1
|
Lucas-Romero J, Rivera-Arconada I, Lopez-Garcia JA. Noise or signal? Spontaneous activity of dorsal horn neurons: patterns and function in health and disease. Pflugers Arch 2024; 476:1171-1186. [PMID: 38822875 PMCID: PMC11271371 DOI: 10.1007/s00424-024-02971-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2023] [Revised: 04/10/2024] [Accepted: 05/05/2024] [Indexed: 06/03/2024]
Abstract
Spontaneous activity refers to the firing of action potentials by neurons in the absence of external stimulation. Initially considered an artifact or "noise" in the nervous system, it is now recognized as a potential feature of neural function. Spontaneous activity has been observed in various brain areas, in experimental preparations from different animal species, and in live animals and humans using non-invasive imaging techniques. In this review, we specifically focus on the spontaneous activity of dorsal horn neurons of the spinal cord. We use a historical perspective to set the basis for a novel classification of the different patterns of spontaneous activity exhibited by dorsal horn neurons. Then we examine the origins of this activity and propose a model circuit to explain how the activity is generated and transmitted to the dorsal horn. Finally, we discuss possible roles of this activity during development and during signal processing under physiological conditions and pain states. By analyzing recent studies on the spontaneous activity of dorsal horn neurons, we aim to shed light on its significance in sensory processing. Understanding the different patterns of activity, the origins of this activity, and the potential roles it may play, will contribute to our knowledge of sensory mechanisms, including pain, to facilitate the modeling of spinal circuits and hopefully to explore novel strategies for pain treatment.
Collapse
Affiliation(s)
- Javier Lucas-Romero
- Department of Systems Biology, University of Alcala, 28805, Madrid, Spain
- Department of Physical Therapy, Washington University School of Medicine, Washington University in St. Louis, St. Louis, MO, 63108, USA
| | | | - Jose Antonio Lopez-Garcia
- Department of Systems Biology, University of Alcala, 28805, Madrid, Spain.
- Departamento de Biologia de Sistemas, Edificio de Medicina, Universidad de Alcala, Ctra. Madrid-Barcelona, Km 33,600, 28805, Alcala de Henares, Madrid, Spain.
| |
Collapse
|
2
|
Safronov BV, Szucs P. Novel aspects of signal processing in lamina I. Neuropharmacology 2024; 247:109858. [PMID: 38286189 DOI: 10.1016/j.neuropharm.2024.109858] [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: 11/24/2023] [Revised: 01/12/2024] [Accepted: 01/25/2024] [Indexed: 01/31/2024]
Abstract
The most superficial layer of the spinal dorsal horn, lamina I, is a key element of the nociceptive processing system. It contains different types of projection neurons (PNs) and local-circuit neurons (LCNs) whose functional roles in the signal processing are poorly understood. This article reviews recent progress in elucidating novel anatomical features and physiological properties of lamina I PNs and LCNs revealed by whole-cell recordings in ex vivo spinal cord. This article is part of the Special Issue on "Ukrainian Neuroscience".
Collapse
Affiliation(s)
- Boris V Safronov
- Neuronal Networks Group, Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal.
| | - Peter Szucs
- Department of Anatomy, Histology and Embryology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary; HUN-REN-DE Neuroscience Research Group, Debrecen, Hungary
| |
Collapse
|
3
|
Garcia-Ramirez DL, Singh S, McGrath JR, Ha NT, Dougherty KJ. Identification of adult spinal Shox2 neuronal subpopulations based on unbiased computational clustering of electrophysiological properties. Front Neural Circuits 2022; 16:957084. [PMID: 35991345 PMCID: PMC9385948 DOI: 10.3389/fncir.2022.957084] [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: 05/30/2022] [Accepted: 07/08/2022] [Indexed: 11/13/2022] Open
Abstract
Spinal cord neurons integrate sensory and descending information to produce motor output. The expression of transcription factors has been used to dissect out the neuronal components of circuits underlying behaviors. However, most of the canonical populations of interneurons are heterogeneous and require additional criteria to determine functional subpopulations. Neurons expressing the transcription factor Shox2 can be subclassified based on the co-expression of the transcription factor Chx10 and each subpopulation is proposed to have a distinct connectivity and different role in locomotion. Adult Shox2 neurons have recently been shown to be diverse based on their firing properties. Here, in order to subclassify adult mouse Shox2 neurons, we performed multiple analyses of data collected from whole-cell patch clamp recordings of visually-identified Shox2 neurons from lumbar spinal slices. A smaller set of Chx10 neurons was included in the analyses for validation. We performed k-means and hierarchical unbiased clustering approaches, considering electrophysiological variables. Unlike the categorizations by firing type, the clusters displayed electrophysiological properties that could differentiate between clusters of Shox2 neurons. The presence of clusters consisting exclusively of Shox2 neurons in both clustering techniques suggests that it is possible to distinguish Shox2+Chx10- neurons from Shox2+Chx10+ neurons by electrophysiological properties alone. Computational clusters were further validated by immunohistochemistry with accuracy in a small subset of neurons. Thus, unbiased cluster analysis using electrophysiological properties is a tool that can enhance current interneuronal subclassifications and can complement groupings based on transcription factor and molecular expression.
Collapse
Affiliation(s)
| | | | | | | | - Kimberly J. Dougherty
- Department of Neurobiology and Anatomy, Marion Murray Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA, United States
| |
Collapse
|
4
|
Wang H, Chen W, Dong Z, Xing G, Cui W, Yao L, Zou WJ, Robinson HL, Bian Y, Liu Z, Zhao K, Luo B, Gao N, Zhang H, Ren X, Yu Z, Meixiong J, Xiong WC, Mei L. A novel spinal neuron connection for heat sensation. Neuron 2022; 110:2315-2333.e6. [PMID: 35561677 DOI: 10.1016/j.neuron.2022.04.021] [Citation(s) in RCA: 15] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2021] [Revised: 03/14/2022] [Accepted: 04/19/2022] [Indexed: 12/30/2022]
Abstract
Heat perception enables acute avoidance responses to prevent tissue damage and maintain body thermal homeostasis. Unlike other modalities, how heat signals are processed in the spinal cord remains unclear. By single-cell gene profiling, we identified ErbB4, a transmembrane tyrosine kinase, as a novel marker of heat-sensitive spinal neurons in mice. Ablating spinal ErbB4+ neurons attenuates heat sensation. These neurons receive monosynaptic inputs from TRPV1+ nociceptors and form excitatory synapses onto target neurons. Activation of ErbB4+ neurons enhances the heat response, while inhibition reduces the heat response. We showed that heat sensation is regulated by NRG1, an activator of ErbB4, and it involves dynamic activity of the tyrosine kinase that promotes glutamatergic transmission. Evidence indicates that the NRG1-ErbB4 signaling is also engaged in hypersensitivity of pathological pain. Together, these results identify a spinal neuron connection consisting of ErbB4+ neurons for heat sensation and reveal a regulatory mechanism by the NRG1-ErbB4 signaling.
Collapse
Affiliation(s)
- Hongsheng Wang
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Wenbing Chen
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Zhaoqi Dong
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Guanglin Xing
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Wanpeng Cui
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Lingling Yao
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Wen-Jun Zou
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Heath L Robinson
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Yaoyao Bian
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Zhipeng Liu
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Kai Zhao
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Bin Luo
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Nannan Gao
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Hongsheng Zhang
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Xiao Ren
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - Zheng Yu
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
| | - James Meixiong
- Solomon H. Snyder Department of Neuroscience and Medical Scientist Training Program, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Wen-Cheng Xiong
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA; Louis Stokes Cleveland Veterans Affairs Medical Center, Cleveland, OH 44106, USA
| | - Lin Mei
- Department of Neurosciences, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA; Louis Stokes Cleveland Veterans Affairs Medical Center, Cleveland, OH 44106, USA.
| |
Collapse
|
5
|
Zhu M, Yan Y, Cao X, Zeng F, Xu G, Shen W, Li F, Luo L, Wang Z, Zhang Y, Zhang X, Zhang D, Liu T. Electrophysiological and Morphological Features of Rebound Depolarization Characterized Interneurons in Rat Superficial Spinal Dorsal Horn. Front Cell Neurosci 2021; 15:736879. [PMID: 34621158 PMCID: PMC8490703 DOI: 10.3389/fncel.2021.736879] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Accepted: 08/25/2021] [Indexed: 11/18/2022] Open
Abstract
Substantia gelatinosa (SG) neurons, which are located in the spinal dorsal horn (lamina II), have been identified as the “central gate” for the transmission and modulation of nociceptive information. Rebound depolarization (RD), a biophysical property mediated by membrane hyperpolarization that is frequently recorded in the central nervous system, contributes to shaping neuronal intrinsic excitability and, in turn, contributes to neuronal output and network function. However, the electrophysiological and morphological properties of SG neurons exhibiting RD remain unclarified. In this study, whole-cell patch-clamp recordings were performed on SG neurons from parasagittal spinal cord slices. RD was detected in 44.44% (84 out of 189) of the SG neurons recorded. We found that RD-expressing neurons had more depolarized resting membrane potentials, more hyperpolarized action potential (AP) thresholds, higher AP amplitudes, shorter AP durations, and higher spike frequencies in response to depolarizing current injection than neurons without RD. Based on their firing patterns and morphological characteristics, we propose that most of the SG neurons with RD mainly displayed tonic firing (69.05%) and corresponded to islet cell morphology (58.82%). Meanwhile, subthreshold currents, including the hyperpolarization-activated cation current (Ih) and T-type calcium current (IT), were identified in SG neurons with RD. Blockage of Ih delayed the onset of the first spike in RD, while abolishment of IT significantly blunted the amplitude of RD. Regarding synaptic inputs, SG neurons with RD showed lower frequencies in both spontaneous and miniature excitatory synaptic currents. Furthermore, RD-expressing neurons received either Aδ- or C-afferent-mediated monosynaptic and polysynaptic inputs. However, RD-lacking neurons received afferents from monosynaptic and polysynaptic Aδ fibers and predominantly polysynaptic C-fibers. These findings demonstrate that SG neurons with RD have a specific cell-type distribution, and may differentially process somatosensory information compared to those without RD.
