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Lo HH, Munkongcharoen T, Muijen RM, Gurung R, Umredkar AG, Baker MD. Application of near infra-red laser light increases current threshold in optic nerve consistent with increased Na +-dependent transport. Pflugers Arch 2024; 476:847-859. [PMID: 38421407 PMCID: PMC11033230 DOI: 10.1007/s00424-024-02932-1] [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: 10/26/2023] [Revised: 02/06/2024] [Accepted: 02/22/2024] [Indexed: 03/02/2024]
Abstract
Increases in the current threshold occur in optic nerve axons with the application of infra-red laser light, whose mechanism is only partly understood. In isolated rat optic nerve, laser light was applied near the site of electrical stimulation, via a flexible fibre optic. Paired applications of light produced increases in threshold that were reduced on the second application, the response recovering with increasing delays, with a time constant of 24 s. 3-min duration single applications of laser light gave rise to a rapid increase in threshold followed by a fade, whose time-constant was between 40 and 50 s. After-effects were sometimes apparent following the light application, where the resting threshold was reduced. The increase in threshold was partially blocked by 38.6 mM Li+ in combination with 5 μ M bumetanide, a manoeuvre increasing refractoriness and consistent with axonal depolarization. Assessing the effect of laser light on the nerve input resistance ruled out a previously suggested fall in myelin resistance as contributing to threshold changes. These data appear consistent with an axonal membrane potential that partly relies on temperature-dependent electroneutral Na+ influx, and where fade in the response to the laser may be caused by a gradually diminishing Na+ pump-induced hyperpolarization, in response to falling intracellular [Na+].
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Affiliation(s)
- Hin Heng Lo
- Neuroscience, Surgery and Trauma, Blizard Institute, QMUL, Whitechapel, London, E1 2AT, UK
| | - Tawan Munkongcharoen
- Neuroscience, Surgery and Trauma, Blizard Institute, QMUL, Whitechapel, London, E1 2AT, UK
| | - Rosa M Muijen
- Neuroscience, Surgery and Trauma, Blizard Institute, QMUL, Whitechapel, London, E1 2AT, UK
| | - Ritika Gurung
- Neuroscience, Surgery and Trauma, Blizard Institute, QMUL, Whitechapel, London, E1 2AT, UK
| | - Anjali G Umredkar
- Neuroscience, Surgery and Trauma, Blizard Institute, QMUL, Whitechapel, London, E1 2AT, UK
| | - Mark D Baker
- Neuroscience, Surgery and Trauma, Blizard Institute, QMUL, Whitechapel, London, E1 2AT, UK.
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Austerschmidt LJ, Schottler NI, Miller AM, Baker MD. Changing the firing threshold for normal optic nerve axons by the application of infra-red laser light. Sci Rep 2021; 11:20528. [PMID: 34654844 PMCID: PMC8519963 DOI: 10.1038/s41598-021-00084-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2021] [Accepted: 10/05/2021] [Indexed: 11/26/2022] Open
Abstract
Normal optic nerve axons exhibit a temperature dependence, previously explained by a membrane potential hyperpolarization on warming. We now report that near infra-red laser light, delivered via a fibre optic light guide, also affects axonal membrane potential and threshold, at least partly through a photo-thermal effect. Application of light to optic nerve, at the recording site, gave rise to a local membrane potential hyperpolarization over a period of about a minute, and increased the size of the depolarizing after potential. Application near the site of electrical stimulation reversibly raised current-threshold, and the change in threshold recorded over minutes of irradiation was significantly increased by the application of the Ih blocker, ZD7288 (50 µM), indicating Ih limits the hyperpolarizing effect of light. Light application also had fast effects on nerve behaviour, increasing threshold without appreciable delay (within seconds), probably by a mechanism independent of kinetically fast K+ channels and Na+ channel inactivation, and hypothesized to be caused by reversible changes in myelin function.
