calcium concentration ([Ca 2+ ] i ) in astrocyte processes located near action potential–generating sites in the axon initial segment (AIS) and nodes of Ranvier of myelinated axons. This released adenosine triphosphate, which was converted extracellularly to adenosine and thus, through A 2a receptors, activated HCN2-containing cation channels that regulate two aspects of myelinated axon function: excitability of the AIS and speed of action potential propagation. Variations in astrocyte-derived adenosine level between wake and sleep states or during energy deprivation could thus control white matter information flow and neural circuit function.

Voltage-gated sodium channels cluster in macromolecular complexes at nodes of Ranvier to promote rapid nerve impulse conduction in vertebrate nerves. Node assembly in peripheral nerves is thought to be initiated at heminodes at the extremities of myelinating Schwann cells, and fusion of heminodes results in the establishment of nodes. Here we show that assembly of 'early clusters' of nodal proteins in the murine axonal membrane precedes heminode formation. The neurofascin (Nfasc) proteins are essential for node assembly, and the formation of early clusters also requires neuronal Nfasc. Early clusters are mobile and their proteins are dynamically recruited by lateral diffusion. They can undergo fusion not only with each other but also with heminodes, thus contributing to the development of nodes in peripheral axons. The formation of early clusters constitutes the earliest stage in peripheral node assembly and expands the repertoire of strategies that have evolved to establish these essential structures., Competing Interests: EM, AG, DB, MZ, DS, PB No competing interests declared, (© 2021, Malavasi et al.)

Neuronal remodeling and myelination are two fundamental processes during neurodevelopment. How they influence each other remains largely unknown, even though their coordinated execution is critical for circuit function and often disrupted in neuropsychiatric disorders. It is unclear whether myelination stabilizes axon branches during remodeling or whether ongoing remodeling delays myelination. By modulating synaptic transmission, cytoskeletal dynamics, and axonal transport in mouse motor axons, we show that local axon remodeling delays myelination onset and node formation. Conversely, glial differentiation does not determine the outcome of axon remodeling. Delayed myelination is not due to a limited supply of structural components of the axon-glial unit but rather is triggered by increased transport of signaling factors that initiate myelination, such as neuregulin. Further, transport of promyelinating signals is regulated via local cytoskeletal maturation related to activity-dependent competition. Our study reveals an axon branch-specific fine-tuning mechanism that locally coordinates axon remodeling and myelination., (© 2021 Wang et al.)

Objectives: Prolonged cardiac arrest is known to cause global ischemic brain injury and functional impairment. Upon resuscitation, electroencephalographic recordings of brain activity begin to resume and can potentially be used to monitor neurologic recovery. We have previously shown that intrathecal orexin shows promise as a restorative drug and arousal agent in rodents. Our goal is to determine the electrophysiology effects of orexin in a rodent model of asphyxial cardiac arrest, focusing on the electroencephalographic activity in the gamma and super-gamma bands (indicative of return of higher brain function)., Design: Experimental animal study., Setting: University-based animal research laboratory., Subjects: Adult male Wistar rats., Interventions: In an established model of asphyxial cardiac arrest ( n = 24), we treated half of Wistar rats with orexin administered intranasally by atomizer 30 minutes post return of spontaneous circulation in one of two dose levels (10 and 50 µM); the rest were treated with saline as control. Continuous electroencephalographic recording was obtained and quantitatively analyzed for the gamma fraction. Gamma and high-frequency super-gamma band measures were compared against clinical recovery according to Neuro-Deficit Score., Measurements and Main Results: Compared with the control cohort, the high-dose orexin cohort showed significantly better Neuro-Deficit Score 4 hours after return of spontaneous circulation (55.17 vs 47.58; p < 0.02) and significantly higher mean gamma fraction (0.251 vs 0.177; p < 0.02) in cerebral regions surveyed by rostral electrodes for the first 170 minutes after administration of orexin., Conclusions: Our findings support early and continuous monitoring of electroencephalography-based gamma activity as a marker of better functional recovery after intranasal administration of orexin as measured by Neuro-Deficit Score in an established animal model of asphyxial cardiac arrest., Competing Interests: The authors have disclosed that they do not have any potential conflicts of interest., (Copyright © 2021 The Authors. Published by Wolters Kluwer Health, Inc. on behalf of the Society of Critical Care Medicine.)

Ion channel complexes promote action potential initiation at the mammalian axon initial segment (AIS), and modulation of AIS size by recruitment or loss of proteins can influence neuron excitability. Although endocytosis contributes to AIS turnover, how membrane proteins traffic to this proximal axonal domain is incompletely understood. Neurofascin186 (Nfasc186) has an essential role in stabilising the AIS complex to the proximal axon, and the AIS channel protein Kv7.3 regulates neuron excitability. Therefore, we have studied how these proteins reach the AIS. Vesicles transport Nfasc186 to the soma and axon terminal where they fuse with the neuronal plasma membrane. Nfasc186 is highly mobile after insertion in the axonal membrane and diffuses bidirectionally until immobilised at the AIS through its interaction with AnkyrinG. Kv7.3 is similarly recruited to the AIS. This study reveals how key proteins are delivered to the AIS and thereby how they may contribute to its functional plasticity., Competing Interests: AG, EM, DS, PB No competing interests declared, (© 2020, Ghosh et al.)

Cellular hyperexcitability is a salient feature of fragile X syndrome animal models. The cellular basis of hyperexcitability and how it responds to changing activity states is not fully understood. Here, we show increased axon initial segment length in CA1 of the Fmr1 -/y mouse hippocampus, with increased cellular excitability. This change in length does not result from reduced AIS plasticity, as prolonged depolarization induces changes in AIS length independent of genotype. However, depolarization does reduce cellular excitability, the magnitude of which is greater in Fmr1 -/y neurons. Finally, we observe reduced functional inputs from the entorhinal cortex, with no genotypic difference in the firing rates of CA1 pyramidal neurons. This suggests that AIS-dependent hyperexcitability in Fmr1 -/y mice may result from adaptive or homeostatic regulation induced by reduced functional synaptic connectivity. Thus, while AIS length and intrinsic excitability contribute to cellular hyperexcitability, they may reflect a homeostatic mechanism for reduced synaptic input onto CA1 neurons., Competing Interests: Declaration of Interests The authors declare no competing interests., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)

Proteome and transcriptome analyses aim at comprehending the molecular profiles of the brain, its cell-types and subcellular compartments including myelin. Despite the relevance of the peripheral nervous system for normal sensory and motor capabilities, analogous approaches to peripheral nerves and peripheral myelin have fallen behind evolving technical standards. Here we assess the peripheral myelin proteome by gel-free, label-free mass-spectrometry for deep quantitative coverage. Integration with RNA-Sequencing-based developmental mRNA-abundance profiles and neuropathy disease genes illustrates the utility of this resource. Notably, the periaxin-deficient mouse model of the neuropathy Charcot-Marie-Tooth 4F displays a highly pathological myelin proteome profile, exemplified by the discovery of reduced levels of the monocarboxylate transporter MCT1/SLC16A1 as a novel facet of the neuropathology. This work provides the most comprehensive proteome resource thus far to approach development, function and pathology of peripheral myelin, and a straightforward, accurate and sensitive workflow to address myelin diversity in health and disease., Competing Interests: SS, OJ, ME, NK, LW, DS, KK, DH, RJ, RF, MS, MR, PB, HW No competing interests declared, (© 2020, Siems et al.)

