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Carroll AS, Park SB, Lin CSY, Taylor MS, Kwok F, Simon NG, Reilly MM, Kiernan MC, Vucic S. Axonal excitability as an early biomarker of nerve involvement in hereditary transthyretin amyloidosis. Clin Neurophysiol 2024; 159:81-95. [PMID: 38377648 DOI: 10.1016/j.clinph.2024.01.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2023] [Revised: 12/26/2023] [Accepted: 01/22/2024] [Indexed: 02/22/2024]
Abstract
OBJECTIVES The treatment of hereditary transthyretin amyloidosis polyneuropathy (ATTRv-PN) has been revolutionised by genetic therapies, with dramatic improvements in patient outcomes. Whilst the optimal timing of treatment initiation remains unknown, early treatment is desirable. Consequently, the aim of the study was to develop biomarkers of early nerve dysfunction in ATTRv-PN. METHODS Ulnar motor and sensory axonal excitability studies were prospectively undertaken on 22 patients with pathogenic hereditary transthyretin amyloid (ATTRv) gene variants, 12 with large fibre neuropathy (LF+) and 10 without (LF-), with results compared to age- and sex-matched healthy controls. RESULTS In motor axons we identified a continuum of change from healthy controls, to LF- and LF+ ATTRv with progressive reduction in hyperpolarising threshold electrotonus (TEh40(10-20 ms): p = 0.04, TEh40(20-40 ms): p = 0.01 and TEh40(90-10 ms): p = 0.01), suggestive of membrane depolarisation. In sensory axons lower levels of subexcitability were observed on single (SubEx) and double pulse (SubEx2) recovery cycle testing in LF+ (SubEx: p = 0.015, SubEx2: p = 0.015, RC(2-1): p = 0.04) suggesting reduced nodal slow potassium conductance, which promotes sensory hyperexcitability, paraesthesia and pain. There were no differences in sensory or motor excitability parameters when comparing different ATTRv variants. CONCLUSIONS These progressive changes seen across the disease spectrum in ATTRv-PN suggest that axonal excitability has utility to identify early and progressive nerve dysfunction in ATTRv, regardless of genotype. SIGNIFICANCE Axonal excitability is a promising early biomarker of nerve dysfunction in ATTRv-PN.
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Affiliation(s)
- Antonia S Carroll
- Brain and Mind Centre, Faculty of Medicine and Health, Translational Research Collective University of Sydney, and Department of Neurology, Royal Prince Alfred Hospital, Sydney, Australia; Westmead Amyloidosis Centre, Westmead Hospital, University of Sydney, Sydney, Australia; Centre for Neuromuscular Disease, Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, London, UK.
| | - Susanna B Park
- Brain and Mind Centre, Faculty of Medicine and Health, School of Medical Sciences, University of Sydney, Sydney, Australia
| | - Cindy S Y Lin
- Brain and Mind Centre, Faculty of Medicine and Health, Translational Research Collective University of Sydney, and Department of Neurology, Royal Prince Alfred Hospital, Sydney, Australia
| | - Mark S Taylor
- Westmead Amyloidosis Centre, Westmead Hospital, University of Sydney, Sydney, Australia
| | - Fiona Kwok
- Westmead Amyloidosis Centre, Westmead Hospital, University of Sydney, Sydney, Australia
| | - Neil G Simon
- Faculty of Medicine and Health Sciences, Macquarie University, Sydney, Australia
| | - Mary M Reilly
- Centre for Neuromuscular Disease, Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, London, UK
| | - Matthew C Kiernan
- Brain and Mind Centre, Faculty of Medicine and Health, Translational Research Collective University of Sydney, and Department of Neurology, Royal Prince Alfred Hospital, Sydney, Australia
| | - Steve Vucic
- Brain and Nerve Centre, Concord Hospital, University of Sydney, Sydney, Australia
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Schmid L, Klotz T, Röhrle O, Powers RK, Negro F, Yavuz UŞ. Postinhibitory excitation in motoneurons can be facilitated by hyperpolarization-activated inward currents: A simulation study. PLoS Comput Biol 2024; 20:e1011487. [PMID: 38241412 PMCID: PMC10843122 DOI: 10.1371/journal.pcbi.1011487] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2023] [Revised: 02/05/2024] [Accepted: 01/09/2024] [Indexed: 01/21/2024] Open
Abstract
Postinhibitory excitation is a transient overshoot of a neuron's baseline firing rate following an inhibitory stimulus and can be observed in vivo in human motoneurons. However, the biophysical origin of this phenomenon is still unknown and both reflex pathways and intrinsic motoneuron properties have been proposed. We hypothesized that postinhibitory excitation in motoneurons can be facilitated by hyperpolarization-activated inward currents (h-currents). Using an electrical circuit model, we investigated how h-currents can modulate the postinhibitory response of motoneurons. Further, we analyzed the spike trains of human motor units from the tibialis anterior muscle during reciprocal inhibition. The simulations revealed that the activation of h-currents by an inhibitory postsynaptic potential can cause a short-term increase in a motoneuron's firing probability. This result suggests that the neuron can be excited by an inhibitory stimulus. In detail, the modulation of the firing probability depends on the time delay between the inhibitory stimulus and the previous action potential. Further, the postinhibitory excitation's strength correlates with the inhibitory stimulus's amplitude and is negatively correlated with the baseline firing rate as well as the level of input noise. Hallmarks of h-current activity, as identified from the modeling study, were found in 50% of the human motor units that showed postinhibitory excitation. This study suggests that h-currents can facilitate postinhibitory excitation and act as a modulatory system to increase motoneuron excitability after a strong inhibition.
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Affiliation(s)
- Laura Schmid
- Institute for Modelling and Simulation of Biomechanical Systems, University of Stuttgart, Stuttgart, Germany
| | - Thomas Klotz
- Institute for Modelling and Simulation of Biomechanical Systems, University of Stuttgart, Stuttgart, Germany
| | - Oliver Röhrle
- Institute for Modelling and Simulation of Biomechanical Systems, University of Stuttgart, Stuttgart, Germany
- Stuttgart Center for Simulation Sciences (SC SimTech), University of Stuttgart, Stuttgart, Germany
| | - Randall K. Powers
- Department of Physiology and Biophysics, University of Washington, Seattle, Washington, United States of America
| | - Francesco Negro
- Department of Clinical and Experimental Sciences, Università degli Studi di Brescia, Brescia, Italy
| | - Utku Ş. Yavuz
- Department of Biomedical Signals and Systems, Faculty of Electrical Engineering, Mathematics and Computer Sciences, University of Twente, Enschede, Netherlands
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Chien CY, Wang JD, Lin CC. Nerve excitability test and lead toxicity: a case-control study. J Occup Med Toxicol 2023; 18:19. [PMID: 37653420 PMCID: PMC10472560 DOI: 10.1186/s12995-023-00385-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2023] [Accepted: 08/11/2023] [Indexed: 09/02/2023] Open
Abstract
BACKGROUND Although conventional electrophysiological parameters have been proposed as clinical indicators for monitoring lead neuropathies, their correlations with blood lead level are weak. In this study, we investigated the applicability of nerve excitability tests (NETs) to evaluate lead intoxication. METHODS Fourteen workers who were exposed to lead with an elevated blood level ranging from 17.8 to 64.9 µg/dL and 20 healthy controls with similar ages and body heights were enrolled. Both workers and controls underwent nerve conduction studies (NCSs), motor evoked potentials (MEPs) with transcranial magnetic stimulation (TMS), and NETs. RESULTS NCSs showed prolonged distal latencies and decreased motor nerve conduction velocity of median nerves in the workers but without significant correlation to blood lead level (BLL). Significantly prolonged MEP latency was observed in the workers (+ 6 ms). NETs demonstrated hyperpolarized resting membrane potentials in stimulus-response curves and changes in the property of potassium channels under a hyperpolarized current in threshold electrotonus, implying that lead hyperpolarized nerves by interfering with potassium channels. NETs also showed a better correlation with BLL than conventional electrophysiological parameters. CONCLUSIONS Axonal hyperpolarization and central conduction delay are more apparently reflecting elevated BLL than NCS. NET may have the potential for early detection of lead neuropathy.
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Affiliation(s)
- Chung-Yao Chien
- Department of Neurology, College of Medicine, National Cheng Kung University Hospital, National Cheng Kung University, 138 Sheng Li Road, Tainan, 704, Taiwan
| | - Jung-Der Wang
- Department of Public Health, College of Medicine, National Cheng Kung University, Tainan, Taiwan
- Department of Occupational and Environmental Medicine, National Cheng Kung University Hospital, Tainan, Taiwan
| | - Chou-Ching Lin
- Department of Neurology, College of Medicine, National Cheng Kung University Hospital, National Cheng Kung University, 138 Sheng Li Road, Tainan, 704, Taiwan.
- Department of Biomedical Engineering, National Cheng Kung University, Tainan, Taiwan.
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4
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Pia H, Nochi Z, Kristensen AG, Pelz B, Goetz M, Hoeink JN, Blockeel AJ, Mouraux A, Truini A, Finnerup NB, Phillips KG, Treede RD, Tankisi H. The test–retest reliability of large and small fiber nerve excitability testing with threshold tracking. Clin Neurophysiol Pract 2023; 8:71-78. [PMID: 37181417 PMCID: PMC10172996 DOI: 10.1016/j.cnp.2023.03.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2023] [Revised: 03/08/2023] [Accepted: 03/26/2023] [Indexed: 04/09/2023] Open
Abstract
Objective Standard nerve excitability testing (NET) predominantly assesses Aα- and Aβ-fiber function, but a method examining small afferents would be of great interest in pain studies. Here, we examined the properties of a novel perception threshold tracking (PTT) method that preferentially activates Aδ-fibers using weak currents delivered by a novel multipin electrode and compared its reliability with NET. Methods Eighteen healthy subjects (mean age:34.06 ± 2.0) were examined three times with motor and sensory NET and PTT in morning and afternoon sessions on the same day (intra-day reliability) and after a week (inter-day reliability). NET was performed on the median nerve, while PTT stimuli were delivered through a multipin electrode located on the forearm. During PTT, subjects indicated stimulus perception via a button press and the intensity of the current was automatically increased or decreased accordingly by Qtrac software. This allowed changes in the perception threshold to be tracked during strength-duration time constant (SDTC) and threshold electrotonus protocols. Results The coefficient of variation (CoV) and interclass coefficient of variation (ICC) showed good-excellent reliability for most NET parameters. PTT showed poor reliability for both SDTC and threshold electrotonus parameters. There was a significant correlation between large (sensory NET) and small (PTT) fiber SDTC when all sessions were pooled (r = 0.29, p = 0.03). Conclusions Threshold tracking technique can be applied directly to small fibers via a psychophysical readout, but with the current technique, the reliability is poor. Significance Further studies are needed to examine whether Aβ-fiber SDTC may be a surrogate biomarker for peripheral nociceptive signalling.