Collapse
Affiliation(s)
- Mengye Zhu
- Department of Pain Medicine, The First Affiliated Hospital of Nanchang University, Nanchang, China.,Institute of Pain Medicine, Jiangxi Academy of Clinical and Medical Sciences, Nanchang, China
| | - Yi Yan
- Department of Pain Medicine, The First Affiliated Hospital of Nanchang University, Nanchang, China.,Institute of Pain Medicine, Jiangxi Academy of Clinical and Medical Sciences, Nanchang, China
| | - Xuezhong Cao
- Department of Pain Medicine, The First Affiliated Hospital of Nanchang University, Nanchang, China.,Institute of Pain Medicine, Jiangxi Academy of Clinical and Medical Sciences, Nanchang, China
| | - Fei Zeng
- Department of Pain Medicine, The First Affiliated Hospital of Nanchang University, Nanchang, China.,Institute of Pain Medicine, Jiangxi Academy of Clinical and Medical Sciences, Nanchang, China
| | - Gang Xu
- Department of Pain Medicine, The First Affiliated Hospital of Nanchang University, Nanchang, China.,Institute of Pain Medicine, Jiangxi Academy of Clinical and Medical Sciences, Nanchang, China
| | - Wei Shen
- Department of Pain Medicine, The First Affiliated Hospital of Nanchang University, Nanchang, China.,Institute of Pain Medicine, Jiangxi Academy of Clinical and Medical Sciences, Nanchang, China
| | - Fan Li
- Department of Pain Medicine, The First Affiliated Hospital of Nanchang University, Nanchang, China.,Institute of Pain Medicine, Jiangxi Academy of Clinical and Medical Sciences, Nanchang, China
| | - Lingyun Luo
- Department of Pain Medicine, The First Affiliated Hospital of Nanchang University, Nanchang, China.,Institute of Pain Medicine, Jiangxi Academy of Clinical and Medical Sciences, Nanchang, China
| | - Zhijian Wang
- Department of Pain Medicine, The First Affiliated Hospital of Nanchang University, Nanchang, China.,Institute of Pain Medicine, Jiangxi Academy of Clinical and Medical Sciences, Nanchang, China
| | - Yong Zhang
- Department of Pain Medicine, The First Affiliated Hospital of Nanchang University, Nanchang, China.,Institute of Pain Medicine, Jiangxi Academy of Clinical and Medical Sciences, Nanchang, China
| | - Xuexue Zhang
- Department of Pain Medicine, The First Affiliated Hospital of Nanchang University, Nanchang, China.,Institute of Pain Medicine, Jiangxi Academy of Clinical and Medical Sciences, Nanchang, China
| | - Daying Zhang
- Department of Pain Medicine, The First Affiliated Hospital of Nanchang University, Nanchang, China.,Institute of Pain Medicine, Jiangxi Academy of Clinical and Medical Sciences, Nanchang, China
| | - Tao Liu
- Center for Experimental Medicine, The First Affiliated Hospital of Nanchang University, Nanchang, China
| |
Collapse
|
6
|
Sinha GP, Prasoon P, Smith BN, Taylor BK. Fast A-type currents shape a rapidly adapting form of delayed short latency firing of excitatory superficial dorsal horn neurons that express the neuropeptide Y Y1 receptor. J Physiol 2021; 599:2723-2750. [PMID: 33768539 DOI: 10.1113/jp281033] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2020] [Accepted: 03/17/2021] [Indexed: 01/29/2023] Open
Abstract
KEY POINTS Neuropeptide Y Y1 receptor-expressing neurons in the dorsal horn of the spinal cord contribute to chronic pain. For the first time, we characterized the firing patterns of Y1-expressing neurons in Y1eGFP reporter mice. Under hyperpolarized conditions, most Y1eGFP neurons exhibited fast A-type potassium currents and delayed, short-latency firing (DSLF). Y1eGFP DSLF neurons were almost always rapidly adapting and often exhibited rebound spiking, characteristics of spinal pain neurons under the control of T-type calcium channels. These results will inspire future studies to determine whether tissue or nerve injury downregulates the channels that underlie A-currents, thus unmasking membrane hyperexcitability in Y1-expressing dorsal horn neurons, leading to persistent pain. ABSTRACT Neuroanatomical and behavioural evidence indicates that neuropeptide Y Y1 receptor-expressing interneurons (Y1-INs) in the superficial dorsal horn (SDH) are predominantly excitatory and contribute to chronic pain. Using an adult ex vivo spinal cord slice preparation from Y1eGFP reporter mice, we characterized firing patterns in response to steady state depolarizing current injection of GFP-positive cells in lamina II, the great majority of which expressed Y1 mRNA (88%). Randomly sampled (RS) and Y1eGFP neurons exhibited five firing patterns: tonic, initial burst, phasic, delayed short-latency <180 ms (DSLF) and delayed long-latency >180 ms (DLLF). When studied at resting membrane potential, most RS neurons exhibited delayed firing, while most Y1eGFP neurons exhibited phasic firing. A preconditioning membrane hyperpolarization produced only subtle changes in the firing patterns of RS neurons, but dramatically shifted Y1eGFP neurons to DSLF (46%) and DLLF (24%). In contrast to RS DSLF neurons, which rarely exhibited spike frequency adaptation, Y1eGFP DSLF neurons were almost always rapidly adapting, a characteristic of nociceptive-responsive SDH neurons. Rebound spiking was more prevalent in Y1eGFP neurons (6% RS vs. 32% Y1eGFP), indicating enrichment of T-type calcium currents. Y1eGFP DSLF neurons exhibited fast A-type potassium currents that are known to delay or limit action potential firing and exhibited smaller current density as compared to RS DSLF neurons. Our results will inspire future studies to determine whether tissue or nerve injury downregulates channels that contribute to A-currents, thus potentially unmasking T-type calcium channel activity and membrane hyperexcitability in Y1-INs, leading to persistent pain.
Collapse
Affiliation(s)
- Ghanshyam P Sinha
- Department of Anesthesiology and Perioperative Medicine, Pittsburgh Center for Pain Research, and the Pittsburgh Project to end Opioid Misuse, University of Pittsburgh, Pittsburgh, PA, USA
| | - Pranav Prasoon
- Department of Anesthesiology and Perioperative Medicine, Pittsburgh Center for Pain Research, and the Pittsburgh Project to end Opioid Misuse, University of Pittsburgh, Pittsburgh, PA, USA
| | - Bret N Smith
- Department of Neuroscience, University of Kentucky, Lexington, KY, USA
| | - Bradley K Taylor
- Department of Anesthesiology and Perioperative Medicine, Pittsburgh Center for Pain Research, and the Pittsburgh Project to end Opioid Misuse, University of Pittsburgh, Pittsburgh, PA, USA
| |
Collapse
|
7
|
Pradier B, McCormick SJ, Tsuda AC, Chen RW, Atkinson AL, Westrick MR, Buckholtz CL, Kauer JA. Properties of neurons in the superficial laminae of trigeminal nucleus caudalis. Physiol Rep 2020; 7:e14112. [PMID: 31215180 PMCID: PMC6581829 DOI: 10.14814/phy2.14112] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2019] [Accepted: 04/24/2019] [Indexed: 02/03/2023] Open
Abstract
The trigeminal nucleus caudalis (TNc) receives extensive afferent innervation from peripheral sensory neurons of the trigeminal ganglion (TG), and is the first central relay in the circuitry underpinning orofacial pain. Despite the initial characterization of the neurons in the superficial laminae, many questions remain. Here we report on electrophysiological properties of 535 superficial lamina I/II TNc neurons. Based on their firing pattern, we assigned these cells to five main groups, including (1) tonic, (2) phasic, (3) delayed, (4) H‐current, and (5) tonic‐phasic neurons, groups that exhibit distinct intrinsic properties and share some similarity with groups identified in the spinal dorsal horn. Driving predominantly nociceptive TG primary afferents using optogenetic stimulation in TRPV1/ChR2 animals, we found that tonic and H‐current cells are most likely to receive pure monosynaptic input, whereas delayed neurons are more likely to exhibit inputs that appear polysynaptic. Finally, for the first time in TNc neurons, we used unsupervised clustering analysis methods and found that the kinetics of the action potentials and other intrinsic properties of these groups differ significantly from one another. Unsupervised spectral clustering based solely on a single voltage response to rheobase current was sufficient to group cells with shared properties independent of action potential discharge pattern, indicating that this approach can be effectively applied to identify functional neuronal subclasses. Together, our data illustrate that cells in the TNc with distinct patterns of TRPV1/ChR2 afferent innervation are physiologically diverse, but can be understood as a few major groups of cells having shared functional properties.
Collapse
Affiliation(s)
- Bruno Pradier
- Department of Molecular Pharmacology, Physiology & Biotechnology, Brown University, Carney Institute for Brain Science, Providence, Rhode Island
| | - Samuel J McCormick
- Department of Molecular Pharmacology, Physiology & Biotechnology, Brown University, Carney Institute for Brain Science, Providence, Rhode Island
| | - Ayumi C Tsuda
- Department of Molecular Pharmacology, Physiology & Biotechnology, Brown University, Carney Institute for Brain Science, Providence, Rhode Island
| | - Rudy W Chen
- Department of Molecular Pharmacology, Physiology & Biotechnology, Brown University, Carney Institute for Brain Science, Providence, Rhode Island
| | - Abigail L Atkinson
- Department of Molecular Pharmacology, Physiology & Biotechnology, Brown University, Carney Institute for Brain Science, Providence, Rhode Island
| | - Mollie R Westrick
- Department of Molecular Pharmacology, Physiology & Biotechnology, Brown University, Carney Institute for Brain Science, Providence, Rhode Island
| | - Caroline L Buckholtz
- Department of Molecular Pharmacology, Physiology & Biotechnology, Brown University, Carney Institute for Brain Science, Providence, Rhode Island
| | - Julie A Kauer
- Department of Molecular Pharmacology, Physiology & Biotechnology, Brown University, Carney Institute for Brain Science, Providence, Rhode Island
| |
Collapse
|
8
|
Abstract
Lidocaine, as the only local anesthetic approved for intravenous administration in the clinic, can relieve neuropathic pain, hyperalgesia, and complex regional pain syndrome. Intravenous injection of lidocaine during surgery is considered as an effective strategy to control postoperative pain, but the mechanism of its analgesic effect has not been fully elucidated. This paper intends to review recent studies on the mechanism of the analgesic effect of lidocaine. To the end, we conducted an electronic search of the PubMed database. The search period was from 5 years before June 2019. Lidocaine was used as the search term. A total of 659 documents were obtained, we included 17 articles. These articles combined with the 34 articles found by hand searching made up the 51 articles that were ultimately included. We reviewed the analgesic mechanism of lidocaine in the central nervous system.
Collapse
Affiliation(s)
- Xi Yang
- Department of Anesthesiology, Translational Neuroscience Center, West China Hospital, Sichuan University
- Department of Anesthesiology, Sichuan Academy of Medical Sciences & Sichuan Provincial People's Hospital
| | - Xinchuan Wei
- Department of Anesthesiology, Sichuan Academy of Medical Sciences & Sichuan Provincial People's Hospital
| | - Yi Mu
- National Office for Maternal and Child Health Surveillance of China, West China Second University Hospital, Sichuan University, Chengdu, Sichuan, China
| | - Qian Li
- Department of Anesthesiology, Translational Neuroscience Center, West China Hospital, Sichuan University
| | - Jin Liu
- Department of Anesthesiology, Translational Neuroscience Center, West China Hospital, Sichuan University
| |
Collapse
|
9
|
Quindlen-Hotek JC, Kent AR, De Anda P, Kartha S, Benison AM, Winkelstein BA. Changes in Neuronal Activity in the Anterior Cingulate Cortex and Primary Somatosensory Cortex With Nonlinear Burst and Tonic Spinal Cord Stimulation. Neuromodulation 2020; 23:594-604. [PMID: 32027444 DOI: 10.1111/ner.13116] [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: 08/07/2019] [Revised: 11/20/2019] [Accepted: 01/02/2020] [Indexed: 12/14/2022]
Abstract
INTRODUCTION Although nonlinear burst and tonic SCS are believed to treat neuropathic pain via distinct pain pathways, the effectiveness of these modalities on brain activity in vivo has not been investigated. This study compared neuronal firing patterns in the brain after nonlinear burst and tonic SCS in a rat model of painful radiculopathy. METHODS Neuronal activity was recorded in the ACC or S1 before and after nonlinear burst or tonic SCS on day 7 following painful cervical nerve root compression (NRC) or sham surgery. The amplitude of nonlinear burst SCS was set at 60% and 90% motor threshold to investigate the effect of lower amplitude SCS on brain activity. Neuronal activity was recorded during and immediately following light brush and noxious pinch of the paw. Change in neuron firing was measured as the percent change in spikes post-SCS relative to pre-SCS baseline. RESULTS ACC activity decreases during brush after 60% nonlinear burst compared to tonic (p < 0.05) after NRC and compared to 90% nonlinear burst (p < 0.04) and pre-SCS baseline (p < 0.03) after sham. ACC neuron activity decreases (p < 0.01) during pinch after 60% and 90% nonlinear burst compared to tonic for NRC. The 60% of nonlinear burst decreases (p < 0.02) ACC firing during pinch in both groups compared to baseline. In NRC S1 neurons, tonic SCS decreases (p < 0.01) firing from baseline during light brush; 60% nonlinear burst decreases (p < 0.01) firing from baseline during brush and pinch. CONCLUSIONS Nonlinear burst SCS reduces firing in the ACC from a painful stimulus; a lower amplitude nonlinear burst appears to have the greatest effect. Tonic and nonlinear burst SCS may have comparable effects in S1.
