1
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Flett S, Garcia J, Cowley KC. Spinal electrical stimulation to improve sympathetic autonomic functions needed for movement and exercise after spinal cord injury: a scoping clinical review. J Neurophysiol 2022; 128:649-670. [PMID: 35894427 DOI: 10.1152/jn.00205.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Spinal cord injury (SCI) results in sensory, motor and autonomic dysfunction. Obesity, cardiovascular and metabolic diseases are highly prevalent after SCI. Although inadequate voluntary activation of skeletal muscle contributes, it is absent or inadequate activation of thoracic spinal sympathetic neural circuitry and sub-optimal activation of homeostatic (cardiovascular, temperature) and metabolic support systems that truly limits exercise capacity, particularly for those with cervical SCI. Thus, when electrical spinal cord stimulation (SCS) studies aimed at improving motor functions began mentioning effects on exercise-related autonomic functions, a potential new area of clinical application appeared. To survey this new area of potential benefit, we performed a systematic scoping review of clinical SCS studies involving these spinally mediated autonomic functions. Nineteen studies were included, 8 used transcutaneous and 11 used epidural SCS. Improvements in BP at rest or in response to orthostatic challenge were investigated most systematically, whereas reports of improved temperature regulation, whole body metabolism and peak exercise performance were mainly anecdotal. Effective stimulation locations and parameters varied between studies, suggesting multiple stimulation parameters and rostrocaudal spinal locations may influence the same sympathetic function. Brainstem and spinal neural mechanisms providing excitatory drive to sympathetic neurons that activate homeostatic and metabolic tissues that provide support for movement and exercise and their integration with locomotor neural circuitry are discussed. A unifying conceptual framework for the integrated neural control of locomotor and sympathetic function is presented which may inform future research needed to take full advantage of SCS for improving these spinally mediated autonomic functions.
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Affiliation(s)
- Sarah Flett
- Department of Physiology and Pathophysiology, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Juanita Garcia
- Department of Physiology and Pathophysiology, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Kristine C Cowley
- Department of Physiology and Pathophysiology, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, Manitoba, Canada
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2
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Shevtsova NA, Li EZ, Singh S, Dougherty KJ, Rybak IA. Ipsilateral and Contralateral Interactions in Spinal Locomotor Circuits Mediated by V1 Neurons: Insights from Computational Modeling. Int J Mol Sci 2022; 23:5541. [PMID: 35628347 PMCID: PMC9146873 DOI: 10.3390/ijms23105541] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2022] [Revised: 05/11/2022] [Accepted: 05/12/2022] [Indexed: 02/01/2023] Open
Abstract
We describe and analyze a computational model of neural circuits in the mammalian spinal cord responsible for generating and shaping locomotor-like oscillations. The model represents interacting populations of spinal neurons, including the neurons that were genetically identified and characterized in a series of previous experimental studies. Here, we specifically focus on the ipsilaterally projecting V1 interneurons, their possible role in the spinal locomotor circuitry, and their involvement in the generation of locomotor oscillations. The proposed connections of these neurons and their involvement in different neuronal pathways in the spinal cord allow the model to reproduce the results of optogenetic manipulations of these neurons under different experimental conditions. We suggest the existence of two distinct populations of V1 interneurons mediating different ipsilateral and contralateral interactions within the spinal cord. The model proposes explanations for multiple experimental data concerning the effects of optogenetic silencing and activation of V1 interneurons on the frequency of locomotor oscillations in the intact cord and hemicord under different experimental conditions. Our simulations provide an important insight into the organization of locomotor circuitry in the mammalian spinal cord.
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Affiliation(s)
| | | | | | | | - Ilya A. Rybak
- Department of Neurobiology and Anatomy, College of Medicine, Drexel University, Philadelphia, PA 19129, USA; (N.A.S.); (E.Z.L.); (S.S.); (K.J.D.)
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3
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Chalif JI, de Lourdes Martínez-Silva M, Pagiazitis JG, Murray AJ, Mentis GZ. Control of mammalian locomotion by ventral spinocerebellar tract neurons. Cell 2022; 185:328-344.e26. [PMID: 35063074 PMCID: PMC8852337 DOI: 10.1016/j.cell.2021.12.014] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2021] [Revised: 11/09/2021] [Accepted: 12/13/2021] [Indexed: 01/22/2023]
Abstract
Locomotion is a complex behavior required for animal survival. Vertebrate locomotion depends on spinal interneurons termed the central pattern generator (CPG), which generates activity responsible for the alternation of flexor and extensor muscles and the left and right side of the body. It is unknown whether multiple or a single neuronal type is responsible for the control of mammalian locomotion. Here, we show that ventral spinocerebellar tract neurons (VSCTs) drive generation and maintenance of locomotor behavior in neonatal and adult mice. Using mouse genetics, physiological, anatomical, and behavioral assays, we demonstrate that VSCTs exhibit rhythmogenic properties and neuronal circuit connectivity consistent with their essential role in the locomotor CPG. Importantly, optogenetic activation and chemogenetic silencing reveals that VSCTs are necessary and sufficient for locomotion. These findings identify VSCTs as critical components for mammalian locomotion and provide a paradigm shift in our understanding of neural control of complex behaviors.
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Affiliation(s)
- Joshua I. Chalif
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA,Dept. of Neurology, Columbia University, New York, NY 10032, USA
| | - María de Lourdes Martínez-Silva
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA,Dept. of Neurology, Columbia University, New York, NY 10032, USA
| | - John G. Pagiazitis
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA,Dept. of Neurology, Columbia University, New York, NY 10032, USA
| | - Andrew J. Murray
- Sainsbury Wellcome Centre, University College London, 25 Howland Street, London W1T 4JG, UK
| | - George Z. Mentis
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA,Dept. of Neurology, Columbia University, New York, NY 10032, USA,Dept. of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA,Corresponding author & Lead contact: Tel: +1-212-305-9846,
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4
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Merlet AN, Harnie J, Frigon A. Inhibition and Facilitation of the Spinal Locomotor Central Pattern Generator and Reflex Circuits by Somatosensory Feedback From the Lumbar and Perineal Regions After Spinal Cord Injury. Front Neurosci 2021; 15:720542. [PMID: 34393721 PMCID: PMC8355562 DOI: 10.3389/fnins.2021.720542] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2021] [Accepted: 07/08/2021] [Indexed: 02/03/2023] Open
Abstract
Somatosensory feedback from peripheral receptors dynamically interacts with networks located in the spinal cord and brain to control mammalian locomotion. Although somatosensory feedback from the limbs plays a major role in regulating locomotor output, those from other regions, such as lumbar and perineal areas also shape locomotor activity. In mammals with a complete spinal cord injury, inputs from the lumbar region powerfully inhibit hindlimb locomotion, while those from the perineal region facilitate it. Our recent work in cats with a complete spinal cord injury shows that they also have opposite effects on cutaneous reflexes from the foot. Lumbar inputs increase the gain of reflexes while those from the perineal region decrease it. The purpose of this review is to discuss how somatosensory feedback from the lumbar and perineal regions modulate the spinal locomotor central pattern generator and reflex circuits after spinal cord injury and the possible mechanisms involved. We also discuss how spinal cord injury can lead to a loss of functional specificity through the abnormal activation of functions by somatosensory feedback, such as the concurrent activation of locomotion and micturition. Lastly, we discuss the potential functions of somatosensory feedback from the lumbar and perineal regions and their potential for promoting motor recovery after spinal cord injury.