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Ruijs TQ, Koopmans IW, de Kam ML, van Esdonk MJ, Koltzenburg M, Groeneveld GJ, Heuberger JA. Effects of Mexiletine and Lacosamide on Nerve Excitability in Healthy Subjects: A Randomized, Double-Blind, Placebo-Controlled, Crossover Study. Clin Pharmacol Ther 2022; 112:1008-1019. [PMID: 35762293 PMCID: PMC9795956 DOI: 10.1002/cpt.2694] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2022] [Accepted: 06/12/2022] [Indexed: 01/01/2023]
Abstract
Selective voltage-gated sodium channel blockers are of growing interest as treatment for pain. For drug development of such compounds, it would be critical to have a biomarker that can be used for proof-of-mechanism. We aimed to evaluate whether drug-induced changes in sodium conductance can be detected in the peripheral nerve excitability profile in 18 healthy subjects. In a randomized, double-blind, 3-way crossover study, effects of single oral doses of 333 mg mexiletine and 300 mg lacosamide were compared with placebo. On each study visit, motor and sensory nerve excitability measurements of the median nerve were performed (predose; and 3 and 6 hours postdose) using Qtrac. Treatment effects were calculated using an analysis of covariance (ANCOVA) with baseline as covariate. Mexiletine and lacosamide had significant effects on multiple motor and sensory nerve excitability variables. Depolarizing threshold electrotonus (TEd40 (40-60 ms)) decreased by mexiletine (estimated difference (ED) -1.37% (95% confidence interval (CI): -2.20, -0.547; P = 0.002) and lacosamide (ED -1.27%, 95% CI: -2.10, -0.443; P = 0.004) in motor nerves. Moreover, mexiletine and lacosamide decreased superexcitability (less negative) in motor nerves (ED 1.74%, 95% CI: 0.615, 2.87; P = 0.004, and ED 1.47%, 95% CI: 0.341, 2.60; P = 0.013, respectively). Strength-duration time constant decreased after lacosamide in motor- (ED -0.0342 ms, 95% CI: -0.0571, -0.0112; P = 0.005) and sensory nerves (ED -0.0778 ms, 95% CI: -0.116, -0.0399; P < 0.001). Mexiletine and lacosamide significantly decrease excitability of motor and sensory nerves, in line with their suggested mechanism of action. Results of this study indicate that nerve excitability threshold tracking can be an effective pharmacodynamic biomarker. The method could be a valuable tool in clinical drug development.
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Affiliation(s)
- Titia Q. Ruijs
- Centre for Human Drug ResearchLeidenThe Netherlands,Leiden University Medical CentreLeidenThe Netherlands
| | - Ingrid W. Koopmans
- Centre for Human Drug ResearchLeidenThe Netherlands,Leiden University Medical CentreLeidenThe Netherlands
| | | | | | | | - Geert Jan Groeneveld
- Centre for Human Drug ResearchLeidenThe Netherlands,Leiden University Medical CentreLeidenThe Netherlands
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Themistocleous AC, Kristensen AG, Sola R, Gylfadottir SS, Bennedsgaard K, Itani M, Krøigård T, Ventzel L, Sindrup SH, Jensen TS, Bostock H, Serra J, Finnerup NB, Tankisi H, Bennett DLH. Axonal excitability does not differ between painful and painless diabetic or chemotherapy-induced distal symmetrical polyneuropathy in a multi-centre observational study. Ann Neurol 2022; 91:506-520. [PMID: 35150149 PMCID: PMC9313833 DOI: 10.1002/ana.26319] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2021] [Revised: 01/18/2022] [Accepted: 02/07/2022] [Indexed: 11/16/2022]
Abstract
Objective Axonal excitability reflects ion channel function, and it is proposed that this may be a biomarker in painful (vs painless) polyneuropathy. Our objective was to investigate the relationship between axonal excitability parameters and chronic neuropathic pain in deeply phenotyped cohorts with diabetic or chemotherapy‐induced distal symmetrical polyneuropathy. Methods Two hundred thirty‐nine participants with diabetic polyneuropathy were recruited from sites in the UK and Denmark, and 39 participants who developed chemotherapy‐induced polyneuropathy were recruited from Denmark. Participants were separated into those with probable or definite neuropathic pain and those without neuropathic pain. Axonal excitability of large myelinated fibers was measured with the threshold tracking technique. The stimulus site was the median nerve, and the recording sites were the index finger (sensory studies) and abductor pollicis brevis muscle (motor studies). Results Participants with painless and painful polyneuropathy were well matched across clinical variables. Sensory and motor axonal excitability measures, including recovery cycle, threshold electrotonus, strength–duration time constant, and current–threshold relationship, did not show differences between participants with painful and painless diabetic polyneuropathy, and there were only minor changes for chemotherapy‐induced polyneuropathy. Interpretation Axonal excitability did not significantly differ between painful and painless diabetic or chemotherapy‐induced polyneuropathy in a multicenter observational study. Threshold tracking assesses the excitability of myelinated axons; the majority of nociceptors are unmyelinated, and although there is some overlap of the "channelome" between these axonal populations, our results suggest that alternative measures such as microneurography are required to understand the relationship between sensory neuron excitability and neuropathic pain. ANN NEUROL 2022;91:506–520
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Affiliation(s)
| | - Alexander Gramm Kristensen
- Department of Clinical Medicine, Aarhus University, Aarhus, Denmark.,Department of Clinical Neurophysiology, Aarhus University Hospital, Aarhus, Denmark
| | - Roma Sola
- Neuroscience Technologies, Barcelona, Spain.,MC Mutual, Barcelona, Spain
| | - Sandra Sif Gylfadottir
- Danish Pain Research Center, Department of Clinical Medicine, Aarhus University, Aarhus, Denmark.,Department of Neurology, Aarhus University Hospital, Aarhus, Denmark
| | - Kristine Bennedsgaard
- Danish Pain Research Center, Department of Clinical Medicine, Aarhus University, Aarhus, Denmark.,Department of Neurology, Aarhus University Hospital, Aarhus, Denmark
| | - Mustapha Itani
- Department of Neurology, Odense University Hospital, Odense, Denmark
| | - Thomas Krøigård
- Department of Neurology, Odense University Hospital, Odense, Denmark
| | - Lise Ventzel
- Danish Pain Research Center, Department of Clinical Medicine, Aarhus University, Aarhus, Denmark
| | | | - Troels Staehelin Jensen
- Danish Pain Research Center, Department of Clinical Medicine, Aarhus University, Aarhus, Denmark.,Department of Neurology, Aarhus University Hospital, Aarhus, Denmark
| | - Hugh Bostock
- UCL Queen Square Institute of Neurology, London, United Kingdom
| | - Jordi Serra
- Neuroscience Technologies, Barcelona, Spain.,MC Mutual, Barcelona, Spain
| | - Nanna B Finnerup
- Danish Pain Research Center, Department of Clinical Medicine, Aarhus University, Aarhus, Denmark.,Department of Neurology, Aarhus University Hospital, Aarhus, Denmark
| | - Hatice Tankisi
- Department of Clinical Medicine, Aarhus University, Aarhus, Denmark.,Department of Clinical Neurophysiology, Aarhus University Hospital, Aarhus, Denmark
| | - David L H Bennett
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
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7
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McIlduff C, Wainger B, Freeman R, Samaan S, Yator I, Gutierrez H, Verga S, Rutkove S. The threshold tracking nerve conduction study technique: Experience of clinical users unfamiliar with a research-grade neuronal excitability system. Clin Neurophysiol Pract 2022; 7:319-324. [PMID: 36353647 PMCID: PMC9637722 DOI: 10.1016/j.cnp.2022.08.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2022] [Revised: 08/04/2022] [Accepted: 08/22/2022] [Indexed: 11/06/2022] Open
Abstract
Threshold tracking nerve conduction studies (TTNCSs) measure axon excitability. TTNCSs can objectively characterize neuronal dysfunction and treatment response. An available research-grade TTNCS system has not been widely implemented . Clinical electrophysiologists with varying levels of experience can perform TTNCSs. A user-friendly system and education about TTNCSs could broaden use of the technique.
Objective To 1) explore if clinical electrophysiologists with different degrees of experience performing standard nerve conduction studies could run a threshold tracking nerve conduction study (TTNCS) protocol and 2) learn how clinical users view a research-grade TTNCSs neuronal excitability system. Methods Five clinical electrophysiologists conducted a TTNCS session using QTracS and then completed a questionnaire describing their impressions. Results All of the electrophysiologists completed the QTracS protocol on an initial attempt. Perceived strengths comprised the ease of preparatory steps and quick protocol speed. Identified drawbacks included an unwieldly user-interface. The electrophysiologists indicated that knowledge of TTNCS principles and applications would be critical for incorporation of the method into clinical use. Conclusions This pilot study suggests that clinical electrophysiologists can carry out TTNCSs with a research-grade system. The development of a more user-friendly program, along with dedicated education and training, could lead to wider application of the TTNCS technique. Significance Considered together with clinical presentation and other biomarkers, increased use of TTNCSs could provide improved assessment of neuromuscular disease and treatment response.
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8
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Neuropathy in sporadic inclusion body myositis: A multi-modality neurophysiological study. Clin Neurophysiol 2020; 131:2766-2776. [PMID: 32928695 DOI: 10.1016/j.clinph.2020.07.025] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2020] [Revised: 07/09/2020] [Accepted: 07/22/2020] [Indexed: 02/03/2023]
Abstract
OBJECTIVE Sporadic inclusion body myositis (sIBM) has been associated with neuropathy. This study employs nerve excitability studies to re-examine this association and attempt to understand underlying pathophysiological mechanisms. METHODS Twenty patients with sIBM underwent median nerve motor and sensory excitability studies, clinical assessments, conventional nerve conduction testing (NCS) and quantitative thermal threshold studies. These results were compared to established normal controls, or results from a normal cohort of older control individuals. RESULTS Seven sIBM patients (35%) demonstrated abnormalities in conventional NCS, with ten patients (50%) demonstrating abnormalities in thermal thresholds. Median nerve motor and sensory excitability differed significantly in sIBM patients when compared to normal controls. None of these neurophysiological markers correlated significantly with clinical markers of sIBM severity. CONCLUSION A concurrent neuropathy exists in a significant proportion of sIBM patients, with nerve excitability studies revealing changes possibly consistent with axolemmal depolarization or concurrent neuronal adaptation to myopathy. Neuropathy in sIBM does not correlate with muscle disease severity and may reflect a differing tissue response to a common pathogenic factor. SIGNIFICANCE This study affirms the presence of a concurrent neuropathy in a large proportion of sIBM patients that appears independent of the severity of myopathy.
