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Yu L, Liu M, Li F, Wang Q, Wang M, So KF, Qu Y, Zhou L. Celsr2 Knockout Alleviates Inhibitory Synaptic Stripping and Benefits Motoneuron Survival and Axon Regeneration After Branchial Plexus Avulsion. Mol Neurobiol 2023; 60:1884-1900. [PMID: 36593433 PMCID: PMC9984348 DOI: 10.1007/s12035-022-03198-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2022] [Accepted: 12/23/2022] [Indexed: 01/04/2023]
Abstract
Axotomy-induced synaptic stripping modulates survival and axon regeneration of injured motoneurons. Celsr2 is supposed to mediate homophilic interactions of neighboring cells during development, and its role in synaptic stripping remains unknow. In a model of brachial plexus avulsion, Celsr2 knockout improved functional recovery, motoneuron survival, and axon regeneration. Celsr2 was indicated to express in spinal motoneurons, excitatory and inhibitory interneurons, astrocytes, and a subset of oligodendrocytes using Celsr2LacZ mice. Double immunostaining showed that the coverage of inhibitory and excitatory vesicles on injured motoneurons were remarkably reduced after injury, whereas more inhibitory vesicles were maintained in Celsr2-/- mutants than control mice. In the ultrastructure, the density of inhibitory F-boutons on injured motoneurons was higher in Celsr2-/- mutants than controls. Conditional knockout of Celsr2 in astrocytes or oligodendrocytes showed the similar axotomy-induced synaptic withdrawal to the control. RNAseq of injured spinal samples identified 12 MHC I molecules with significant changes between Celsr2-/- and control mice. After injury, expression of MHC I surrounding injured motoneurons was increased, particularly high in Celsr2-/- mutants. In conclusion, Celsr2 knockout enhances MHC I signaling, alleviates inhibitory synaptic stripping cell-autonomously, and contributes to motoneuron survival and regeneration, and Celsr2 is a potential target for neural repair.
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Affiliation(s)
- Lingtai Yu
- Guangdong-Hongkong-Macau CNS Regeneration Institute of Jinan University, Key Laboratory of CNS Regeneration (Jinan University)-Ministry of Education, Guangzhou, 510632, People's Republic of China
| | - Mengfan Liu
- Guangdong-Hongkong-Macau CNS Regeneration Institute of Jinan University, Key Laboratory of CNS Regeneration (Jinan University)-Ministry of Education, Guangzhou, 510632, People's Republic of China
| | - Fuxiang Li
- Guangdong-Hongkong-Macau CNS Regeneration Institute of Jinan University, Key Laboratory of CNS Regeneration (Jinan University)-Ministry of Education, Guangzhou, 510632, People's Republic of China
| | - Qianghua Wang
- Guangdong-Hongkong-Macau CNS Regeneration Institute of Jinan University, Key Laboratory of CNS Regeneration (Jinan University)-Ministry of Education, Guangzhou, 510632, People's Republic of China
| | - Meizhi Wang
- Guangdong-Hongkong-Macau CNS Regeneration Institute of Jinan University, Key Laboratory of CNS Regeneration (Jinan University)-Ministry of Education, Guangzhou, 510632, People's Republic of China
| | - Kwok-Fai So
- Guangdong-Hongkong-Macau CNS Regeneration Institute of Jinan University, Key Laboratory of CNS Regeneration (Jinan University)-Ministry of Education, Guangzhou, 510632, People's Republic of China.,Department of Neurology and Stroke Center, The First Affiliated Hospital & Clinical Neuroscience Institute of Jinan University, Guangzhou, 510632, People's Republic of China.,Neuroscience and Neurorehabilitation Institute, University of Health and Rehabilitation Sciences, Qingdao, 266071, Shandong, People's Republic of China.,Co-Innovation Center of Neuroregeneration, Nantong University, Jiangsu, People's Republic of China
| | - Yibo Qu
- Guangdong-Hongkong-Macau CNS Regeneration Institute of Jinan University, Key Laboratory of CNS Regeneration (Jinan University)-Ministry of Education, Guangzhou, 510632, People's Republic of China.,Co-Innovation Center of Neuroregeneration, Nantong University, Jiangsu, People's Republic of China
| | - Libing Zhou
- Guangdong-Hongkong-Macau CNS Regeneration Institute of Jinan University, Key Laboratory of CNS Regeneration (Jinan University)-Ministry of Education, Guangzhou, 510632, People's Republic of China. .,Department of Neurology and Stroke Center, The First Affiliated Hospital & Clinical Neuroscience Institute of Jinan University, Guangzhou, 510632, People's Republic of China. .,Neuroscience and Neurorehabilitation Institute, University of Health and Rehabilitation Sciences, Qingdao, 266071, Shandong, People's Republic of China. .,Co-Innovation Center of Neuroregeneration, Nantong University, Jiangsu, People's Republic of China.