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Affiliation(s)
- Angèle N Merlet
- Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, Centre de Recherche du CHUS, Université de Sherbrooke, Sherbrooke, QC, Canada
| | - Jonathan Harnie
- Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, Centre de Recherche du CHUS, Université de Sherbrooke, Sherbrooke, QC, Canada
| | - Alain Frigon
- Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, Centre de Recherche du CHUS, Université de Sherbrooke, Sherbrooke, QC, Canada
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5
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Expiratory abdominal muscle nerve is active at flexor phase, while inspiratory phrenic nerve is not active during locomotion evoked by 5-HT and NMDA in the neonatal rat. Neurosci Res 2021; 174:9-18. [PMID: 34324893 DOI: 10.1016/j.neures.2021.07.004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2021] [Revised: 07/15/2021] [Accepted: 07/21/2021] [Indexed: 11/21/2022]
Abstract
Abdominal muscles are involved in respiration and locomotion. In the isolated pons-spinal cord-rib attached preparation from neonatal rat, the phrenic nerve and abdominal muscles show inspiratory and expiratory activity, respectively. Using this preparation, we investigated whether the bath application of NMDA and 5-HT could evoke locomotor activities in the fourth cervical ventral root (C4VR), phrenic nerve, and abdominal muscle nerve (ilioinguinal nerve, IIG-n). We also observed rib and abdominal muscle movements visually. The phrenic nerve and C4VR showed inspiratory activity consistently under the control conditions, whereas IIG-n showed expiratory activity only at the beginning of the experiment. During the chemically-induced locomotion, both C4VR and IIG-n showed locomotor activity, and IIG-n in particular showed flexor activity. During the flexor activity, lateral bending of the rib cage to the recording site was observed. The phrenic nerve showed weak or no apparent locomotor activity. We concluded that the central pattern generator (CPG) for locomotion provides stronger excitatory synaptic inputs to C4 motoneurons innervating neck and shoulder muscles than the inputs to the phrenic motoneurons. Thus, the locomotor CPG provides a suitable amount of inputs to the functionally proper motoneurons. This preparation will be useful to explore how the respiratory and locomotor CPGs select proper motoneurons to give synaptic inputs and are coordinated with each other.
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6
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Matzner H, Zelinger M, Cherniak M, Anglister L, Lev-Tov A. Rhythmogenic networks are potently modulated by activation of muscarinic acetylcholine receptors in the rodent spinal cord. J Neurochem 2021; 158:1263-1273. [PMID: 33735482 DOI: 10.1111/jnc.15354] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2020] [Revised: 03/10/2021] [Accepted: 03/11/2021] [Indexed: 02/02/2023]
Abstract
Electrical stimulation of the spinal cord is a potent means for activating mammalian stepping in the absence of the descending control from the brain. Previously, we have shown that stimulation of pain delivering (Aδ) sacrocaudal afferents (SCA) has a powerful capacity to activate the sacral and lumbar rhythmogenic networks in the neonatal rodent spinal cord. Relatively little is known about the neural pathways involved in activation of the locomotor networks by Aδ afferents, on their mechanism of action and on the possibility to modulate their activity. We have shown that elevation of the endogenous level of acetylcholine at the sacral cord by blocking cholinesterase could modulate the SCA-induced locomotor rhythm in a muscarinic receptor-dependent mechanism. Here, we review these and more recent findings and report that controlled stimulation of SCA in the presence of muscarine is a potent activator of the locomotor network. The possible mechanisms involved in the muscarinic modulation of the locomotor rhythm are discussed in terms of the differential projections of sacral relay neurons, activated by SCA stimulation, to the lumbar locomotor rhythm generators, and to their target motoneurons. Altogether, our studies show that manipulations of cholinergic networks offer a simple and powerful means to control the activity of locomotor networks in the absence of supraspinal control.
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Affiliation(s)
- Henry Matzner
- Department of Medical Neurobiology, Institute for Medical Research - Israel-Canada, IMRIC, Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Moshe Zelinger
- Department of Medical Neurobiology, Institute for Medical Research - Israel-Canada, IMRIC, Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Meir Cherniak
- Department of Medical Neurobiology, Institute for Medical Research - Israel-Canada, IMRIC, Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Lili Anglister
- Department of Medical Neurobiology, Institute for Medical Research - Israel-Canada, IMRIC, Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Aharon Lev-Tov
- Department of Medical Neurobiology, Institute for Medical Research - Israel-Canada, IMRIC, Hebrew University-Hadassah Medical School, Jerusalem, Israel
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7
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Moshonkina T, Grishin A, Bogacheva I, Gorodnichev R, Ovechkin A, Siu R, Edgerton VR, Gerasimenko Y. Novel Non-invasive Strategy for Spinal Neuromodulation to Control Human Locomotion. Front Hum Neurosci 2021; 14:622533. [PMID: 33519405 PMCID: PMC7838433 DOI: 10.3389/fnhum.2020.622533] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2020] [Accepted: 12/14/2020] [Indexed: 11/13/2022] Open
Affiliation(s)
- Tatiana Moshonkina
- Pavlov Institute of Physiology, Russian Academy of Sciences, St. Petersburg, Russia
| | - Alexander Grishin
- Pavlov Institute of Physiology, Russian Academy of Sciences, St. Petersburg, Russia
| | - Irina Bogacheva
- Pavlov Institute of Physiology, Russian Academy of Sciences, St. Petersburg, Russia
| | - Ruslan Gorodnichev
- Velikie Luki State Academy of Physical Education and Sports, Velikiye Luki, Russia
| | - Alexander Ovechkin
- Kentucky Spinal Cord Injury Research Center, Frazier Rehab Institute, University of Louisville Health, University of Louisville, Louisville, KY, United States.,Department of Neurological Surgery, University of Louisville, Louisville, KY, United States
| | - Ricardo Siu
- Kentucky Spinal Cord Injury Research Center, Frazier Rehab Institute, University of Louisville Health, University of Louisville, Louisville, KY, United States
| | - V Reggie Edgerton
- Department of Neurobiology, and Neurosurgery, University of California, Los Angeles, Los Angeles, CA, United States.,Institut Guttmann Hospital de Neurorehabilitació, Institut Universitari adscrit a la Universitat Autònoma de Barcelona, Barcelona, Spain.,Faculty of Science, The Center for Neuroscience and Regenerative Medicine, University of Technology Sydney, Ultimo, NSW, Australia
| | - Yury Gerasimenko
- Pavlov Institute of Physiology, Russian Academy of Sciences, St. Petersburg, Russia.,Department of Physiology and Biophysics, University of Louisville, Louisville, KY, United States
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8
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Musienko PE, Lyalka VF, Gorskii OV, Merkulyeva N, Gerasimenko YP, Deliagina TG, Zelenin PV. Comparison of operation of spinal locomotor networks activated by supraspinal commands and by epidural stimulation of the spinal cord in cats. J Physiol 2020; 598:3459-3483. [PMID: 32445488 PMCID: PMC8106146 DOI: 10.1113/jp279460] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Accepted: 05/18/2020] [Indexed: 01/01/2023] Open
Abstract
KEY POINTS Epidural electrical stimulation (ES) of the spinal cord restores/improves locomotion in patients. ES-evoked locomotor movements differ to some extent from the normal ones. Operation of the locomotor network during ES is unknown. We compared the activity of individual spinal neurons during locomotion initiated by signals from the brainstem and by ES. We demonstrated that the spinal network generating locomotion under each of the two conditions is formed by the same neurons. A part of this network operates similarly under the two conditions, suggesting that it is essential for generation of locomotion under both conditions. Another part of this network operates differently under the two conditions, suggesting that it is responsible for differences in the movement kinematics observed under the two conditions. ABSTRACT Locomotion is a vital motor function for both animals and humans. Epidural electrical stimulation (ES) of the spinal cord is used to restore/improve locomotor movements in patients. However, operation of locomotor networks during ES has never been studied. Here we compared the activity of individual spinal neurons recorded in decerebrate cats of either sex during locomotion initiated by supraspinal commands (caused by stimulation of the mesencephalic locomotor region, MLR) and by ES. We found that under both conditions, the same neurons had modulation of their activity related to the locomotor rhythm, suggesting that the network generating locomotion under the two conditions is formed by the same neurons. About 40% of these neurons had stable modulation (i.e. small dispersion of their activity phase in sequential cycles), as well as a similar phase and shape of activity burst in MLR- and ES-evoked locomotor cycles. We suggest that these neurons form a part of the locomotor network that operates similarly under the two conditions, and are critical for generation of locomotion. About 23% of the modulated neurons had stable modulation only during MLR-evoked locomotion. We suggest that these neurons are responsible for some differences in kinematics of MLR- and ES-evoked locomotor movements. Finally, 25% of the modulated neurons had unstable modulation during both MLR- and ES-evoked locomotion. One can assume that these neurons contribute to maintenance of the excitability level of locomotor networks necessary for generation of stepping, or belong to postural networks, activated simultaneously with locomotor networks by both MLR stimulation and ES.