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Moldovan M. Threshold tracking as a tool to study activity-dependent axonal plasticity. Clin Neurophysiol 2020; 131:1381-1382. [PMID: 32224021 DOI: 10.1016/j.clinph.2020.03.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2020] [Accepted: 03/10/2020] [Indexed: 11/26/2022]
Affiliation(s)
- Mihai Moldovan
- Department of Clinical Neurophysiology, Rigshospitalet, Copenhagen, Denmark; Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark.
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10
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Klein CS, Rymer WZ, Fisher MA. Altered nerve excitability properties after stroke are potentially associated with reduced neuromuscular activation. Clin Neurophysiol 2020; 131:1407-1418. [PMID: 32184063 DOI: 10.1016/j.clinph.2020.02.009] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2018] [Revised: 01/22/2020] [Accepted: 02/16/2020] [Indexed: 12/17/2022]
Abstract
OBJECTIVE To determine limb differences in motor axon excitability properties in stroke survivors and their relation to maximal electromyographic (EMG) activity. METHODS The median nerve was stimulated to record compound muscle action potentials (CMAP) from the abductor pollicis brevis (APB) in 28 stroke subjects (57.3 ± 7.5 y) and 24 controls (56.7 ± 9.3 y). RESULTS Paretic limb axons differed significantly from non-paretic limb axons including (1) smaller superexcitability and subexcitability, (2) higher threshold during subthreshold depolarizing currents, (3) greater accommodation (S3) to hyperpolarization, and (4) a larger stimulus-response slope. There were smaller differences between the paretic and control limbs. Responses in the paretic limb were reproduced in a model by a 5.6 mV hyperpolarizing shift in the activation voltage of Ih (the current activated by hyperpolarization), together with an 11.8% decrease in nodal Na+ conductance or a 0.9 mV depolarizing shift in the Na+ activation voltage. Subjects with larger deficits in APB maximal voluntary EMG had larger limb differences in excitability properties. CONCLUSIONS Stroke leads to altered modulation of Ih and altered Na+ channel properties that may be partially attributed to a reduction in neuromuscular activation. SIGNIFICANCE Plastic changes occur in the axon node and internode that likely influence axon excitability.
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Affiliation(s)
- C S Klein
- Guangdong Work Injury Rehabilitation Center, Guangzhou 510440, China; Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL 60611, USA.
| | - W Z Rymer
- Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL 60611, USA; Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
| | - M A Fisher
- Department of Neurology, Hines VAH, Hines, IL 60141, USA; Loyola University Chicago Medical Center, 2160 S. First Ave., Maywood, IL 60153, USA
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11
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Bell JM, Lorenz C, Jones KE. Nerve excitability differences in slow and fast motor axons of the rat: more than just Ih. J Neurophysiol 2019; 122:1728-1734. [PMID: 31533011 DOI: 10.1152/jn.00269.2019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The objective was to determine biophysical differences between fast and slow motor axons using threshold tracking and demonstrate confounds related to anesthetic. Nerve excitability of motor axons innervating the slow-twitch soleus (SOL) and fast-twitch tibialis anterior (TA) muscles was tested. The experiments were conducted with pentobarbital sodium (SP) anesthetic and compared with previous results that used ketamine-xylazine (KX). Nerve excitability indices measured with SP show definitive differences between TA and SOL motor axons that extend beyond previous reports. Nerve excitability indices sensitive to changes in Ih indicated an increase in SOL axons compared with TA axons [e.g., S3 t = 7.949 (df = 10), P < 0.001; hyperpolarizing threshold electrotonus (90-100 ms), t = 2.659 (df = 20); P = 0.01; hyperpolarizing I/V slope, t = 4.308 (df = 19); P < 0.001]. SOL axons also had a longer strength-duration time constant [t = 3.35 (df = 20); P = 0.003] and a longer and larger magnitude relative refractory period [RRP (ms) t = 3.53 (df = 12); P = 0.004; Refractoriness at 2 ms, t = 0.0055 (df = 9); P = 0.006]. Anesthetic choice affected many measures of peripheral nerve excitability with differences most apparent in tests of threshold electrotonus and recovery cycle. For example, recovery cycle with KX lacked a clear superexcitable and late subexcitable period. We conclude that KX had a confounding effect on nerve excitability results consistent with ischemic depolarization. Results using SP revealed the full extent of differences in nerve excitability measures between putative slow and fast motor axons of the rat. These results provide empirical evidence, beyond conduction velocity, that the biophysical properties of motor axons vary with the type of muscle fiber innervated. These differences suggest that fast axons may be predisposed to dysfunction during hyperpolarizing stresses, e.g., electrogenic sodium pumping following sustained impulse conduction.NEW & NOTEWORTHY Nerve excitability testing is a tool used to provide insight into the properties of ion channels in peripheral nerves. It is used clinically to assess pathophysiology of axons. Researchers customarily think of motor axons as homogeneous; however, we demonstrate there are clear differences between fast and slow axons in the rat. This is important for interpreting results with selective motor neuronopathy, like aging where fast axons are at high risk of degeneration.
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Affiliation(s)
- James M Bell
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, Alberta, Canada.,Department of Computing Science, University of Alberta, Edmonton, Alberta, Canada
| | - Chad Lorenz
- Faculty of Kinesiology, Sport and Recreation, University of Alberta, Edmonton, Alberta, Canada
| | - Kelvin E Jones
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, Alberta, Canada.,Faculty of Kinesiology, Sport and Recreation, University of Alberta, Edmonton, Alberta, Canada
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Kiernan MC, Bostock H, Park SB, Kaji R, Krarup C, Krishnan AV, Kuwabara S, Lin CSY, Misawa S, Moldovan M, Sung J, Vucic S, Wainger BJ, Waxman S, Burke D. Measurement of axonal excitability: Consensus guidelines. Clin Neurophysiol 2019; 131:308-323. [PMID: 31471200 DOI: 10.1016/j.clinph.2019.07.023] [Citation(s) in RCA: 59] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2019] [Revised: 07/17/2019] [Accepted: 07/24/2019] [Indexed: 12/12/2022]
Abstract
Measurement of axonal excitability provides an in vivo indication of the properties of the nerve membrane and of the ion channels expressed on these axons. Axonal excitability techniques have been utilised to investigate the pathophysiological mechanisms underlying neurological diseases. This document presents guidelines derived for such studies, based on a consensus of international experts, and highlights the potential difficulties when interpreting abnormalities in diseased axons. The present manuscript provides a state-of-the-art review of the findings of axonal excitability studies and their interpretation, in addition to suggesting guidelines for the optimal performance of excitability studies.
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Affiliation(s)
- Matthew C Kiernan
- Brain and Mind Centre, University of Sydney and Institute of Clinical Neurosciences, Royal Prince Alfred Hospital, Sydney 2006, Australia.
| | - Hugh Bostock
- UCL Queen Square Institute of Neurology, London WC1N 3BG, United Kingdom
| | - Susanna B Park
- Brain and Mind Centre, University of Sydney and Institute of Clinical Neurosciences, Royal Prince Alfred Hospital, Sydney 2006, Australia
| | - Ryuji Kaji
- National Utano Hospital, 8-Narutaki Ondoyamacho, Ukyoku, Kyoto 616-8255, Japan
| | - Christian Krarup
- Department of Neuroscience, University of Copenhagen and Department of Clinical Neurophysiology, Rigshospitalet, Blegdamsvej 9, 2100 Copenhagen, Denmark
| | - Arun V Krishnan
- Prince of Wales Clinical School, University of New South Wales, Sydney, Australia
| | - Satoshi Kuwabara
- Department of Neurology, Graduate School of Medicine, Chiba University, Japan
| | - Cindy Shin-Yi Lin
- Brain and Mind Centre, University of Sydney and Institute of Clinical Neurosciences, Royal Prince Alfred Hospital, Sydney 2006, Australia
| | - Sonoko Misawa
- Department of Neurology, Graduate School of Medicine, Chiba University, Japan
| | - Mihai Moldovan
- Department of Neuroscience, University of Copenhagen and Department of Clinical Neurophysiology, Rigshospitalet, Blegdamsvej 9, 2100 Copenhagen, Denmark
| | - Jiaying Sung
- Taipei Medical University, Wanfang Hospital, Taipei, Taiwan
| | - Steve Vucic
- Department of Neurology, Westmead Hospital, Western Clinical School, University of Sydney, Australia
| | - Brian J Wainger
- Department of Neurology and Anesthesiology, Critical Care & Pain Medicine, Massachusetts General Hospital, Boston, MA 02114, USA
| | - Stephen Waxman
- Department of Neurology, Yale Medical School, New Haven, CT 06510, USA; Neurorehabilitation Research Center, Veterans Affairs Hospital, West Haven, CT 06516, USA
| | - David Burke
- Brain and Mind Centre, University of Sydney and Institute of Clinical Neurosciences, Royal Prince Alfred Hospital, Sydney 2006, Australia
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Kovalchuk MO, Franssen H, Scheijmans FEV, Van Schelven LJ, Van Den Berg LH, Sleutjes BTHM. Warming nerves for excitability testing. Muscle Nerve 2019; 60:279-285. [PMID: 31241195 DOI: 10.1002/mus.26621] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2018] [Revised: 06/21/2019] [Accepted: 06/23/2019] [Indexed: 11/07/2022]
Abstract
INTRODUCTION The aim of this study was to find the best method of warming the median nerve before excitability testing to a standard temperature. METHODS In 5 healthy subjects, the forearm and hand were warmed for 1 h to 37°C by infrared lamp, water blanket, or water bath. Recordings were performed before and during warming every 10 min. Excitability indices were fitted by exponential relations, thereby calculating the time needed to reach 95% of their asymptotic end value. RESULTS Distal motor latency, refractory period, and superexcitability at 10 ms changed exponentially with time. Warming by water bath took the shortest time (24 min); this was followed by warming by infrared lamp (34 min) and water blanket (35 min). CONCLUSIONS Warming by water bath is the quickest way. The other methods took only moderately more time. Future studies need to specify both warming method and warming time before excitability testing. Muscle Nerve, 2019.