Selection of the correct targets for myelination and regulation of myelin sheath growth are essential for central nervous system (CNS) formation and function. Through a genetic screen in zebrafish and complementary analyses in mice, we find that loss of oligodendrocyte Neurofascin leads to mistargeting of myelin to cell bodies, without affecting targeting to axons. In addition, loss of Neurofascin reduces CNS myelination by impairing myelin sheath growth. Time-lapse imaging reveals that the distinct myelinating processes of individual oligodendrocytes can engage in target selection and sheath growth at the same time and that Neurofascin concomitantly regulates targeting and growth. Disruption to Caspr, the neuronal binding partner of oligodendrocyte Neurofascin, also impairs myelin sheath growth, likely reflecting its association in an adhesion complex at the axon-glial interface with Neurofascin. Caspr does not, however, affect myelin targeting, further indicating that Neurofascin independently regulates distinct aspects of CNS myelination by individual oligodendrocytes in vivo., (Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved.)

The process of myelination in the nervous system requires a coordinated formation of both transient and stable supramolecular complexes. Myelin-specific proteins play key roles in these assemblies, which may link membranes to each other or connect the myelinating cell cytoskeleton to the extracellular matrix. The myelin protein periaxin is known to play an important role in linking the Schwann cell cytoskeleton to the basal lamina through membrane receptors, such as the dystroglycan complex. Mutations that truncate periaxin from the C terminus cause demyelinating peripheral neuropathy, Charcot-Marie-Tooth (CMT) disease type 4F, indicating a function for the periaxin C-terminal region in myelination. We identified the cytoplasmic domain of β4 integrin as a specific high-affinity binding partner for periaxin. The C-terminal region of periaxin remains unfolded and flexible when bound to the third fibronectin type III domain of β4 integrin. Our data suggest that periaxin is able to link the Schwann cell cytoplasm to the basal lamina through a two-pronged interaction via different membrane protein complexes, which bind close to the N and C terminus of this elongated, flexible molecule.

In the central nervous system, the formation of nodes of Ranvier, the short, unmyelinated regions of the axon where voltage-gated sodium channels that mediate saltatory conduction in myelinated nerves are concentrated, is orchestrated by oligodendrocytes, the myelinating cells of the CNS. While transmission electron microscopy remains the gold standard for the study of how the nodal region is organized, this approach is both technically demanding and time-consuming. The availability of antibodies that can be used to label paranodal myelin and the underlying axonal domains that are formed as a result of myelination allows for the precise analysis of the nodal region. In this chapter, we describe the method used to prepare teased fiber preparations of CNS white matter. Teased fiber preparations facilitate the rapid, quantitative analysis of a large number of nodes of Ranvier per animal compared to conventional histological approaches.

The Neurofascins (NFASCs) are a family of proteins encoded by alternative transcripts of NFASC that cooperate in the assembly of the node of Ranvier in myelinated nerves. Differential expression of NFASC in neurons and glia presents a remarkable example of cell-type specific expression of protein isoforms with a common overall function. In mice there are three NFASC isoforms: Nfasc186 and Nfasc140, located in the axonal membrane at the node of Ranvier, and Nfasc155, a glial component of the paranodal axoglial junction. Nfasc186 and Nfasc155 are the major isoforms at mature nodes and paranodes, respectively. Conditional deletion of the glial isoform Nfasc155 in mice causes severe motor coordination defects and death at 16-17 days after birth. We describe a proband with severe congenital hypotonia, contractures of fingers and toes, and no reaction to touch or pain. Whole exome sequencing revealed a homozygous NFASC variant chr1:204953187-C>T (rs755160624). The variant creates a premature stop codon in 3 out of four NFASC human transcripts and is predicted to specifically eliminate Nfasc155 leaving neuronal Neurofascin intact. The selective absence of Nfasc155 and disruption of the paranodal junction was confirmed by an immunofluorescent study of skin biopsies from the patient versus control. We propose that the disease in our proband is the first reported example of genetic deficiency of glial Neurofascin isoforms in humans and that the severity of the condition reflects the importance of the Nfasc155 in forming paranodal axoglial junctions and in determining the structure and function of the node of Ranvier.

Vertebrate nervous systems rely on rapid nerve impulse transmission to support their complex functions. Fast conduction depends on ensheathment of nerve axons by myelin-forming glia and the clustering of high concentrations of voltage-gated sodium channels (Nav) in the axonal gaps between myelinated segments. These gaps are the nodes of Ranvier. Depolarization of the axonal membrane initiates the action potential responsible for impulse transmission, and the Nav help ensure that this is restricted to nodes. In the central nervous system, the formation of nodes and the clustering of Nav in nodal complexes is achieved when oligodendrocytes extend their processes and ultimately ensheath axons with myelin. However, the mechanistic relationship between myelination and the formation of nodal complexes is unclear. Here we review recent work in the central nervous system that shows that axons, by assembling distinct cytoskeletal interfaces, are not only active participants in oligodendrocyte process migration but are also significant contributors to the mechanisms by which myelination causes Nav clustering. We also discuss how the segregation of membrane protein complexes through their interaction with distinct cytoskeletal complexes may play a wider role in establishing surface domains in axons.