Collapse
Affiliation(s)
| | | | - Patrisia De Anda
- Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, USA
| | - Sonia Kartha
- Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, USA
| | | | - Beth A Winkelstein
- Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, USA.,Department of Neurosurgery, University of Pennsylvania, Philadelphia, PA, USA
| |
Collapse
|
10
|
Caylor J, Reddy R, Yin S, Cui C, Huang M, Huang C, Rao R, Baker DG, Simmons A, Souza D, Narouze S, Vallejo R, Lerman I. Spinal cord stimulation in chronic pain: evidence and theory for mechanisms of action. Bioelectron Med 2019; 5:12. [PMID: 31435499 PMCID: PMC6703564 DOI: 10.1186/s42234-019-0023-1] [Citation(s) in RCA: 105] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2019] [Accepted: 05/30/2019] [Indexed: 12/30/2022] Open
Abstract
Well-established in the field of bioelectronic medicine, Spinal Cord Stimulation (SCS) offers an implantable, non-pharmacologic treatment for patients with intractable chronic pain conditions. Chronic pain is a widely heterogenous syndrome with regard to both pathophysiology and the resultant phenotype. Despite advances in our understanding of SCS-mediated antinociception, there still exists limited evidence clarifying the pathways recruited when patterned electric pulses are applied to the epidural space. The rapid clinical implementation of novel SCS methods including burst, high frequency and dorsal root ganglion SCS has provided the clinician with multiple options to treat refractory chronic pain. While compelling evidence for safety and efficacy exists in support of these novel paradigms, our understanding of their mechanisms of action (MOA) dramatically lags behind clinical data. In this review, we reconstruct the available basic science and clinical literature that offers support for mechanisms of both paresthesia spinal cord stimulation (P-SCS) and paresthesia-free spinal cord stimulation (PF-SCS). While P-SCS has been heavily examined since its inception, PF-SCS paradigms have recently been clinically approved with the support of limited preclinical research. Thus, wide knowledge gaps exist between their clinical efficacy and MOA. To close this gap, many rich investigative avenues for both P-SCS and PF-SCS are underway, which will further open the door for paradigm optimization, adjunctive therapies and new indications for SCS. As our understanding of these mechanisms evolves, clinicians will be empowered with the possibility of improving patient care using SCS to selectively target specific pathophysiological processes in chronic pain.
Collapse
Affiliation(s)
- Jacob Caylor
- Department of Anesthesiology, Center for Pain Medicine, University of California San Diego School of Medicine, La Jolla, CA USA
| | - Rajiv Reddy
- Department of Anesthesiology, Center for Pain Medicine, University of California San Diego School of Medicine, La Jolla, CA USA
| | - Sopyda Yin
- Department of Anesthesiology, Center for Pain Medicine, University of California San Diego School of Medicine, La Jolla, CA USA
| | - Christina Cui
- Department of Anesthesiology, Center for Pain Medicine, University of California San Diego School of Medicine, La Jolla, CA USA
| | - Mingxiong Huang
- Department of Radiology, University of California San Diego School of Medicine, La Jolla, CA USA
- Department of Radiology, VA San Diego Healthcare System, La Jolla, CA USA
| | - Charles Huang
- Department of Radiology, VA San Diego Healthcare System, La Jolla, CA USA
- Department of Bioengineering, Stanford University, Palo Alto, CA USA
| | - Ramesh Rao
- Department of Electrical and Computer Engineering, University of California San Diego, La Jolla, CA USA
| | - Dewleen G. Baker
- VA Center of Excellence for Stress and Mental Health, VA San Diego Healthcare System, La Jolla, CA USA
- Department of Psychiatry, University of California San Diego School of Medicine, La Jolla, CA USA
| | - Alan Simmons
- VA Center of Excellence for Stress and Mental Health, VA San Diego Healthcare System, La Jolla, CA USA
- Department of Psychiatry, University of California San Diego School of Medicine, La Jolla, CA USA
| | - Dmitri Souza
- Center for Pain Medicine, Western Reserve Hospital. Department of Surgery, Northeast Ohio Medical School (NEOMED), Athens, OH USA
| | - Samer Narouze
- Center for Pain Medicine, Western Reserve Hospital. Department of Surgery, Northeast Ohio Medical School (NEOMED), Athens, OH USA
| | - Ricardo Vallejo
- Basic Science Research, Millennium Pain Center, Bloomington, IL USA
- School of Biological Sciences, Illinois State University, Normal, IL USA
- Department of Psychology, Illinois Wesleyan University, Bloomington, IL USA
| | - Imanuel Lerman
- Department of Anesthesiology, Center for Pain Medicine, University of California San Diego School of Medicine, La Jolla, CA USA
- VA Center of Excellence for Stress and Mental Health, VA San Diego Healthcare System, La Jolla, CA USA
- Department of Radiology, VA San Diego Healthcare System, La Jolla, CA USA
- Department of Electrical and Computer Engineering, University of California San Diego, La Jolla, CA USA
- Present Address: VA San Diego, 3350 La Jolla Village Dr, (MC116A), San Diego, CA 92161 USA
| |
Collapse
|
11
|
Merighi A. The histology, physiology, neurochemistry and circuitry of the substantia gelatinosa Rolandi (lamina II) in mammalian spinal cord. Prog Neurobiol 2018; 169:91-134. [PMID: 29981393 DOI: 10.1016/j.pneurobio.2018.06.012] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Revised: 06/07/2018] [Accepted: 06/30/2018] [Indexed: 02/06/2023]
Abstract
The substantia gelatinosa Rolandi (SGR) was first described about two centuries ago. In the following decades an enormous amount of information has permitted us to understand - at least in part - its role in the initial processing of pain and itch. Here, I will first provide a comprehensive picture of the histology, physiology, and neurochemistry of the normal SGR. Then, I will analytically discuss the SGR circuits that have been directly demonstrated or deductively envisaged in the course of the intensive research on this area of the spinal cord, with particular emphasis on the pathways connecting the primary afferent fibers and the intrinsic neurons. The perspective existence of neurochemically-defined sets of primary afferent neurons giving rise to these circuits will be also discussed, with the proposition that a cross-talk between different subsets of peptidergic fibers may be the structural and functional substrate of additional gating mechanisms in SGR. Finally, I highlight the role played by slow acting high molecular weight modulators in these gating mechanisms.
Collapse
Affiliation(s)
- Adalberto Merighi
- Department of Veterinary Sciences, University of Turin, Largo Paolo Braccini 2, I-10095 Grugliasco (TO), Italy.
| |
Collapse
|
12
|
Diverse firing properties and Aβ-, Aδ-, and C-afferent inputs of small local circuit neurons in spinal lamina I. Pain 2016; 157:475-487. [PMID: 26797505 DOI: 10.1097/j.pain.0000000000000394] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Spinal lamina I is a key element of the pain processing system, which integrates primary afferent input and relays it to supraspinal areas. More than 90% of neurons in this layer are local circuit neurons, whose role in the signal processing is poorly understood. We performed whole-cell recordings in a spinal cord preparation with attached dorsal roots to examine morphological features and physiological properties of small local circuit neurons (n = 47) in lamina I. Cells successfully filled with biocytin (n = 17) had fusiform (n = 10), flattened (n = 4), and multipolar (n = 3) somatodendritic morphology; their axons branched extensively and terminated in laminae I-III. Intrinsic firing properties were diverse; in addition to standard tonic (n = 16), adapting (n = 7), and delayed (n = 6) patterns, small local circuit neurons also generated rhythmic discharges (n = 6) and plateau potentials (n = 10), the latter were suppressed by the L-type Ca(2+)-channel blocker nifedipine. The neurons received monosynaptic inputs from Aδ and C afferents and could generate bursts of spikes on the root stimulation. In addition, we identified lamina I neurons (n = 7) with direct inputs from the low-threshold Aβ afferents, which could be picked up by ventral dendrites protruding to lamina III. Stimulation of afferents also evoked a disynaptic inhibition of neurons. Thus, small local circuit neurons exhibit diverse firing properties, can generate rhythmic discharges and plateau potentials, and their dendrites extending into several laminae allow broad integration of Aβ-, Aδ-, and C-afferent inputs. These properties are required for processing diverse modalities of nociceptive inputs in lamina I and may underlie spinal sensitization to pain.
Collapse
|
13
|
Roza C, Mazo I, Rivera-Arconada I, Cisneros E, Alayón I, López-García JA. Analysis of spontaneous activity of superficial dorsal horn neurons in vitro: neuropathy-induced changes. Pflugers Arch 2016; 468:2017-2030. [PMID: 27726011 DOI: 10.1007/s00424-016-1886-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2016] [Revised: 09/06/2016] [Accepted: 09/26/2016] [Indexed: 01/17/2023]
Abstract
The superficial dorsal horn contains large numbers of interneurons which process afferent and descending information to generate the spinal nociceptive message. Here, we set out to evaluate whether adjustments in patterns and/or temporal correlation of spontaneous discharges of these neurons are involved in the generation of central sensitization caused by peripheral nerve damage. Multielectrode arrays were used to record from discrete groups of such neurons in slices from control or nerve damaged mice. Whole-cell recordings of individual neurons were also obtained. A large proportion of neurons recorded extracellularly showed well-defined patterns of spontaneous firing. Clock-like neurons (CL) showed regular discharges at ∼6 Hz and represented 9 % of the sample in control animals. They showed a tonic-firing pattern to direct current injection and depolarized membrane potentials. Irregular fast-burst neurons (IFB) produced short-lasting high-frequency bursts (2-5 spikes at ∼100 Hz) at irregular intervals and represented 25 % of the sample. They showed bursting behavior upon direct current injection. Of the pairs of neurons recorded, 10 % showed correlated firing. Correlated pairs always included an IFB neuron. After nerve damage, the mean spontaneous firing frequency was unchanged, but the proportion of CL increased significantly (18 %) and many of these neurons appeared to acquire a novel low-threshold A-fiber input. Similarly, the percentage of IFB neurons was unaltered, but synchronous firing was increased to 22 % of the pairs studied. These changes may contribute to transform spinal processing of nociceptive inputs following peripheral nerve damage. The specific roles that these neurons may play are discussed.