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Affiliation(s)
- Pavel E Musienko
- Institute of Translational Biomedicine, St. Petersburg State University, St. Petersburg, 199034, Russia
- Pavlov Institute of Physiology, St. Petersburg, 199034, Russia
| | - Vladimir F Lyalka
- Department of Neuroscience, Karolinska Institute, Stockholm, SE-17177, Sweden
| | - Oleg V Gorskii
- Pavlov Institute of Physiology, St. Petersburg, 199034, Russia
| | - Natalia Merkulyeva
- Institute of Translational Biomedicine, St. Petersburg State University, St. Petersburg, 199034, Russia
- Pavlov Institute of Physiology, St. Petersburg, 199034, Russia
| | | | - Tatiana G Deliagina
- Department of Neuroscience, Karolinska Institute, Stockholm, SE-17177, Sweden
| | - Pavel V Zelenin
- Department of Neuroscience, Karolinska Institute, Stockholm, SE-17177, Sweden
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9
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Majczyński H, Cabaj AM, Jordan LM, Sławińska U. Contribution of 5-HT 2 Receptors to the Control of the Spinal Locomotor System in Intact Rats. Front Neural Circuits 2020; 14:14. [PMID: 32425760 PMCID: PMC7212388 DOI: 10.3389/fncir.2020.00014] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2019] [Accepted: 03/24/2020] [Indexed: 11/13/2022] Open
Abstract
Applying serotonergic (5-HT) agonists or grafting of fetal serotonergic cells into the spinal cord improves locomotion after spinal cord injury. Little is known about the role of 5-HT receptors in the control of voluntary locomotion, so we administered inverse agonists of 5-HT2 (Cyproheptadine; Cypr), 5-HT2A neutral antagonist (Volinanserin; Volin), 5-HT2C neutral antagonist (SB 242084), and 5-HT2B/2C inverse agonist (SB 206553) receptors intrathecally in intact rats and monitored their effects on unrestrained locomotion. An intrathecal cannula was introduced at the low thoracic level and pushed caudally until the tip reached the L2/L3 or L5/L6 spinal segments. Locomotor performance was evaluated using EMG activity of hindlimb muscles during locomotion on a 2 m long runway. Motoneuron excitability was estimated using EMG recordings during dorsi- and plantar flexion at the ankle. Locomotion was dramatically impaired after the blockage of 5-HT2A receptors. The effect of Cypr was more pronounced than that of Volin since in the L5/L6 rats Cypr (but not Volin) induced significant alteration of the strength of interlimb coordination followed by total paralysis. These agents significantly decreased locomotor EMG amplitude and abolished or substantially decreased stretch reflexes. Blocking 5-HT2B/2C receptors had no effect either on locomotion or reflexes. We suggest that in intact rats serotonin controls timing and amplitude of muscle activity by acting on 5-HT2A receptors on both CPG interneurons and motoneurons, while 5-HT2B/2C receptors are not involved in control of the locomotor pattern in lumbar spinal cord.
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Affiliation(s)
- Henryk Majczyński
- Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland
| | - Anna M Cabaj
- Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland
| | - Larry M Jordan
- Department of Physiology and Pathophysiology, University of Manitoba, Winnipeg, MB, Canada
| | - Urszula Sławińska
- Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland
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10
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Serotonergic modulation of sacral dorsal root stimulation-induced locomotor output in newborn rat. Neuropharmacology 2019; 170:107815. [PMID: 31634501 DOI: 10.1016/j.neuropharm.2019.107815] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2019] [Revised: 10/14/2019] [Accepted: 10/15/2019] [Indexed: 12/22/2022]
Abstract
Descending neuromodulators from the brainstem play a major role in the development and regulation of spinal sensorimotor functions. Here, the contribution of serotonergic signaling in the lumbar spinal cord was investigated in the context of the generation of locomotor activity. Experiments were performed on in vitro spinal cord preparations from newborn rats (0-5 days). Rhythmic locomotor episodes (fictive locomotion) triggered by tonic electrical stimulations (2Hz, 30s) of a single sacral dorsal root were recorded from bilateral flexor-dominated (L2) and extensor-dominated (L5) ventral roots. We found that the activity pattern induced by sacral stimulation evolves over the 5 post-natal (P) day period. Although alternating rhythmic flexor-like motor bursts were expressed at all ages, the locomotor pattern of extensor-like bursting was progressively lost from P1 to P5. At later stages, serotonin (5-HT) and quipazine (5-HT2A receptor agonist) at concentrations sub-threshold for direct locomotor network activation promoted sacral stimulation-induced fictive locomotion. The 5-HT2A receptor antagonist ketanserin could reverse the agonist's action but was ineffective when fictive locomotion was already expressed in the absence of 5-HT (mainly before P2). Although inhibiting 5-HT7 receptors with SB266990 did not affect locomotor pattern organization, activating 5-HT1A receptors with 8-OH-DPAT specifically deteriorated extensor phase motor burst activity. We conclude that during the first 5 post-natal days in rat, serotonergic signaling in the lumbar cord becomes increasingly critical for the expression of fictive locomotion. Our findings therefore further underline the importance of both descending serotonergic and sensory afferent pathways in shaping locomotor activity during postnatal development. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.
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11
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V1 interneurons regulate the pattern and frequency of locomotor-like activity in the neonatal mouse spinal cord. PLoS Biol 2019; 17:e3000447. [PMID: 31513565 PMCID: PMC6759197 DOI: 10.1371/journal.pbio.3000447] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2018] [Revised: 09/24/2019] [Accepted: 08/20/2019] [Indexed: 11/28/2022] Open
Abstract
In the mouse spinal cord, V1 interneurons are a heterogeneous population of inhibitory spinal interneurons that have been implicated in regulating the frequency of the locomotor rhythm and in organizing flexor and extensor alternation. By introducing archaerhodopsin into engrailed-1-positive neurons, we demonstrate that the function of V1 neurons in locomotor-like activity is more complex than previously thought. In the whole cord, V1 hyperpolarization increased the rhythmic synaptic drive to flexor and extensor motoneurons, increased the spiking in each cycle, and slowed the locomotor-like rhythm. In the hemicord, V1 hyperpolarization accelerated the rhythm after an initial period of tonic activity, implying that a subset of V1 neurons are active in the hemicord, which was confirmed by calcium imaging. Hyperpolarizing V1 neurons resulted in an equalization of the duty cycle in flexor and extensors from an asymmetrical pattern in control recordings in which the extensor bursts were longer than the flexor bursts. Our results suggest that V1 interneurons are composed of several subsets with different functional roles. Furthermore, during V1 hyperpolarization, the default state of the locomotor central pattern generator (CPG) is symmetrical, with antagonist motoneurons each firing with an approximately 50% duty cycle. We hypothesize that one function of the V1 population is to set the burst durations of muscles to be appropriate to their biomechanical function and to adapt to the environmental demands, such as changes in locomotor speed. An optogenetic study in mice shows that inhibitory neurons that express engrailed-1 regulate the pattern and frequency of locomotor-like activity in the developing mouse spinal cord.
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12
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Gerasimenko Y, Preston C, Zhong H, Roy RR, Edgerton VR, Shah PK. Rostral lumbar segments are the key controllers of hindlimb locomotor rhythmicity in the adult spinal rat. J Neurophysiol 2019; 122:585-600. [PMID: 30943092 DOI: 10.1152/jn.00810.2018] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The precise location and functional organization of the spinal neuronal locomotor-related networks in adult mammals remain unclear. Our recent neurophysiological findings provided empirical evidence that the rostral lumbar spinal cord segments play a critical role in the initiation and generation of the rhythmic activation patterns necessary for hindlimb locomotion in adult spinal rats. Since added epidural stimulation at the S1 segments significantly enhanced the motor output generated by L2 stimulation, these data also suggested that the sacral spinal cord provides a strong facilitory influence in rhythm initiation and generation. However, whether L2 will initiate hindlimb locomotion in the absence of S1 segments, and whether S1 segments can facilitate locomotion in the absence of L2 segments remain unknown. Herein, adult rats received complete spinal cord transections at T8 and then at either L2 or S1. Rats with spinal cord transections at T8 and S1 remained capable of generating coordinated hindlimb locomotion when receiving epidural stimulation at L2 and when ensembles of locomotor related loadbearing input were present. In contrast, minimal locomotion was observed when S1 stimulation was delivered after spinal cord transections at T8 and L2. Results were similar when the nonspecific serotonergic agonists were administered. These results demonstrate in adult rats that rostral lumbar segments are essential for the regulation of hindlimb locomotor rhythmicity. In addition, the more caudal spinal networks alone cannot control locomotion in the absence of the rostral segments around L2 even when loadbearing rhythmic proprioceptive afferent input is imposed.NEW & NOTEWORTHY The exact location of the spinal neuronal locomotor-related networks in adult mammals remains unknown. The present data demonstrate that when the rostral lumbar spinal segments (~L2) are completely eliminated in thoracic spinal adult rats, hindlimb stepping is not possible with neurochemical modulation of the lumbosacral cord. In contrast, eliminating the sacral cord retains stepping ability. These observations highlight the importance of rostral lumbar segments in generating effective mammalian locomotion.