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2
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Davis LA, Fogarty MJ, Brown A, Sieck GC. Structure and Function of the Mammalian Neuromuscular Junction. Compr Physiol 2022; 12:3731-3766. [PMID: 35950651 PMCID: PMC10461538 DOI: 10.1002/cphy.c210022] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The mammalian neuromuscular junction (NMJ) comprises a presynaptic terminal, a postsynaptic receptor region on the muscle fiber (endplate), and the perisynaptic (terminal) Schwann cell. As with any synapse, the purpose of the NMJ is to transmit signals from the nervous system to muscle fibers. This neural control of muscle fibers is organized as motor units, which display distinct structural and functional phenotypes including differences in pre- and postsynaptic elements of NMJs. Motor units vary considerably in the frequency of their activation (both motor neuron discharge rate and duration/duty cycle), force generation, and susceptibility to fatigue. For earlier and more frequently recruited motor units, the structure and function of the activated NMJs must have high fidelity to ensure consistent activation and continued contractile response to sustain vital motor behaviors (e.g., breathing and postural balance). Similarly, for higher force less frequent behaviors (e.g., coughing and jumping), the structure and function of recruited NMJs must ensure short-term reliable activation but not activation sustained for a prolonged period in which fatigue may occur. The NMJ is highly plastic, changing structurally and functionally throughout the life span from embryonic development to old age. The NMJ also changes under pathological conditions including acute and chronic disease. Such neuroplasticity often varies across motor unit types. © 2022 American Physiological Society. Compr Physiol 12:1-36, 2022.
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Affiliation(s)
- Leah A. Davis
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
| | - Matthew J. Fogarty
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
| | - Alyssa Brown
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
| | - Gary C. Sieck
- Department of Physiology & Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, USA
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3
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Myers JH, Denman K, DuPont C, Hawash AA, Novak KR, Koesters A, Grabner M, Dayal A, Voss AA, Rich MM. The mechanism underlying transient weakness in myotonia congenita. eLife 2021; 10:e65691. [PMID: 33904400 PMCID: PMC8079152 DOI: 10.7554/elife.65691] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2020] [Accepted: 03/24/2021] [Indexed: 12/23/2022] Open
Abstract
In addition to the hallmark muscle stiffness, patients with recessive myotonia congenita (Becker disease) experience debilitating bouts of transient weakness that remain poorly understood despite years of study. We performed intracellular recordings from muscle of both genetic and pharmacologic mouse models of Becker disease to identify the mechanism underlying transient weakness. Our recordings reveal transient depolarizations (plateau potentials) of the membrane potential to -25 to -35 mV in the genetic and pharmacologic models of Becker disease. Both Na+ and Ca2+ currents contribute to plateau potentials. Na+ persistent inward current (NaPIC) through NaV1.4 channels is the key trigger of plateau potentials and current through CaV1.1 Ca2+ channels contributes to the duration of the plateau. Inhibiting NaPIC with ranolazine prevents the development of plateau potentials and eliminates transient weakness in vivo. These data suggest that targeting NaPIC may be an effective treatment to prevent transient weakness in myotonia congenita.
