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Su TF, Hamilton JD, Guo Y, Potas JR, Shivdasani MN, Moalem-Taylor G, Fridman GY, Aplin FP. Peripheral direct current reduces naturally evoked nociceptive activity at the spinal cord in rodent models of pain. J Neural Eng 2024; 21:026044. [PMID: 38579742 DOI: 10.1088/1741-2552/ad3b6c] [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: 08/25/2023] [Accepted: 04/05/2024] [Indexed: 04/07/2024]
Abstract
Objective.Electrical neuromodulation is an established non-pharmacological treatment for chronic pain. However, existing devices using pulsatile stimulation typically inhibit pain pathways indirectly and are not suitable for all types of chronic pain. Direct current (DC) stimulation is a recently developed technology which affects small-diameter fibres more strongly than pulsatile stimulation. Since nociceptors are predominantly small-diameter Aδand C fibres, we investigated if this property could be applied to preferentially reduce nociceptive signalling.Approach.We applied a DC waveform to the sciatic nerve in rats of both sexes and recorded multi-unit spinal activity evoked at the hindpaw using various natural stimuli corresponding to different sensory modalities rather than broad-spectrum electrical stimulus. To determine if DC neuromodulation is effective across different types of chronic pain, tests were performed in models of neuropathic and inflammatory pain.Main results.We found that in both pain models tested, DC application reduced responses evoked by noxious stimuli, as well as tactile-evoked responses which we suggest may be involved in allodynia. Different spinal activity of different modalities were reduced in naïve animals compared to the pain models, indicating that physiological changes such as those mediated by disease states could play a larger role than previously thought in determining neuromodulation outcomes.Significance.Our findings support the continued development of DC neuromodulation as a method for reduction of nociceptive signalling, and suggests that it may be effective at treating a broader range of aberrant pain conditions than existing devices.
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Affiliation(s)
- Tom F Su
- School of Biomedical Sciences, University of New South Wales, Sydney, New South Wales, Australia
| | - Jack D Hamilton
- School of Biomedical Sciences, University of New South Wales, Sydney, New South Wales, Australia
| | - Yiru Guo
- School of Biomedical Sciences, University of New South Wales, Sydney, New South Wales, Australia
| | - Jason R Potas
- School of Biomedical Sciences, University of New South Wales, Sydney, New South Wales, Australia
- Eccles Institute, John Curtin School of Medical Research, The Australian National University, Canberra, Australian Capital Territory, Australia
| | - Mohit N Shivdasani
- Graduate School of Biomedical Engineering, University of New South Wales, Sydney, New South Wales, Australia
| | - Gila Moalem-Taylor
- School of Biomedical Sciences, University of New South Wales, Sydney, New South Wales, Australia
| | - Gene Y Fridman
- Department of Otolaryngology, Head and Neck Surgery, Johns Hopkins University, Baltimore, MD, United States of America
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, United States of America
- Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, MD, United States of America
| | - Felix P Aplin
- School of Biomedical Sciences, University of New South Wales, Sydney, New South Wales, Australia
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2
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Cheng C, Foxworthy GE, Fridman GY. A Cuff Lead for Delivering Ionic Direct Current (iDC) to Block Neural Activities of Sciatic Nerve. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2023; 2023:1-4. [PMID: 38083560 DOI: 10.1109/embc40787.2023.10340183] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2023]
Abstract
Direct current (DC) applied extracellularly can block action potential (AP) propagation in a neuron. This suppression paradigm has been proposed as a possible treatment for blocking nociceptive pain. However, the application of DC is limited in duration due to the charge injection constraint imposed by the evolution of electrochemical reactions at the metal electrode. To prolong the application of DC, a microfluidic lead filled with conductive electrolyte can be used to separate the metal electrode from the target nerve. Here, we describe a tripolar nerve cuff lead fabricated with biocompatible silicone to block the APs in the rat sciatic nerve. This lead has a self-curling silicone membrane to wrap around sciatic nerve for secured mechanical attachment and electrical isolation between the nerve and the surrounding muscle. In-vivo testing showed that delivering 1.4mA DC via the cuff lead blocked the nerve activity and reduced the evoked compound action potential (eCAP) to 30% of its unblocked response.