Charcot-Marie-Tooth (CMT) disease comprises up to 80 monogenic inherited neuropathies of the peripheral nervous system (PNS) that collectively result in demyelination and axon degeneration. The majority of CMT disease is primarily either dysmyelinating or demyelinating in which mutations affect the ability of Schwann cells to either assemble or stabilize peripheral nerve myelin. CMT4F is a recessive demyelinating form of the disease caused by mutations in the Periaxin ( PRX ) gene . Periaxin (Prx) interacts with Dystrophin Related Protein 2 (Drp2) in an adhesion complex with the laminin receptor Dystroglycan (Dag). In mice the Prx/Drp2/Dag complex assembles adhesive domains at the interface between the abaxonal surface of the myelin sheath and the cytoplasmic surface of the Schwann cell plasma membrane. Assembly of these appositions causes the formation of cytoplasmic channels called Cajal bands beneath the surface of the Schwann cell plasma membrane. Loss of either Periaxin or Drp2 disrupts the appositions and causes CMT in both mouse and man. In a mouse model of CMT4F, complete loss of Periaxin first prevents normal Schwann cell elongation resulting in abnormally short internodal distances which can reduce nerve conduction velocity, and subsequently precipitates demyelination. Distinct functional domains responsible for Periaxin homodimerization and interaction with Drp2 to form the Prx/Drp2/Dag complex have been identified at the N-terminus of Periaxin. However, CMT4F can also be caused by a mutation that results in the truncation of Periaxin at the extreme C-terminus with the loss of 391 amino acids. By modelling this in mice, we show that loss of the C-terminus of Periaxin results in a surprising reduction in Drp2. This would be predicted to cause the observed instability of both appositions and myelin, and contribute significantly to the clinical phenotype in CMT4F., Competing Interests: No competing interests were disclosed.

Nodes of Ranvier in the axons of myelinated neurons are exemplars of the specialized cell surface domains typical of polarized cells. They are rich in voltage-gated sodium channels (Nav) and thus underpin rapid nerve impulse conduction in the vertebrate nervous system [1]. Although nodal proteins cluster in response to myelination, how myelin-forming glia influence nodal assembly is poorly understood. An axoglial adhesion complex comprising glial Neurofascin155 and axonal Caspr/Contactin flanks mature nodes [2]. We have shown that assembly of this adhesion complex at the extremities of migrating oligodendroglial processes promotes process convergence along the axon during central nervous system (CNS) node assembly [3]. Here we show that anchorage of this axoglial complex to the axon cytoskeleton is essential for efficient CNS node formation. When anchorage is disrupted, both the adaptor Protein 4.1B and the cytoskeleton protein βII spectrin are mislocalized in the axon, and assembly of the node of Ranvier is significantly delayed. Nodal proteins and migrating oligodendroglial processes are no longer juxtaposed, and single detached nodal complexes replace the symmetrical heminodes found in both the CNS and peripheral nervous system (PNS) during development. We propose that axoglial adhesion complexes contribute to the formation of an interface between cytoskeletal elements enriched in Protein 4.1B and βII spectrin and those enriched in nodal ankyrinG and βIV spectrin. This clusters nascent nodal complexes at heminodes and promotes their timely coalescence to form the mature node of Ranvier. These data demonstrate a role for the axon cytoskeleton in the assembly of a critical neuronal domain, the node of Ranvier., (Copyright © 2017 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Antibodies to Contactin-1 and Neurofascin 155 (Nfasc155) have recently been associated with subsets of patients with chronic inflammatory demyelinating polyneuropathy (CIDP). Contactin-1 and Nfasc155 are cell adhesion molecules that constitute the septate-like junctions observed by electron microscopy in the paranodes of myelinated axons. Antibodies to Contactin-1 have been shown to affect the localization of paranodal proteins both in patient nerve biopsies and in animal models after passive transfer. However, it is unclear whether these antibodies alter the paranodal ultrastructure. We examined by electron microscopy sural nerve biopsies from two patients presenting with anti-Nfasc155 antibodies, and also four patients lacking antibodies, three normal controls, and five patients with other neuropathies. We found that patients with anti-Nfasc155 antibodies presented a selective loss of the septate-like junctions at all paranodes examined. Further, cellular processes penetrated into the expanded spaces between the paranodal myelin loops and the axolemma in these patients. These patients presented with important nerve conduction slowing and demyelination. Also, the reactivity of anti-Nfasc155 antibodies from these patients was abolished in neurofascin-deficient mice, confirming that the antibodies specifically target paranodal proteins. Our data indicate that anti-Nfasc155 destabilizes the paranodal axo-glial junctions and may participate in conduction deterioration., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Unlabelled: Schwann cells (SCs), ensheathing glia of the peripheral nervous system, support axonal survival and function. Abnormalities in SC metabolism affect their ability to provide this support and maintain axon integrity. To further interrogate this metabolic influence on axon-glial interactions, we generated OGT-SCKO mice with SC-specific deletion of the metabolic/nutrient sensing protein O-GlcNAc transferase that mediates the O-linked addition of N-acetylglucosamine (GlcNAc) moieties to Ser and Thr residues. The OGT-SCKO mice develop tomaculous demyelinating neuropathy characterized by focal thickenings of the myelin sheath (tomacula), progressive demyelination, axonal loss, and motor and sensory nerve dysfunction. Proteomic analysis identified more than 100 O-GlcNAcylated proteins in rat sciatic nerve, including Periaxin (PRX), a myelin protein whose mutation causes inherited neuropathy in humans. PRX lacking O-GlcNAcylation is mislocalized within the myelin sheath of these mutant animals. Furthermore, phenotypes of OGT-SCKO and Prx-deficient mice are very similar, suggesting that metabolic control of PRX O-GlcNAcylation is crucial for myelin maintenance and axonal integrity., Significance Statement: The nutrient sensing protein O-GlcNAc transferase (OGT) mediates post-translational O-linked N-acetylglucosamine (GlcNAc) modification. Here we find that OGT functions in Schwann cells (SCs) to maintain normal myelin and prevent axonal loss. SC-specific deletion of OGT (OGT-SCKO mice) causes a tomaculous demyelinating neuropathy accompanied with progressive axon degeneration and motor and sensory nerve dysfunction. We also found Periaxin (PRX), a myelin protein whose mutation causes inherited neuropathy in humans, is O-GlcNAcylated. Importantly, phenotypes of OGT-SCKO and Prx mutant mice are very similar, implying that compromised PRX function contributes to the neuropathy of OGT-SCKO mice. This study will be useful in understanding how SC metabolism contributes to PNS function and in developing new strategies for treating peripheral neuropathy by targeting SC function., (Copyright © 2016 the authors 0270-6474/16/369633-14$15.00/0.)