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Affiliation(s)
- Yury Gerasimenko
- Pavlov Institute of Physiology, Russian Academy of Sciences, St. Petersburg, Russia.,Department of Integrative Biology and Physiology, University of California, Los Angeles, California
| | - Chet Preston
- Department of Physical Therapy, School of Health Technology and Management, Stony Brook University, Stony Brook, New York
| | - Hui Zhong
- Department of Integrative Biology and Physiology, University of California, Los Angeles, California
| | - Roland R Roy
- Department of Integrative Biology and Physiology, University of California, Los Angeles, California
| | - V Reggie Edgerton
- Department of Integrative Biology and Physiology, University of California, Los Angeles, California.,Department of Neurobiology, David Geffen School of Medicine at University of California, Los Angeles, California.,Department of Neurosurgery, David Geffen School of Medicine at University of California, Los Angeles, California.,Brain Research Institute, University of California, Los Angeles, California.,Institute Guttmann. Hospital de Neurorehabilitació, Institut Universitari Adscrit a la Universitat Autònoma de Barcelona, Badalona, Spain.,Centre for Neuroscience and Regenerative Medicine, Faculty of Science, University of Technology Sydney, Ultimo, New South Wales, Australia.,Department of Neurology, David Geffen School of Medicine at University of California, Los Angeles, California
| | - Prithvi K Shah
- Department of Physical Therapy, School of Health Technology and Management, Stony Brook University, Stony Brook, New York.,Department of Neurobiology, Stony Brook University, Stony Brook, New York
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13
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Anglister L, Cherniak M, Lev-Tov A. Ascending pathways that mediate cholinergic modulation of lumbar motor activity. J Neurochem 2017; 142 Suppl 2:82-89. [PMID: 28791705 DOI: 10.1111/jnc.14065] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2017] [Revised: 05/01/2017] [Accepted: 05/03/2017] [Indexed: 01/10/2023]
Abstract
Deciphering neuronal pathways that reactivate spinal central pattern generators (CPGs) and modulate the activity of spinal motoneurons in mammals in the absence of supraspinal control is important for understanding of neural control of movement and for developing novel therapeutic approaches to improve the mobility of spinal cord injury patients. Previously, we showed that the sacral and lumbar cholinergic system could potently modulate the locomotor CPGs in newborn rodents. Here, we review these and our more recent studies of sacral relay neurons with lumbar projections to the locomotor CPGs and to lumbar motoneurons and demonstrate that sacral and lumbar cholinergic components have the capacity to control the frequency of the locomotor CPGs and at the same time the motor output of the activated lumbar motoneurons during motor behavior. A model describing the suggested ascending sacro-lumbar connectivity involved in modulation of the locomotor rhythm by sacral cholinergic components is proposed and discussed. This is an article for the special issue XVth International Symposium on Cholinergic Mechanisms.
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Affiliation(s)
- Lili Anglister
- Department of Medical Neurobiology, IMRIC, the Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Meir Cherniak
- Department of Medical Neurobiology, IMRIC, the Hebrew University-Hadassah Medical School, Jerusalem, Israel
| | - Aharon Lev-Tov
- Department of Medical Neurobiology, IMRIC, the Hebrew University-Hadassah Medical School, Jerusalem, Israel
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Shaping the Output of Lumbar Flexor Motoneurons by Sacral Neuronal Networks. J Neurosci 2016; 37:1294-1311. [PMID: 28025254 DOI: 10.1523/jneurosci.2213-16.2016] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2016] [Revised: 12/11/2016] [Accepted: 12/14/2016] [Indexed: 12/27/2022] Open
Abstract
The ability to improve motor function in spinal cord injury patients by reactivating spinal central pattern generators (CPGs) requires the elucidation of neurons and pathways involved in activation and modulation of spinal networks in accessible experimental models. Previously we reported on adrenoceptor-dependent sacral control of lumbar flexor motoneuron firing in newborn rats. The current work focuses on clarification of the circuitry and connectivity involved in this unique modulation and its potential use. Using surgical manipulations of the spinal gray and white matter, electrophysiological recordings, and confocal microscopy mapping, we found that methoxamine (METH) activation of sacral networks within the ventral aspect of S2 segments was sufficient to produce alternating rhythmic bursting (0.15-1 Hz) in lumbar flexor motoneurons. This lumbar rhythm depended on continuity of the ventral funiculus (VF) along the S2-L2 segments. Interrupting the VF abolished the rhythm and replaced it by slow unstable bursting. Calcium imaging of S1-S2 neurons, back-labeled via the VF, revealed that ∼40% responded to METH, mostly by rhythmic firing. All uncrossed projecting METH responders and ∼70% of crossed projecting METH responders fired with the concurrent ipsilateral motor output, while the rest (∼30%) fired with the contralateral motor output. We suggest that METH-activated sacral CPGs excite ventral clusters of sacral VF neurons to deliver the ascending drive required for direct rhythmic activation of lumbar flexor motoneurons. The capacity of noradrenergic-activated sacral CPGs to modulate the activity of lumbar networks via sacral VF neurons provides a novel way to recruit rostral lumbar motoneurons and modulate the output required to execute various motor behaviors. SIGNIFICANCE STATEMENT Spinal central pattern generators (CPGs) produce the rhythmic output required for coordinating stepping and stabilizing the body axis during movements. Electrical stimulation and exogenous drugs can reactivate the spinal CPGs and improve the motor function in the absence of descending supraspinal control. Since the body-stabilizing sacral networks can activate and modulate the limb-moving lumbar circuitry, it is important to clarify the functional organization of sacral and lumbar networks and their linking pathways. Here we decipher the ascending circuitry linking adrenoceptor-activated sacral CPGs and lumbar flexor motoneurons, thereby providing novel insights into mechanisms by which sacral circuitry recruits lumbar flexors, and enhances the motor output during lumbar afferent-induced locomotor rhythms. Moreover, our findings might help to improve drug/electrical stimulation-based therapy to accelerate locomotor-based rehabilitation.
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15
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Interactions between Dorsal and Ventral Root Stimulation on the Generation of Locomotor-Like Activity in the Neonatal Mouse Spinal Cord. eNeuro 2016; 3:eN-NWR-0101-16. [PMID: 27419215 PMCID: PMC4937207 DOI: 10.1523/eneuro.0101-16.2016] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2016] [Revised: 05/24/2016] [Accepted: 05/31/2016] [Indexed: 12/23/2022] Open
Abstract
We investigated whether dorsal (DR) and ventral root (VR) stimulus trains engage common postsynaptic components to activate the central pattern generator (CPG) for locomotion in the neonatal mouse spinal cord. VR stimulation did not activate the first order interneurons mediating the activation of the locomotor CPG by sacrocaudal afferent stimulation. Simultaneous stimulation of adjacent dorsal or ventral root pairs, subthreshold for evoking locomotor-like activity, did not summate to activate the CPG. This suggests that locomotor-like activity is triggered when a critical class of efferent or afferent axons is stimulated and does not depend on the number of stimulated axons or activated postsynaptic neurons. DR- and VR-evoked episodes exhibited differences in the coupling between VR pairs. In DR-evoked episodes, the coupling between the ipsilateral and contralateral flexor/extensor roots was similar and stronger than the bilateral extensor roots. In VR-evoked episodes, ipsilateral flexor/extensor coupling was stronger than both the contralateral flexor/extensor and the bilateral extensor coupling. For both types of stimulation, the coupling was greatest between the bilateral L1/L2 flexor-dominated roots. This indicates that the recruitment and/or the firing pattern of motoneurons differed in DR and VR-evoked episodes. However, the DR and VR trains do not appear to activate distinct CPGs because trains of DR and VR stimuli at frequencies too low to evoke locomotor-like activity did so when they were interleaved. These results indicate that the excitatory actions of VR stimulation converge onto the CPG through an unknown pathway that is not captured by current models of the locomotor CPG.