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Affiliation(s)
- Maria O Kovalchuk
- Department of Neurology, University Medical Center Utrecht, Brain Center, Utrecht University, P.O. Box 85500, 3508 GA, Utrecht, The Netherlands
| | - Hessel Franssen
- Department of Neurology, University Medical Center Utrecht, Brain Center, Utrecht University, P.O. Box 85500, 3508 GA, Utrecht, The Netherlands
| | - Féline E V Scheijmans
- Department of Neurology, University Medical Center Utrecht, Brain Center, Utrecht University, P.O. Box 85500, 3508 GA, Utrecht, The Netherlands
| | - Leonard J Van Schelven
- Department of Medical Technology and Clinical Physics, University Medical Center Utrecht, The Netherlands
| | - Leonard H Van Den Berg
- Department of Neurology, University Medical Center Utrecht, Brain Center, Utrecht University, P.O. Box 85500, 3508 GA, Utrecht, The Netherlands
| | - Boudewijn T H M Sleutjes
- Department of Neurology, University Medical Center Utrecht, Brain Center, Utrecht University, P.O. Box 85500, 3508 GA, Utrecht, The Netherlands
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14
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Marmoy OR, Furlong PL, Moore CEG. Upper and lower limb motor axons demonstrate differential excitability and accommodation to strong hyperpolarizing currents during induced hyperthermia. J Neurophysiol 2019; 121:2061-2070. [PMID: 30917073 DOI: 10.1152/jn.00464.2018] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Length-dependent peripheral neuropathy typically involves the insidious onset of sensory loss in the lower limbs before later progressing proximally. Recent evidence proposes hyperpolarization-activated cyclic nucleotide-gated (HCN) channels as dysfunctional in rodent models of peripheral neuropathy, and therefore differential expression of HCN channels in the lower limbs was hypothesized as a pathophysiological mechanism accounting for the pattern of symptomatology within this study. We studied six healthy participants, using motor axon excitability including strong and long [-70% and -100% hyperpolarizing threshold electrotonus (TEh)] hyperpolarizing currents to preferably study HCN channel function from the median and tibial nerves from high (40%) and low (20%) threshold. This was recorded at normothermia (~32°C) and then repeated during hyperthermia (~40°C) as an artificial hyperpolarizing axon stress. Significant differences between recovery cycle, superexcitability, accommodation to small depolarizing currents, and alterations in late stages of the inward-rectifying currents of strongest (-70% and -100% TEh) currents were observed in the lower limbs during hyperthermia. We demonstrate differences in late IH current flow, which implies higher expression of HCN channel isoforms. The findings also indicate their potential inference in the symptomatology of length-dependent peripheral neuropathies and may be a unique target for minimizing symptomatology and pathogenesis in acquired disease. NEW & NOTEWORTHY This study demonstrates nerve excitability differences between the upper and lower limbs during hyperthermia, an experimentally induced axonal stress. The findings indicate that there is differential expression of slow hyperpolarization-activated cyclic nucleotide-gated (HCN) channel isoforms between the upper and lower limbs, which was demonstrated through strong, long hyperpolarizing currents during hyperthermia. Such mechanisms may underlie postural control but render the lower limbs susceptible to dysfunction in disease states.
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Affiliation(s)
- Oliver R Marmoy
- Department of Clinical Neurophysiology, Portsmouth Hospitals NHS Trust, Portsmouth , United Kingdom.,Aston University , Birmingham , United Kingdom
| | | | - Christopher E G Moore
- Department of Clinical Neurophysiology, Portsmouth Hospitals NHS Trust, Portsmouth , United Kingdom
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15
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Czesnik D, Howells J, Bartl M, Veiz E, Ketzler R, Kemmet O, Walters AS, Trenkwalder C, Burke D, Paulus W. I h contributes to increased motoneuron excitability in restless legs syndrome. J Physiol 2018; 597:599-609. [PMID: 30430565 DOI: 10.1113/jp275341] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2018] [Accepted: 10/18/2018] [Indexed: 12/17/2022] Open
Abstract
KEY POINTS Restless legs patients complain about sensory and motor symptoms leading to sleep disturbances. Symptoms include painful sensations, an urge to move and involuntary leg movements. The responsible mechanisms of restless legs syndrome are still not known, although current studies indicate an increased neuronal network excitability. Reflex studies indicate the involvement of spinal structures. Peripheral mechanisms have not been investigated so far. In the present study, we provide evidence of increased hyperpolarization-activated cyclic nucleotide-gated (HCN) channel-mediated inward rectification in motor axons. The excitability of sensory axons was not changed. We conclude that, in restless legs syndrome, an increased HCN current in motoneurons may play a pathophysiological role, such that these channels could represent a valuable target for pharmaceutical intervention. ABSTRACT Restless legs syndrome is a sensorimotor network disorder. So far, the responsible pathophysiological mechanisms are poorly understood. In the present study, we provide evidence that the excitability of peripheral motoneurons contributes to the pathophysiology of restless legs syndrome. In vivo excitability studies on motor and sensory axons of the median nerve were performed on patients with idiopathic restless legs syndrome (iRLS) who were not currently on treatment. The iRLS patients had greater accommodation in motor but not sensory axons to long-lasting hyperpolarization compared to age-matched healthy subjects, indicating greater inward rectification in iRLS. The most reasonable explanation is that hyperpolarization-activated cyclic nucleotide-gated (HCN) channels open at less hyperpolarized membrane potentials, a view supported by mathematical modelling. The half-activation potential for HCN channels (Bq) was the single best parameter that accounted for the difference between normal controls and iRLS data. A 6 mV depolarization of Bq reduced the discrepancy between the normal control model and the iRLS data by 92.1%. Taken together, our results suggest an increase in the excitability of motor units in iRLS that could enhance the likelihood of leg movements. The abnormal axonal properties are consistent with other findings indicating that the peripheral system is part of the network involved in iRLS.
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Affiliation(s)
- Dirk Czesnik
- Department of Clinical Neurophysiology, Medical School Göttingen, University of Göttingen, Göttingen, Germany
| | - James Howells
- Brain & Mind Centre, The University of Sydney, Sydney, NSW, Australia
| | - Michael Bartl
- Department of Clinical Neurophysiology, Medical School Göttingen, University of Göttingen, Göttingen, Germany
| | - Elisabeth Veiz
- Department of Clinical Neurophysiology, Medical School Göttingen, University of Göttingen, Göttingen, Germany
| | - Rebecca Ketzler
- Department of Clinical Neurophysiology, Medical School Göttingen, University of Göttingen, Göttingen, Germany
| | - Olga Kemmet
- Department of Clinical Neurophysiology, Medical School Göttingen, University of Göttingen, Göttingen, Germany
| | - Arthur S Walters
- Division of Sleep Medicine, School of Medicine, Medical Center North, Vanderbilt University, Nashville, TN, USA
| | - Claudia Trenkwalder
- Clinic of Neurosurgery, University Medical Center, Paracelsus Klinik Kassel, Göttingen, Germany
| | - David Burke
- Royal Prince Alfred Hospital and The University of Sydney, Sydney, NSW, Australia
| | - Walter Paulus
- Department of Clinical Neurophysiology, Medical School Göttingen, University of Göttingen, Göttingen, Germany
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16
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Makker PGS, Matamala JM, Park SB, Lees JG, Kiernan MC, Burke D, Moalem‐Taylor G, Howells J. A unified model of the excitability of mouse sensory and motor axons. J Peripher Nerv Syst 2018; 23:159-173. [DOI: 10.1111/jns.12278] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2018] [Revised: 06/13/2018] [Accepted: 06/13/2018] [Indexed: 11/29/2022]
Affiliation(s)
- Preet G. S. Makker
- School of Medical SciencesUniversity of New South Wales Sydney Australia
| | | | - Susanna B. Park
- Brain and Mind CentreThe University of Sydney Sydney Australia
| | - Justin G. Lees
- School of Medical SciencesUniversity of New South Wales Sydney Australia
| | - Matthew C. Kiernan
- Brain and Mind CentreThe University of Sydney Sydney Australia
- Royal Prince Alfred HospitalThe University of Sydney Sydney Australia
| | - David Burke
- Royal Prince Alfred HospitalThe University of Sydney Sydney Australia
| | - Gila Moalem‐Taylor
- School of Medical SciencesUniversity of New South Wales Sydney Australia
| | - James Howells
- Brain and Mind CentreThe University of Sydney Sydney Australia
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17
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Matamala JM, Howells J, Dharmadasa T, Huynh W, Park SB, Burke D, Kiernan MC. Excitability of sensory axons in amyotrophic lateral sclerosis. Clin Neurophysiol 2018; 129:1472-1478. [PMID: 29661595 DOI: 10.1016/j.clinph.2018.03.014] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2018] [Revised: 02/22/2018] [Accepted: 03/11/2018] [Indexed: 12/11/2022]
Abstract
OBJECTIVE To evaluate the excitability of sensory axons in patients with amyotrophic lateral sclerosis (ALS). METHODS Comprehensive sensory nerve excitability studies were prospectively performed on 28 sporadic ALS patients, compared to age-matched controls. Sensory nerve action potentials were recorded from digit 2 following median nerve stimulation at the wrist. Disease severity was measured using motor unit number estimation (MUNE), the revised ALS Functional Rating Scale (ALSFRS-R) and the MRC scale. RESULTS There were no significant differences in standard and extended measures of nerve excitability between ALS patients and controls. These unchanged excitability measures included accommodation to long-lasting hyperpolarization and the threshold changes after two supramaximal stimuli during the recovery cycle. Excitability parameters did not correlate with MUNE, ALSFRS-R, APB MRC scale or disease duration. CONCLUSIONS This cross-sectional study has identified normal axonal membrane properties in myelinated sensory axons of ALS patients. Previously described sensory abnormalities could be the result of axonal fallout, possibly due to a ganglionopathy, or to involvement of central sensory pathways rostral to gracile and cuneate nuclei. SIGNIFICANCE These results demonstrate the absence of generalized dysfunction of the membrane properties of sensory axons in ALS in the face of substantial deficits in motor function.