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Affiliation(s)
- Jessica H Myers
- Department of Neuroscience, Cell Biology and Physiology, Wright State UniversityDaytonUnited States
| | - Kirsten Denman
- Department of Neuroscience, Cell Biology and Physiology, Wright State UniversityDaytonUnited States
| | - Chris DuPont
- Department of Neuroscience, Cell Biology and Physiology, Wright State UniversityDaytonUnited States
| | - Ahmed A Hawash
- Department of Dermatology & Cutaneous Surgery, University of MiamiMiamiUnited States
| | | | - Andrew Koesters
- Naval Medical Research Unit, Wright Patterson Air Force BaseDaytonUnited States
| | - Manfred Grabner
- Department of Pharmacology, Medical University of InnsbruckInnsbruckAustria
| | - Anamika Dayal
- Department of Pharmacology, Medical University of InnsbruckInnsbruckAustria
| | - Andrew A Voss
- Department of Biology, Wright State UniversityDaytonUnited States
| | - Mark M Rich
- Department of Neuroscience, Cell Biology and Physiology, Wright State UniversityDaytonUnited States
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4
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Deardorff AS, Romer SH, Fyffe RE. Location, location, location: the organization and roles of potassium channels in mammalian motoneurons. J Physiol 2021; 599:1391-1420. [DOI: 10.1113/jp278675] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2020] [Accepted: 01/08/2021] [Indexed: 11/08/2022] Open
Affiliation(s)
- Adam S. Deardorff
- Department of Neuroscience, Cell Biology and Physiology, Wright State University Boonshoft School of Medicine Dayton OH 45435 USA
- Department of Neurology and Internal Medicine, Wright State University Boonshoft School of Medicine Dayton OH 45435 USA
| | - Shannon H. Romer
- Odyssey Systems Environmental Health Effects Laboratory, Navy Medical Research Unit‐Dayton Wright‐Patterson Air Force Base OH 45433 USA
| | - Robert E.W. Fyffe
- Department of Neuroscience, Cell Biology and Physiology, Wright State University Boonshoft School of Medicine Dayton OH 45435 USA
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5
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γ-Aminobutyric acid (GABA) from satellite glial cells tonically depresses the excitability of primary afferent fibers. Neurosci Res 2020; 170:50-58. [PMID: 32987088 DOI: 10.1016/j.neures.2020.08.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2020] [Revised: 08/10/2020] [Accepted: 08/26/2020] [Indexed: 01/08/2023]
Abstract
Primary afferent fibers express extrasynaptic GABAA and GABAB receptors in the axons and soma. However, whether these receptors are tonically activated by ambient GABA and the source of the neurotransmitter is presently unknown. Here, we show that GABA release from dorsal root ganglia (DRG) does not depend on extracellular calcium, but depends upon calcium released from intracellular stores, and is mediated by Best1 channels. Using a preparation consisting of the spinal nerve in continuity with the DRG and the dorsal root, we found that endogenous GABA tonically activates GABA receptors, depressing the excitability of the primary afferents. In addition, using HPLC we found that GABA is released in the DRG, and by immunofluorescence microscopy we show the presence of GABA, the Best1 channel, and some enzymes of the putrescine pathway of GABA biosynthesis, in glutamine synthase- and GFAP-positive satellite glial cells. Last, we found that the blockade of the Best1 channel activity reduced the excitability of primary afferents and prevented the activation of the GABA receptors. These results suggest that satellite glial cells may be the source of endogenous GABA released in the DRG via Best1 channels, which tonically activates extrasynaptic GABA receptors.
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6
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Modulatory Roles of ATP and Adenosine in Cholinergic Neuromuscular Transmission. Int J Mol Sci 2020; 21:ijms21176423. [PMID: 32899290 PMCID: PMC7503321 DOI: 10.3390/ijms21176423] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 08/29/2020] [Accepted: 09/01/2020] [Indexed: 12/23/2022] Open
Abstract
A review of the data on the modulatory action of adenosine 5’-triphosphate (ATP), the main co-transmitter with acetylcholine, and adenosine, the final ATP metabolite in the synaptic cleft, on neuromuscular transmission is presented. The effects of these endogenous modulators on pre- and post-synaptic processes are discussed. The contribution of purines to the processes of quantal and non-quantal secretion of acetylcholine into the synaptic cleft, as well as the influence of the postsynaptic effects of ATP and adenosine on the functioning of cholinergic receptors, are evaluated. As usual, the P2-receptor-mediated influence is minimal under physiological conditions, but it becomes very important in some pathophysiological situations such as hypothermia, stress, or ischemia. There are some data demonstrating the same in neuromuscular transmission. It is suggested that the role of endogenous purines is primarily to provide a safety factor for the efficiency of cholinergic neuromuscular transmission.