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Affiliation(s)
- Lavinia J Austerschmidt
- Centre for Neuroscience, Surgery and Trauma, Blizard Institute, QMUL 4 Newark Street Whitechapel, London, E1 2AT, UK
| | - Nadine I Schottler
- Centre for Neuroscience, Surgery and Trauma, Blizard Institute, QMUL 4 Newark Street Whitechapel, London, E1 2AT, UK
| | - Alyssa M Miller
- Centre for Neuroscience, Surgery and Trauma, Blizard Institute, QMUL 4 Newark Street Whitechapel, London, E1 2AT, UK
- Yusuf Hamied Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK
| | - Mark D Baker
- Centre for Neuroscience, Surgery and Trauma, Blizard Institute, QMUL 4 Newark Street Whitechapel, London, E1 2AT, UK.
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Allen-Philbey K, Stennett A, Begum T, Johnson AC, Dobson R, Giovannoni G, Gnanapavan S, Marta M, Smets I, Turner BP, Baker D, Mathews J, Schmierer K. Experience with the COVID-19 AstraZeneca vaccination in people with multiple sclerosis. Mult Scler Relat Disord 2021; 52:103028. [PMID: 34049216 PMCID: PMC8129799 DOI: 10.1016/j.msard.2021.103028] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2021] [Revised: 05/04/2021] [Accepted: 05/10/2021] [Indexed: 02/09/2023]
Abstract
Background Some people with multiple sclerosis (pwMS) are at increased risk of severe Coronavirus disease 19 (COVID-19) and should be rapidly vaccinated. However, vaccine supplies are limited, and there are concerns about side-effects, particularly with the ChAdOx1nCoV-19 (AstraZeneca) vaccine. Objectives To report our first experience of pwMS receiving the AstraZeneca vaccine. Methods Service evaluation. pwMS using the MS service at Barts Health NHS Trust were sent questionnaires to report symptoms following vaccination. Results Thirty-three responses were returned, 29/33 pwMS received a first dose of AstraZeneca vaccine, the remaining four received a first dose of BioNTech/Pfizer vaccine. All but two patients (94%) reported any symptoms including a sore arm (70%), flu-like symptoms (64%), fever (21%), fatigue (27%), and headache (21%). In more than 2/3 patients, symptoms lasted up to 48 hours, and with the exception of two pwMS reporting symptom duration of 10 and 12 days, respectively, symptoms in the remainder resolved within seven days. No severe adverse effects occurred. Conclusions pwMS report transient symptoms following AstraZeneca vaccination, characteristics of which were similar to those reported in the non-MS population. Symptoms may be more pronounced in pwMS due to the temperature-dependent delay in impulse propagation (Uhthoff's phenomenon) due to demyelination.
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Affiliation(s)
- K Allen-Philbey
- The Blizard Institute, Centre for Neuroscience, Surgery & Trauma, Queen Mary University of London, Barts and The London School of Medicine & Dentistry, London, United Kingdom; Clinical Board Medicine (Neuroscience), The Royal London Hospital, Barts Health NHS Trust, London, United Kingdom
| | - A Stennett
- The Blizard Institute, Centre for Neuroscience, Surgery & Trauma, Queen Mary University of London, Barts and The London School of Medicine & Dentistry, London, United Kingdom; Clinical Board Medicine (Neuroscience), The Royal London Hospital, Barts Health NHS Trust, London, United Kingdom
| | - T Begum
- Clinical Board Medicine (Neuroscience), The Royal London Hospital, Barts Health NHS Trust, London, United Kingdom
| | - A C Johnson
- Clinical Board Medicine (Neuroscience), The Royal London Hospital, Barts Health NHS Trust, London, United Kingdom
| | - R Dobson
- Clinical Board Medicine (Neuroscience), The Royal London Hospital, Barts Health NHS Trust, London, United Kingdom; Preventive Neurology Unit, Wolfson Institute of Preventive Medicine, Queen Mary University of London, Barts and The London School of Medicine & Dentistry, London, United Kingdom
| | - G Giovannoni