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Affiliation(s)
| | - James Howells
- Brain and Mind Centre, University of Sydney, Sydney, NSW 2050, Australia
| | - Thanuja Dharmadasa
- Brain and Mind Centre, University of Sydney, Sydney, NSW 2050, Australia
| | - William Huynh
- Brain and Mind Centre, University of Sydney, Sydney, NSW 2050, Australia
| | - Susanna B Park
- Brain and Mind Centre, University of Sydney, Sydney, NSW 2050, Australia
| | - David Burke
- Sydney Medical School, University of Sydney, Sydney, NSW 2006, Australia; Department of Neurology, Royal Prince Alfred Hospital, Sydney, NSW 2050, Australia
| | - Matthew C Kiernan
- Brain and Mind Centre, University of Sydney, Sydney, NSW 2050, Australia; Sydney Medical School, University of Sydney, Sydney, NSW 2006, Australia; Department of Neurology, Royal Prince Alfred Hospital, Sydney, NSW 2050, Australia
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18
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Lai HJ, Chen CL, Tsai LK. Increase of hyperpolarization-activated cyclic nucleotide-gated current in the aberrant excitability of spinal muscular atrophy. Ann Neurol 2018; 83:494-507. [PMID: 29394509 DOI: 10.1002/ana.25168] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2017] [Revised: 01/22/2018] [Accepted: 01/30/2018] [Indexed: 11/08/2022]
Abstract
OBJECTIVE The pathophysiology of spinal muscular atrophy (SMA) is still unclear. METHODS The nerve excitability test in SMA patients and a mouse model of SMA was carried out to explore the pathophysiology of nodal and internodal currents, and quantitative PCR, western blotting, and whole-cell patch-clamp recording were used for the identified hypothesis. RESULTS The nerve excitability test in SMA patients showed increased inward rectification in the current-threshold relationship and increased overshoot after hyperpolarizing threshold electrotonus, which indicates increased hyperpolarization-activated cyclic nucleotide-gated (HCN) current; these findings correlated with disease severity. Increased inward rectification in the current-threshold relationship was reproducible in a mouse model of mild SMA, and the abnormality preceded the decline of compound motor action potential amplitudes. Furthermore, quantitative PCR of spinal cord tissues and western blotting of the spinal cord and sciatic nerves showed increased HCN1 and HCN2 expression in SMA mice, and voltage-clamp recording in dissociated spinal motor neurons from SMA mice also showed increased HCN current density. Treatment with ZD7288, an HCN channel blocker, also reduced early mortality, improved motor function, and restored neuromuscular junction architecture in a mouse model of severe SMA. INTERPRETATION This study shows that increased HCN current underlies the pathophysiology of SMA and can be a novel non-SMN target for SMA therapy. Ann Neurol 2018;83:494-507.
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Affiliation(s)
- Hsing-Jung Lai
- Department of Neurology, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan.,Institute of Physiology, National Taiwan University, Taipei, Taiwan
| | - Chien-Lin Chen
- Department of Neurology, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan
| | - Li-Kai Tsai
- Department of Neurology, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan
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19
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Howells J, Bostock H, Park SB, Kiernan MC, Burke D. Tracking small sensory nerve action potentials in human axonal excitability studies. J Neurosci Methods 2018; 298:45-53. [DOI: 10.1016/j.jneumeth.2018.02.003] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2017] [Revised: 01/08/2018] [Accepted: 02/08/2018] [Indexed: 10/18/2022]
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20
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Kovalchuk MO, Franssen H, Van Schelven LJ, Sleutjes BTHM. Comparing excitability at 37°C versus at 20°C: Differences between motor and sensory axons. Muscle Nerve 2017; 57:574-580. [DOI: 10.1002/mus.25960] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/02/2017] [Indexed: 11/06/2022]
Affiliation(s)
- Maria O. Kovalchuk
- Department of Neurology and Neurosurgery, Brain Center Rudolf MagnusUniversity Medical Center UtrechtUtrecht The Netherlands
| | - Hessel Franssen
- Department of Neurology and Neurosurgery, Brain Center Rudolf MagnusUniversity Medical Center UtrechtUtrecht The Netherlands
| | - Leonard J. Van Schelven
- Department of Medical Technology and Clinical PhysicsUniversity Medical Center UtrechtUtrecht the Netherlands
| | - Boudewijn T. H. M. Sleutjes
- Department of Neurology and Neurosurgery, Brain Center Rudolf MagnusUniversity Medical Center UtrechtUtrecht The Netherlands
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21
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Weerasinghe D, Menon P, Vucic S. Hyperpolarization-activated cyclic-nucleotide-gated channels potentially modulate axonal excitability at different thresholds. J Neurophysiol 2017; 118:3044-3050. [PMID: 28904107 DOI: 10.1152/jn.00576.2017] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Revised: 09/06/2017] [Accepted: 09/12/2017] [Indexed: 11/22/2022] Open
Abstract
Hyperpolarization-activated cyclic-nucleotide-gated (HCN) channels mediate differences in sensory and motor axonal excitability at different thresholds in animal models. Importantly, HCN channels are responsible for voltage-gated inward rectifying (Ih) currents activated during hyperpolarization. The Ih currents exert a crucial role in determining the resting membrane potential and have been implicated in a variety of neurological disorders, including neuropathic pain. In humans, differences in biophysical properties of motor and sensory axons at different thresholds remain to be elucidated and could provide crucial pathophysiological insights in peripheral neurological diseases. Consequently, the aim of this study was to characterize sensory and motor axonal function at different threshold. Median nerve motor and sensory axonal excitability studies were undertaken in 15 healthy subjects (45 studies in total). Tracking targets were set to 20, 40, and 60% of maximum for sensory and motor axons. Hyperpolarizing threshold electrotonus (TEh) at 90-100 ms was significantly increased in lower threshold sensory axons times (F = 11.195, P < 0.001). In motor axons, the hyperpolarizing current/threshold (I/V) gradient was significantly increased in lower threshold axons (F = 3.191, P < 0.05). The minimum I/V gradient was increased in lower threshold motor and sensory axons. In conclusion, variation in the kinetics of HCN isoforms could account for the findings in motor and sensory axons. Importantly, assessing the function of HCN channels in sensory and motor axons of different thresholds may provide insights into the pathophysiological processes underlying peripheral neurological diseases in humans, particularly focusing on the role of HCN channels with the potential of identifying novel treatment targets.NEW & NOTEWORTHY Hyperpolarization-activated cyclic-nucleotide-gated (HCN) channels, which underlie inward rectifying currents (Ih), appear to mediate differences in sensory and motor axonal properties. Inward rectifying currents are increased in lower threshold motor and sensory axons, although different HCN channel isoforms appear to underlie these changes. While faster activating HCN channels seem to underlie Ih changes in sensory axons, slower activating HCN isoforms appear to be mediating the differences in Ih conductances in motor axons of different thresholds. The differences in HCN gating properties could explain the predilection for dysfunction of sensory and motor axons in specific neurological diseases.
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Affiliation(s)
| | - Parvathi Menon
- Department of Neurology, Westmead Hospital, Sydney, Australia; and.,Westmead Clinical School, The University of Sydney, Sydney, Australia
| | - Steve Vucic
- Department of Neurology, Westmead Hospital, Sydney, Australia; and .,Westmead Clinical School, The University of Sydney, Sydney, Australia
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22
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Zhang Y, Bucher D, Nadim F. Ionic mechanisms underlying history-dependence of conduction delay in an unmyelinated axon. eLife 2017; 6. [PMID: 28691900 PMCID: PMC5519330 DOI: 10.7554/elife.25382] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2017] [Accepted: 07/06/2017] [Indexed: 11/13/2022] Open
Abstract
Axonal conduction velocity can change substantially during ongoing activity, thus modifying spike interval structures and, potentially, temporal coding. We used a biophysical model to unmask mechanisms underlying the history-dependence of conduction. The model replicates activity in the unmyelinated axon of the crustacean stomatogastric pyloric dilator neuron. At the timescale of a single burst, conduction delay has a non-monotonic relationship with instantaneous frequency, which depends on the gating rates of the fast voltage-gated Na+ current. At the slower timescale of minutes, the mean value and variability of conduction delay increase. These effects are because of hyperpolarization of the baseline membrane potential by the Na+/K+ pump, balanced by an h-current, both of which affect the gating of the Na+ current. We explore the mechanisms of history-dependence of conduction delay in axons and develop an empirical equation that accurately predicts this history-dependence, both in the model and in experimental measurements.
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Affiliation(s)
- Yang Zhang
- Department of Mathematical Sciences, New Jersey Institute of Technology, Newark, United States
| | - Dirk Bucher
- Federated Department of Biological Sciences, NJIT and Rutgers University, Newark, United States
| | - Farzan Nadim
- Department of Mathematical Sciences, New Jersey Institute of Technology, Newark, United States.,Federated Department of Biological Sciences, NJIT and Rutgers University, Newark, United States
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23
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Klein CS, Zhao CN, Liu H, Zhou P. Differences in excitability properties between medial gastrocnemius, tibialis anterior, and abductor pollicis brevis motor axons. Muscle Nerve 2017. [PMID: 28621464 DOI: 10.1002/mus.25722] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
INTRODUCTION Excitability properties of motor nerves to different muscles are different, but the explanation is uncertain. We characterized motor axon excitability properties to the medial gastrocnemius (MG) in 27 adults, and made comparisons with the peroneal nerve to the tibialis anterior (TA) and median nerve to the abductor pollicis brevis (APB) in 10 subjects. METHODS Recordings of multiple excitability properties were made using threshold tracking, stimulating the nerves at the wrist or knee. RESULTS Threshold electrotonus and superexcitability differed between nerves (APB>MG>TA axons) that may reflect differences in fast K+ conductance. APB axons had larger S2 accommodation and undershoot than TA and MG axons, indicating greater slow K+ conductance. TA axons demonstrated greater accommodation during hyperpolarizing currents than MG and APB axons, suggestive of greater inwardly rectifying current. DISCUSSION Inherent differences in several conductances underlie nerve differences in excitability, presumably related to muscle or motoneuron properties. Muscle Nerve 57: E60-E69, 2018.
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Affiliation(s)
- Cliff S Klein
- Guangdong Work Injury Rehabilitation Center, 68 Qide Road, Baiyun District, Guangzhou, China, 510440
| | - Chen Ning Zhao
- Guangdong Work Injury Rehabilitation Center, 68 Qide Road, Baiyun District, Guangzhou, China, 510440
| | - Hui Liu
- Guangdong Work Injury Rehabilitation Center, 68 Qide Road, Baiyun District, Guangzhou, China, 510440
| | - Ping Zhou
- Guangdong Work Injury Rehabilitation Center, 68 Qide Road, Baiyun District, Guangzhou, China, 510440.,Department of Physical Medicine and Rehabilitation, University of Texas Health Science Center at Houston, Houston, Texas, USA, 77030
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Tomlinson SE, Howells J, Burke D. In vivo assessment of neurological channelopathies: Application of peripheral nerve excitability studies. Neuropharmacology 2017; 132:98-107. [PMID: 28476643 DOI: 10.1016/j.neuropharm.2017.04.045] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2017] [Revised: 04/19/2017] [Accepted: 04/29/2017] [Indexed: 12/14/2022]
Abstract
With the rapid evolution of understanding of neurological channelopathies comes a need for sensitive tools to evaluate patients in clinical practice. Neurological channelopathies with a single-gene basis can manifest as seizures, headache, ataxia, vertigo, confusion, weakness and neuropathic pain and it is likely that other genetic factors contribute to the phenotype of many of these disorders. Ion channel dysfunction can result in abnormal cell membrane excitability but utilisation of advanced neurophysiology techniques has lagged behind developments in clinical, genetic and imaging evaluation of channelopathies. However, momentum in the application of in vivo axonal excitability testing sees these tests emerging as valuable tools, with the capacity to provide sensitive and specific insights into the mechanism of disease. While single-channel function cannot be directly measured in vivo, evaluation of subjects with single-gene channelopathies has provided insights into the effects of mutation-related alterations of membrane excitability, as well as compensatory adaptive changes. By showing how ion channel dysfunction can affect axonal excitability in vivo, studies of the excitability of peripheral nerve axons complement in vitro analysis of single channel activity. The interpretation of results is enhanced by mathematical modelling of axonal function and insights provided by in vitro work. This article is part of the Special Issue entitled 'Channelopathies.'