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16
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Abstract
Neural networks that can generate rhythmic motor output in the absence of sensory feedback, commonly called central pattern generators (CPGs), are involved in many vital functions such as locomotion or respiration. In certain circumstances, these neural networks must interact to produce coordinated motor behavior adapted to environmental constraints and to satisfy the basic needs of an organism. In this context, we recently reported the existence of an ascending excitatory influence from lumbar locomotor CPG circuitry to the medullary respiratory networks that is able to depolarize neurons of the parafacial respiratory group during fictive locomotion and to subsequently induce an increased respiratory rhythmicity (Le Gal et al., 2014b). Here, using an isolated in vitro brainstem-spinal cord preparation from neonatal rat in which the respiratory and the locomotor networks remain intact, we show that during fictive locomotion induced either pharmacologically or by sacrocaudal afferent stimulation, the activity of both thoracolumbar expiratory motoneurons and interneurons is rhythmically modulated with the locomotor activity. Completely absent in spinal inspiratory cells, this rhythmic pattern is highly correlated with the hindlimb ipsilateral flexor activities. Furthermore, silencing brainstem neural circuits by pharmacological manipulation revealed that this locomotor-related drive to expiratory motoneurons is solely dependent on propriospinal pathways. Together these data provide the first evidence in the newborn rat spinal cord for the existence of bimodal respiratory-locomotor motoneurons and interneurons onto which both central efferent expiratory and locomotor drives converge, presumably facilitating the coordination between the rhythmogenic networks responsible for two different motor functions. Significance statement: In freely moving animals, distant regions of the brain and spinal cord controlling distinct motor acts must interact to produce the best adapted behavioral response to environmental constraints. In this context, it is well established that locomotion and respiration must to be tightly coordinated to reduce muscular interferences and facilitate breathing rate acceleration during exercise. Here, using electrophysiological recordings in an isolated in vitro brainstem-spinal cord preparation from neonatal rat, we report that the locomotor-related signal produced by the lumbar central pattern generator for locomotion selectively modulates the intracellular activity of spinal respiratory neurons engaged in expiration. Our results thus contribute to our understanding of the cellular bases for coordinating the rhythmic neural circuitry responsible for different behaviors.
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Dingu N, Deumens R, Taccola G. Electrical Stimulation Able to Trigger Locomotor Spinal Circuits Also Induces Dorsal Horn Activity. Neuromodulation 2015; 19:38-46. [DOI: 10.1111/ner.12354] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Revised: 07/29/2015] [Accepted: 09/01/2015] [Indexed: 12/22/2022]
Affiliation(s)
- Nejada Dingu
- Neuroscience Department; International School for Advanced Studies (SISSA); Trieste Italy
- SPINAL (Spinal Person Injury Neurorehabilitation Applied Laboratory); Istituto di Medicina Fisica e Riabilitazione (IMFR); Udine Italy
| | - Ronald Deumens
- Institute of Neuroscience; Université catholique de Louvain (UCL); Brussels Belgium
| | - Giuliano Taccola
- Neuroscience Department; International School for Advanced Studies (SISSA); Trieste Italy
- SPINAL (Spinal Person Injury Neurorehabilitation Applied Laboratory); Istituto di Medicina Fisica e Riabilitazione (IMFR); Udine Italy
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18
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Abstract
Effective quadrupedal locomotor behaviors require the coordination of many muscles in the limbs, back, neck, and tail. Because of the spinal motoneuronal somatotopic organization, motor coordination implies interactions among distant spinal networks. Here, we investigated some of the interactions between the lumbar locomotor networks that control limb movements and the thoracic networks that control the axial muscles involved in trunk movement. For this purpose, we used an in vitro isolated newborn rat spinal cord (from T2 to sacrococcygeal) preparation. Using extracellular ventral root recordings, we showed that, while the thoracic cord possesses an intrinsic rhythmogenic capacity, the lumbar circuits, if they are rhythmically active, will entrain the rhythmicity of the thoracic circuitry. However, if the lumbar circuits are rhythmically active, these latter circuits will entrain the rhythmicity of the thoracic circuitry. Blocking the synaptic transmission in some thoracic areas revealed that the lumbar locomotor network could trigger locomotor bursting in distant thoracic segments through short and long propriospinal pathways. Patch-clamp recordings revealed that 72% of the thoracic motoneurons (locomotor-driven motoneurons) expressed membrane potential oscillations and spiking activity coordinated with the locomotor activity expressed by the lumbar cord. A biphasic excitatory (glutamatergic)/inhibitory (glycinergic) synaptic drive was recorded in thoracic locomotor-driven motoneurons. Finally, we found evidence that part of this locomotor drive involved a monosynaptic component coming directly from the lumbar locomotor network. We conclude that the lumbar locomotor network plays a central role in the generation of locomotor outputs in the thoracic cord by acting at both the premotoneuronal and motoneuronal levels.
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MacKenzie SJ, Yi JL, Singla A, Russell TM, Calancie B. Innervation and function of rat tail muscles for modeling cauda equina injury and repair. Muscle Nerve 2015; 52:94-102. [PMID: 25346299 DOI: 10.1002/mus.24498] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2013] [Revised: 09/26/2014] [Accepted: 10/17/2014] [Indexed: 12/23/2022]
Abstract
INTRODUCTION The rat tail exhibits functional impairment after cauda equina injury. Our goal was to better understand the innervation and roles of muscles that control the tail. METHODS Adult rats received either: (1) ventral root injury; (2) caudales nerve injury; or (3) mapping of sacrococcygeal myotomes. Activation of small muscles within the tail itself (intrinsics) was compared with that of larger lumbosacral muscles acting on the tail (extrinsics). Behavioral testing of tail movement was done 1 week later. RESULTS Rats that received ventral root injury exhibited multiple behavioral deficits, whereas rats with injury to caudales nerves maintained more fully preserved tail movement. Mapping studies revealed much broader overlap of myotomes for extrinsic muscles. CONCLUSIONS Extrinsic tail muscles play a greater role in tail movement in the rat than their intrinsic counterparts and are innervated by multiple neurological segments. These findings have major implications for future research on cauda equina injury.
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Affiliation(s)
- Samuel J MacKenzie
- Department of Neuroscience, Upstate Medical University, Syracuse, New York, USA
| | - Juneyoung L Yi
- Department of Neurosurgery, Institute for Human Performance, Upstate Medical University, 750 East Adams Street, Syracuse, New York, 13210, USA
| | - Amit Singla
- Department of Neurosurgery, Institute for Human Performance, Upstate Medical University, 750 East Adams Street, Syracuse, New York, 13210, USA
| | - Thomas M Russell
- Department of Neuroscience, Upstate Medical University, Syracuse, New York, USA
| | - Blair Calancie
- Department of Neurosurgery, Institute for Human Performance, Upstate Medical University, 750 East Adams Street, Syracuse, New York, 13210, USA
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20
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Cherniak M, Etlin A, Strauss I, Anglister L, Lev-Tov A. The sacral networks and neural pathways used to elicit lumbar motor rhythm in the rodent spinal cord. Front Neural Circuits 2014; 8:143. [PMID: 25520624 PMCID: PMC4253665 DOI: 10.3389/fncir.2014.00143] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2014] [Accepted: 11/11/2014] [Indexed: 01/17/2023] Open
Abstract
Identification of neural networks and pathways involved in activation and modulation of spinal central pattern generators (CPGs) in the absence of the descending control from the brain is important for further understanding of neural control of movement and for developing innovative therapeutic approaches to improve the mobility of spinal cord injury patients. Activation of the hindlimb innervating segments by sacrocaudal (SC) afferent input and by specific application of neurochemicals to the sacral networks is feasible in the isolated spinal cord preparation of the newborn rat. Here we review our recent studies of sacral relay neurons with lumbar projections and evaluate their role in linking the sacral and thoracolumbar (TL) networks during different motor behaviors. Our major findings show that: (1) heterogeneous groups of dorsal, intermediate and ventral sacral-neurons with ventral and lateral ascending funicular projections mediate the activation of the locomotor CPGs through sacral sensory input; and (2) rhythmic excitation of lumbar flexor motoneurons, produced by bath application of alpha-1 adrenoceptor agonists to the sacral segments is mediated exclusively by ventral clusters of sacral-neurons with lumbar projections through the ventral funiculus.