Collapse
Affiliation(s)
- Carolina Roza
- Dpto. Biología de Sistemas, Edificio de Medicina, Universidad de Alcalá, Campus Universitario, 28871, Alcalá de Henares, Madrid, Spain
| | - Irene Mazo
- Dpto. Biología de Sistemas, Edificio de Medicina, Universidad de Alcalá, Campus Universitario, 28871, Alcalá de Henares, Madrid, Spain
| | - Iván Rivera-Arconada
- Dpto. Biología de Sistemas, Edificio de Medicina, Universidad de Alcalá, Campus Universitario, 28871, Alcalá de Henares, Madrid, Spain
| | - Elsa Cisneros
- Dpto. Biología de Sistemas, Edificio de Medicina, Universidad de Alcalá, Campus Universitario, 28871, Alcalá de Henares, Madrid, Spain
| | - Ismel Alayón
- Dpto. Biología de Sistemas, Edificio de Medicina, Universidad de Alcalá, Campus Universitario, 28871, Alcalá de Henares, Madrid, Spain
| | - José A López-García
- Dpto. Biología de Sistemas, Edificio de Medicina, Universidad de Alcalá, Campus Universitario, 28871, Alcalá de Henares, Madrid, Spain.
| |
Collapse
|
14
|
Wolff M, Czorlich P, Nagaraj C, Schnöbel-Ehehalt R, Li Y, Kwapiszewska G, Olschewski H, Heschl S, Olschewski A. Amitriptyline and carbamazepine utilize voltage-gated ion channel suppression to impair excitability of sensory dorsal horn neurons in thin tissue slice: An in vitro study. Neurosci Res 2016; 109:16-27. [DOI: 10.1016/j.neures.2016.02.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2015] [Revised: 02/15/2016] [Accepted: 02/18/2016] [Indexed: 11/27/2022]
|
15
|
Dougherty PM, Chen J. Relationship of membrane properties, spike burst responses, laminar location, and functional class of dorsal horn neurons recorded in vitro. J Neurophysiol 2016; 116:1137-51. [PMID: 27334950 PMCID: PMC5013171 DOI: 10.1152/jn.00187.2016] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2016] [Accepted: 06/19/2016] [Indexed: 01/08/2023] Open
Abstract
The input-output and discharge properties of neurons are shaped by both passive and active electrophysiological membrane properties. Whole cell patch-clamp recordings in lamina I-III neurons in an isolated preparation of the whole spinal cord of juvenile rats with attached dorsal roots and dorsal root ganglia were used to further define which of these properties provides the most impactful classification strategy. A total of 95 neurons were recorded in segment L5 and were classified based on the responses to L4 dorsal root stimulation. The results showed that high-threshold and silent neurons had higher membrane resistance and more negative resting membrane potential than low-threshold or wide-dynamic-range neurons. Rheobase in low-threshold and wide-dynamic-range neurons was significantly lower than that of high-threshold or silent neurons. Four types of firing patterns were identified in response to depolarizing current injections. Low-threshold cells most frequently showed a phasic firing pattern characterized by a short initial burst of action potentials, single spiking or irregular firing bursts at the onset of a depolarizing pulse. High-threshold and wide-dynamic-range neurons were characterized by tonic firing with trains of spikes occurring at regular intervals throughout the current pulse. The majority of silent neurons displayed a delayed onset of firing in response to current injection. These results indicate that the passive membrane properties of spinal neurons are tuned to optimize the responses to particular subsets of afferent stimuli.
Collapse
Affiliation(s)
- Patrick M Dougherty
- Division of Anesthesiology and Critical Care Medicine, Department of Pain Medicine, University of Texas M.D. Anderson Cancer Center, Houston, Texas; and
| | - Jinghong Chen
- Shanghai Mental Health Center, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| |
Collapse
|
16
|
Hou S, Kemp K, Grabois M. A Systematic Evaluation of Burst Spinal Cord Stimulation for Chronic Back and Limb Pain. Neuromodulation 2016; 19:398-405. [DOI: 10.1111/ner.12440] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2016] [Revised: 02/16/2016] [Accepted: 03/09/2016] [Indexed: 11/28/2022]
Affiliation(s)
- Saiyun Hou
- Department of Physical Medicine and Rehabilitation; Baylor College of Medicine; Houston TX USA
| | - Kenneth Kemp
- Department of Physical Medicine and Rehabilitation; Baylor College of Medicine; Houston TX USA
| | - Martin Grabois
- Department of Physical Medicine and Rehabilitation; Baylor College of Medicine; Houston TX USA
| |
Collapse
|
17
|
Reactive Oxygen Species Donors Increase the Responsiveness of Dorsal Horn Neurons and Induce Mechanical Hyperalgesia in Rats. Neural Plast 2015; 2015:293423. [PMID: 26457204 PMCID: PMC4592728 DOI: 10.1155/2015/293423] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2015] [Revised: 04/15/2015] [Accepted: 04/22/2015] [Indexed: 12/26/2022] Open
Abstract
Our previous studies suggest that reactive oxygen species (ROS) scavengers have analgesic effect on neuropathic pain through spinal mechanisms in the rat. The studies suggest that superoxide in spinal cord is one of important mediators of persistent pain. To test the hypothesis that increase of superoxide-derived intermediates leads to central sensitization and pain, the effects of an intrathecal injection of chemical ROS donors releasing either OH∙, OCl−, or H2O2 were examined on pain behaviors. Following treatment with t-BOOH (OH∙ donor), dorsal horn neuron responses to mechanical stimuli in normal rats and the changes of neuronal excitability were explored on substantia gelatinosa (SG) neurons using whole-cell patch clamping recordings. Intrathecal administration of t-BOOH or NaOCl (OCl− donor), but not H2O2, significantly decreased mechanical thresholds of hind paws. The responses of wide dynamic range neurons to mechanical stimuli increased after a local application of t-BOOH. The t-BOOH increased the frequency and the amplitude of excitatory postsynaptic potentials, depolarized membrane potential in SG neurons, and increased the frequency of action potentials evoked by depolarizing current pulses. These results suggest that elevated ROS, especially OH∙, in the spinal cord sensitized dorsal horn neurons and produced hyperalgesia in normal rats.
Collapse
|
18
|
Courtney P, Espinet A, Mitchell B, Russo M, Muir A, Verrills P, Davis K. Improved Pain Relief With Burst Spinal Cord Stimulation for Two Weeks in Patients Using Tonic Stimulation: Results From a Small Clinical Study. Neuromodulation 2015; 18:361-6. [PMID: 25879884 PMCID: PMC5029584 DOI: 10.1111/ner.12294] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2014] [Revised: 02/02/2015] [Accepted: 02/18/2015] [Indexed: 12/04/2022]
Abstract
Objectives Conventional spinal cord stimulation (SCS) delivers a tonic waveform with consistent stream of pulses; burst delivers groups of pulses separated by short pulse‐free periods. The current study compared the short‐term safety and efficacy of burst with tonic stimulation in subjects already receiving SCS. Materials and Methods At 4 IRB‐approved sites, 22 subjects previously implanted with an SCS device for intractable, chronic pain gave informed consent and received burst stimulation for 14 days. Subjects reported average daily Visual Analog Scale (VAS) for overall, trunk, and limb pain using tonic stimulation and after 7 and 14 days of burst stimulation. Thoughts about pain were assessed using the Pain Catastrophizing Scale. Areas of paresthesia were assessed during tonic and burst stimulation using body maps. Assessment of patient satisfaction and preferred stimulation occurred after 14 days of burst. Results Average daily overall VAS reduced 46% from a mean of 53.5 (±20.2) mm during tonic SCS to 28.5 (±18.1) mm during burst (p < 0.001); trunk and limb VAS scores were also reduced by 33% and 51%, respectively. During burst, 16 subjects (73%) reported no paresthesia, 5 (23%) reported a reduction, and 1 (4%) reported increased paresthesia. After 14 days, 21 subjects (95%) reported being very satisfied or satisfied with burst. Burst was preferred by 20 subjects (91%), tonic by 1 (5%), and 1 (5%) reported no preference. Better pain relief was the most common reason cited for preference. Conclusions A majority of subjects reported improved pain relief using burst compared with tonic stimulation. Most subjects experienced less paresthesia during burst and preferred burst citing better pain relief.
Collapse
Affiliation(s)
| | | | - Bruce Mitchell
- Metro Spine Clinic, Caulfield South, Victoria, Australia
| | - Marc Russo
- Hunter Pain Clinic, Newcastle, NSW, Australia
| | - Andrew Muir
- Melbourne Pain Group, Glen Waverly, Victoria, Australia
| | - Paul Verrills
- Metro Spine Clinic, Caulfield South, Victoria, Australia
| | | |
Collapse
|
19
|
Rivera-Arconada I, Lopez-Garcia JA. Characterisation of rebound depolarisation in mice deep dorsal horn neurons in vitro. Pflugers Arch 2014; 467:1985-96. [PMID: 25292284 DOI: 10.1007/s00424-014-1623-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Revised: 09/19/2014] [Accepted: 09/30/2014] [Indexed: 10/24/2022]
Abstract
Spinal dorsal horn neurons constitute the first relay for pain processing and participate in the processing of other sensory, motor and autonomic information. At the cellular level, intrinsic excitability is a factor contributing to network function. In turn, excitability is set by the array of ionic conductance expressed by neurons. Here, we set out to characterise rebound depolarisation following hyperpolarisation, a feature frequently described in dorsal horn neurons but never addressed in depth. To this end, an in vitro preparation of the spinal cord from mice pups was used combined with whole-cell recordings in current and voltage clamp modes. Results show the expression of H- and/or T-type currents in a significant proportion of dorsal horn neurons. The expression of these currents determines the presence of rebound behaviour at the end of hyperpolarising pulses. T-type calcium currents were associated to high-amplitude rebounds usually involving high-frequency action potential firing. H-currents were associated to low-amplitude rebounds less prone to elicit firing or firing at lower frequencies. For a large proportion of neurons expressing both currents, the H-current constitutes a mechanism to ensure a faster response after hyperpolarisations, adjusting the latency of the rebound firing. We conclude that rebound depolarisation and firing are intrinsic factors to many dorsal horn neurons that may constitute a mechanism to integrate somatosensory information in the spinal cord, allowing for a rapid switch from inhibited-to-excited states.
Collapse
Affiliation(s)
- Ivan Rivera-Arconada
- Department of Biología de Sistemas (Área Fisiología) Edificio de Medicina, Universidad de Alcala, 28871, Alcalá de Henares, Madrid, Spain
| | | |
Collapse
|
20
|
Wolff M, Schnöbel-Ehehalt R, Mühling J, Weigand MA, Olschewski A. Mechanisms of Lidocaine’s Action on Subtypes of Spinal Dorsal Horn Neurons Subject to the Diverse Roles of Na+ and K+ Channels in Action Potential Generation. Anesth Analg 2014; 119:463-470. [DOI: 10.1213/ane.0000000000000280] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
|
21
|
De Ridder D, Vanneste S, Freeman W. The Bayesian brain: Phantom percepts resolve sensory uncertainty. Neurosci Biobehav Rev 2014; 44:4-15. [PMID: 22516669 DOI: 10.1016/j.neubiorev.2012.04.001] [Citation(s) in RCA: 135] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2012] [Revised: 03/13/2012] [Accepted: 04/01/2012] [Indexed: 12/23/2022]
Affiliation(s)
- Dirk De Ridder
- Brai(2)n, TRI & Department of Neurosurgery, University Hospital Antwerp, Belgium.
| | - Sven Vanneste
- Brai(2)n, TRI & Department of Neurosurgery, University Hospital Antwerp, Belgium; Department of Translational Neuroscience, Faculty of Medicine, University of Antwerp, Belgium
| | - Walter Freeman
- Department of Molecular & Cell Biology, University of California at Berkeley, USA
| |
Collapse
|
22
|
Luz LL, Szucs P, Safronov BV. Peripherally driven low-threshold inhibitory inputs to lamina I local-circuit and projection neurones: a new circuit for gating pain responses. J Physiol 2014; 592:1519-34. [PMID: 24421354 DOI: 10.1113/jphysiol.2013.269472] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Spinal lamina I is a key element of the pain processing system which relays primary afferent input to supraspinal areas. However, little is known about how the signal is modulated by its intrinsic network including local-circuit neurones (LCNs) and much less numerous anterolateral tract projection neurones (PNs). Here, we used whole-cell patch clamp recordings in an isolated spinal cord preparation to examine properties of identified LCNs (n = 85) and PNs (n = 73) in their functionally preserved local networks. Forty LCNs showed spontaneous rhythmic firing (2-7 Hz) at zero current injection, which persisted in the presence of blockers of fast synaptic transmission. In the remaining cases, most LCNs and PNs fired tonically in response to depolarizing current injections. We identified LCNs and PNs receiving low-threshold primary afferent-driven inhibitory inputs, which in many cases were disynaptic and temporally preceded classical high-threshold excitatory inputs. This direct inhibitory link between low-threshold afferents and PNs can function as a postsynaptic gate controlling the nociceptive information flow in the spinal cord. The LCNs were found to be integrated into the superficial dorsal horn network by their receipt of monosynaptic and disynaptic inputs from other lamina I and II neurones. One-third of LCNs and two-thirds of PNs tested responded to substance P application. Thus, substance P released by a noxious afferent stimulation may excite PNs in two ways: directly, and via the activation of presynaptic LCN circuitries. In conclusion, we have described important properties of identified lamina I neurones and their roles in a new circuit for gating pain responses.