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7
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Vernillo G, Temesi J, Martin M, Krüger RL, Millet GY. Spinal contribution to neuromuscular recovery differs between elbow-flexor and knee-extensor muscles after a maximal sustained fatiguing task. J Neurophysiol 2020; 124:763-773. [PMID: 32755359 DOI: 10.1152/jn.00273.2020] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Data from studies of elbow-flexor (EF) or knee-extensor (KE) muscles suggest that a fatigue-related decrease in motoneuron excitability only occurs in EF. It is unknown how motoneuron excitability changes after sustained fatiguing maximal voluntary isometric contractions (MVICs) in EF and KE in the same participants. In two sessions, eight healthy men performed a 2-min MVIC of EF or KE to induce fatigue with brief MVICs before and six times after the 2-min MVIC. Electromyographic responses elicited by corticospinal tract stimulation at the transmastoid [cervicomedullary motor-evoked potential (CMEP)] or thoracic [thoracic motor-evoked potential (TMEP)] level were recorded from EF and KE, respectively. To account for muscle excitability, CMEPs and TMEPs were normalized to maximal M-wave (Mmax) elicited by peripheral nerve stimulation during each brief MVIC. Immediately after the 2-min MVIC, biceps brachii and brachioradialis CMEP/Mmax were 88% (SD 11%) (P = 0.026) and 87% (SD 12%) (P = 0.029) of pre-MVIC (PRE) values, respectively, and remained lower than PRE after 5 s of recovery [91% (SD 8%), P = 0.036 and 87% (SD 13%), P = 0.046, respectively]. No subsequent time points differed from PRE (all P ≥ 0.253). TMEP/Mmax for rectus femoris and vastus lateralis were not different from PRE at any time during the recovery period (all P > 0.050). A different recovery pattern in motoneuron excitability occurred in EF as it recovered by 60 s whereas KE motoneurons were unaffected by the fatiguing task. The present findings may contribute to better understand muscle-specific neurophysiological differences in spinal excitability.NEW & NOTEWORTHY By comparing the changes in motoneuron excitability in elbow-flexor and knee-extensor muscles after sustained fatiguing maximal voluntary contractions, this study shows that motoneuron recovery behavior depends on the muscle performing the exercise. A different recovery pattern in motoneuron excitability occurs in elbow flexors as it recovered by 60 s whereas knee extensors were unaffected by fatigue. This finding can help to increase understanding of the effect of a fatigue and subsequent recovery on neural processes.
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Affiliation(s)
- Gianluca Vernillo
- Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada.,Department of Biomedical Sciences for Health, Università degli Studi di Milano, Milan, Italy
| | - John Temesi
- Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada.,Faculty of Health & Life Sciences, Northumbria University, Newcastle upon Tyne, United Kingdom
| | - Matthieu Martin
- Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada
| | - Renata L Krüger
- Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada
| | - Guillaume Y Millet
- Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada.,Univ Lyon, UJM-Saint-Etienne, Inter-university Laboratory of Human Movement Biology, EA 7424, F-42023, Saint-Etienne, France.,Institut Universitaire de France (IUF)
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8
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V2a interneuron diversity tailors spinal circuit organization to control the vigor of locomotor movements. Nat Commun 2018; 9:3370. [PMID: 30135498 PMCID: PMC6105610 DOI: 10.1038/s41467-018-05827-9] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2018] [Accepted: 07/31/2018] [Indexed: 01/12/2023] Open
Abstract
Locomotion is a complex motor task generated by spinal circuits driving motoneurons in a precise sequence to control the timing and vigor of movements, but the underlying circuit logic remains to be understood. Here we reveal, in adult zebrafish, how the diversity and selective distribution of two V2a interneuron types within the locomotor network transform commands into an appropriate, task-dependent circuit organization. Bursting-type V2a interneurons with unidirectional axons predominantly target distal dendrites of slow motoneurons to provide potent, non-linear excitation involving NMDA-dependent potentiation. A second type, non-bursting V2a interneurons with bidirectional axons, predominantly target somata of fast motoneurons, providing weaker, non-potentiating excitation. Together, this ensures the rapid, first-order recruitment of the slow circuit, while reserving the fast circuit for highly salient stimuli involving synchronous inputs. Our results thus identify how interneuron diversity is captured and transformed into a parsimonious task-specific circuit design controlling the vigor of locomotion.