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Affiliation(s)
- Meir Cherniak
- Department of Medical Neurobiology, Institute for Medical Research-Israel-Canada, IMRIC, The Hebrew University Medical School Jerusalem, Israel
| | - Alex Etlin
- Department of Medical Neurobiology, Institute for Medical Research-Israel-Canada, IMRIC, The Hebrew University Medical School Jerusalem, Israel
| | - Ido Strauss
- Department of Medical Neurobiology, Institute for Medical Research-Israel-Canada, IMRIC, The Hebrew University Medical School Jerusalem, Israel
| | - Lili Anglister
- Department of Medical Neurobiology, Institute for Medical Research-Israel-Canada, IMRIC, The Hebrew University Medical School Jerusalem, Israel
| | - Aharon Lev-Tov
- Department of Medical Neurobiology, Institute for Medical Research-Israel-Canada, IMRIC, The Hebrew University Medical School Jerusalem, Israel
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21
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Etlin A, Finkel E, Cherniak M, Lev-Tov A, Anglister L. The motor output of hindlimb innervating segments of the spinal cord is modulated by cholinergic activation of rostrally projecting sacral relay neurons. J Mol Neurosci 2014; 53:517-24. [PMID: 24973872 DOI: 10.1007/s12031-014-0351-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2014] [Accepted: 06/05/2014] [Indexed: 10/25/2022]
Abstract
Cholinergic networks have been shown to be involved in generation and modulation of the locomotor rhythmic pattern produced by the mammalian central pattern generators. Here, we show that changes in the endogenous levels of acetylcholine in the sacral segments of the isolated spinal cord of the neonatal rat modulate the locomotor-related output produced by stimulation of sacrocaudal afferents in muscarinic receptor-dependent mechanisms. Cholinergic components we found on sacral relay neurons with lumbar projections through the ventral and lateral funiculi are suggested to mediate this ascending cholinergic modulation. Our findings, possible mechanisms accounting for them, and their potential implications are discussed.
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Affiliation(s)
- Alex Etlin
- Department of Medical Neurobiology, IMRIC, The Hebrew University Medical School, Jerusalem, 9112102, Israel
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22
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Finkel E, Etlin A, Cherniak M, Mor Y, Lev-Tov A, Anglister L. Neuroanatomical basis for cholinergic modulation of locomotor networks by sacral relay neurons with ascending lumbar projections. J Comp Neurol 2014; 522:3437-55. [DOI: 10.1002/cne.23613] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2013] [Revised: 04/10/2014] [Accepted: 04/14/2014] [Indexed: 12/28/2022]
Affiliation(s)
- Eran Finkel
- Department of Medical Neurobiology, IMRIC; Hebrew University-Hadassah Medical School; Jerusalem 91120 Israel
| | - Alex Etlin
- Department of Medical Neurobiology, IMRIC; Hebrew University-Hadassah Medical School; Jerusalem 91120 Israel
| | - Meir Cherniak
- Department of Medical Neurobiology, IMRIC; Hebrew University-Hadassah Medical School; Jerusalem 91120 Israel
| | - Yoav Mor
- Department of Medical Neurobiology, IMRIC; Hebrew University-Hadassah Medical School; Jerusalem 91120 Israel
| | - Aharon Lev-Tov
- Department of Medical Neurobiology, IMRIC; Hebrew University-Hadassah Medical School; Jerusalem 91120 Israel
| | - Lili Anglister
- Department of Medical Neurobiology, IMRIC; Hebrew University-Hadassah Medical School; Jerusalem 91120 Israel
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23
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Remote control of respiratory neural network by spinal locomotor generators. PLoS One 2014; 9:e89670. [PMID: 24586951 PMCID: PMC3930745 DOI: 10.1371/journal.pone.0089670] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2013] [Accepted: 01/21/2014] [Indexed: 12/03/2022] Open
Abstract
During exercise and locomotion, breathing rate rapidly increases to meet the suddenly enhanced oxygen demand. The extent to which direct central interactions between the spinal networks controlling locomotion and the brainstem networks controlling breathing are involved in this rhythm modulation remains unknown. Here, we show that in isolated neonatal rat brainstem-spinal cord preparations, the increase in respiratory rate observed during fictive locomotion is associated with an increase in the excitability of pre-inspiratory neurons of the parafacial respiratory group (pFRG/Pre-I). In addition, this locomotion-induced respiratory rhythm modulation is prevented both by bilateral lesion of the pFRG region and by blockade of neurokinin 1 receptors in the brainstem. Thus, our results assign pFRG/Pre-I neurons a new role as elements of a previously undescribed pathway involved in the functional interaction between respiratory and locomotor networks, an interaction that also involves a substance P-dependent modulating mechanism requiring the activation of neurokinin 1 receptors. This neurogenic mechanism may take an active part in the increased respiratory rhythmicity produced at the onset and during episodes of locomotion in mammals.
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24
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Mandadi S, Hong P, Tran MA, Bráz JM, Colarusso P, Basbaum AI, Whelan PJ. Identification of multisegmental nociceptive afferents that modulate locomotor circuits in the neonatal mouse spinal cord. J Comp Neurol 2014; 521:2870-87. [PMID: 23436436 DOI: 10.1002/cne.23321] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2012] [Revised: 02/08/2013] [Accepted: 02/11/2013] [Indexed: 11/06/2022]
Abstract
Compared to proprioceptive afferent collateral projections, less is known about the anatomical, neurochemical, and functional basis of nociceptive collateral projections modulating lumbar central pattern generators (CPG). Quick response times are critical to ensure rapid escape from aversive stimuli. Furthermore, sensitization of nociceptive afferent pathways can contribute to a pathological activation of motor circuits. We investigated the extent and role of collaterals of capsaicin-sensitive nociceptive sacrocaudal afferent (nSCA) nerves that directly ascend several spinal segments in Lissauer's tract and the dorsal column and regulate motor activity. Anterograde tracing demonstrated direct multisegmental projections of the sacral dorsal root 4 (S4) afferent collaterals in Lissauer's tract and in the dorsal column. Subsets of the traced S4 afferent collaterals expressed transient receptor potential vanilloid 1 (TRPV1), which transduces a nociceptive response to capsaicin. Electrophysiological data revealed that S4 dorsal root stimulation could evoke regular rhythmic bursting activity, and our data suggested that capsaicin-sensitive collaterals contribute to CPG activation across multiple segments. Capsaicin's effect on S4-evoked locomotor activity was potent until the lumbar 5 (L5) segments, and diminished in rostral segments. Using calcium imaging we found elevated calcium transients within Lissauer's tract and dorsal column at L5 segments when compared to the calcium transients only within the dorsal column at the lumbar 2 (L2) segments, which were desensitized by capsaicin. We conclude that lumbar locomotor networks in the neonatal mouse spinal cord are targets for modulation by direct multisegmental nSCA, subsets of which express TRPV1 in Lissauer's tract and the dorsal column. J. Comp. Neurol. 521:2870-2887, 2013. © 2013 Wiley Periodicals, Inc.