- The Blizard Institute, Centre for Neuroscience, Surgery & Trauma, Queen Mary University of London, Barts and The London School of Medicine & Dentistry, London, United Kingdom; Clinical Board Medicine (Neuroscience), The Royal London Hospital, Barts Health NHS Trust, London, United Kingdom; Preventive Neurology Unit, Wolfson Institute of Preventive Medicine, Queen Mary University of London, Barts and The London School of Medicine & Dentistry, London, United Kingdom
| | - S Gnanapavan
- The Blizard Institute, Centre for Neuroscience, Surgery & Trauma, Queen Mary University of London, Barts and The London School of Medicine & Dentistry, London, United Kingdom; Clinical Board Medicine (Neuroscience), The Royal London Hospital, Barts Health NHS Trust, London, United Kingdom
| | - M Marta
- The Blizard Institute, Centre for Neuroscience, Surgery & Trauma, Queen Mary University of London, Barts and The London School of Medicine & Dentistry, London, United Kingdom; Clinical Board Medicine (Neuroscience), The Royal London Hospital, Barts Health NHS Trust, London, United Kingdom
| | - I Smets
- The Blizard Institute, Centre for Neuroscience, Surgery & Trauma, Queen Mary University of London, Barts and The London School of Medicine & Dentistry, London, United Kingdom; Clinical Board Medicine (Neuroscience), The Royal London Hospital, Barts Health NHS Trust, London, United Kingdom
| | - B P Turner
- The Blizard Institute, Centre for Neuroscience, Surgery & Trauma, Queen Mary University of London, Barts and The London School of Medicine & Dentistry, London, United Kingdom; Clinical Board Medicine (Neuroscience), The Royal London Hospital, Barts Health NHS Trust, London, United Kingdom
| | - D Baker
- The Blizard Institute, Centre for Neuroscience, Surgery & Trauma, Queen Mary University of London, Barts and The London School of Medicine & Dentistry, London, United Kingdom
| | - J Mathews
- Pharmacy, The Royal London Hospital, Barts Health NHS Trust, London, United Kingdom
| | - K Schmierer
- The Blizard Institute, Centre for Neuroscience, Surgery & Trauma, Queen Mary University of London, Barts and The London School of Medicine & Dentistry, London, United Kingdom; Clinical Board Medicine (Neuroscience), The Royal London Hospital, Barts Health NHS Trust, London, United Kingdom.
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The effects of temperature on the biophysical properties of optic nerve F-fibres. Sci Rep 2020; 10:12755. [PMID: 32728166 PMCID: PMC7391707 DOI: 10.1038/s41598-020-69728-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2020] [Accepted: 07/15/2020] [Indexed: 01/29/2023] Open
Abstract
In multiple sclerosis, exacerbation of symptoms with rising body temperature is associated with impulse conduction failure. The mechanism is not fully understood. Remarkably, normal optic nerve axons also show temperature dependent effects, with a fall in excitability with warming. Here we show two properties of optic nerve axons, accommodation and inward rectification (Ih), respond to temperature changes in a manner consistent with a temperature dependent membrane potential. As we could find no evidence for the functional expression of KV7.2 in the axons, using the K+ channel blocker tetraethylammonium ions, we suggest this may explain the membrane potential lability. In order to understand how the axonal membrane potential may show temperature dependence, we have developed a hypothesis involving the electroneutral movement of Na+ ions across the axon membrane, that increases with increasing temperature with an appropriate Q10. Part, but probably not all, of the electroneutral Na+ movement is eliminated by removing extracellular Cl− or exposure to bumetanide, consistent with the involvement of the transporter NKCC1. Numerical simulation suggests a change in membrane potential of − 15–20 mV mimics altering temperature between room and physiological in the largest axons.