Spinal muscular atrophy (SMA) is a neuromuscular disease caused by low levels of SMN protein, primarily affecting lower motor neurons. Recent evidence from SMA and related conditions suggests that glial cells can influence disease severity. Here, we investigated the role of glial cells in the peripheral nervous system by creating SMA mice selectively overexpressing SMN in myelinating Schwann cells (Smn -/- ;SMN2 tg/0 ;SMN1 SC ). Restoration of SMN protein levels restricted solely to Schwann cells reversed myelination defects, significantly improved neuromuscular function and ameliorated neuromuscular junction pathology in SMA mice. However, restoration of SMN in Schwann cells had no impact on motor neuron soma loss from the spinal cord or ongoing systemic and peripheral pathology. This study provides evidence for a defined, intrinsic contribution of glial cells to SMA disease pathogenesis and suggests that therapies designed to include Schwann cells in their target tissues are likely to be required in order to rescue myelination defects and associated disease symptoms., (© The Author 2016. Published by Oxford University Press.)

Microtubule-based kinesin motors have many cellular functions, including the transport of a variety of cargos. However, unconventional roles have recently emerged, and kinesins have also been reported to act as scaffolding proteins and signaling molecules. In this work, we further extend the notion of unconventional functions for kinesin motor proteins, and we propose that Kif13b kinesin acts as a signaling molecule regulating peripheral nervous system (PNS) and central nervous system (CNS) myelination. In this process, positive and negative signals must be tightly coordinated in time and space to orchestrate myelin biogenesis. Here, we report that in Schwann cells Kif13b positively regulates myelination by promoting p38γ mitogen-activated protein kinase (MAPK)-mediated phosphorylation and ubiquitination of Discs large 1 (Dlg1), a known brake on myelination, which downregulates the phosphatidylinositol 3-kinase (PI3K)/v-AKT murine thymoma viral oncogene homolog (AKT) pathway. Interestingly, Kif13b also negatively regulates Dlg1 stability in oligodendrocytes, in which Dlg1, in contrast to Schwann cells, enhances AKT activation and promotes myelination. Thus, our data indicate that Kif13b is a negative regulator of CNS myelination. In summary, we propose a novel function for the Kif13b kinesin in glial cells as a key component of the PI3K/AKT signaling pathway, which controls myelination in both PNS and CNS.

Using exome sequencing in an individual with Charcot-Marie-Tooth disease (CMT) we have identified a mutation in the X-linked dystrophin-related protein 2 (DRP2) gene. A 60-year-old gentleman presented to our clinic and underwent clinical, electrophysiological and skin biopsy studies. The patient had clinical features of a length dependent sensorimotor neuropathy with an age of onset of 50 years. Neurophysiology revealed prolonged latencies with intermediate conduction velocities but no conduction block or temporal dispersion. A panel of 23 disease causing genes was sequenced and ultimately was uninformative. Whole exome sequencing revealed a stop mutation in DRP2, c.805C>T (Q269*). DRP2 interacts with periaxin and dystroglycan to form the periaxin-DRP2-dystroglycan complex which plays a role in the maintenance of the well-characterized Cajal bands of myelinating Schwann cells. Skin biopsies from our patient revealed a lack of DRP2 in myelinated dermal nerves by immunofluorescence. Furthermore electron microscopy failed to identify Cajal bands in the patient's dermal myelinated axons in keeping with ultrastructural pathology seen in the Drp2 knockout mouse. Both the electrophysiologic and dermal nerve twig pathology support the interpretation that this patient's DRP2 mutation causes characteristic morphological abnormalities recapitulating the Drp2 knockout model and potentially represents a novel genetic cause of CMT., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Rapid nerve conduction in myelinated nerves requires the clustering of voltage-gated sodium channels at nodes of Ranvier. The Neurofascin (Nfasc) gene has a unique role in node formation because it encodes glial and neuronal isoforms of neurofascin (Nfasc155 and Nfasc186, respectively) with key functions in assembling the nodal macromolecular complex. A third neurofascin, Nfasc140, has also been described; however, neither the cellular origin nor function of this isoform was known. Here we show that Nfasc140 is a neuronal protein strongly expressed during mouse embryonic development. Expression of Nfasc140 persists but declines during the initial stages of node formation, in contrast to Nfasc155 and Nfasc186, which increase. Nevertheless, Nfasc140, like Nfasc186, can cluster voltage-gated sodium channels (Nav) at the developing node of Ranvier and can restore electrophysiological function independently of Nfasc155 and Nfasc186. This suggests that Nfasc140 complements the function of Nfasc155 and Nfasc186 in initial stages of the assembly and stabilization of the nodal complex. Further, Nfasc140 is reexpressed in demyelinated white matter lesions of postmortem brain tissue from human subjects with multiple sclerosis. This expands the critical role of the Nfasc gene in the function of myelinated axons and reveals further redundancy in the mechanisms required for the formation of this crucial structure in the vertebrate nervous system., (Copyright © 2015 Zhang et al.)

Neuron-glia interactions establish functional membrane domains along myelinated axons. These include nodes of Ranvier, paranodal axoglial junctions and juxtaparanodes. Paranodal junctions are the largest vertebrate junctional adhesion complex, and they are essential for rapid saltatory conduction and contribute to assembly and maintenance of nodes. However, the molecular mechanisms underlying paranodal junction assembly are poorly understood. Ankyrins are cytoskeletal scaffolds traditionally associated with Na(+) channel clustering in neurons and are important for membrane domain establishment and maintenance in many cell types. Here we show that ankyrin-B, expressed by Schwann cells, and ankyrin-G, expressed by oligodendrocytes, are highly enriched at the glial side of paranodal junctions where they interact with the essential glial junctional component neurofascin 155. Conditional knockout of ankyrins in oligodendrocytes disrupts paranodal junction assembly and delays nerve conduction during early development in mice. Thus, glial ankyrins function as major scaffolds that facilitate early and efficient paranodal junction assembly in the developing CNS.

Postnatal synapse elimination plays a critical role in sculpting and refining neural connectivity throughout the central and peripheral nervous systems, including the removal of supernumerary axonal inputs from neuromuscular junctions (NMJs). Here, we reveal a novel and important role for myelinating glia in regulating synapse elimination at the mouse NMJ, where loss of a single glial cell protein, the glial isoform of neurofascin (Nfasc155), was sufficient to disrupt postnatal remodeling of synaptic circuitry. Neuromuscular synapses were formed normally in mice lacking Nfasc155, including the establishment of robust neuromuscular synaptic transmission. However, loss of Nfasc155 was sufficient to cause a robust delay in postnatal synapse elimination at the NMJ across all muscle groups examined. Nfasc155 regulated neuronal remodeling independently of its canonical role in forming paranodal axo-glial junctions, as synapse elimination occurred normally in mice lacking the axonal paranodal protein Caspr. Rather, high-resolution proteomic screens revealed that loss of Nfasc155 from glial cells was sufficient to disrupt neuronal cytoskeletal organization and trafficking pathways, resulting in reduced levels of neurofilament light (NF-L) protein in distal axons and motor nerve terminals. Mice lacking NF-L recapitulated the delayed synapse elimination phenotype observed in mice lacking Nfasc155, suggesting that glial cells regulate synapse elimination, at least in part, through modulation of the axonal cytoskeleton. Together, our study reveals a glial cell-dependent pathway regulating the sculpting of neuronal connectivity and synaptic circuitry in the peripheral nervous system., (Copyright © 2014 the authors 0270-6474/14/3412904-15$15.00/0.)