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van Boekholdt L, Kerstens S, Khatoun A, Asamoah B, Mc Laughlin M. tDCS peripheral nerve stimulation: a neglected mode of action? Mol Psychiatry 2021; 26:456-461. [PMID: 33299136 DOI: 10.1038/s41380-020-00962-6] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/22/2020] [Revised: 10/19/2020] [Accepted: 11/16/2020] [Indexed: 11/09/2022]
Abstract
Transcranial direct current stimulation (tDCS) is a noninvasive neuromodulation method widely used by neuroscientists and clinicians for research and therapeutic purposes. tDCS is currently under investigation as a treatment for a range of psychiatric disorders. Despite its popularity, a full understanding of tDCS's underlying neurophysiological mechanisms is still lacking. tDCS creates a weak electric field in the cerebral cortex which is generally assumed to cause the observed effects. Interestingly, as tDCS is applied directly on the skin, localized peripheral nerve endings are exposed to much higher electric field strengths than the underlying cortices. Yet, the potential contribution of peripheral mechanisms in causing tDCS's effects has never been systemically investigated. We hypothesize that tDCS induces arousal and vigilance through peripheral mechanisms. We suggest that this may involve peripherally-evoked activation of the ascending reticular activating system, in which norepinephrine is distributed throughout the brain by the locus coeruleus. Finally, we provide suggestions to improve tDCS experimental design beyond the standard sham control, such as topical anesthetics to block peripheral nerves and active controls to stimulate non-target areas. Broad adoption of these measures in all tDCS experiments could help disambiguate peripheral from true transcranial tDCS mechanisms.
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Affiliation(s)
- Luuk van Boekholdt
- Exp ORL, Department of Neuroscience, Leuven Brain Institute, KU Leuven, Leuven, Belgium
| | - Silke Kerstens
- Exp ORL, Department of Neuroscience, Leuven Brain Institute, KU Leuven, Leuven, Belgium
| | - Ahmad Khatoun
- Exp ORL, Department of Neuroscience, Leuven Brain Institute, KU Leuven, Leuven, Belgium
| | - Boateng Asamoah
- Exp ORL, Department of Neuroscience, Leuven Brain Institute, KU Leuven, Leuven, Belgium
| | - Myles Mc Laughlin
- Exp ORL, Department of Neuroscience, Leuven Brain Institute, KU Leuven, Leuven, Belgium.
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Ahmed U, Chang YC, Cracchiolo M, Lopez MF, Tomaio JN, Datta-Chaudhuri T, Zanos TP, Rieth L, Al-Abed Y, Zanos S. Anodal block permits directional vagus nerve stimulation. Sci Rep 2020; 10:9221. [PMID: 32513973 PMCID: PMC7280203 DOI: 10.1038/s41598-020-66332-y] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2020] [Accepted: 05/14/2020] [Indexed: 11/10/2022] Open
Abstract
Vagus nerve stimulation (VNS) is a bioelectronic therapy for disorders of the brain and peripheral organs, and a tool to study the physiology of autonomic circuits. Selective activation of afferent or efferent vagal fibers can maximize efficacy and minimize off-target effects of VNS. Anodal block (ABL) has been used to achieve directional fiber activation in nerve stimulation. However, evidence for directional VNS with ABL has been scarce and inconsistent, and it is unknown whether ABL permits directional fiber activation with respect to functional effects of VNS. Through a series of vagotomies, we established physiological markers for afferent and efferent fiber activation by VNS: stimulus-elicited change in breathing rate (ΔBR) and heart rate (ΔHR), respectively. Bipolar VNS trains of both polarities elicited mixed ΔHR and ΔBR responses. Cathode cephalad polarity caused an afferent pattern of responses (relatively stronger ΔBR) whereas cathode caudad caused an efferent pattern (stronger ΔHR). Additionally, left VNS elicited a greater afferent and right VNS a greater efferent response. By analyzing stimulus-evoked compound nerve potentials, we confirmed that such polarity differences in functional responses to VNS can be explained by ABL of A- and B-fiber activation. We conclude that ABL is a mechanism that can be leveraged for directional VNS.
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Affiliation(s)
- Umair Ahmed
- Institute of Bioelectronic Medicine, Feinstein Institutes for Medical Research, Manhasset, NY, 11030, USA
| | - Yao-Chuan Chang
- Institute of Bioelectronic Medicine, Feinstein Institutes for Medical Research, Manhasset, NY, 11030, USA
| | - Marina Cracchiolo
- Institute of Bioelectronic Medicine, Feinstein Institutes for Medical Research, Manhasset, NY, 11030, USA
- Biorobotics Institute, Scuola Superiore Sant'Anna, Pisa, Italy
| | - Maria F Lopez
- Institute of Bioelectronic Medicine, Feinstein Institutes for Medical Research, Manhasset, NY, 11030, USA
| | - Jacquelyn N Tomaio
- Institute of Bioelectronic Medicine, Feinstein Institutes for Medical Research, Manhasset, NY, 11030, USA
| | - Timir Datta-Chaudhuri
- Institute of Bioelectronic Medicine, Feinstein Institutes for Medical Research, Manhasset, NY, 11030, USA
| | - Theodoros P Zanos
- Institute of Bioelectronic Medicine, Feinstein Institutes for Medical Research, Manhasset, NY, 11030, USA
| | - Loren Rieth
- Institute of Bioelectronic Medicine, Feinstein Institutes for Medical Research, Manhasset, NY, 11030, USA
| | - Yousef Al-Abed
- Institute of Bioelectronic Medicine, Feinstein Institutes for Medical Research, Manhasset, NY, 11030, USA
| | - Stavros Zanos
- Institute of Bioelectronic Medicine, Feinstein Institutes for Medical Research, Manhasset, NY, 11030, USA.