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Affiliation(s)
- Susan E Tomlinson
- Sydney Medical School, University of Sydney, Sydney, Australia; Department of Neurology, St Vincent's Hospital, Sydney, Australia.
| | - James Howells
- Brain and Mind Centre, University of Sydney, Sydney, Australia
| | - David Burke
- Sydney Medical School, University of Sydney, Sydney, Australia; Department of Neurology, Royal Prince Alfred Hospital, Sydney, Australia
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25
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Hegle AP, Frank CA, Berndt A, Klose M, Allan DW, Accili EA. The Ih Channel Gene Promotes Synaptic Transmission and Coordinated Movement in Drosophila melanogaster. Front Mol Neurosci 2017; 10:41. [PMID: 28286469 PMCID: PMC5323408 DOI: 10.3389/fnmol.2017.00041] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2016] [Accepted: 02/06/2017] [Indexed: 11/13/2022] Open
Abstract
Hyperpolarization-activated cyclic nucleotide-gated “HCN” channels, which underlie the hyperpolarization-activated current (Ih), have been proposed to play diverse roles in neurons. The presynaptic HCN channel is thought to both promote and inhibit neurotransmitter release from synapses, depending upon its interactions with other presynaptic ion channels. In larvae of Drosophila melanogaster, inhibition of the presynaptic HCN channel by the drug ZD7288 reduces the enhancement of neurotransmitter release at motor terminals by serotonin but this drug has no effect on basal neurotransmitter release, implying that the channel does not contribute to firing under basal conditions. Here, we show that genetic disruption of the sole HCN gene (Ih) reduces the amplitude of the evoked response at the neuromuscular junction (NMJ) of third instar larvae by decreasing the number of released vesicles. The anatomy of the (NMJ) is not notably affected by disruption of the Ih gene. We propose that the presynaptic HCN channel is active under basal conditions and promotes neurotransmission at larval motor terminals. Finally, we demonstrate that Ih partial loss-of-function mutant adult flies have impaired locomotion, and, thus, we hypothesize that the presynaptic HCN channel at the (NMJ) may contribute to coordinated movement.
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Affiliation(s)
- Andrew P Hegle
- Department of Cellular and Physiological Sciences, The University of British Columbia Vancouver, BC, Canada
| | - C Andrew Frank
- Department of Anatomy and Cell Biology, The University of Iowa Iowa City, IA, USA
| | - Anthony Berndt
- Department of Cellular and Physiological Sciences, The University of British Columbia Vancouver, BC, Canada
| | - Markus Klose
- Department of Cellular and Physiological Sciences, The University of British Columbia Vancouver, BC, Canada
| | - Douglas W Allan
- Department of Cellular and Physiological Sciences, The University of British Columbia Vancouver, BC, Canada
| | - Eric A Accili
- Department of Cellular and Physiological Sciences, The University of British Columbia Vancouver, BC, Canada
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26
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Howells J, Bostock H, Burke D. Accommodation to hyperpolarization of human axons assessed in the frequency domain. J Neurophysiol 2016; 116:322-35. [PMID: 27098023 DOI: 10.1152/jn.00019.2016] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2016] [Accepted: 04/18/2016] [Indexed: 11/22/2022] Open
Abstract
Human axons in vivo were subjected to subthreshold currents with a threshold impedance amplitude profile to allow the use of frequency domain techniques to determine the propensity for resonant behavior and to clarify the relative contributions of different ion channels to their low-frequency responsiveness. Twenty-four studies were performed on the motor and sensory axons of the median nerve in six subjects. The response to oscillatory currents was tested between direct current (DC) and 16 Hz. A resonant peak at ∼2-2.5 Hz was found in the response of hyperpolarized axons, but there was only a small broad response in axons at resting membrane potential (RMP). A mathematical model of axonal excitability developed using DC pulses provided a good fit to the frequency response for human axons and indicated that the hyperpolarization-activated current Ih and the slow potassium current IKs are principally responsible for the resonance. However, the results indicate that if axons are hyperpolarized by more than -60% of resting threshold, the only conductances that are appreciably active are Ih and the leak conductance, i.e., that the activity of these conductances can be studied in vivo virtually in isolation at hyperpolarized membrane potentials. Given that the leak conductance dampens resonance, it is suggested that the -60% hyperpolarization used here is optimal for Ih As expected, differences between the frequency responses of motor and sensory axons were present and best explained by reduced slow potassium conductance GKs, up-modulation of Ih, and increased persistent Na(+) current INaP (due to depolarization of RMP) in sensory axons.
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Affiliation(s)
- James Howells
- Brain & Mind Centre, The University of Sydney, Sydney, Australia;
| | - Hugh Bostock
- Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, London, United Kingdom; and
| | - David Burke
- Royal Prince Alfred Hospital and The University of Sydney, Sydney, Australia
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Upregulation of axonal HCN current by methylglyoxal: Potential association with diabetic polyneuropathy. Clin Neurophysiol 2015; 126:2226-32. [DOI: 10.1016/j.clinph.2015.02.058] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2014] [Revised: 01/15/2015] [Accepted: 02/01/2015] [Indexed: 11/18/2022]
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Moldovan M, Alvarez S, Rosberg MR, Krarup C. Persistent alterations in active and passive electrical membrane properties of regenerated nerve fibers of man and mice. Eur J Neurosci 2015; 43:388-403. [DOI: 10.1111/ejn.13047] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2015] [Revised: 07/31/2015] [Accepted: 08/13/2015] [Indexed: 12/12/2022]
Affiliation(s)
- Mihai Moldovan
- Department of Neuroscience and Pharmacology; University of Copenhagen; Copenhagen Denmark
- Department of Clinical Neurophysiology; NF3063 Rigshospitalet 9 Blegdamsvej 2100 Copenhagen Denmark
| | - Susana Alvarez
- Department of Neuroscience and Pharmacology; University of Copenhagen; Copenhagen Denmark
- Department of Clinical Neurophysiology; NF3063 Rigshospitalet 9 Blegdamsvej 2100 Copenhagen Denmark
| | - Mette R. Rosberg
- Department of Neuroscience and Pharmacology; University of Copenhagen; Copenhagen Denmark
- Department of Clinical Neurophysiology; NF3063 Rigshospitalet 9 Blegdamsvej 2100 Copenhagen Denmark
| | - Christian Krarup
- Department of Neuroscience and Pharmacology; University of Copenhagen; Copenhagen Denmark
- Department of Clinical Neurophysiology; NF3063 Rigshospitalet 9 Blegdamsvej 2100 Copenhagen Denmark
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Osaki Y, Nodera H, Banzrai C, Endo S, Takayasu H, Mori A, Shimatani Y, Kaji R. Effects of anesthetic agents on in vivo axonal HCN current in normal mice. Clin Neurophysiol 2015; 126:2033-9. [DOI: 10.1016/j.clinph.2014.12.025] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2014] [Revised: 12/01/2014] [Accepted: 12/29/2014] [Indexed: 12/17/2022]
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Czesnik D, Howells J, Negro F, Wagenknecht M, Hanner S, Farina D, Burke D, Paulus W. Increased HCN channel driven inward rectification in benign cramp fasciculation syndrome. Brain 2015; 138:3168-79. [DOI: 10.1093/brain/awv254] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2015] [Accepted: 07/08/2015] [Indexed: 12/13/2022] Open
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Lorenz C, Jones KE. IH activity is increased in populations of slow versus fast motor axons of the rat. Front Hum Neurosci 2014; 8:766. [PMID: 25309406 PMCID: PMC4174588 DOI: 10.3389/fnhum.2014.00766] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2014] [Accepted: 09/10/2014] [Indexed: 11/25/2022] Open
Abstract
Much is known about the electrophysiological variation in motoneuron somata across different motor units. However, comparatively less is known about electrophysiological variation in motor axons and how this could impact function or electrodiagnosis in healthy or diseased states. We performed nerve excitability testing on two groups of motor axons in Sprague–Dawley rats that are known to differ significantly in their chronic daily activity patterns and in the relative proportion of motor unit types: one group innervating the soleus (“slow motor axons”) and the other group innervating the tibialis anterior (“fast motor axons”) muscles. We found that slow motor axons have significantly larger accommodation compared to fast motor axons upon application of a 100 ms hyperpolarizing conditioning stimulus that is 40% of axon threshold (Z = 3.24, p = 0.001) or 20% of axon threshold (Z = 2.67, p = 0.008). Slow motor axons had larger accommodation to hyperpolarizing currents in the current-threshold measurement (-80% Z = 3.07, p = 0.002; -90% Z = 2.98, p = 0.003). In addition, we found that slow motor axons have a significantly smaller rheobase than fast motor axons (Z = -1.99, p = 0.047) accompanied by a lower threshold in stimulus-response curves. The results provide evidence that slow motor axons have greater activity of the hyperpolarization-activated inwardly rectifying cation conductance (IH) than fast motor axons. It is possible that this difference between fast and slow axons is caused by an adaptation to their chronic differences in daily activity patterns, and that this adaptation might have a functional effect on the motor unit. Moreover, these findings indicate that slow and fast motor axons may react differently to pathological conditions.