Fast, saltatory conduction in myelinated nerves requires the clustering of voltage-gated sodium channels (Nav) at nodes of Ranvier in a nodal complex. The Neurofascin (Nfasc) gene encodes neuronal Neurofascin 186 (Nfasc186) at the node and glial Neurofascin 155 at the paranode, and these proteins play a key role in node assembly. However, their role in the maintenance and stability of the node is less well understood. Here we show that by inducible ablation of Nfasc in neurons in adult mice, Nfasc186 expression is reduced by >99% and 94% at PNS and CNS nodes, respectively. Gliomedin and NrCAM at PNS and brevican at CNS nodes are largely lost with neuronal neurofascin; however, Nav at nodes of Ranvier persist, albeit with ∼40% reduction in expression levels. βIV Spectrin, ankyrin G, and, to a lesser extent, the β1 subunit of the sodium channel, are less affected at the PNS node than in the CNS. Nevertheless, there is a 38% reduction in PNS conduction velocity. Loss of Nfasc186 provokes CNS paranodal disorganization, but this does not contribute to loss of Nav. These results show that Nav at PNS nodes are still maintained in a nodal complex when neuronal neurofascin is depleted, whereas the retention of nodal Nav in the CNS, despite more extensive dissolution of the complex, suggests a supportive role for the partially disrupted paranodal axoglial junction in selectively maintaining Nav at the CNS node.

The influences of axon diameter, myelin thickness, and internodal length on the velocity of conduction of peripheral nerve action potentials are unclear. Previous studies have demonstrated a strong dependence of conduction velocity on internodal length. However, a theoretical analysis has suggested that this relationship may be lost above a nodal separation of ∼0.6 mm. Here we measured nerve conduction velocities in a rabbit model of limb lengthening that produced compensatory increases in peripheral nerve growth. Divided tibial bones in one hindlimb were gradually lengthened at 0.7 mm per day using an external frame attached to the bone. This was associated with a significant increase (33%) of internodal length (0.95-1.3 mm) in axons of the tibial nerve that varied in proportion to the mechanical strain in the nerve of the lengthened limb. Axonal diameter, myelin thickness, and g-ratios were not significantly altered by limb lengthening. Despite the substantial increase in internodal length, no significant change was detected in conduction velocity (∼43 m/s) measured either in vivo or in isolated tibial nerves. The results demonstrate that the internode remains plastic in the adult but that increases in internodal length of myelinated adult nerve axons do not result in either deficiency or proportionate increases in their conduction velocity and support the view that the internodal lengths of nerves reach a plateau beyond which their conduction velocities are no longer sensitive to increases in internodal length.

Cardiac Arrest (CA) leads to a global hypoxic-ischemic injury in the brain leading to a poor neurological outcome. Understanding the mechanisms of functional disruption in various regions of the brain may be essential for the development of improved diagnostic and therapeutic solutions. Using controlled laboratory experiment with animal models of CA, our primary focus here is on understanding the functional changes in the thalamus and the cortex, associated with the injury and acute recovery upon resuscitation. Specifically, to study the changes in thalamocortical synchrony through these periods, we acquired local field potentials (LFPs) from the ventroposterior lateral (VPL) nucleus of the thalamus and the forelimb somatosensory cortex (S1FL) in rats after asphyxial CA. Band-specific relative Hilbert phases were used to analyze synchrony between the LFPs. We observed that the CA induced global ischemia changes the local phase-relationships by introducing a phase-lag in both the thalamus and the cortex, while the synchrony between the two regions is nearly completely lost after CA.

Predictions that conduction velocities are sensitive to the distance between nodes of Ranvier in myelinated axons have implications for nervous system function during growth and repair. Internodal lengths defined by Schwann cells in hindlimb nerves, for example, can undergo a 4-fold increase during mouse development, and regenerated nerves have internodes that are uniformly short. Nevertheless, the influence of internodal length on conduction speed has limited experimental support. Here, we examined this problem in mice expressing a mutant version of periaxin, a protein required for Schwann cell elongation. Importantly, elongation of mutant Schwann cells was retarded without significant derangements to myelination or axon caliber. In young mice with short mutant Schwann cells, nerve conduction velocity was reduced and motor function was impaired. This demonstrates a functional relationship between internodal distance and conduction speed. Moreover, as internodes lengthened during postnatal growth, conduction velocities recovered to normal values and mutant mice exhibited normal motor and sensory behavior. This restoration of function confirms a further prediction by Huxley and Stämpfli that conduction speeds should increase as internodal distances lengthen until a "flat maximum" is reached, beyond which no further gains in conduction velocity accrue., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Accurately detecting hidden clinical or behavioral states from sequential measurements is an emerging topic in neuroscience and medicine, which may dramatically impact neural prosthetics, brain-computer interface and drug delivery. For example, early detection of an epileptic seizure from sequential electroencephalographic (EEG) measurements would allow timely administration of anticonvulsant drugs or neurostimulation, thus reducing physical impairment and risks of overtreatment. We develop a Bayesian paradigm for state transition detection that combines optimal control and Markov processes. We define a hidden Markov model of the state evolution and develop a detection policy that minimizes a loss function of both probability of false positives and accuracy (i.e., lag between estimated and actual transition time). Our strategy automatically adapts to each newly acquired measurement based on the state evolution model and the relative loss for false positives and accuracy, thus resulting in a time varying threshold policy. The paradigm was used in two applications: 1) detection of movement onset (behavioral state) from subthalamic single unit recordings in Parkinson's disease patients performing a motor task; 2) early detection of an approaching seizure (clinical state) from multichannel intracranial EEG recordings in rodents treated with pentylenetetrazol chemoconvulsant. Our paradigm performs significantly better than chance and improves over widely used detection algorithms.