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Aplin FP, Fridman GY. Implantable Direct Current Neural Modulation: Theory, Feasibility, and Efficacy. Front Neurosci 2019; 13:379. [PMID: 31057361 PMCID: PMC6482222 DOI: 10.3389/fnins.2019.00379] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2018] [Accepted: 04/02/2019] [Indexed: 12/25/2022] Open
Abstract
Implantable neuroprostheses such as cochlear implants, deep brain stimulators, spinal cord stimulators, and retinal implants use charge-balanced alternating current (AC) pulses to recover delivered charge and thus mitigate toxicity from electrochemical reactions occurring at the metal-tissue interface. At low pulse rates, these short duration pulses have the effect of evoking spikes in neural tissue in a phase-locked fashion. When the therapeutic goal is to suppress neural activity, implants typically work indirectly by delivering excitation to populations of neurons that then inhibit the target neurons, or by delivering very high pulse rates that suffer from a number of undesirable side effects. Direct current (DC) neural modulation is an alternative methodology that can directly modulate extracellular membrane potential. This neuromodulation paradigm can excite or inhibit neurons in a graded fashion while maintaining their stochastic firing patterns. DC can also sensitize or desensitize neurons to input. When applied to a population of neurons, DC can modulate synaptic connectivity. Because DC delivered to metal electrodes inherently violates safe charge injection criteria, its use has not been explored for practical applicability of DC-based neural implants. Recently, several new technologies and strategies have been proposed that address this safety criteria and deliver ionic-based direct current (iDC). This, along with the increased understanding of the mechanisms behind the transcutaneous DC-based modulation of neural targets, has caused a resurgence of interest in the interaction between iDC and neural tissue both in the central and the peripheral nervous system. In this review we assess the feasibility of in-vivo iDC delivery as a form of neural modulation. We present the current understanding of DC/neural interaction. We explore the different design methodologies and technologies that attempt to safely deliver iDC to neural tissue and assess the scope of application for direct current modulation as a form of neuroprosthetic treatment in disease. Finally, we examine the safety implications of long duration iDC delivery. We conclude that DC-based neural implants are a promising new modulation technology that could benefit from further chronic safety assessments and a better understanding of the basic biological and biophysical mechanisms that underpin DC-mediated neural modulation.
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Affiliation(s)
- Felix P Aplin
- Department of Otolaryngology Head and Neck Surgery, Johns Hopkins University, Baltimore, MD, United States
| | - Gene Y Fridman
- Department of Otolaryngology Head and Neck Surgery, Johns Hopkins University, Baltimore, MD, United States.,Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, United States.,Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, MD, United States
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6
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Vrabec TL, Wainright JS, Bhadra N, Shaw L, Kilgore KL, Bhadra N. A Carbon Slurry Separated Interface Nerve Electrode for Electrical Block of Nerve Conduction. IEEE Trans Neural Syst Rehabil Eng 2019; 27:836-845. [PMID: 30951474 DOI: 10.1109/tnsre.2019.2909165] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Direct current (DC) nerve block has been shown to provide a complete block of nerve conduction without unwanted neural firing. Previous work shows that high capacitance electrodes can be used to safely deliver a DC block. Another way of delivering DC safely is through a separated interface nerve electrode (SINE), such that any reactive species that are generated by the passage of DC are contained in a vessel away from the nerve. This design has been enhanced by using a high capacitance carbon "slurry" as the electrode in the external vessel to extend the capacity of the electrode (CSINE). With this new design, it was possible to provide 50 min of continuous nerve block without recharge while still maintaining complete recovery of neural signals. Up to 46 C of charge delivery was applied for a total of 4 h of nerve block with complete recovery. Because of the extended delivery time, it was possible to explore several properties of DC block that would not be revealed without the capability of a long-duration continuous block. It was possible to achieve complete block at lower values of DC if the block was applied for a longer period of time. Depending on the amount of charge applied during the block, the recovery was delayed for a period of time before complete force recovery was restored. These new properties provide novel techniques for device development to optimize charge delivery time and device powering concerns.