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Affiliation(s)
- Chad Lorenz
- Faculty of Physical Education and Recreation, University of Alberta Edmonton, AB, Canada
| | - Kelvin E Jones
- Faculty of Physical Education and Recreation, University of Alberta Edmonton, AB, Canada ; Neuroscience and Mental Health Institute, University of Alberta Edmonton, AB, Canada
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Huynh W, Lin CSY, Krishnan AV, Vucic S, Kiernan MC. Transynaptic Changes Evident in Peripheral Axonal Function After Acute Cerebellar Infarct. THE CEREBELLUM 2014; 13:669-76. [DOI: 10.1007/s12311-014-0577-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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Moldovan M, Lange KHW, Aachmann-Andersen NJ, Kjær TW, Olsen NV, Krarup C. Transient impairment of the axolemma following regional anaesthesia by lidocaine in humans. J Physiol 2014; 592:2735-50. [PMID: 24710060 DOI: 10.1113/jphysiol.2014.270827] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The local anaesthetic lidocaine is known to block voltage-gated Na(+) channels (VGSCs), although at high concentration it was also reported to block other ion channel currents as well as to alter lipid membranes. The aim of this study was to investigate whether the clinical regional anaesthetic action of lidocaine could be accounted for solely by the block of VGSCs or whether other mechanisms are also relevant. We tested the recovery of motor axon conduction and multiple measures of excitability by 'threshold-tracking' after ultrasound-guided distal median nerve regional anaesthesia in 13 healthy volunteers. Lidocaine caused rapid complete motor axon conduction block localized at the wrist. Within 3 h, the force of the abductor pollicis brevis muscle and median motor nerve conduction studies returned to normal. In contrast, the excitability of the motor axons at the wrist remained markedly impaired as indicated by a 7-fold shift of the stimulus-response curves to higher currents with partial recovery by 6 h and full recovery by 24 h. The strength-duration properties were abnormal with markedly increased rheobase and reduced strength-duration time constant. The changes in threshold during electrotonus, especially during depolarization, were markedly reduced. The recovery cycle showed increased refractoriness and reduced superexcitability. The excitability changes were only partly similar to those previously observed after poisoning with the VGSC blocker tetrodotoxin. Assuming an unaltered ion-channel gating, modelling indicated that, apart from up to a 4-fold reduction in the number of functioning VGSCs, lidocaine also caused a decrease of passive membrane resistance and an increase of capacitance. Our data suggest that the lidocaine effects, even at clinical 'sub-blocking' concentrations, could reflect, at least in part, a reversible structural impairment of the axolemma.
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Affiliation(s)
- Mihai Moldovan
- Department of Neuroscience and Pharmacology, University of Copenhagen, Copenhagen, Denmark
| | - Kai Henrik Wiborg Lange
- Department of Anesthesia, Nordsjællands Hospital and University of Copenhagen, Copenhagen, Denmark
| | | | - Troels Wesenberg Kjær
- Department of Clinical Neurophysiology, The Neuroscience Center, Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark
| | - Niels Vidiendal Olsen
- Department of Neuroscience and Pharmacology, University of Copenhagen, Copenhagen, Denmark Department of Neuroanesthesia, The Neuroscience Center, Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark
| | - Christian Krarup
- Department of Neuroscience and Pharmacology, University of Copenhagen, Copenhagen, Denmark Department of Clinical Neurophysiology, The Neuroscience Center, Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark
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Milder DA, Sutherland EJ, Gandevia SC, McNulty PA. Sustained maximal voluntary contraction produces independent changes in human motor axons and the muscle they innervate. PLoS One 2014; 9:e91754. [PMID: 24622330 PMCID: PMC3951451 DOI: 10.1371/journal.pone.0091754] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2013] [Accepted: 02/13/2014] [Indexed: 11/18/2022] Open
Abstract
The repetitive discharges required to produce a sustained muscle contraction results in activity-dependent hyperpolarization of the motor axons and a reduction in the force-generating capacity of the muscle. We investigated the relationship between these changes in the adductor pollicis muscle and the motor axons of its ulnar nerve supply, and the reproducibility of these changes. Ten subjects performed a 1-min maximal voluntary contraction. Activity-dependent changes in axonal excitability were measured using threshold tracking with electrical stimulation at the wrist; changes in the muscle were assessed as evoked and voluntary electromyography (EMG) and isometric force. Separate components of axonal excitability and muscle properties were tested at 5 min intervals after the sustained contraction in 5 separate sessions. The current threshold required to produce the target muscle action potential increased immediately after the contraction by 14.8% (p<0.05), reflecting decreased axonal excitability secondary to hyperpolarization. This was not correlated with the decline in amplitude of muscle force or evoked EMG. A late reversal in threshold current after the initial recovery from hyperpolarization peaked at −5.9% at ∼35 min (p<0.05). This pattern was mirrored by other indices of axonal excitability revealing a previously unreported depolarization of motor axons in the late recovery period. Measures of axonal excitability were relatively stable at rest but less so after sustained activity. The coefficient of variation (CoV) for threshold current increase was higher after activity (CoV 0.54, p<0.05) whereas changes in voluntary (CoV 0.12) and evoked twitch (CoV 0.15) force were relatively stable. These results demonstrate that activity-dependent changes in motor axon excitability are unlikely to contribute to concomitant changes in the muscle after sustained activity in healthy people. The variability in axonal excitability after sustained activity suggests that care is needed when using these measures if the integrity of either the muscle or nerve may be compromised.
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Affiliation(s)
- David A. Milder
- Neuroscience Research Australia, Sydney and University of New South Wales, Sydney, Australia
| | - Emily J. Sutherland
- Neuroscience Research Australia, Sydney and University of New South Wales, Sydney, Australia
| | - Simon C. Gandevia
- Neuroscience Research Australia, Sydney and University of New South Wales, Sydney, Australia
| | - Penelope A. McNulty
- Neuroscience Research Australia, Sydney and University of New South Wales, Sydney, Australia
- * E-mail:
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Franssen H, Straver DC. Pathophysiology of immune-mediated demyelinating neuropathies-part I: Neuroscience. Muscle Nerve 2013; 48:851-64. [DOI: 10.1002/mus.24070] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/26/2013] [Indexed: 11/09/2022]
Affiliation(s)
- Hessel Franssen
- Department of Neurology, Section Neuromuscular Disorders, F02.230, Rudolf Magnus Institute for Neuroscience; University Medical Center Utrecht; Heidelberglaan 100, 3584 CX Utrecht The Netherlands
| | - Dirk C.G. Straver
- Department of Neurology, Section Neuromuscular Disorders, F02.230, Rudolf Magnus Institute for Neuroscience; University Medical Center Utrecht; Heidelberglaan 100, 3584 CX Utrecht The Netherlands
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Howells J, Czesnik D, Trevillion L, Burke D. Excitability and the safety margin in human axons during hyperthermia. J Physiol 2013; 591:3063-80. [PMID: 23613528 DOI: 10.1113/jphysiol.2012.249060] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Abstract Hyperthermia challenges the nervous system's ability to transmit action potentials faithfully. Neuromuscular diseases, particularly those involving demyelination have an impaired safety margin for action potential generation and propagation, and symptoms are commonly accentuated by increases in temperature. The aim of this study was to examine the mechanisms responsible for reduced excitability during hyperthermia. Additionally, we sought to determine if motor and sensory axons differ in their propensity for conduction block during hyperthermia. Recordings of axonal excitability were performed at normal temperatures and during focal hyperthermia for motor and sensory axons in six healthy subjects. There were clear changes in excitability during hyperthermia, with reduced superexcitability following an action potential, faster accommodation to long-lasting depolarization and reduced accommodation to hyperpolarization. A verified model of human motor and sensory axons was used to clarify the effects of hyperthermia. The hyperthermia-induced changes in excitability could be accounted for by increasing the modelled temperature by 6°C (and adjusting the maximum conductances and activation kinetics according to their Q10 values; producing a 2 mV hyperpolarization of resting membrane potential), further hyperpolarizing the voltage dependence of Ih (motor, 11 mV; sensory, 7 mV) and adding a small depolarizing current at the internode (motor, 20 pA; sensory, 30 pA). The modelling suggested that slow K(+) channels play a significant role in reducing axonal excitability during hyperthermia. The further hyperpolarization of the activation of Ih would limit its ability to counter the hyperpolarization produced by activity, thereby allowing conduction block to occur during hyperthermia.
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Affiliation(s)
- James Howells
- Institute of Clinical Neurosciences, Royal Prince Alfred Hospital and The University of Sydney, Sydney, Australia.
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Functional recovery of regenerating motor axons is delayed in mice heterozygously deficient for the myelin protein P(0) gene. Neurochem Res 2013; 38:1266-77. [PMID: 23564290 DOI: 10.1007/s11064-013-1030-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2012] [Revised: 03/06/2013] [Accepted: 03/26/2013] [Indexed: 10/27/2022]
Abstract
Mice with a heterozygous knock-out of the myelin protein P0 gene (P0+/-) develop a neuropathy similar to human Charcot-Marie-Tooth disease. They are indistinguishable from wild-types (WT) at birth and develop a slowly progressing demyelinating neuropathy. The aim of this study was to investigate whether the regeneration capacity of early symptomatic P0+/- is impaired as compared to age matched WT. Right sciatic nerves were lesioned at the thigh in 7-8 months old mice. Tibial motor axons at ankle were investigated by conventional motor conduction studies and axon excitability studies using threshold tracking. To evaluate regeneration we monitored the recovery of motor function after crush, and then compared the fiber distribution by histology. The overall motor performance was investigated using Rotor-Rod. P0+/- had reduced compound motor action potential amplitudes and thinner myelinated axons with only a borderline impairment in conduction and Rotor-Rod. Plantar muscle reinnervation occurred within 21 days in all mice. Shortly after reinnervation the conduction of P0+/- regenerated axons was markedly slower than WT, however, this difference decayed with time. Nevertheless, after 1 month, regenerated P0+/- axons had longer strength-duration time constant, larger threshold changes during hyperpolarizing electrotonus and longer relative refractory period. Their performance at Rotor-Rod remained also markedly impaired. In contrast, the number and diameter distribution of regenerating myelinated fibers became similar to regenerated WT. Our data suggest that in the presence of heterozygously P0 deficient Schwann cells, regenerating motor axons retain their ability to reinnervate their targets and remyelinate, though their functional recovery is delayed.