Collapse
Affiliation(s)
- Liliana L Luz
- Neuronal Networks Group, Instituto de Biologia Molecular e Celular (IBMC), Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal.
| | | | | |
Collapse
|
23
|
Reali C, Russo RE. Neuronal intrinsic properties shape naturally evoked sensory inputs in the dorsal horn of the spinal cord. Front Cell Neurosci 2013; 7:276. [PMID: 24399934 PMCID: PMC3872311 DOI: 10.3389/fncel.2013.00276] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2013] [Accepted: 12/10/2013] [Indexed: 11/13/2022] Open
Abstract
Intrinsic electrophysiological properties arising from specific combinations of voltage-gated channels are fundamental for the performance of small neural networks in invertebrates, but their role in large-scale vertebrate circuits remains controversial. Although spinal neurons have complex intrinsic properties, some tasks produce high-conductance states that override intrinsic conductances, minimizing their contribution to network function. Because the detection and coding of somato-sensory information at early stages probably involves a relatively small number of neurons, we speculated that intrinsic electrophysiological properties are likely involved in the processing of sensory inputs by dorsal horn neurons (DHN). To test this idea, we took advantage of an integrated spinal cord–hindlimbs preparation from turtles allowing the combination of patch-clamp recordings of DHN embedded in an intact network, with accurate control of the extracellular milieu. We found that plateau potentials and low threshold spikes (LTS) -mediated by L- and T-type Ca2+channels, respectively- generated complex dynamics by interacting with naturally evoked synaptic potentials. Inhibitory receptive fields could be changed in sign by activation of the LTS. On the other hand, the plateau potential transformed sensory signals in the time domain by generating persistent activity triggered on and off by brief sensory inputs and windup of the response to repetitive sensory stimulation. Our findings suggest that intrinsic properties dynamically shape sensory inputs and thus represent a major building block for sensory processing by DHN. Intrinsic conductances in DHN appear to provide a mechanism for plastic phenomena such as dynamic receptive fields and sensitization to pain.
Collapse
Affiliation(s)
- Cecilia Reali
- Neurofisiología Celular y Molecular, Instituto de Investigaciones Biológicas Clemente Estable Montevideo, Uruguay
| | - Raúl E Russo
- Neurofisiología Celular y Molecular, Instituto de Investigaciones Biológicas Clemente Estable Montevideo, Uruguay
| |
Collapse
|
24
|
De Ridder D, Plazier M, Kamerling N, Menovsky T, Vanneste S. Burst Spinal Cord Stimulation for Limb and Back Pain. World Neurosurg 2013; 80:642-649.e1. [DOI: 10.1016/j.wneu.2013.01.040] [Citation(s) in RCA: 188] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2012] [Revised: 01/07/2013] [Accepted: 01/11/2013] [Indexed: 10/27/2022]
|
25
|
Rivera-Arconada I, Roza C, Lopez-Garcia JA. Characterization of hyperpolarization-activated currents in deep dorsal horn neurons of neonate mouse spinal cord in vitro. Neuropharmacology 2013; 70:148-55. [PMID: 23376246 DOI: 10.1016/j.neuropharm.2013.01.019] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2012] [Revised: 12/13/2012] [Accepted: 01/17/2013] [Indexed: 10/27/2022]
Abstract
Emerging evidence suggests that blockade of hyperpolarization-activated current (Ih) produces analgesia acting at peripheral sites. However, little is known about the role of this current in central pain-processing structures. The aim of the present work was to characterize the Ih in deep dorsal horn neurons and to assess the role of the current in the transmission of somatosensory signals across spinal circuits. To these purpose in vitro preparations of the spinal cord from mice pups were used in combination with whole cell recordings to characterize the current in native neurons. Extracellular recordings from sensory and motor pathways were performed to assess the role of the current in spinal somatosensory processing. Cesium chloride and ZD7288 were used as current blockers. Most deep dorsal horn neurons showed a functional Ih that was blocked by ZD7288 and cesium. Ih blockade caused hyperpolarization, increased input resistance and potentiation of synaptic responses. Excitatory effects of Ih blockade on synaptic transmission were confirmed in projecting anterolateral axons and ventral roots. Ih modulation by cAMP produced a rightward shift in the voltage dependency curve and blocked excitatory effects of ZD7288 on sensory pathways. Results indicate that Ih currents play a stabilizing role in the spinal cord controlling transmission across sensory and motor spinal pathways via cellular effects on input resistance and excitability. In addition, results suggest that current modulation may alter significantly the role of the current in somatosensory processing.
Collapse
Affiliation(s)
- Ivan Rivera-Arconada
- Departamento de Fisiología, Edificio de Medicina, Universidad de Alcala, Alcala de Henares, 28871 Madrid, Spain
| | | | | |
Collapse
|
26
|
Tian Y, Wang S, Ma Y, Lim G, Kim H, Mao J. Leptin enhances NMDA-induced spinal excitation in rats: A functional link between adipocytokine and neuropathic pain. Pain 2011; 152:1263-1271. [PMID: 21376468 DOI: 10.1016/j.pain.2011.01.054] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2010] [Revised: 01/18/2011] [Accepted: 01/27/2011] [Indexed: 11/18/2022]
Abstract
Recent studies have shown that leptin (an adipocytokine) played an important role in nociceptive behavior induced by nerve injury, but the cellular mechanism of this action remains unclear. Using the whole-cell patch-clamp recording from rat's spinal cord slices, we showed that superfusion of leptin onto spinal cord slices dose-dependently enhanced N-methyl-d-aspartate (NMDA) receptor-mediated currents in spinal cord lamina II neurons. At the cellular level, the effect of leptin on spinal NMDA-induced currents was mediated through the leptin receptor and the JAK2/STAT3 (but not PI3K or MAPK) pathway, as the leptin effect was abolished in leptin receptor-deficient (db/db) mice and inhibited by a JAK/STAT inhibitor. Moreover, we demonstrated in naïve rats that a single intrathecal administration of leptin enhanced spontaneous biting, scratching, and licking behavior induced by intrathecal NMDA and that repeated intrathecal administration of leptin elicited thermal hyperalgesia and mechanical allodynia, which was attenuated by the noncompetitive NMDA receptor antagonist MK-801. Intrathecal leptin also upregulated the expression of NMDA receptors and pSTAT3 within the rat's spinal cord dorsal horn, and intrathecal MK-801 attenuated this leptin effect as well. Our data demonstrate a relationship between leptin and NMDA receptor-mediated spinal neuronal excitation and its functional role in nociceptive behavior. Since leptin contributes to nociceptive behavior induced by nerve injury, the present findings suggest an important cellular link between the leptin's spinal effect and the NMDA receptor-mediated cellular mechanism of neuropathic pain. A functional link is demonstrated between leptin, an adipocytokine, and the cellular mechanisms of neuropathic pain via enhancement of function and expression of spinal N-methyl-d-aspartate receptors.
Collapse
Affiliation(s)
- Yinghong Tian
- MGH Center for Translational Pain Research, Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA Department of Physiology, Southern Medical University, Guangzhou 510515, China
| | | | | | | | | | | |
Collapse
|
27
|
Voltage-Dependent Behavior of Delayed-Firing Neurons in the Rat Substantia Gelatinosa. NEUROPHYSIOLOGY+ 2011. [DOI: 10.1007/s11062-011-9155-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
|
28
|
Cui L, Kim YR, Kim HY, Lee SC, Shin HS, Szabó G, Erdélyi F, Kim J, Kim SJ. Modulation of synaptic transmission from primary afferents to spinal substantia gelatinosa neurons by group III mGluRs in GAD65-EGFP transgenic mice. J Neurophysiol 2010; 105:1102-11. [PMID: 21177998 DOI: 10.1152/jn.00108.2010] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Group III metabotropic glutamate receptors (mGluRs) are involved in nociceptive transmission in the spinal cord. However, the cellular mechanism underlying the modulation of synaptic transmission from nociceptive primary afferents to dorsal horn neurons by group III mGluRs has yet to be explored. In this study, we used transgenic mice expressing enhanced green fluorescent protein (EGFP) under the control of the glutamate decarboxylase (GAD) 65 promoter to identify specific subpopulations of GABAergic inhibitory interneurons. By GABA immunolabeling, we confirmed the majority of GAD65-EGFP-expressing neurons were GABAergic. Because GAD65-EGFP-expressing neurons have not been examined in detail before, we first investigated the physiological properties of GAD65-EGFP- and non-EGFP-expressing neurons in substantia gelatinosa (SG) of the spinal dorsal horn. Membrane properties, such as the resting membrane potential, membrane capacitance, action potential threshold, and action potential height, differed significantly between these two groups of neurons. Most EGFP-expressing neurons displayed a tonic firing pattern (73% of recorded neurons) and received monosynaptic Aδ and/or C primary afferent inputs (85% of recorded neurons). In contrast, we observed a delayed firing pattern in 53% of non-EGFP-expressing neurons. After identifying the physiological properties of EGFP-expressing neurons, we tested the effects of group III mGluRs on synaptic transmission pharmacologically. A group III mGluR agonist, L-AP4, attenuated Aδ fiber-evoked synaptic transmission but did not affect C fiber-evoked synaptic transmission to EGFP-expressing neurons. Similar primary afferent-specific inhibition by L-AP4 was also observed in non-EGFP-expressing neurons. Moreover, Aδ fiber-evoked synaptic transmission was suppressed by a selective mGluR7 agonist, AMN082. These results suggest that modulation of the synaptic transmission from primary afferents to SG neurons by group III mGluR agonist is specific to the type of nociceptive primary afferents but not to the type of target neurons.