Cajal bands are cytoplasmic channels flanked by appositions where the abaxonal surface of Schwann cell myelin apposes and adheres to the overlying plasma membrane. These appositions contain a dystroglycan complex that includes periaxin and dystrophin-related protein 2 (Drp2). Loss of periaxin disrupts appositions and Cajal bands in Schwann cells and causes a severe demyelinating neuropathy in mouse and human. Here, we investigated the role of mouse Drp2 in apposition assembly and Cajal band function and compared it with periaxin. We show that periaxin and Drp2 are not only both required to form appositions, but they must also interact. Periaxin-Drp2 interaction is also required for Drp2 phosphorylation, but phosphorylation is not required for the assembly of appositions. Drp2 loss causes corresponding increases in Dystrophin family members, utrophin and dystrophin Dp116, although dystroglycan remains unchanged. We also show that all dystroglycan complexes in Schwann cells use the uncleaved form of β-dystroglycan. Drp2-null Schwann cells have disrupted appositions and Cajal bands, and they undergo focal hypermyelination and concomitant demyelination. Nevertheless, they do not have the short internodal lengths and associated reduced nerve conduction velocity seen in the absence of periaxin, showing that periaxin regulates Schwann cell elongation independent of its role in the dystroglycan complex. We conclude that the primary role of the dystroglycan complex in appositions is to stabilize and limit the radial growth of myelin.

Most Legionella culture tests are performed on building water samples that have been shipped to analytical laboratories for analysis. Significant (≥ 1 log₁₀ unit) changes in results were observed in 52% of held samples (6 h or longer, ambient temperature) drawn from building water systems in a 42-sample initial survey. It was not practical to use the spread plate protocol for on-site "t = 0" cultures in a larger, more diverse survey of thousands of building water systems. Two thousand four hundred twenty-one (2421) building water samples were split for on-site analysis using a field culture protocol and then also cultured after overnight shipment to the lab for analysis with the standardized spread plate method. Legionella test results from building water system samples are usually interpreted as ≥ a numerical detection or action limit. Therefore, binary statistical analyses were calculated by setting t = 0 culture results to "true". Overall in this survey, 10.4% of water samples sent to the laboratory for analysis returned either false-positive or false-negative results. The overall positive predictive value of results was poor (36%). Most (83%) false-positive results were returned from utility water systems. Most (74%) false-negative results were returned from potable water systems. These inaccuracies have serious implications in regard to interpretation and use of Legionella test results. The overall negative predictive value of results was excellent (99%) and also it was good (92%) for results from a polymerase chain reaction (PCR) assay that can be therefore used as a negative screening method., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

In developing peripheral nerves, differentiating Schwann cells sort individual axons from bundles and ensheath them to generate multiple layers of myelin. In recent years, there has been an increased understanding of the extracellular and intracellular factors that initiate and stimulate Schwann cell myelination, together with a growing appreciation of some of the signaling pathways involved. However, our knowledge of how Schwann cell growth is regulated during myelination is still incomplete. The mammalian target of rapamycin (mTOR) is a core kinase in two major complexes, mTORC1 and mTORC2, that regulate cell growth and differentiation in a variety of mammalian cells. Here we show that elimination of mTOR from murine Schwann cells prevented neither radial sorting nor the initiation of myelination. However, normal postnatal growth of myelinating Schwann cells, both radially and longitudinally, was highly retarded. The myelin sheath in the mutant was much thinner than normal; nevertheless, sheath thickness relative to axon diameter (g-ratio) remained constant in both wild-type and mutant nerves from P14 to P90. Although axon diameters were normal in the mutant at the initiation of myelination, further growth as myelination proceeded was retarded, and this was associated with reduced phosphorylation of neurofilaments. Consistent with thinner axonal diameters and internodal lengths, conduction velocities in mutant quadriceps nerves were also reduced. These data establish a critical role for mTOR signaling in both the longitudinal and radial growth of the myelinating Schwann cell.

Transparency of the ocular lens depends on symmetric packing and membrane organization of highly elongated hexagonal fiber cells. These cells possess an extensive, well-ordered cortical cytoskeleton to maintain cell shape and to anchor membrane components. Periaxin (Prx), a PDZ domain protein involved in myelin sheath stabilization, is also a component of adhaerens plaques in lens fiber cells. Here we show that Prx is expressed in lens fibers and exhibits maturation dependent redistribution, clustering discretely at the tricellular junctions in mature fiber cells. Prx exists in a macromolecular complex with proteins involved in membrane organization including ankyrin-B, spectrin, NrCAM, filensin, ezrin and desmoyokin. Importantly, Prx knockout mouse lenses were found to be softer and more easily deformed than normal lenses, revealing disruptions in fiber cell hexagonal packing, membrane skeleton and membrane stability. These observations suggest a key role for Prx in maturation, packing, and membrane organization of lens fiber cells. Hence, there may be functional parallels between the roles of Prx in membrane stabilization of the myelin sheath and the lens fiber cell., (Copyright © 2011 Elsevier Inc. All rights reserved.)

The axon initial segment (AIS) is critical for the initiation and propagation of action potentials. Assembly of the AIS requires interactions between scaffolding molecules and voltage-gated sodium channels, but the molecular mechanisms that stabilize the AIS are poorly understood. The neuronal isoform of Neurofascin, Nfasc186, clusters voltage-gated sodium channels at nodes of Ranvier in myelinated nerves: here, we investigate its role in AIS assembly and stabilization. Inactivation of the Nfasc gene in cerebellar Purkinje cells of adult mice causes rapid loss of Nfasc186 from the AIS but not from nodes of Ranvier. This causes AIS disintegration, impairment of motor learning and the abolition of the spontaneous tonic discharge typical of Purkinje cells. Nevertheless, action potentials with a modified waveform can still be evoked and basic motor abilities remain intact. We propose that Nfasc186 optimizes communication between mature neurons by anchoring the key elements of the adult AIS complex., (Copyright © 2011 Elsevier Inc. All rights reserved.)

The early detection of epileptic seizures requires computing relevant statistics from multivariate data and defining a robust decision strategy as a function of these statistics that accurately detects the transition from the normal to the peri-ictal (problematic) state. We model the afflicted brain as a hidden Markov model (HMM) with two hidden clinical states (normal and peri-ictal). The output of the HMM is a statistic computed from multivariate neural measurements. A Bayesian framework is developed to analyze the a posteriori conditional probability of being in peri-ictal state given current and past output measurements. We apply this method to multichannel intracortical EEGs (iEEGs) from the thalamo-cortical ictal pathway in an epilepsy rat model. We first define the output statistic as the max singular value of a connectivity matrix computed on the EEG channels with spectral techniques Then, we estimate the HMM transition probabilities from this statistic and track the a posteriori probability of being in peri-ictal state (the "information state variable"). We show how the information state variable changes as a function of time and we predict a seizure when this variable becomes greater than 0.5. This Bayesian strategy significantly improves over chance level and heuristically-chosen threshold-based predictors.