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Affiliation(s)
- Sravan Mandadi
- Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, T2N 4N1, Canada; Department of Physiology and Pharmacology, University of Calgary, Calgary, Alberta, T2N 4N1, Canada
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25
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Charrier V, Cabelguen JM. Fictive rhythmic motor patterns produced by the tail spinal cord in salamanders. Neuroscience 2013; 255:191-202. [PMID: 24161283 DOI: 10.1016/j.neuroscience.2013.10.020] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Revised: 09/11/2013] [Accepted: 10/10/2013] [Indexed: 11/18/2022]
Abstract
Most investigations into the role of the body axis in vertebrate locomotion have focused on the trunk, although in most tetrapods, the tail also plays an active role. In salamanders, the tail contributes to propulsion during swimming and to dynamic balance and maneuverability during terrestrial locomotion. The aim of the present study was to obtain information concerning the neural mechanisms that produce tail muscle contractions during locomotion in the salamander Pleurodeles waltlii. We recorded the ventral root activities in in vitro spinal cord preparations in which locomotor-like activity was induced via bath application of N-methyl-d-aspartate (20μM) and d-serine (10μM). Recordings showed that the tail spinal cord is capable of producing propagated waves of motor activity that alternate between the left and right sides. Lesion experiments further revealed that the tail rhythmogenic network is composed of a double chain of identical hemisegmental oscillators. Finally, using spinal cord preparations bathed in a chamber partitioned into two pools, we revealed efficient short-distance coupling between the trunk and tail networks. Together, our results demonstrate the existence of a pattern generator for rhythmic tail movements in the salamander and show that the global architecture of the tail network is similar to that previously proposed for the mid-trunk locomotor network in the salamander. Our findings further support the view that salamanders can control their trunk and tail independently during stepping movements. The relevance of our results in relation to the generation of tail muscle contractions in freely moving salamanders is discussed.
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Affiliation(s)
- V Charrier
- Neurocentre Magendie, INSERM U 862 - Université de Bordeaux, 146 rue Léo Saignat, F-33077 Bordeaux Cedex, France.
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26
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Changes in the spinal segmental motor output for stepping during development from infant to adult. J Neurosci 2013; 33:3025-36a. [PMID: 23407959 DOI: 10.1523/jneurosci.2722-12.2013] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Human stepping movements emerge in utero and show several milestones during development to independent walking. Recently, imaging has become an essential tool for investigating the development and function of pattern generation networks in the spinal cord. Here we examine the development of the spinal segmental output by mapping the distribution of motoneuron activity in the lumbosacral spinal cord during stepping in newborns, toddlers, preschoolers, and adults. Newborn stepping is characterized by an alternating bilateral motor output with only two major components that are active at all lumbosacral levels of the spinal cord. This feature was similar across different cycle durations of neonate stepping. The alternating spinal motor output is consistent with a simpler organization of neuronal networks in neonates. Furthermore, a remarkable feature of newborn stepping is a higher overall activation of lumbar versus sacral segments, consistent with a rostrocaudal excitability gradient. In toddlers, the stance-related motor pool activity migrates to the sacral cord segments, while the lumbar motoneurons are separately activated at touchdown. In the adult, the lumbar and sacral patterns become more dissociated with shorter activation times. We conclude that the development of human locomotion from the neonate to the adult starts from a rostrocaudal excitability gradient and involves a gradual functional reorganization of the pattern generation circuitry.
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27
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Characterization of sacral interneurons that mediate activation of locomotor pattern generators by sacrocaudal afferent input. J Neurosci 2013; 33:734-47. [PMID: 23303951 DOI: 10.1523/jneurosci.4390-12.2013] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Identification of the neural pathways involved in retraining the spinal central pattern generators (CPGs) by afferent input in the absence of descending supraspinal control is feasible in isolated rodent spinal cords where the locomotor CPGs are potently activated by sacrocaudal afferent (SCA) input. Here we study the involvement of sacral neurons projecting rostrally through the ventral funiculi (VF) in activation of the CPGs by sensory stimulation. Fluorescent labeling and immunostaining showed that VF neurons are innervated by primary afferents immunoreactive for vesicular glutamate transporters 1 and 2 and by intraspinal neurons. Calcium imaging revealed that 55% of the VF neurons were activated by SCA stimulation. The activity of VF neurons and the sacral and lumbar CPGs was abolished when non-NMDA receptors in the sacral segments were blocked by the antagonist CNQX. When sacral NMDA receptors were blocked by APV, the sacral CPGs were suppressed, VF neurons with nonrhythmic activity were recruited and a moderate-drive locomotor rhythm developed during SCA stimulation. In contrast, when the sacral CPGs were activated by SCA stimulation, rhythmic and nonrhythmic VF neurons were recruited and the locomotor rhythm was most powerful. The activity of 73 and 27% of the rhythmic VF neurons was in-phase with the ipsilateral and contralateral motor output, respectively. Collectively, our studies indicate that sacral VF neurons serve as a major link between SCA and the hindlimb CPGs and that the ability of SCA to induce stepping can be enhanced by the sacral CPGs. The nature of the ascending drive to lumbar CPGs, the identity of subpopulations of VF neurons, and their potential role in activating the locomotor rhythm are discussed.
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28
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Dose F, Taccola G. Coapplication of noisy patterned electrical stimuli and NMDA plus serotonin facilitates fictive locomotion in the rat spinal cord. J Neurophysiol 2012; 108:2977-90. [DOI: 10.1152/jn.00554.2012] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
A new stimulating protocol [fictive locomotion-induced stimulation (FL istim)], consisting of intrinsically variable weak waveforms applied to a single dorsal root is very effective (though not optimal as it eventually wanes away) in activating the locomotor program of the isolated rat spinal cord. The present study explored whether combination of FL istim with low doses of pharmacological agents that raise network excitability might further improve the functional outcome, using this in vitro model. FL istim was applied together with N-methyl-d-aspartate (NMDA) + serotonin, while fictive locomotion (FL) was electrophysiologically recorded from lumbar ventral roots. Superimposing FL istim on FL evoked by these neurochemicals persistently accelerated locomotor-like cycles to a set periodicity and modulated cycle amplitude depending on FL istim rate. Trains of stereotyped rectangular pulses failed to replicate this phenomenon. The GABAB agonist baclofen dose dependently inhibited, in a reversible fashion, FL evoked by either FL istim or square pulses. Sustained episodes of FL emerged when FL istim was delivered, at an intensity subthreshold for FL, in conjunction with subthreshold pharmacological stimulation. Such an effect was, however, not found when high potassium solution instead of NMDA + serotonin was used. These results suggest that the combined action of subthreshold FL istim (e.g., via epidural stimulation) and neurochemicals should be tested in vivo to improve locomotor rehabilitation after injury. In fact, reactivation of spinal locomotor circuits by conventional electrical stimulation of afferent fibers is difficult, while pharmacological activation of spinal networks is clinically impracticable due to concurrent unwanted effects. We speculate that associating subthreshold chemical and electrical inputs might decrease side effects when attempting to evoke human locomotor patterns.
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Affiliation(s)
- Francesco Dose
- Neuroscience Area International School for Advanced Studies, Trieste, Italy; and
- Spinal Person Injury Neurorehabilitation Applied Laboratory, Istituto di Medicina Fisica e Riabilitazione, Udine, Italy
| | - Giuliano Taccola
- Neuroscience Area International School for Advanced Studies, Trieste, Italy; and
- Spinal Person Injury Neurorehabilitation Applied Laboratory, Istituto di Medicina Fisica e Riabilitazione, Udine, Italy
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Hochman S, Gozal EA, Hayes HB, Anderson JT, DeWeerth SP, Chang YH. Enabling techniques for in vitro studies on mammalian spinal locomotor mechanisms. Front Biosci (Landmark Ed) 2012; 17:2158-80. [PMID: 22652770 DOI: 10.2741/4043] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The neonatal rodent spinal cord maintained in vitro is a powerful model system to understand the central properties of spinal circuits generating mammalian locomotion. We describe three enabling approaches that incorporate afferent input and attached hindlimbs. (i) Sacral dorsal column stimulation recruits and strengthens ongoing locomotor-like activity, and implementation of a closed positive-feedback paradigm is shown to support its stimulation as an untapped therapeutic site for locomotor modulation. (ii) The spinal cord hindlimbs-restrained preparation allows suction electrode electromyographic recordings from many muscles. Inducible complex motor patterns resemble natural locomotion, and insights into circuit organization are demonstrated during spontaneous motor burst 'deletions', or following sensory stimuli such as tail and paw pinch. (iii) The spinal cord hindlimbs-pendant preparation produces unrestrained hindlimb stepping. It incorporates mechanical limb perturbations, kinematic analyses, ground reaction force monitoring, and the use of treadmills to study spinal circuit operation with movement-related patterns of sensory feedback while providing for stable whole-cell recordings from spinal neurons. Such techniques promise to provide important additional insights into locomotor circuit organization.