Collapse
Affiliation(s)
- Lian Cui
- Department of Physiology, Seoul National University College of Medicine, Yeongeon-dong, Jongro-gu, Seoul 110-799, Korea
| | | | | | | | | | | | | | | | | |
Collapse
|
29
|
Melnick IV. A-type K+ current dominates somatic excitability of delayed firing neurons in rat substantia gelatinosa. Synapse 2010; 65:601-7. [PMID: 21484879 DOI: 10.1002/syn.20879] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2010] [Accepted: 03/10/2010] [Indexed: 11/08/2022]
Abstract
Substantia gelatinosa neurons display three main types of intrinsic firing behavior: tonic, adapting, and delayed onset. Here, voltage-gated currents expressed by delayed firing neurons were studied in nucleated patches obtained in spinal cord slices of 3-5 weeks-old rats. Inward Na+ current was negligible under these conditions and was usually occluded by superposition of much larger outward currents. Two kinds of outward currents were found, an A-type (K(A) ) and delayed rectifier (K(DR) ) potassium currents. K(A) activated rapidly (<1.5 ms at >-20 mV) and operated at subthreshold membrane potentials; voltages of steady-state half-maximal activation and inactivation were -38.7 and -87.2 mV, respectively. Inactivation was biexponential with a dominant fast component (~90%, time constant ∼8 ms). K(DR) activated more slowly (<8 ms at >-20 mV), half-maximal activation was -23.6 mV, and decayed mono-exponentially with a time constant 70-110 ms. Maximal amplitudes of K(A) were almost 10-times larger than those of K(DR) , their respective densities were 8.5 and 0.97 μS μm⁻². Tetraethylammonium, 5 mM, blocked K(DR) but not K(A) , whereas both currents were depressed by 5 mM 4-aminopyridine. In current-clamp recordings, 4-action potential but not tetraethylammonium abolished firing delay suggesting the causative role of K(A) . Thus, the predominance of fast K(A) over other somatic currents is a distinctive feature of delayed firing neurons among all other types of substantia gelatinosa neurons and likely explains the appearance of their typical firing delay.
Collapse
Affiliation(s)
- Igor V Melnick
- Deparment of General Physiology, Bogomoletz Institute of Physiology, Kiev, Ukraine.
| |
Collapse
|
30
|
Electrically silent neurons in the substantia gelatinosa of the rat spinal cord. ACTA ACUST UNITED AC 2010. [DOI: 10.15407/fz56.05.034] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
|
31
|
Norepinephrine can act via alpha(2)-adrenoceptors to reduce the hyper-excitability of spinal dorsal horn neurons following chronic nerve injury. J Formos Med Assoc 2010; 109:438-45. [PMID: 20610145 DOI: 10.1016/s0929-6646(10)60075-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2009] [Revised: 07/08/2009] [Accepted: 08/11/2009] [Indexed: 11/27/2022] Open
Abstract
BACKGROUND/PURPOSE Rats display behavioral signs of neuropathic pain lasting for months in the chronic constriction injury (CCI) model. During intrathecal anesthesia, the administered drugs mainly diffuse directly into the superficial neurons in the spinal dorsal horn. This study aimed to investigate the effect of bath application of norepinephrine on whole cell patch clamp recordings from spinal cord slices of CCI rats with allodynia. METHODS An assessment of paw withdrawal threshold in response to mechanical stimulation was performed on the operated side on the day before surgery and was repeated after recovery from anesthesia and on the 7(th) and 14(th) days after surgery. Spinal cord slice preparations containing dorsal horn neurons were obtained from both sham-operated rats and CCI rats (after the 14(th) postoperative day behavior test). RESULTS Compared with normal controls, CCI rats had significantly lower levels of both hyperpolarization and spike threshold in single action potentials recorded from lamina I and II neurons of the spinal dorsal horn. In contrast, a series of action potential recordings showed that the percentage of spiking neurons of the spinal dorsal horn of CCI rats were significantly higher than those of normal controls. The CCI-induced reduction in hyperpolarization, as well as the increased numbers of spinal dorsal horn spiking neurons could be significantly reduced by norepinephrine application. The norepinephrine-induced increased hyperpolarization and input resistance could be abolished by the application of an alpha(2)-adrenoceptor antagonist (idazoxan; 200 nM). CONCLUSION The results suggest that chronic nerve injury may induce neuropathic pain by increasing the excitability of spinal dorsal horn neurons. This excitability can be reduced by norepinephrine.
Collapse
|
32
|
Takeda M, Takahashi M, Nasu M, Matsumoto S. In vivo patch-clamp analysis of response properties of rat primary somatosensory cortical neurons responding to noxious stimulation of the facial skin. Mol Pain 2010; 6:30. [PMID: 20500889 PMCID: PMC2891679 DOI: 10.1186/1744-8069-6-30] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2010] [Accepted: 05/26/2010] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Although it has been widely accepted that the primary somatosensory (SI) cortex plays an important role in pain perception, it still remains unclear how the nociceptive mechanisms of synaptic transmission occur at the single neuron level. The aim of the present study was to examine whether noxious stimulation applied to the orofacial area evokes the synaptic response of SI neurons in urethane-anesthetized rats using an in vivo patch-clamp technique. RESULTS In vivo whole-cell current-clamp recordings were performed in rat SI neurons (layers III-IV). Twenty-seven out of 63 neurons were identified in the mechanical receptive field of the orofacial area (36 neurons showed no receptive field) and they were classified as non-nociceptive (low-threshold mechanoreceptive; 6/27, 22%) and nociceptive neurons. Nociceptive neurons were further divided into wide-dynamic range neurons (3/27, 11%) and nociceptive-specific neurons (18/27, 67%). In the majority of these neurons, a proportion of the excitatory postsynaptic potentials (EPSPs) reached the threshold, and then generated random discharges of action potentials. Noxious mechanical stimuli applied to the receptive field elicited a discharge of action potentials on the barrage of EPSPs. In the case of noxious chemical stimulation applied as mustard oil to the orofacial area, the membrane potential shifted depolarization and the rate of spontaneous discharges gradually increased as did the noxious pinch-evoked discharge rates, which were usually associated with potentiated EPSP amplitudes. CONCLUSIONS The present study provides evidence that SI neurons in deep layers III-V respond to the temporal summation of EPSPs due to noxious mechanical and chemical stimulation applied to the orofacial area and that these neurons may contribute to the processing of nociceptive information, including hyperalgesia.
Collapse
Affiliation(s)
- Mamoru Takeda
- Department of Physiology, School of Life Dentistry at Tokyo, Nippon Dental University, 1-9-20, Fujimi-cho, Chiyoda-ku, Tokyo, 102-8159, Japan.
| | | | | | | |
Collapse
|
33
|
Changes in membrane excitability and potassium currents in sensitized dorsal horn neurons of mice pups. J Neurosci 2010; 30:5376-83. [PMID: 20392959 DOI: 10.1523/jneurosci.4359-09.2010] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Rationally, an increased intrinsic excitability of dorsal horn neurons could be a factor contributing to alter the gain of the nociceptive system during central sensitization, however direct evidence is scarce. Here we have examined this hypothesis using current and voltage-clamp recordings from dorsal horn neurons in the spinal cord in vitro preparation obtained from mice pups of either sex. Cords were extracted from carrageenan-pretreated and control animals to allow for comparison. Dorsal horn neurons from treated animals showed significantly larger and faster synaptic responses. Synaptic changes started developing shortly after inflammation (1 h) and developed further after a longer-term inflammation (20 h). However, these neurons showed biphasic changes in membrane excitability with an increase shortly after inflammation and a decrease in the longer term. Concomitant changes were observed in transient (I(A)) and sustained potassium currents (I(DR)). Prolonged superfusion of naive spinal cords with NMDA led to a decreased neuronal excitability and to increased potassium currents. Results suggest that excitability plays a role more complex than expected during the process of central sensitization of dorsal horn neurons and that modulation of potassium currents may contribute to shape the changing states of excitability. The decreased excitability observed after long-term inflammation is interpreted as a homeostatic correction to an abnormal state of synaptic activity.
Collapse
|
34
|
Wu SX, Wang W, Li H, Wang YY, Feng YP, Li YQ. The synaptic connectivity that underlies the noxious transmission and modulation within the superficial dorsal horn of the spinal cord. Prog Neurobiol 2010; 91:38-54. [DOI: 10.1016/j.pneurobio.2010.01.005] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2009] [Revised: 12/10/2009] [Accepted: 01/14/2010] [Indexed: 01/27/2023]
|
35
|
Breton JD, Poisbeau P, Darbon P. Antinociceptive action of oxytocin involves inhibition of potassium channel currents in lamina II neurons of the rat spinal cord. Mol Pain 2009; 5:63. [PMID: 19909537 PMCID: PMC2780383 DOI: 10.1186/1744-8069-5-63] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2009] [Accepted: 11/12/2009] [Indexed: 11/29/2022] Open
Abstract
Background Growing evidence in the literature shows that oxytocin (OT) has a strong spinal anti-nociceptive action. Oxytocinergic axons originating from a subpopulation of paraventricular hypothalamic neurons establish synaptic contacts with lamina II interneurons but little is known about the functional role of OT with respect to neuronal firing and excitability. Results Using the patch-clamp technique, we have recorded lamina II interneurons in acute transverse lumbar spinal cord slices of rats (15 to 30 days old) and analyzed the OT effects on action potential firing ability. In the current clamp mode, we found that bath application of a selective OT-receptor agonist (TGOT) reduced firing in the majority of lamina II interneurons exhibiting a bursting firing profile, but never in those exhibiting a single spike discharge upon depolarization. Interestingly, OT-induced reduction in spike frequency and increase of firing threshold were often observed, leading to a conversion of the firing profile from repetitive and delayed profiles into phasic ones and sometimes further into single spike profile. The observed effects following OT-receptor activation were completely abolished when the OT-receptor agonist was co-applied with a selective OT-receptor antagonist. In current and voltage clamp modes, we show that these changes in firing are strongly controlled by voltage-gated potassium currents. More precisely, transient IA currents and delayed-rectifier currents were reduced in amplitude and transient IA current was predominantly inactivated after OT bath application. Conclusion This effect of OT on the firing profile of lamina II neurons is in good agreement with the antinociceptive and analgesic properties of OT described in vivo.
Collapse
Affiliation(s)
- Jean Didier Breton
- Nociception and Pain Department, Institut des Neurosciences Cellulaires et Intégratives, Centre National de la Recherche Scientifique, Université de Strasbourg, France.
| | | | | |
Collapse
|
36
|
Davies AJ, North RA. Electrophysiological and morphological properties of neurons in the substantia gelatinosa of the mouse trigeminal subnucleus caudalis. Pain 2009; 146:214-21. [PMID: 19703729 DOI: 10.1016/j.pain.2009.07.038] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2009] [Revised: 07/07/2009] [Accepted: 07/28/2009] [Indexed: 11/25/2022]
Abstract
The excitability of the second order neurons within the trigeminal subnucleus caudalis underlies pain perception and processing in migraine and trigeminal neuralgia. These neurons were studied with whole-cell patch-clamp technique in slices from mouse brain stem. Electrical and morphological characteristics of 56 neurons were determined. Four categories were distinguished from electrophysiological properties: tonic (39%), phasic (34%), delayed (16%) and single spiking (11%). These categories did not show distinct morphological properties. Neurons had tetrodotoxin-sensitive sodium currents that activated and inactivated within milliseconds. They also showed a high voltage-activated, slowly inactivating calcium current: up to half of this current was blocked by omega-conotoxin GVIA (1microM) and omega-agatoxin IVA (100-300 nM), but it was not affected by nifedipine (10microM). Exogenously applied capsaicin (1microM) and alphabetamethylene-5'-adenosine triphosphate (100microM) elicited large amplitude, spontaneous excitatory postsynaptic currents that were blocked by capsazepine (10microM) and 5-[(3-phenoxybenzyl)-(1,2,3,4-tetrahydro-naphthalen-1-yl)-carbamoyl]-benzene-1,2,4-tricarboxylic acid (A-317491: 10microM), respectively. Thus, neurons of the mouse trigeminal subnucleus caudalis substantia gelatinosa exhibit N-type and P/Q-type voltage-gated calcium channels, and receive presynaptic afferents that express TRPV1 and P2X(2/3) receptors. These results suggest possible therapeutic interventions, and serve as a basis for the characterization of cellular changes that may underlie trigeminal neuropathic pain.