Objective: Injury during routine spinal cord procedures could result in devastating consequences for the surgical patient. Spinal cord monitoring through somatosensory evoked potentials (SEPs) remains a viable method for prevention of serious injury., Methods: The adaptive coherence estimation (ACE) is a method to iteratively calculate signal match quality through successive filter entrainment. Here we compare the speed of detection with ACE to conventional amplitude measurements. Both absolute magnitude of ACE and amplitude as well as slope change detector algorithm (Farley-Hinich) was run as well to determine the earliest time when a significant change occurred., Results: The standard error for the ACE algorithm is close to one tenth of the amplitude measure, Since the ACE algorithm achieved low variance during baseline measurement, we were able to achieve rapid detection of injury. For absolute magnitude detection ACE was faster than amplitude for the 20 g injury weight class. It took an average of 10 epochs to detect the injury with adaptive coherence and nearly 19 with standard amplitude metrics using absolute magnitude changes. Abrupt change detection methods using slope change show that ACE provides more favorable detection capabilities comparable to amplitude. Additionally, there was a significant increase in the ROC curve between ACE and amplitude alone (p<0.05)., Conclusions: Because of its excellent detection capabilities, the adaptive coherence method provides an excellent supplement to traditional amplitude for capturing injury-related changes in SEPs., Significance: Adaptive coherence remains a viable method for rapidly and accurately detecting spinal injury., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Syncoilin is an atypical type III intermediate filament (IF) protein, which is expressed in muscle and is associated with the dystrophin-associated protein complex. Here, we show that syncoilin is expressed in both the central and peripheral nervous systems. Isoform Sync1 is dominant in the brain, but isoform Sync2 is dominant in the spinal cord and sciatic nerve. Peripherin is a type III IF protein that has been shown to colocalise and interact with syncoilin. Our analyses suggest that syncoilin might function to modulate formation of peripherin filament networks through binding to peripherin isoforms. Peripherin is associated with the disease amyotrophic lateral sclerosis (ALS), thus establishing a link between syncoilin and ALS. A neuronal analysis of the syncoilin-null mouse (Sync(-/-)) revealed a reduced ability in accelerating treadmill and rotarod tests. This phenotype might be attributable to the impaired function of extensor digitorum longus muscle and type IIb fibres caused by a shift from large- to small-calibre motor axons in the ventral root.

Objective: To evaluate an electroencephalography (EEG)-based index, the Cerebral Health Index in babies (CHI/b), for identification of neonates with high Sarnat scores and abnormal EEG as markers of hypoxic ischemic encephalopathy (HIE) after perinatal asphyxia., Study Design: This is a retrospective study using 30 min of EEG data collected from 20 term neonates with HIE and 20 neurologically normal neonates. The HIE diagnosis was made on clinical grounds based on history and examination findings. The maximum-modified clinical Sarnat score was used to grade HIE severity within 72 h of life. All neonates underwent 2-channel bedside EEG monitoring. A trained electroencephalographer blinded to clinical data visually classified each EEG as normal, mild or severely abnormal. The CHI/b was trained using data from Channel 1 and tested on Channel 2., Result: The CHI/b distinguished among HIE and controls (P<0.02) and among the three visually interpreted EEG categories (P<0.0002). It showed a sensitivity of 82.4% and specificity of 100% in detecting high grades of neonatal encephalopathy (Sarnat 2 and 3), with an area under the receiver operator characteristic (ROC) curve of 0.912. CHI/b also identified differences between normal vs mildly abnormal (P<0.005), mild vs severely abnormal (P<0.01) and normal vs severe (P<0.002) EEG groups. An ROC curve analysis showed that the optimal ability of CHI/b to discriminate poor outcome was 89.7% (sensitivity: 87.5%; specificity: 82.4%)., Conclusion: The CHI/b identified neonates with high Sarnat scores and abnormal EEG. These results support its potential as an objective indicator of neurological injury in infants with HIE.

All but the smallest-diameter axons in the central nervous system are myelinated, but the signals that initiate myelination are unknown. Our prior work has shown that integrin signaling forms part of the cell-cell interactions that ensure only those oligodendrocytes contacting axons survive. Here, therefore, we have asked whether integrins regulate the interactions that lead to myelination. Using homologous recombination to insert a single-copy transgene into the hypoxanthine phosphoribosyl transferase (hprt) locus, we find that mice expressing a dominant-negative beta1 integrin in myelinating oligodendrocytes require a larger axon diameter to initiate timely myelination. Mice with a conditional deletion of focal adhesion kinase (a signaling molecule activated by integrins) exhibit a similar phenotype. Conversely, transgenic mice expressing dominant-negative beta3 integrin in oligodendrocytes display no myelination abnormalities. We conclude that beta1 integrin plays a key role in the axoglial interactions that sense axon size and initiate myelination, such that loss of integrin signaling leads to a delay in myelination of small-diameter axons.

Neuromuscular junctions (NMJs) are normally thought to comprise three major cell types: skeletal muscle fibres, motor neuron terminals and perisynaptic terminal Schwann cells. Here we studied a fourth population of junctional cells in mice and rats, revealed using a novel cytoskeletal antibody (2166). These cells lie outside the synaptic basal lamina but form caps over NMJs during postnatal development. NMJ-capping cells also bound rPH, HM-24, CD34 antibodies and cholera toxin B subunit. Bromodeoxyuridine incorporation indicated activation, proliferation and spread of NMJ-capping cells following denervation in adults, in advance of terminal Schwann cell sprouting. The NMJ-capping cell reaction coincided with expression of tenascin-C but was independent of this molecule because capping cells also dispersed after denervation in tenascin-C-null mutant mice. NMJ-capping cells also dispersed after local paralysis with botulinum toxin and in atrophic muscles of transgenic R6/2 mice. We conclude that NMJ-capping cells (proposed name 'kranocytes') represent a neglected, canonical cellular constituent of neuromuscular junctions where they could play a permissive role in synaptic regeneration.

Rapid nerve impulse conduction in myelinated axons requires the concentration of voltage-gated sodium channels at nodes of Ranvier. Myelin-forming oligodendrocytes in the central nervous system (CNS) induce the clustering of sodium channels into nodal complexes flanked by paranodal axoglial junctions. However, the molecular mechanisms for nodal complex assembly in the CNS are unknown. Two isoforms of Neurofascin, neuronal Nfasc186 and glial Nfasc155, are components of the nodal and paranodal complexes, respectively. Neurofascin-null mice have disrupted nodal and paranodal complexes. We show that transgenic Nfasc186 can rescue the nodal complex when expressed in Nfasc(-/-) mice in the absence of the Nfasc155-Caspr-Contactin adhesion complex. Reconstitution of the axoglial adhesion complex by expressing transgenic Nfasc155 in oligodendrocytes also rescues the nodal complex independently of Nfasc186. Furthermore, the Nfasc155 adhesion complex has an additional function in promoting the migration of myelinating processes along CNS axons. We propose that glial and neuronal Neurofascins have distinct functions in the assembly of the CNS node of Ranvier.