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Cheah BC, Lin CS, Park SB, Vucic S, Krishnan AV, Kiernan MC. Progressive axonal dysfunction and clinical impairment in amyotrophic lateral sclerosis. Clin Neurophysiol 2012; 123:2460-7. [DOI: 10.1016/j.clinph.2012.06.020] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2011] [Revised: 05/22/2012] [Accepted: 06/06/2012] [Indexed: 01/01/2023]
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Long-term nerve excitability changes by persistent Na+ current blocker ranolazine. Neurosci Lett 2012; 524:101-6. [PMID: 22824305 DOI: 10.1016/j.neulet.2012.07.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2012] [Revised: 07/04/2012] [Accepted: 07/08/2012] [Indexed: 01/23/2023]
Abstract
The persistent Na(+) current (Na(p)) in peripheral axons plays an important functional role in controlling the axonal excitability. Abnormal Na(p) is believed to contribute to neurodegeneration and neuropathic pain, and thus it is an attractive therapeutic target. To assess the chronic behavior of selective Na(p) blockade, axonal excitability testing was performed in vivo in normal male mice exposed to ranolazine by recording the tail sensory nerve action potentials (SNAPs). Seven days after administering ranolazine i.p. (50mg/kg) daily for 1 week, nerve excitability testing showed decreased strength-duration time constant in the ranolazine group in comparison to the control (P<0.03). This change is explained by the long-term effects of ranolazine on Na(p). Importantly, ranolazine showed no effect on other ion channels that influence axonal excitability. Further study is needed to assess the chronic Na(p) blockade as a useful therapy in peripheral nerve diseases associated with abnormal nerve excitability.
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Nodera H, Rutkove SB. Accommodation to hyperpolarizing currents: Differences between motor and sensory nerves in mice. Neurosci Lett 2012; 518:111-6. [DOI: 10.1016/j.neulet.2012.04.065] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2012] [Revised: 04/12/2012] [Accepted: 04/25/2012] [Indexed: 12/22/2022]
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41
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Changes of the peripheral nerve excitability in vivo induced by the persistent Na+ current blocker ranolazine. Neurosci Lett 2012; 518:36-40. [DOI: 10.1016/j.neulet.2012.04.050] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2012] [Revised: 04/10/2012] [Accepted: 04/19/2012] [Indexed: 02/01/2023]
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42
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Howells J, Trevillion L, Bostock H, Burke D. The voltage dependence of I(h) in human myelinated axons. J Physiol 2012; 590:1625-40. [PMID: 22310314 DOI: 10.1113/jphysiol.2011.225573] [Citation(s) in RCA: 113] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
HCN channels are responsible for I(h), a voltage-gated inwardly rectifying current activated by hyperpolarization. This current appears to be more active in human sensory axons than motor and may play a role in the determination of threshold. Differences in I(h) are likely to be responsible for the high variability in accommodation to hyperpolarization seen in different subjects. The aim of this study was to characterise this current in human axons, both motor and sensory. Recordings of multiple axonal excitability properties were performed in 10 subjects, with a focus on the changes in threshold evoked by longer and stronger hyperpolarizing currents than normally studied. The findings confirm that accommodation to hyperpolarization is greater in sensory than motor axons in all subjects, but the variability between subjects was greater than the modality difference. An existing model of motor axons was modified to take into account the behaviour seen with longer and stronger hyperpolarization, and a mathematical model of human sensory axons was developed based on the data collected. The differences in behaviour of sensory and motor axons and the differences between different subjects are best explained by modulation of the voltage dependence, along with a modest increase of expression of the underlying conductance of I(h). Accommodation to hyperpolarization for the mean sensory data is fitted well with a value of -94.2 mV for the mid-point of activation (V(0.5)) of I(h) as compared to -107.3 mV for the mean motor data. The variation in response to hyperpolarization between subjects is accounted for by varying this parameter for each modality (sensory: -89.2 to -104.2 mV; motor -87.3 to -127.3 mV). These voltage differences are within the range that has been described for physiological modulation of I(h) function. The presence of slowly activated I(h) isoforms on both motor and sensory axons was suggested by modelling a large internodal leak current and a masking of the Na(+)/K(+)-ATPase pump activity by a tonic depolarization. In addition to an increased activation of I(h), the modelling suggests that in sensory axons the nodal slow K(+) conductance is reduced, with consequent depolarization of resting membrane potential, and action potential of shorter duration.
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Affiliation(s)
- James Howells
- Institute of Clinical Neurosciences, Royal Prince Alfred Hospital and The University of Sydney, Sydney, Australia.
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Murray J, Jankelowitz S. A comparison of the excitability of motor axons innervating the APB and ADM muscles. Clin Neurophysiol 2011; 122:2290-3. [PMID: 21561804 DOI: 10.1016/j.clinph.2011.04.007] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2010] [Revised: 03/19/2011] [Accepted: 04/10/2011] [Indexed: 11/24/2022]
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Farrar MA, Vucic S, Lin CSY, Park SB, Johnston HM, du Sart D, Bostock H, Kiernan MC. Dysfunction of axonal membrane conductances in adolescents and young adults with spinal muscular atrophy. Brain 2011; 134:3185-97. [PMID: 21926101 PMCID: PMC3212713 DOI: 10.1093/brain/awr229] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Spinal muscular atrophy is distinct among neurodegenerative conditions of the motor neuron, with onset in developing and maturing patients. Furthermore, the rate of degeneration appears to slow over time, at least in the milder forms. To investigate disease pathophysiology and potential adaptations, the present study utilized axonal excitability studies to provide insights into axonal biophysical properties and explored correlation with clinical severity. Multiple excitability indices (stimulus–response curve, strength–duration time constant, threshold electrotonus, current–threshold relationship and recovery cycle) were investigated in 25 genetically characterized adolescent and adult patients with spinal muscular atrophy, stimulating the median motor nerve at the wrist. Results were compared with 50 age-matched controls. The Medical Research Council sum score and Spinal Muscular Atrophy Functional Rating Scale were used to define the strength and motor functional status of patients with spinal muscular atrophy. In patients with spinal muscular atrophy, there were reductions in compound muscle action potential amplitude (P < 0.0005) associated with reduction in stimulus response slope (P < 0.0005), confirming significant axonal loss. In the patients with mild or ambulatory spinal muscular atrophy, there was reduction of peak amplitude without alteration in axonal excitability; in contrast, in the non-ambulatory or severe spinal muscular atrophy cohort prominent changes in axonal function were apparent. Specifically, there were steep changes in the early phase of hyperpolarization in threshold electrotonus (P < 0.0005) that correlated with clinical severity. Additionally, there were greater changes in depolarizing threshold electrotonus (P < 0.0005) and prolongation of the strength-duration time constant (P = 0.001). Mathematical modelling of the excitability changes obtained in patients with severe spinal muscular atrophy supported a mixed pathology comprising features of axonal degeneration and regeneration. The present study has provided novel insight into the pathophysiology of spinal muscular atrophy, with identification of functional abnormalities involving axonal K+ and Na+ conductances and alterations in passive membrane properties, the latter linked to the process of neurodegeneration.
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Bucher D, Goaillard JM. Beyond faithful conduction: short-term dynamics, neuromodulation, and long-term regulation of spike propagation in the axon. Prog Neurobiol 2011; 94:307-46. [PMID: 21708220 PMCID: PMC3156869 DOI: 10.1016/j.pneurobio.2011.06.001] [Citation(s) in RCA: 120] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2011] [Revised: 05/27/2011] [Accepted: 06/07/2011] [Indexed: 12/13/2022]
Abstract
Most spiking neurons are divided into functional compartments: a dendritic input region, a soma, a site of action potential initiation, an axon trunk and its collaterals for propagation of action potentials, and distal arborizations and terminals carrying the output synapses. The axon trunk and lower order branches are probably the most neglected and are often assumed to do nothing more than faithfully conducting action potentials. Nevertheless, there are numerous reports of complex membrane properties in non-synaptic axonal regions, owing to the presence of a multitude of different ion channels. Many different types of sodium and potassium channels have been described in axons, as well as calcium transients and hyperpolarization-activated inward currents. The complex time- and voltage-dependence resulting from the properties of ion channels can lead to activity-dependent changes in spike shape and resting potential, affecting the temporal fidelity of spike conduction. Neural coding can be altered by activity-dependent changes in conduction velocity, spike failures, and ectopic spike initiation. This is true under normal physiological conditions, and relevant for a number of neuropathies that lead to abnormal excitability. In addition, a growing number of studies show that the axon trunk can express receptors to glutamate, GABA, acetylcholine or biogenic amines, changing the relative contribution of some channels to axonal excitability and therefore rendering the contribution of this compartment to neural coding conditional on the presence of neuromodulators. Long-term regulatory processes, both during development and in the context of activity-dependent plasticity may also affect axonal properties to an underappreciated extent.
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Affiliation(s)
- Dirk Bucher
- The Whitney Laboratory and Department of Neuroscience, University of Florida, St. Augustine, FL 32080, USA.
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Moldovan M, Alvarez S, Pinchenko V, Klein D, Nielsen FC, Wood JN, Martini R, Krarup C. Na(v)1.8 channelopathy in mutant mice deficient for myelin protein zero is detrimental to motor axons. ACTA ACUST UNITED AC 2010; 134:585-601. [PMID: 21169333 DOI: 10.1093/brain/awq336] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
Myelin protein zero mutations were found to produce Charcot-Marie-Tooth disease phenotypes with various degrees of myelin impairment and axonal loss, ranging from the mild 'demyelinating' adult form to severe and early onset forms. Protein zero deficient homozygous mice ( ) show a severe and progressive dysmyelinating neuropathy from birth with compromised myelin compaction, hypomyelination and distal axonal degeneration. A previous study using immunofluorescence showed that motor nerves deficient of myelin protein zero upregulate the Na(V)1.8 voltage gated sodium channel isoform, which is normally present only in restricted populations of sensory axons. The aim of this study was to investigate the function of motor axons in protein zero-deficient mice with particular emphasis on ectopic Na(V)1.8 voltage gated sodium channel. We combined 'threshold tracking' excitability studies with conventional nerve conduction studies, behavioural studies using rotor-rod measurements, and histological measures to assess membrane dysfunction and its progression in protein zero deficient homozygous mutants as compared with age-matched wild-type controls. The involvement of Na(V)1.8 was investigated by pharmacologic block using the subtype-selective Na(V)1.8 blocker A-803467 and chronically in Na(V)1.8 knock-outs. We found that in the context of dysmyelination, abnormal potassium ion currents and membrane depolarization, the ectopic Na(V)1.8 channels further impair the motor axon excitability in protein zero deficient homozygous mutants to an extent that precipitates conduction failure in severely affected axons. Our data suggest that a Na(V)1.8 channelopathy contributed to the poor motor function of protein zero deficient homozygous mutants, and that the conduction failure was associated with partially reversible reduction of the electrically evoked muscle response and of the clinical function as indicated by the partial recovery of function at rotor-rod measurements. As a consequence of these findings of partially reversible dysfunction, we propose that the Na(V)1.8 voltage gated sodium channel should be considered as a novel therapeutic target for Charcot-Marie-Tooth disease.
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Affiliation(s)
- Mihai Moldovan
- Institute of Neuroscience and Pharmacology, Panum, University of Copenhagen, Denmark
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