Collapse
Affiliation(s)
- Alexander J Davies
- Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK.
| | | |
Collapse
|
37
|
Olschewski A, Schnoebel-Ehehalt R, Li Y, Tang B, Bräu ME, Wolff M. Mexiletine and Lidocaine Suppress the Excitability of Dorsal Horn Neurons. Anesth Analg 2009; 109:258-64. [DOI: 10.1213/ane.0b013e3181a3d5d8] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
|
38
|
Sibilla S, Ballerini L. GABAergic and glycinergic interneuron expression during spinal cord development: dynamic interplay between inhibition and excitation in the control of ventral network outputs. Prog Neurobiol 2009; 89:46-60. [PMID: 19539686 DOI: 10.1016/j.pneurobio.2009.06.001] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2008] [Revised: 04/10/2009] [Accepted: 06/09/2009] [Indexed: 11/28/2022]
Abstract
A key objective of neuroscience research is to understand the processes leading to mature neural circuitries in the central nervous system (CNS) that enable the control of different behaviours. During development, network-constitutive neurons undergo dramatic rearrangements, involving their intrinsic properties, such as the blend of ion channels governing their firing activity, and their synaptic interactions. The spinal cord is no exception to this rule; in fact, in the ventral horn the maturation of motor networks into functional circuits is a complex process where several mechanisms cooperate to achieve the development of motor control. Elucidating such a process is crucial in identifying neurons more vulnerable to degenerative or traumatic diseases or in developing new strategies aimed at rebuilding damaged tissue. The focus of this review is on recent advances in understanding the spatio-temporal expression of the glycinergic/GABAergic system and on the contribution of this system to early network function and to motor pattern transformation along with spinal maturation. During antenatal development, the operation of mammalian spinal networks strongly depends on the activity of glycinergic/GABAergic neurons, whose action is often excitatory until shortly before birth when locomotor networks acquire the ability to generate alternating motor commands between flexor and extensor motor neurons. At this late stage of prenatal development, GABA-mediated excitation is replaced by synaptic inhibition mediated by glycine and/or GABA. At this stage of spinal maturation, the large majority of GABAergic neurons are located in the dorsal horn. We propose that elucidating the role of inhibitory systems in development will improve our knowledge on the processes regulating spinal cord maturation.
Collapse
Affiliation(s)
- Sara Sibilla
- Life Science Department, Center for Neuroscience B.R.A.I.N., University of Trieste, via Fleming 22, 34127 Trieste, Italy
| | | |
Collapse
|
39
|
Abstract
Hyperalgesia and allodynia are frequent symptoms of disease and may be useful adaptations to protect vulnerable tissues. Both may, however, also emerge as diseases in their own right. Considerable progress has been made in developing clinically relevant animal models for identifying the most significant underlying mechanisms. This review deals with experimental models that are currently used to measure (sect. II) or to induce (sect. III) hyperalgesia and allodynia in animals. Induction and expression of hyperalgesia and allodynia are context sensitive. This is discussed in section IV. Neuronal and nonneuronal cell populations have been identified that are indispensable for the induction and/or the expression of hyperalgesia and allodynia as summarized in section V. This review focuses on highly topical spinal mechanisms of hyperalgesia and allodynia including intrinsic and synaptic plasticity, the modulation of inhibitory control (sect. VI), and neuroimmune interactions (sect. VII). The scientific use of language improves also in the field of pain research. Refined definitions of some technical terms including the new definitions of hyperalgesia and allodynia by the International Association for the Study of Pain are illustrated and annotated in section I.
Collapse
Affiliation(s)
- Jürgen Sandkühler
- Department of Neurophysiology, Center for Brain Research, Medical University of Vienna, Vienna, Austria
| |
Collapse
|
40
|
Melnick I. Morphophysiologic properties of islet cells in substantia gelatinosa of the rat spinal cord. Neurosci Lett 2009; 446:65-9. [PMID: 18817844 DOI: 10.1016/j.neulet.2008.09.027] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2008] [Revised: 09/11/2008] [Accepted: 09/13/2008] [Indexed: 11/29/2022]
Abstract
Substantia gelatinosa (SG) neurons of the spinal cord are highly heterogeneous in their morphophysiologic properties and could be categorized on several subtypes. Here the properties of islet cells in rat SG (approximately 11%) are described with the use of confocal microscopy and patch-clamp recording. The cells had significantly longer and thicker dendritic trees among all other neurons. Only these cells expressed slow inward current activated by hyperpolarization, which could be blocked by Cs+ but not Ba2+, presumably representing H-current (Ih). Possibly due to Ih, islet cells had peculiar membrane and firing responses. Of note the membrane potential showed a sag in response to hyperpolarization while depolarization triggered action potentials (APs) in a tonic-like pattern. APs, however, occurred with larger maximal frequencies and in response to broader stimulation intensities than in other tonically firing neurons. Neuronal variability in SG and possible functional roles of islet cells are discussed.
Collapse
Affiliation(s)
- Igor Melnick
- Department of General Physiology of Nervous System, Bogomoletz Institute of Physiology, Bogomoletz street 4, Kiev 01024, Ukraine.
| |
Collapse
|
41
|
Walsh MA, Graham BA, Brichta AM, Callister RJ. Evidence for a critical period in the development of excitability and potassium currents in mouse lumbar superficial dorsal horn neurons. J Neurophysiol 2009; 101:1800-12. [PMID: 19176612 DOI: 10.1152/jn.90755.2008] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The output of superficial dorsal horn (SDH; laminae I-II) neurons is critical for processing nociceptive, thermal, and tactile information. Like other neurons, the combined effects of synaptic inputs and intrinsic membrane properties determine their output. It is well established that peripheral synaptic inputs to SDH neurons undergo extensive reorganization during pre- and postnatal development. It is unclear, however, how membrane properties or the subthreshold whole cell currents that shape SDH neuron output change during this period. Here we assess the intrinsic membrane properties and whole cell currents in mouse SDH neurons during late embryonic and early postnatal development (E15-P25). Transverse slices were prepared from lumbar spinal cord and whole cell recordings were obtained at 32 degrees C. During this developmental period resting membrane potential (RMP) became more hyperpolarized (by approximately 10 mV, E15-E17 vs. P21-P25) and input resistance decreased (1,074 +/- 78 vs. 420 +/- 27 MOmega). In addition, action potential (AP) amplitude and AP afterhyperpolarization increased, whereas AP half-width decreased. Before and after birth (E15-P10), AP discharge evoked by intracellular current injection was limited to a single AP at depolarization onset in many neurons (>41%). In older animals (P11-P25) this changed, with AP discharge consisting of brief bursts at current onset ( approximately 46% of neurons). Investigation of major subthreshold whole cell currents showed the rapid A-type potassium current (I(Ar)) dominated at all ages examined (90% of neurons at E15-E17, decreasing to >50% after P10). I(Ar) expression levels, based on peak current amplitude, increased during development. Steady-state inactivation and activation for I(Ar) were slightly less potent in E15-E17 versus P21-P25 neurons at potentials near RMP (-55 mV). Together, our data indicate that intrinsic properties and I(Ar) expression change dramatically in SDH neurons during development, with the greatest alterations occurring on either side of a critical period, P6-P10.
Collapse
Affiliation(s)
- M A Walsh
- School of Biomedical Sciences, Faculty of Health, The University of Newcastle, Callaghan, NSW 2308, Australia
| | | | | | | |
Collapse
|
42
|
Melnick IV. Physiological types of substantia gelatinosa neurons in the rat spinal cord. NEUROPHYSIOLOGY+ 2008. [DOI: 10.1007/s11062-008-9030-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
43
|
Biophysical basis for three distinct dynamical mechanisms of action potential initiation. PLoS Comput Biol 2008; 4:e1000198. [PMID: 18846205 PMCID: PMC2551735 DOI: 10.1371/journal.pcbi.1000198] [Citation(s) in RCA: 190] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2008] [Accepted: 09/03/2008] [Indexed: 11/19/2022] Open
Abstract
Transduction of graded synaptic input into trains of all-or-none action
potentials (spikes) is a crucial step in neural coding. Hodgkin identified three
classes of neurons with qualitatively different analog-to-digital transduction
properties. Despite widespread use of this classification scheme, a
generalizable explanation of its biophysical basis has not been described. We
recorded from spinal sensory neurons representing each class and reproduced
their transduction properties in a minimal model. With phase plane and
bifurcation analysis, each class of excitability was shown to derive from
distinct spike initiating dynamics. Excitability could be converted between all
three classes by varying single parameters; moreover, several parameters, when
varied one at a time, had functionally equivalent effects on excitability. From
this, we conclude that the spike-initiating dynamics associated with each of
Hodgkin's classes represent different outcomes in a nonlinear
competition between oppositely directed, kinetically mismatched currents. Class
1 excitability occurs through a saddle node on invariant circle bifurcation when
net current at perithreshold potentials is inward (depolarizing) at steady
state. Class 2 excitability occurs through a Hopf bifurcation when, despite net
current being outward (hyperpolarizing) at steady state, spike initiation occurs
because inward current activates faster than outward current. Class 3
excitability occurs through a quasi-separatrix crossing when fast-activating
inward current overpowers slow-activating outward current during a stimulus
transient, although slow-activating outward current dominates during constant
stimulation. Experiments confirmed that different classes of spinal lamina I
neurons express the subthreshold currents predicted by our simulations and,
further, that those currents are necessary for the excitability in each cell
class. Thus, our results demonstrate that all three classes of excitability
arise from a continuum in the direction and magnitude of subthreshold currents.
Through detailed analysis of the spike-initiating process, we have explained a
fundamental link between biophysical properties and qualitative differences in
how neurons encode sensory input. Information is transmitted through the nervous system in the form of action
potentials or spikes. Contrary to popular belief, a spike is not generated
instantaneously when membrane potential crosses some preordained threshold. In
fact, different neurons employ different rules to determine when and why they
spike. These different rules translate into diverse spiking patterns that have
been observed experimentally and replicated time and again in computational
models. In this study, our aim was not simply to replicate different spiking
patterns; instead, we sought to provide deeper insight into the connection
between biophysics and neural coding by relating each to the process of spike
initiation. We show that Hodgkin's three classes of excitability result
from a nonlinear competition between oppositely directed, kinetically mismatched
currents; the outcome of that competition is manifested as dynamically distinct
spike-initiating mechanisms. Our results highlight the benefits of forward
engineering minimal models capable of reproducing phenomena of interest and then
dissecting those models in order to identify general explanations of how those
phenomena arise. Furthermore, understanding nonlinear dynamical processes such
as spike initiation is crucial for definitively explaining how biophysical
properties impact neural coding.
Collapse
|
44
|
Graham BA, Brichta AM, Callister RJ. Recording Temperature Affects the Excitability of Mouse Superficial Dorsal Horn Neurons, In Vitro. J Neurophysiol 2008; 99:2048-59. [DOI: 10.1152/jn.01176.2007] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Superficial dorsal horn (SDH) neurons in laminae I–II of the spinal cord play an important role in processing noxious stimuli. These neurons represent a heterogeneous population and are divided into various categories according to their action potential (AP) discharge during depolarizing current injection. We recently developed an in vivo mouse preparation to examine functional aspects of nociceptive processing and AP discharge in SDH neurons and to extend investigation of pain mechanisms to the genetic level of analysis. Not surprisingly, some in vivo data obtained at body temperature (37°C) differed from those generated at room temperature (22°C) in spinal cord slices. In the current study we examine how temperature influences SDH neuron properties by making recordings at 22 and 32°C in transverse spinal cord slices prepared from L3–L5 segments of adult mice (C57Bl/6). Patch-clamp recordings (KCH3SO4 internal) were made from visualized SDH neurons. At elevated temperature all SDH neurons had reduced input resistance and smaller, briefer APs. Resting membrane potential and AP afterhyperpolarization amplitude were temperature sensitive only in subsets of the SDH population. Notably, elevated temperature increased the prevalence of neurons that did not discharge APs during current injection. These reluctant firing neurons expressed a rapid A-type potassium current, which is enhanced at higher temperatures and thus restrains AP discharge. When compared with previously published whole cell recordings obtained in vivo (37°C) our results suggest that, on balance, in vitro data collected at elevated temperature more closely resemble data collected under in vivo conditions.