Cytoskeletal scaffolding complexes help organize specialized membrane domains with unique functions on the surface of cells. In this study, we define the scaffolding potential of the Schwann cell dystrophin glycoprotein complex (DGC) by establishing the presence of four syntrophin isoforms, (alpha1, beta1, beta2, and gamma2), and one dystrobrevin isoform, (alpha-dystrobrevin-1), in the abaxonal membrane. Furthermore, we demonstrate the existence of two separate DGCs in Schwann cells that divide the abaxonal membrane into spatially distinct domains, the DRP2/periaxin rich plaques and the Cajal bands that contain Dp116, utrophin, alpha-dystrobrevin-1 and four syntrophin isoforms. Finally, we show that the two different DGCs can scaffold unique accessory molecules in distinct areas of the Schwann cell membrane. Specifically, the cholesterol transporter ABCA1, associates with the Dp116/syntrophin complex in Cajal bands and is excluded from the DRP2/periaxin rich plaques., ((c) 2008 Wiley-Liss, Inc.)

Mutations in the EGR2 gene cause a spectrum of Charcot-Marie-Tooth disease and related inherited peripheral neuropathies. We ascertained ten consecutive patients with various EGR2 mutations, report a novel de novo mutation, and provide longitudinal clinical data to characterize the natural history of the peripheral neuropathy. We confirmed that respiratory compromise and cranial nerve dysfunction are commonly associated with EGR2 mutations and can be useful in guiding molecular diagnosis. We also contrast morphological studies in the context of the I268N homozygous recessive mutation affecting the NAB repressor binding site and the R359W dominant-negative mutation in the zinc-finger domain.

Signaling by laminins and axonal neuregulin has been implicated in regulating axon sorting by myelin-forming Schwann cells. However, the signal transduction mechanisms are unknown. Focal adhesion kinase (FAK) has been linked to alpha6beta1 integrin and ErbB receptor signaling, and we show that myelination by Schwann cells lacking FAK is severely impaired. Mutant Schwann cells could interdigitate between axon bundles, indicating that FAK signaling was not required for process extension. However, Schwann cell FAK was required to stimulate cell proliferation, suggesting that amyelination was caused by insufficient Schwann cells. ErbB2 receptor and AKT were robustly phosphorylated in mutant Schwann cells, indicating that neuregulin signaling from axons was unimpaired. These findings demonstrate the vital relationship between axon defasciculation and Schwann cell number and show the importance of FAK in regulating cell proliferation in the developing nervous system.

Voltage-gated sodium channels are concentrated in myelinated nerves at the nodes of Ranvier flanked by paranodal axoglial junctions. Establishment of these essential nodal and paranodal domains is determined by myelin-forming glia, but the mechanisms are not clear. Here, we show that two isoforms of Neurofascin, Nfasc155 in glia and Nfasc186 in neurons, are required for the assembly of these specialized domains. In Neurofascin-null mice, neither paranodal adhesion junctions nor nodal complexes are formed. Transgenic expression of Nfasc155 in the myelinating glia of Nfasc-/- nerves rescues the axoglial adhesion complex by recruiting the axonal proteins Caspr and Contactin to the paranodes. However, in the absence of Nfasc186, sodium channels remain diffusely distributed along the axon. Our study shows that the two major Neurofascins play essential roles in assembling the nodal and paranodal domains of myelinated axons; therefore, they are essential for the transition to saltatory conduction in developing vertebrate nerves.

The evolution of complex nervous systems in vertebrates has been accompanied by, and probably dependent on, the acquisition of the myelin sheath. Although there has been substantial progress in our understanding of the factors that determine glial cell fate, much less is known about the cellular mechanisms that determine how the myelin sheath is extended and stabilized around axons. This review highlights four crucial stages of myelination, namely, the selection of axons and initiation of cell-cell interactions between them and glial cells, the establishment of stable intercellular contact and assembly of the nodes of Ranvier, regulation of myelin thickness and, finally, longitudinal extension of myelin segments in response to the lengthening of axons during postnatal growth.

Purpose: Anterior thalamic nucleus (AN) deep brain stimulation (DBS) is effective in raising EEG and clonic seizure threshold in experimental models. Little is known about the specific properties of DBS that afford its anticonvulsant effect. We sought to test the hypothesis that experimental seizures and the anticonvulsant action of AN DBS alter the underlying regional neurochemistry of AN, specifically with facilitation of the serotonergic system to local electrical stimulation., Methods: Halothane-anesthetized adult Sprague-Dawley male rats underwent stereotactically guided bilateral placement of bipolar stimulating steel electrodes and dialysis probes-guide cannulae in AN and posterior thalamus (PT), and placement of four epidural EEG screw electrodes 48 h before experiments. Both stimulated (AN DBS) and nonstimulated (NO DBS) animals (n=7 per group) were infused with i.v. pentylenetetrazol (PTZ, 5.5 mg/kg/min). Simultaneous thalamic and cortical EEG were recorded, and microdialysis samples were collected from AN and PT in 20-min epochs. AN stimulation was delivered (150 microA; 0.1-ms pulse duration) 40 min before and continued during PTZ infusion., Results: Bilateral AN stimulation delayed the onset of EEG seizures compared with controls: 82+/-8 vs. 58+/-5 min (p=0.02). PTZ infusion alone, or together with stimulation, resulted in a steady increase in norepinephrine (NE), but not dopamine, at AN and PT sites (p<0.001). Although extracellular serotonin was measured at very low levels, the metabolite, 5-hydroxyindoleacetic acid (5-HIAA) increased selectively in AN after stimulation and during preconvulsant infusion of PTZ (p<0.001), returning to baseline after the first generalized seizure., Conclusions: These data suggest that PTZ and DBS together enhance the nonselective release of NE in thalamic nuclei while specifically stimulating AN-localized serotonin. Low serotonin levels at baseline and during STIM alone or PTZ infusion may indicate efficient reuptake systems for serotonin, with 5-HIAA serving as a surrogate marker for serotonergic activity. Modulation of the AN-specific serotonergic activity may be critical in altering PTZ seizure threshold and be an important neurotransmitter system underlying the efficacy of AN DBS.