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9
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Intraspinal Grafting of Serotonergic Neurons Modifies Expression of Genes Important for Functional Recovery in Paraplegic Rats. Neural Plast 2018; 2018:4232706. [PMID: 30147717 PMCID: PMC6083740 DOI: 10.1155/2018/4232706] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2018] [Revised: 05/23/2018] [Accepted: 06/04/2018] [Indexed: 01/08/2023] Open
Abstract
Serotonin (5-hydroxytryptamine; 5-HT) plays an important role in control of locomotion, partly through direct effects on motoneurons. Spinal cord complete transection (SCI) results in changes in 5-HT receptors on motoneurons that influence functional recovery. Activation of 5-HT2A and 5-HT7 receptors improves locomotor hindlimb movements in paraplegic rats. Here, we analyzed the mRNA of 5-HT2A and 5-HT7 receptors (encoded by Htr2a and Htr7 genes, resp.) in motoneurons innervating tibialis anterior (TA) and gastrocnemius lateralis (GM) hindlimb muscles and the tail extensor caudae medialis (ECM) muscle in intact as well as spinal rats. Moreover, the effect of intraspinal grafting of serotonergic neurons on Htr2a and Htr7 gene expression was examined to test the possibility that the graft origin 5-HT innervation in the spinal cord of paraplegic rats could reverse changes in gene expression induced by SCI. Our results indicate that SCI at the thoracic level leads to changes in Htr2a and Htr7 gene expression, whereas transplantation of embryonic serotonergic neurons modifies these changes in motoneurons innervating hindlimb muscles but not those innervating tail muscles. This suggests that the upregulation of genes critical for locomotor recovery, resulting in limb motoneuron plasticity, might account for the improved locomotion in grafted animals.
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10
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Stein PSG. Central pattern generators in the turtle spinal cord: selection among the forms of motor behaviors. J Neurophysiol 2018; 119:422-440. [PMID: 29070633 PMCID: PMC5867383 DOI: 10.1152/jn.00602.2017] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Revised: 10/16/2017] [Accepted: 10/17/2017] [Indexed: 12/29/2022] Open
Abstract
Neuronal networks in the turtle spinal cord have considerable computational complexity even in the absence of connections with supraspinal structures. These networks contain central pattern generators (CPGs) for each of several behaviors, including three forms of scratch, two forms of swim, and one form of flexion reflex. Each behavior is activated by a specific set of cutaneous or electrical stimuli. The process of selection among behaviors within the spinal cord has multisecond memories of specific motor patterns. Some spinal cord interneurons are partially shared among several CPGs, whereas other interneurons are active during only one type of behavior. Partial sharing is a proposed mechanism that contributes to the ability of the spinal cord to generate motor pattern blends with characteristics of multiple behaviors. Variations of motor patterns, termed deletions, assist in characterization of the organization of the pattern-generating components of CPGs. Single-neuron recordings during both normal and deletion motor patterns provide support for a CPG organizational structure with unit burst generators (UBGs) whose members serve a direction of a specific degree of freedom of the hindlimb, e.g., the hip-flexor UBG, the hip-extensor UBG, the knee-flexor UBG, the knee-extensor UBG, etc. The classic half-center hypothesis that includes all the hindlimb flexors in a single flexor half-center and all the hindlimb extensors in a single extensor half-center lacks the organizational complexity to account for the motor patterns produced by turtle spinal CPGs. Thus the turtle spinal cord is a valuable model system for studies of mechanisms responsible for selection and generation of motor behaviors. NEW & NOTEWORTHY The concept of the central pattern generator (CPG) is a major tenet in motor neuroethology that has influenced the design and interpretations of experiments for over a half century. This review concentrates on the turtle spinal cord and describes studies from the 1970s to the present responsible for key developments in understanding the CPG mechanisms responsible for the selection and production of coordinated motor patterns during turtle hindlimb motor behaviors.