Collapse
|
45
|
Graham BA, Brichta AM, Schofield PR, Callister RJ. Altered potassium channel function in the superficial dorsal horn of the spastic mouse. J Physiol 2007; 584:121-36. [PMID: 17690143 PMCID: PMC2277054 DOI: 10.1113/jphysiol.2007.138198] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
The spastic mouse has a naturally occurring glycine receptor (GlyR) mutation that disrupts synaptic input in both motor and sensory pathways. Here we use the spastic mouse to examine how this altered inhibitory drive affects neuronal intrinsic membrane properties and signal processing in the superficial dorsal horn (SDH), where GlyRs contribute to pain processing mechanisms. We first used in vitro patch clamp recording in spinal cord slices (L3-L5 segments) to examine intrinsic membrane properties of SDH neurones in spastic and age-matched wildtype controls ( approximately P23). Apart from a modest reduction ( approximately 3 mV) in resting membrane potential (RMP), neurones in spastic mice have membrane and action potential (AP) properties identical to wildtype controls. There was, however, a substantial reorganization of AP discharge properties in neurones from spastic mice, with a significant increase (14%) in the proportion of delayed firing neurones. This was accompanied by a change in the voltage sensitivity of rapid A-currents, a possible mechanism for increased delayed firing. To assess the functional consequences of these changes, we made in vivo patch-clamp recordings from SDH neurones in urethane anaesthetized (2.2 g kg(-1), i.p.) spastic and wildtype mice ( approximately P37), and examined responses to innocuous and noxious mechanical stimulation of the hindpaw. Overall, responses recorded in wildtype and spastic mice were similar; however, in spastic mice a small population of spontaneously active neurones ( approximately 10%) exhibited elevated spontaneous discharge frequency and post-pinch discharge rates. Together, these results are consistent with the altered intrinsic membrane properties of SDH neurones observed in vitro having functional consequences for pain processing mechanisms in the spastic mouse in vivo. We propose that alterations in potassium channel function in the spastic mouse compensate, in part, for reduced glycinergic inhibition and thus maintain normal signal processing in the SDH.
Collapse
Affiliation(s)
- B A Graham
- School of Biomedical Sciences, Faculty of Health, The University of Newcastle, Callaghan, NSW 2308, Australia
| | | | | | | |
Collapse
|
46
|
Graham BA, Brichta AM, Callister RJ. Moving from an averaged to specific view of spinal cord pain processing circuits. J Neurophysiol 2007; 98:1057-63. [PMID: 17567772 DOI: 10.1152/jn.00581.2007] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Neurons in the superficial dorsal horn (SDH) of the spinal cord play a critical role in processing potentially painful or noxious signals from skin, muscle, and viscera. Many acute pain therapies are based on the notion that altering the excitability of SDH neurons can block or gate these signals and reduce pain. This same notion also underlies treatments for certain chronic pain states. Basic scientists are now beginning to identify a number of potential molecular targets for spinal cord-based pain therapies with a focus on ion channels and receptors that can alter neuronal excitability. The current challenge in pain research is to identify which are the most promising targets and how their manipulation alters pain processing. In this review, we propose that our understanding of spinal pain processing mechanisms and translation of these discoveries into pain therapies could be improved by 1) better appreciating and understanding neuronal heterogeneity in the SDH; 2) establishing connectivity patterns among SDH neuron types; and 3) testing and extending findings made in vitro to intact (in vivo) animal models. As this information becomes available, it will be possible to determine the precise distribution of potential therapeutic targets on various SDH neuron types within specific circuits known to be functionally important in spinal pain processing.
Collapse
Affiliation(s)
- B A Graham
- School of Biomedical Sciences, Faculty of Health, Univ. of Newcastle, Callaghan, NSW 2308, Australia
| | | | | |
Collapse
|
47
|
Wolff M, Heugel P, Hempelmann G, Scholz A, Mühling J, Olschewski A. Clonidine reduces the excitability of spinal dorsal horn neurones. Br J Anaesth 2007; 98:353-61. [PMID: 17307779 DOI: 10.1093/bja/ael379] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
BACKGROUND Clonidine has often been applied in combination with local anaesthetics for spinal or epidural anaesthesia. This study was designed to investigate the local anaesthetic-like action of clonidine in superficial dorsal horn neurones. The superficial laminae of the dorsal horn contain three groups of neurones: tonic-, adapting-, and single-spike-firing neurones which are important neuronal structures for pain transmission, receiving most of their primary sensory input from Adelta and C fibres. METHODS Whole cell patch clamp recordings from spinal cord slices of Wistar rats were used to study the action of clonidine on the generation of single and series of action potentials. Voltage clamp recordings in isolated somata were performed to study the effect of clonidine on voltage-gated Na(+) and different types of K(+) currents. RESULTS Firing frequencies of trains of action potentials in tonic-firing neurones are reduced at low concentrations (10 microM) of clonidine, but not in adapting- or single-spike-firing neurones. High concentrations of clonidine (700 microM) are necessary to modify the shape of single action potentials. Low concentrations of clonidine shift the steady-state inactivation curve of Na(+) currents to more negative potentials. At clinical concentrations (6-100 microM) clonidine partially inhibits voltage-gated Na(+) and K(+) channels. CONCLUSIONS Clonidine suppresses the generation of action potentials in tonic-firing spinal dorsal horn neurones. This may be explained, in part, by an interaction with voltage-gated Na(+) and K(+) currents. Clonidine could therefore contribute to analgesia during local anaesthesia.
Collapse
Affiliation(s)
- M Wolff
- Clinic for Anaesthesiology, Intensive Care Medicine, and Pain Therapy, Giessen, Germany.
| | | | | | | | | | | |
Collapse
|
48
|
Santos SFA, Rebelo S, Derkach VA, Safronov BV. Excitatory interneurons dominate sensory processing in the spinal substantia gelatinosa of rat. J Physiol 2007; 581:241-54. [PMID: 17331995 PMCID: PMC2075233 DOI: 10.1113/jphysiol.2006.126912] [Citation(s) in RCA: 125] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Substantia gelatinosa (SG, lamina II) is a spinal cord region where most unmyelinated primary afferents terminate and the central nociceptive processing begins. It is formed by several distinct groups of interneurons whose functional properties and synaptic connections are poorly understood, in part, because recordings from synaptically coupled pairs of SG neurons are quite challenging due to a very low probability of finding connected cells. Here, we describe an efficient method for identifying synaptically coupled interneurons in rat spinal cord slices and characterizing their excitatory or inhibitory function. Using tight-seal whole-cell recordings and a cell-attached stimulation technique, we routinely tested about 1500 SG interneurons, classifying 102 of them as monosynaptically connected to neurons in lamina I-III. Surprisingly, the vast majority of SG interneurons (n = 87) were excitatory and glutamatergic, while only 15 neurons were inhibitory. According to their intrinsic firing properties, these 102 SG neurons were also classified as tonic (n = 49), adapting (n = 17) or delayed-firing neurons (n = 36). All but two tonic neurons and all adapting neurons were excitatory interneurons. Of 36 delayed-firing neurons, 23 were excitatory and 13 were inhibitory. We conclude that sensory integration in the intrinsic SG neuronal network is dominated by excitatory interneurons. Such organization of neuronal circuitries in the spinal SG can be important for nociceptive encoding.
Collapse
Affiliation(s)
- Sónia F A Santos
- Instituto de Biologia Molecular e Celular-IBMC, Universidade do Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal
| | | | | | | |
Collapse
|
49
|
Abstract
Throughout the mammalian spinal cord, interneurones have been shown to exhibit distinct firing patterns in response to a step of injected current. In this study of ventral horn interneurones in a thick slice preparation of the lumbar cord of 11-19-day-old-rats, four distinct firing patterns were observed and classified as repetitive-firing, repetitive/burst, initial-burst or single-spiking. The hypothesis that a persistent sodium current was the predominant determinant of cell firing behaviour was investigated. A slow voltage ramp was used to assess persistent inward currents (PICs). Cells with repetitive-firing patterns had significantly larger PICs than cells displaying repetitive/burst, initial-burst or single-spiking patterns. Repetitive-firing, repetitive/burst and initial-burst-firing cells were reduced to a single-spiking pattern with the application of riluzole, which also markedly reduced the persistent sodium current. Persistent sodium current was found to account for most of the PIC with only a small contribution from L-type calcium current. These results suggest that the persistent sodium current plays a major role in determining firing patterns in these cells.
Collapse
Affiliation(s)
- Renée D Theiss
- Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
| | | | | |
Collapse
|
50
|
Graham BA, Brichta AM, Callister RJ. Pinch-current injection defines two discharge profiles in mouse superficial dorsal horn neurones, in vitro. J Physiol 2006; 578:787-98. [PMID: 17124264 PMCID: PMC2151331 DOI: 10.1113/jphysiol.2006.123349] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Neurones in the superficial dorsal horn (SDH) are a major target for nociceptive afferents and play an important role in pain processing. One approach to understanding the role of SDH neurones has been to study their action potential (AP) discharge in spinal cord slices during injection of depolarizing step-currents. Four or five neurone subpopulations are typically identified based on AP discharge, with various roles proposed for each in pain processing. During noxious peripheral stimulation in vivo, however, SDH neurones are activated via synaptic inputs. This produces a conductance change with different somato-dendritic distributions and temporal characteristics to that provided by a somatic step-current injection. Here we introduce an alternative approach to studying SDH neurone discharge under in vitro conditions. We recorded voltage-clamp responses in SDH neurones, in vivo, during noxious mechanical stimulation of the hindpaw (1 s pinch, approximately 100 g mm(-2)). From these recordings a representative 'pinch-current' was selected and subsequently injected into SDH neurones in spinal cord slices (recording temperature 32 degrees C). Pinch-current-evoked discharge was compared to that evoked by rectangular step-current injections. Pinch- and step-current-evoked AP discharge frequency was highly correlated (r2 = 0.61). This was also true for rheobase current comparisons (r2 = 0.61). Conversely, latency to discharge and discharge duration were not correlated when step- and pinch-current responses were compared. When neurones were grouped according to step-current-evoked discharge, five distinct patterns were apparent (tonic firing, initial bursting, delayed firing, single spiking, and reluctant firing). In contrast, pinch-current responses separated into two clear patterns of activity (robust and resistant firing). During pinch-current injection, tonic-firing and initial-bursting neurones exhibited robust AP discharge with similar characteristics. In contrast, single-spiking and reluctant-firing neurones were resistant to AP discharge. Delayed-firing neurones exhibited pinch-current responses that were transitional between those of tonic-firing/initial-bursting and single-spiking/reluctant-firing neurones. Injection of digitally filtered pinch-currents indicated that transient current fluctuations are necessary for robust repetitive discharge in initial-bursting neurones. These data suggest the functional significance of the diverse step-current-evoked firing patterns, previously reported in SDH neurones remains to be fully understood. When a 'facsimile' current profile or pinch-current is used in place of step-currents, AP discharge diversity is much reduced.
Collapse
Affiliation(s)
- B A Graham
- School of Biomedical Sciences, Faculty of Health, The University of Newcastle, Callaghan, NSW 2308, Australia
| | | | | |
Collapse
|