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Brown AM, Evans RD, Smith PA, Rich LR, Ransom BR. Hypothermic neuroprotection during reperfusion following exposure to aglycemia in central white matter is mediated by acidification. Physiol Rep 2019; 7:e14007. [PMID: 30834716 PMCID: PMC6399195 DOI: 10.14814/phy2.14007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2019] [Accepted: 01/30/2019] [Indexed: 11/24/2022] Open
Abstract
Hypoglycemia is a common iatrogenic consequence of type 1 diabetes therapy that can lead to central nervous system injury and even death if untreated. In the absence of clinically effective neuroprotective drugs we sought to quantify the putative neuroprotective effects of imposing hypothermia during the reperfusion phase following aglycemic exposure to central white matter. Mouse optic nerves (MONs), central white matter tracts, were superfused with oxygenated artificial cerebrospinal fluid (aCSF) containing 10 mmol/L glucose at 37°C. The supramaximal compound action potential (CAP) was evoked and axon conduction was assessed as the CAP area. Extracellular lactate was measured using an enzyme biosensor. Exposure to aglycemia, simulated by omitting glucose from the aCSF, resulted in axon injury, quantified by electrophysiological recordings, electron microscopic analysis confirming axon damage, the extent of which was determined by the duration of aglycemia exposure. Hypothermia attenuated injury. Exposing MONs to hypothermia during reperfusion resulted in improved CAP recovery compared with control recovery measured at 37°C, an effect attenuated in alkaline aCSF. Hypothermia decreases pH implying that the hypothermic neuroprotection derives from interstitial acidification. These results have important clinical implications demonstrating that hypothermic intervention during reperfusion can improve recovery in central white matter following aglycemia.
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Affiliation(s)
- Angus M. Brown
- School of Life SciencesQueens Medical CentreUniversity of NottinghamNottinghamUnited Kingdom
- Department of NeurologySchool of MedicineUniversity of WashingtonSeattleWashington
| | - Richard D. Evans
- School of Life SciencesQueens Medical CentreUniversity of NottinghamNottinghamUnited Kingdom
| | - Paul A. Smith
- School of Life SciencesQueens Medical CentreUniversity of NottinghamNottinghamUnited Kingdom
| | - Laura R. Rich
- School of Life SciencesQueens Medical CentreUniversity of NottinghamNottinghamUnited Kingdom
| | - Bruce R. Ransom
- Department of NeurologySchool of MedicineUniversity of WashingtonSeattleWashington
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Barlow BM, Joos B, Trinh AK, Longtin A. Cooling reverses pathological bifurcations to spontaneous firing caused by mild traumatic injury. CHAOS (WOODBURY, N.Y.) 2018; 28:106328. [PMID: 30384659 DOI: 10.1063/1.5040288] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/16/2018] [Accepted: 08/23/2018] [Indexed: 06/08/2023]
Abstract
Mild traumatic injury can modify the key sodium (Na+) current underlying the excitability of neurons. It causes the activation and inactivation properties of this current to become shifted to more negative trans-membrane voltages. This so-called coupled left shift (CLS) leads to a chronic influx of Na+ into the cell that eventually causes spontaneous or "ectopic" firing along the axon, even in the absence of stimuli. The bifurcations underlying this enhanced excitability have been worked out in full ionic models of this effect. Here, we present computational evidence that increased temperature T can exacerbate this pathological state. Conversely, and perhaps of clinical relevance, mild cooling is shown to move the naturally quiescent cell further away from the threshold of ectopic behavior. The origin of this stabilization-by-cooling effect is analyzed by knocking in and knocking out, one at a time, various processes thought to be T-dependent. The T-dependence of the Na+ current, quantified by its Q 10-Na factor, has the biggest impact on the threshold, followed by Q 10-pump of the sodium-potassium exchanger. Below the ectopic boundary, the steady state for the gating variables and the resting potential are not modified by temperature, since our model separately tallies the Na+ and K+ ions including their separate leaks through the pump. When only the gating kinetics are considered, cooling is detrimental, but in the full T-dependent model, it is beneficial because the other processes dominate. Cooling decreases the pump's activity, and since the pump hyperpolarizes, less hyperpolarization should lead to more excitability and ectopic behavior. But actually the opposite happens in the full model because decreased pump activity leads to smaller gradients of Na+ and K+, which in turn decreases the driving force of the Na+ current.