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Affiliation(s)
- Paul S G Stein
- Department of Biology, Washington University , St. Louis, Missouri
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11
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Finn HT, Rouffet DM, Kennedy DS, Green S, Taylor JL. Motoneuron excitability of the quadriceps decreases during a fatiguing submaximal isometric contraction. J Appl Physiol (1985) 2018; 124:970-979. [PMID: 29357479 DOI: 10.1152/japplphysiol.00739.2017] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
During fatiguing voluntary contractions, the excitability of motoneurons innervating arm muscles decreases. However, the behavior of motoneurons innervating quadriceps muscles is unclear. Findings may be inconsistent because descending cortical input influences motoneuron excitability and confounds measures during exercise. To overcome this limitation, we examined effects of fatigue on quadriceps motoneuron excitability tested during brief pauses in descending cortical drive after transcranial magnetic stimulation (TMS). Participants ( n = 14) performed brief (~5-s) isometric knee extension contractions before and after a 10-min sustained contraction at ~25% maximal electromyogram (EMG) of vastus medialis (VM) on one ( n = 5) or two ( n = 9) days. Electrical stimulation over thoracic spine elicited thoracic motor evoked potentials (TMEP) in quadriceps muscles during ongoing voluntary drive and 100 ms into the silent period following TMS (TMS-TMEP). Femoral nerve stimulation elicited maximal M-waves (Mmax). On the 2 days, either large (~50% Mmax) or small (~15% Mmax) TMS-TMEPs were elicited. During the 10-min contraction, VM EMG was maintained ( P = 0.39), whereas force decreased by 52% (SD 13%) ( P < 0.001). TMEP area remained unchanged ( P = 0.9), whereas large TMS-TMEPs decreased by 49% (SD 28%) ( P = 0.001) and small TMS-TMEPs by 71% (SD 22%) ( P < 0.001). This decline was greater for small TMS-TMEPs ( P = 0.019; n = 9). Therefore, without the influence of descending drive, quadriceps TMS-TMEPs decreased during fatigue. The greater reduction for smaller responses, which tested motoneurons that were most active during the contraction, suggests a mechanism related to repetitive activity contributes to reduced quadriceps motoneuron excitability during fatigue. By contrast, the unchanged TMEP suggests that ongoing drive compensates for altered motoneuron excitability. NEW & NOTEWORTHY We provide evidence that the excitability of quadriceps motoneurons decreases with fatigue. Our results suggest that altered intrinsic properties brought about by repetitive activation of the motoneurons underlie their decreased excitability. Furthermore, we note that testing during voluntary contraction may not reflect the underlying depression of motoneuron excitability because of compensatory changes in ongoing voluntary drive. Thus, this study provides evidence that processes intrinsic to the motoneuron contribute to muscle fatigue of the knee extensors.
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Affiliation(s)
- Harrison T Finn
- Neuroscience Research Australia, Randwick, New South Wales , Australia.,University of New South Wales , Kensington, New South Wales , Australia
| | - David M Rouffet
- Victoria University , Melbourne, Victoria , Australia.,Australian Institute for Musculoskeletal Science, Victoria University , Melbourne , Australia.,Institute of Sport, Exercise, and Active Living, Victoria University , Melbourne , Australia
| | - David S Kennedy
- University of Sydney, Cumberland, New South Wales , Australia.,University of Technology , Ultimo, New South Wales , Australia
| | - Simon Green
- Western Sydney University, Campbelltown, New South Wales , Australia
| | - Janet L Taylor
- Neuroscience Research Australia, Randwick, New South Wales , Australia.,University of New South Wales , Kensington, New South Wales , Australia.,Edith Cowan University , Perth, Western Australia , Australia
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12
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Ceballos-Villegas ME, Saldaña Mena JJ, Gutierrez Lozano AL, Sepúlveda-Cañamar FJ, Huidobro N, Manjarrez E, Lomeli J. The Complexity of H-wave Amplitude Fluctuations and Their Bilateral Cross-Covariance Are Modified According to the Previous Fitness History of Young Subjects under Track Training. Front Hum Neurosci 2017; 11:530. [PMID: 29163107 PMCID: PMC5671983 DOI: 10.3389/fnhum.2017.00530] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2017] [Accepted: 10/18/2017] [Indexed: 12/28/2022] Open
Abstract