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Ou P, Fridman G. Electronics for a Safe Direct Current Stimulator. IEEE BIOMEDICAL CIRCUITS AND SYSTEMS CONFERENCE : HEALTHCARE TECHNOLOGY : [PROCEEDINGS]. IEEE BIOMEDICAL CIRCUITS AND SYSTEMS CONFERENCE 2018; 2017. [PMID: 30406219 DOI: 10.1109/biocas.2017.8325191] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Commercially available neuroprostheses, while successful and effective, are limited in their functionality by their reliance on pulsatile stimulation. Direct current (DC) has been shown to have great potential for the purposes of neuromodulation; however, direct current cannot be applied directly to neurons due to the charge injection thresholds of electrodes. We are developing a Safe Direct Current Stimulator (SDCS) that applies ionic direct current (iDC) without inducing toxic electrochemical reactions. The current design of the SDCS uses a series of eight valves in conjunction with four electrodes to rectify ionic current in microfluidic channels. This paper outlines the design, implementation, and testing of the electronics of the SDCS. These electronics will ultimately be interfaced with a separate microfluidic circuit in the device prototype. Testing the outputs of the electronics confirmed adherence to its design requirements. The completion of the SDCS electronics enables the further development of iDC as a mechanism for neuromodulation.
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Affiliation(s)
- Patrick Ou
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, USA
| | - Gene Fridman
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, USA
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Vrabec T, Bhadra N, Van Acker G, Bhadra N, Kilgore K. Continuous Direct Current Nerve Block Using Multi Contact High Capacitance Electrodes. IEEE Trans Neural Syst Rehabil Eng 2016; 25:517-529. [PMID: 27411224 DOI: 10.1109/tnsre.2016.2589541] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Charge-balanced direct current (CBDC) nerve block can be used to block nerve conduction in peripheral nerves. Previous work demonstrated that the CBDC waveform could be used to achieve a 10% duty cycle of block to non-block repeatedly for at least two hours. We demonstrate that the duty cycle of this approach can be significantly increased by utilizing multiple electrode contacts and cycling the CBDC waveform between each contact in a "carousel" configuration. Using this approach, we demonstrated in an acute rat sciatic nerve preparation, that a 30% duty cycle complete block can be achieved with two contacts; and a 100% duty cycle block (>95% complete block) can be achieved with four contacts. This latter configuration utilized a 4-s block plateau, with 3 s between successive plateaus at each contact and a recharge phase amplitude that was 34% of the block amplitude. Further optimization of the carousel approach can be achieved to improve block effectiveness and minimize total electrode length. This approach may have significant clinical use in cases where a partial or complete block of peripheral nerve activity is required. In one example case, we achieved continuous block for 22 min without degradation of nerve conduction. Future study will be required to further optimize this technique and to demonstrate safety for chronic human use.
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9
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Vrabec T, Bhadra N, Wainright J, Bhadra N, Franke M, Kilgore K. Characterization of high capacitance electrodes for the application of direct current electrical nerve block. Med Biol Eng Comput 2015; 54:191-203. [PMID: 26358242 DOI: 10.1007/s11517-015-1385-5] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2015] [Accepted: 09/01/2015] [Indexed: 10/23/2022]
Abstract
Direct current (DC) can briefly produce a reversible nerve conduction block in acute experiments. However, irreversible reactions at the electrode-tissue interface have prevented its use in both acute and chronic settings. A high capacitance material (platinum black) using a charge-balanced waveform was evaluated to determine whether brief DC block (13 s) could be achieved repeatedly (>100 cycles) without causing acute irreversible reduction in nerve conduction. Electrochemical techniques were used to characterize the electrodes to determine appropriate waveform parameters. In vivo experiments on DC motor conduction block of the rat sciatic nerve were performed to characterize the acute neural response to this novel nerve block system. Complete nerve motor conduction block of the rat sciatic nerve was possible in all experiments, with the block threshold ranging from -0.15 to -3.0 mA. DC pulses were applied for 100 cycles with no nerve conduction reduction in four of the six platinum black electrodes tested. However, two of the six electrodes exhibited irreversible conduction degradation despite charge delivery that was within the initial Q (capacitance) value of the electrode. Degradation of material properties occurred in all experiments, pointing to a possible cause of the reduction in nerve conduction in some platinum black experiments .