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Affiliation(s)
- B M Barlow
- Department of Physics, Centre for Neural Dynamics, University of Ottawa, 150 Louis Pasteur Priv., Ottawa, Ontario K1N6N5, Canada
| | - B Joos
- Department of Physics, Centre for Neural Dynamics, University of Ottawa, 150 Louis Pasteur Priv., Ottawa, Ontario K1N6N5, Canada
| | - A K Trinh
- Department of Physics, Centre for Neural Dynamics, University of Ottawa, 150 Louis Pasteur Priv., Ottawa, Ontario K1N6N5, Canada
| | - A Longtin
- Department of Physics, Centre for Neural Dynamics, University of Ottawa, 150 Louis Pasteur Priv., Ottawa, Ontario K1N6N5, Canada
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Kanagaratnam M, Pendleton C, Souza DA, Pettit J, Howells J, Baker MD. Diuretic-sensitive electroneutral Na + movement and temperature effects on central axons. J Physiol 2017; 595:3471-3482. [PMID: 28213919 PMCID: PMC5451713 DOI: 10.1113/jp273963] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Accepted: 02/13/2017] [Indexed: 01/26/2023] Open
Abstract
Key points Optic nerve axons get less excitable with warming. F‐fibre latency does not shorten at temperatures above 30°C. Action potential amplitude falls when the Na+‐pump is blocked, an effect speeded by warming. Diuretics reduce the rate of action potential fall in the presence of ouabain. Our data are consistent with electroneutral entry of Na+ occurring in axons and contributing to setting the resting potential.
Abstract Raising the temperature of optic nerve from room temperature to near physiological has effects on the threshold, refractoriness and superexcitability of the shortest latency (fast, F) nerve fibres, consistent with hyperpolarization. The temperature dependence of peak impulse latency was weakened at temperatures above 30°C suggesting a temperature‐sensitive process that slows impulse propagation. The amplitude of the supramaximal compound action potential gets larger on warming, whereas in the presence of bumetanide and amiloride (blockers of electroneutral Na+ movement), the action potential amplitude consistently falls. This suggests a warming‐induced hyperpolarization that is reduced by blocking electroneutral Na+ movement. In the presence of ouabain, the action potential collapses. This collapse is speeded by warming, and exposure to bumetanide and amiloride slows the temperature‐dependent amplitude decline, consistent with a warming‐induced increase in electroneutral Na+ entry. Blocking electroneutral Na+ movement is predicted to be useful in the treatment of temperature‐dependent symptoms under conditions with reduced safety factor (Uhthoff's phenomenon) and provide a route to neuroprotection. Optic nerve axons get less excitable with warming. F‐fibre latency does not shorten at temperatures above 30°C. Action potential amplitude falls when the Na+‐pump is blocked, an effect speeded by warming. Diuretics reduce the rate of action potential fall in the presence of ouabain. Our data are consistent with electroneutral entry of Na+ occurring in axons and contributing to setting the resting potential.
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Affiliation(s)
- Meneka Kanagaratnam
- Neuroscience and Trauma centre, Blizard Institute, Queen Mary University of London, 4 Newark Street, Whitechapel, London, E1 2AT, UK
| | - Christopher Pendleton
- Neuroscience and Trauma centre, Blizard Institute, Queen Mary University of London, 4 Newark Street, Whitechapel, London, E1 2AT, UK
| | - Danilo Almeida Souza
- Neuroscience and Trauma centre, Blizard Institute, Queen Mary University of London, 4 Newark Street, Whitechapel, London, E1 2AT, UK
| | - Joseph Pettit
- Neuroscience and Trauma centre, Blizard Institute, Queen Mary University of London, 4 Newark Street, Whitechapel, London, E1 2AT, UK
| | - James Howells
- Brain and Mind Research Institute, University of Sydney, 94 Mallet Street, Camperdown, NSW, 2050, Australia
| | - Mark D Baker
- Neuroscience and Trauma centre, Blizard Institute, Queen Mary University of London, 4 Newark Street, Whitechapel, London, E1 2AT, UK
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Affiliation(s)
- Matthew C Kiernan
- Bushell Professor of Neurology, Royal Prince Alfred Hospital; and Brain and Mind Centre, University of Sydney, Sydney, NSW, 2040, Australia
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