The Hoffmann reflex (H-wave) is produced by alpha-motoneuron activation in the spinal cord. A feature of this electromyography response is that it exhibits fluctuations in amplitude even during repetitive stimulation with the same intensity of current. We herein explore the hypothesis that physical training induces plastic changes in the motor system. Such changes are evaluated with the fractal dimension (FD) analysis of the H-wave amplitude-fluctuations (H-wave FD) and the cross-covariance (CCV) between the bilateral H-wave amplitudes. The aim of this study was to compare the H-wave FD as well as the CCV before and after track training in sedentary individuals and athletes. The training modality in all subjects consisted of running three times per week (for 13 weeks) in a concrete road of 5 km. Given the different physical condition of sedentary vs. athletes, the running time between sedentary and athletes was different. After training, the FD was significantly increased in sedentary individuals but significantly reduced in athletes, although there were no changes in spinal excitability in either group of subjects. Moreover, the CCV between bilateral H-waves exhibited a significant increase in athletes but not in sedentary individuals. These differential changes in the FD and CCV indicate that the plastic changes in the complexity of the H-wave amplitude fluctuations as well as the synaptic inputs to the Ia-motoneuron systems of both legs were correlated to the previous fitness history of the subjects. Furthermore, these findings demonstrate that the FD and CCV can be employed as indexes to study plastic changes in the human motor system.
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Affiliation(s)
- Maria E Ceballos-Villegas
- Sección de Posgrado e Investigación, Laboratorio de Neurofisiología Humana y Control Motor, Escuela Superior de Medicina, Instituto Politécnico Nacional, Mexico City, Mexico
| | - Juan J Saldaña Mena
- Escuela de Quiropráctica, Universidad Estatal del Valle de Ecatepec, Ecatepec de Morelos, Mexico
| | - Ana L Gutierrez Lozano
- Sección de Posgrado e Investigación, Laboratorio de Neurofisiología Humana y Control Motor, Escuela Superior de Medicina, Instituto Politécnico Nacional, Mexico City, Mexico
| | | | - Nayeli Huidobro
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, Puebla, Mexico
| | - Elias Manjarrez
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, Puebla, Mexico
| | - Joel Lomeli
- Sección de Posgrado e Investigación, Laboratorio de Neurofisiología Humana y Control Motor, Escuela Superior de Medicina, Instituto Politécnico Nacional, Mexico City, Mexico
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13
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Synaptic Excitation in Spinal Motoneurons Alternates with Synaptic Inhibition and Is Balanced by Outward Rectification during Rhythmic Motor Network Activity. J Neurosci 2017; 37:9239-9248. [PMID: 28842417 DOI: 10.1523/jneurosci.0800-17.2017] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2017] [Revised: 08/10/2017] [Accepted: 08/17/2017] [Indexed: 11/21/2022] Open
Abstract
Regular firing in spinal motoneurons of red-eared turtles (Trachemys scripta elegans, either sex) evoked by steady depolarization at rest is replaced by irregular firing during functional network activity. The transition caused by increased input conductance and synaptic fluctuations in membrane potential was suggested to originate from intense concurrent inhibition and excitation. We show that the conductance increase in motoneurons during functional network activity is mainly caused by intrinsic outward rectification near threshold for action potentials by activation of voltage and Ca2+ gated K channels. Intrinsic outward rectification facilitates spiking by focusing synaptic depolarization near threshold for action potentials. By direct recording of synaptic currents, we also show that motoneurons are activated by out-of-phase peaks in excitation and inhibition during network activity, whereas continuous low-level concurrent inhibition and excitation may contribute to irregular firing.SIGNIFICANCE STATEMENT Neurons embedded in active neural networks can enter a high-conductance state. High-conductance states were observed in spinal motoneurons during rhythmic motor behavior. Assuming no change in intrinsic conductance, it was suggested that the high-conductance state in motoneurons originated from balanced inhibition and excitation. In this study, we demonstrate that intrinsic outward rectification significantly contributes to the high-conductance state. Outward rectification balances synaptic excitation and maintains membrane potential near spike threshold. In addition, direct synaptic current recordings show out-of-phase excitation and inhibition in motoneurons during rhythmic network activity.
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