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Affiliation(s)
- Tina Vrabec
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA.
| | - Niloy Bhadra
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA.
| | - Jesse Wainright
- Department of Chemical Engineering, Case Western Reserve University, Cleveland, OH, USA.
| | - Narendra Bhadra
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA.
| | - Manfred Franke
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA.
| | - Kevin Kilgore
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA. .,MetroHealth Medical Center, Cleveland, OH, USA. .,Louis Stokes Cleveland Department, Veterans Affairs Medical Center, Cleveland, OH, USA.
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Tai C, Roppolo JR, de Groat WC. Analysis of nerve conduction block induced by direct current. J Comput Neurosci 2009; 27:201-10. [PMID: 19255835 DOI: 10.1007/s10827-009-0137-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2008] [Revised: 01/13/2009] [Accepted: 01/20/2009] [Indexed: 11/30/2022]
Abstract
The mechanisms of nerve conduction block induced by direct current (DC) were investigated using a lumped circuit model of the myelinated axon based on Frankenhaeuser-Huxley (FH) model. Four types of nerve conduction block were observed including anodal DC block, cathodal DC block, virtual anodal DC block, and virtual cathodal DC block. The concept of activating function was used to explain the blocking locations and relation between these different types of nerve block. Anodal/cathodal DC blocks occurred at the axonal nodes under the block electrode, while virtual anodal/cathodal DC blocks occurred at the nodes several millimeters away from the block electrode. Anodal or virtual anodal DC block was caused by hyperpolarization of the axon membrane resulting in the failure of activating sodium channels by the arriving action potential. Cathodal or virtual cathodal DC block was caused by depolarization of the axon membrane resulting in inactivation of the sodium channel. The threshold of cathodal DC block was lower than anodal DC block in most conditions. The threshold of virtual anodal/cathodal blocks was about three to five times higher than the threshold of anodal/cathodal blocks. The blocking threshold was decreased with an increase of axonal diameter, a decrease of electrode distance to axon, or an increase of temperature. This simulation study, which revealed four possible mechanisms of nerve conduction block in myelinated axons induced by DC current, can guide future animal experiments as well as optimize the design of electrodes to block nerve conduction in neuroprosthetic applications.
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Affiliation(s)
- Changfeng Tai
- Department of Urology, University of Pittsburgh, W1354 Biomedical Science Tower, Pittsburgh, PA 15261, USA.
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Durand S, Fromy B, Humeau A, Sigaudo-Roussel D, Saumet JL, Abraham P. Break excitation alone does not explain the delay and amplitude of anodal current-induced vasodilatation in human skin. J Physiol 2002; 542:549-57. [PMID: 12122152 PMCID: PMC2290427 DOI: 10.1113/jphysiol.2002.022731] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
In iontophoresis experiments, a 'non-specific' current-induced vasodilatation interferes with the effects of the diffused drugs. This current-induced vasodilatation is assumed to rely on an axon reflex due to excitation of cutaneous nociceptors and is weaker and delayed at the anode as compared to the cathode. We analysed whether these anodal specificities could result from a break excitation of nociceptors. Break excitation is the generation of action potentials at the end of a square anodal DC current application, which are generally weaker than those observed at the onset of a same application at the cathode. In eight healthy volunteers, we studied forearm cutaneous laser Doppler flow (LDF) responses to: (1) anodal and cathodal 100 microA current applications of 1, 2, 3, 4 or 5 min; (2) 100 microA anodal applications of 3 min with a progressive ending over 100 s (total charge 23 mC); these were compared to square-ended 100 microA anodal applications of the same total charge (23 mC) or duration (3 min); (3) a 4 min 100 microA anodal application with a 333 msec break at half time. Results (mean +/- S.D.) are expressed as percentage of heat-induced maximal vasodilatation (%MVD). Onset (T(vd)) and amplitude (LDF(peak)) of vasodilatation were determined. We observed that: T(vd) was linearly related to the duration of current application at the anode (slope = 1.01, r(2) = 0.99, P < 0.0001) but not at the cathode (slope = 0.03, r(2) = 0.02, n.s.). Progressive ending of anodal current did not decrease LDF(peak) (63.3 +/- 24.6 %MVD) as compared to square-ending of current application of the same duration (36.9 +/- 22.2 %MVD) or the same total charge (57.1 +/- 23.5 %MVD). A transient break of anodal current did not allow for the vasodilatation to develop until current was permanently stopped. We conclude that, during iontophoresis, anodal break excitation alone cannot account for the delay and amplitude of the vascular response.
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Affiliation(s)
- S Durand
- Laboratoire de Physiologie et Explorations Vasculaires, Centre Hospitalier Universitaire, 49033 Angers Cedex 01, France
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