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Affiliation(s)
- Shawn Hochman
- Department of Physiology, Emory University School of Medicine, Atlanta, Georgia, USA.
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30
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Anesthetic effects on fictive locomotion in the rat isolated spinal cord. Neuroreport 2011; 22:655-9. [PMID: 21817927 DOI: 10.1097/wnr.0b013e32834a20f2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
General anesthetic mechanisms are poorly understood. Anesthetic immobilizing effects occur in the spinal ventral horn. However, a detailed analysis of anesthetic effects on ventral motor networks is lacking. We delivered isoflurane, desflurane, or propofol during NMDA/5-HT-induced, or noxious tail stimulus-evoked, fictive locomotion in neonatal rat isolated spinal cords. Anesthetics changed the frequency, amplitude, and regularity of fictive locomotion with little effect on phase-lag. Isoflurane abolished pharmacologically-induced versus noxious stimulus-induced motor output at similar concentrations. Propofol abolished pharmacologically-induced fictive locomotion through a γ-aminobutyric acid type A-receptor mechanism. Anesthetic effects on pharmacologically-elicted fictive locomotion appear clinically-relevant, and support a ventral horn immobilizing effect on locomotor rhythm generation.
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Talpalar A, Endo T, Löw P, Borgius L, Hägglund M, Dougherty K, Ryge J, Hnasko T, Kiehn O. Identification of Minimal Neuronal Networks Involved in Flexor-Extensor Alternation in the Mammalian Spinal Cord. Neuron 2011; 71:1071-84. [DOI: 10.1016/j.neuron.2011.07.011] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/08/2011] [Indexed: 11/28/2022]
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Long and short multifunicular projections of sacral neurons are activated by sensory input to produce locomotor activity in the absence of supraspinal control. J Neurosci 2010; 30:10324-36. [PMID: 20685976 DOI: 10.1523/jneurosci.1208-10.2010] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Afferent input from load and joint receptors has been shown to reactivate the central pattern generators for locomotion (CPGs) in spinal cord injury patients and thereby improve their motor function and mobility. Elucidation of the pathways interposed between the afferents and CPGs is critical for the determination of the capacity of sensory input to activate the CPGs when the continuity of the white matter tracts is impaired following spinal cord injury. Using electrophysiological recordings, confocal imaging studies of spinal neurons and surgical manipulations of the white matter, we show that the capacity of sacrocaudal afferent (SCA) input to produce locomotor activity in isolated rat spinal cords depends not only on long ascending pathways, but also on recruitment of sacral proprioneurons interposed between the second order neurons and the hindlimb CPGs. We argue that large heterogeneous populations of second-order and proprioneurons whose crossed and uncrossed axons project rostrally through the ventral, ventrolateral/lateral and dorsolateral white matter funiculi contribute to the generation of the rhythm by the stimulated sacrocaudal input. The complex organization and multiple projection patterns of these populations enable the sacrocaudal afferent input to activate the CPGs even if the white matter pathways are severely damaged. Further studies are required to clarify the mechanisms involved in SCA-induced locomotor activity and assess its potential use for the rescue of lost motor functions after spinal cord injury.
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Lev-Tov A, Etlin A, Blivis D. Sensory-induced activation of pattern generators in the absence of supraspinal control. Ann N Y Acad Sci 2010; 1198:54-62. [PMID: 20536920 DOI: 10.1111/j.1749-6632.2009.05424.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Sacrocaudal afferent (SCA) stimulation is used in this work to study neural pathways involved in sensory-activation of central pattern generators (CPGs) in the isolated spinal cord of the neonatal rat. Surgical manipulations of the white matter funiculi and confocal imaging of back-labeled funicular pathways suggest that the CPGs are activated during SCA stimulation by crossed and uncrossed multifunicular projections of sacral neurons and that activation of short projecting proprioneurons is sufficient for the generation of the rhythm by SCA stimulation. The versatile organization of the pathways involved in the SCA-induced rhythm makes it a potent and durable activator of the CPGs in the absence of descending control from the brain. The significance of our findings and their potential clinical use are discussed.
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Affiliation(s)
- A Lev-Tov
- Department of Medical Neurobiology, IMRIC, The Hebrew University Medical School, Jerusalem, Israel.
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Ziskind-Conhaim L, Mentis GZ, Wiesner EP, Titus DJ. Synaptic integration of rhythmogenic neurons in the locomotor circuitry: the case of Hb9 interneurons. Ann N Y Acad Sci 2010; 1198:72-84. [PMID: 20536922 DOI: 10.1111/j.1749-6632.2010.05533.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Innovative molecular and genetic techniques have recently led to the identification of genetically defined populations of ipsilaterally projecting excitatory interneurons with probable functions in the rhythm-generating kernel of the central pattern generators (CPGs). The role of interneuronal populations in specific motor function is determined by their synaptic inputs, intrinsic properties, and target neurons. In this review we examine whether Hb9-expressing interneurons (Hb9 INs) fulfill a set of criteria that are the hallmarks of rhythm generators in the locomotor circuitry. Induced locomotor-like activity in this distinct population of ventral interneurons is in phase with bursts of motor activity, raising the possibility that they are part of the locomotor generator. To increase our understanding of the integrative function of Hb9 INs in the locomotor CPG, we investigated the cellular mechanisms underlying their rhythmic activity and examined the properties of synaptic inputs from low-threshold afferents and possible synaptic contacts with segmental motoneurons. Our findings suggest that the rhythmogenic Hb9 INs are integral components of the sensorimotor circuitry that regulate locomotor-like activity in the spinal cord.
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Affiliation(s)
- Lea Ziskind-Conhaim
- Department of Physiology and Center for Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA.
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35
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Hinckley CA, Wiesner EP, Mentis GZ, Titus DJ, Ziskind-Conhaim L. Sensory modulation of locomotor-like membrane oscillations in Hb9-expressing interneurons. J Neurophysiol 2010; 103:3407-23. [PMID: 20393069 DOI: 10.1152/jn.00996.2009] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The central pattern generator can generate locomotor-like rhythmic activity in the spinal cord in the absence of descending and peripheral inputs, but the motor pattern is regulated by feedback from peripheral sensory inputs that adjust motor outputs to external stimuli. To elucidate the possible role of Hb9-expressing interneurons (Hb9 INs) in the locomotor circuitry, we investigated whether their induced oscillatory activity is modulated by low-threshold afferents in the isolated spinal cords of neonatal Hb9:eGFP transgenic mice. Low-intensity stimulation of segmental afferents generated short-latency, monosynaptic excitatory responses in 62% of Hb9 INs. These were associated with longer-latency (approximately 13 ms) excitatory postsynaptic currents that were evoked in all Hb9 INs, probably by slow conducting afferents that synapse directly onto them. Concomitant morphological analysis confirmed that afferent axons with immunoreactive expression of vesicular glutamate transporter-1 and parvalbumin, presumably from primary afferents, contacted somata and dendrites of all Hb9 INs. Most of the putative synaptic contacts were on distal dendrites that extended to an area with profuse afferent projections. We next examined whether low-threshold afferents in upper (flexor-related) and lower (extensor-related) lumbar segments altered the timing of neurochemically induced locomotor-like rhythms in Hb9 INs and motoneurons. Excitation of flexor-related afferents during the flexor phase delayed the onset of subsequent cycles in both Hb9 INs and segmental motoneurons while maintaining the phase relationship between them. The in-phase correlation between voltage oscillations in Hb9 INs and motor bursts also persisted during the two- to threefold increase in cycle period triggered by extensor-related afferents. Our findings that low-threshold, presumably muscle afferents, synapse directly onto these interneurons and perturb their induced locomotor-like membrane oscillations in a pattern that remains phase-locked with motor bursts support the hypothesis that Hb9 INs are part of the sensorimotor circuitry that regulates the pattern of locomotor rhythms in the isolated cord.
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Affiliation(s)
- Christopher A Hinckley
- Department of Physiology, University of Wisconsin School of Medicine, 1300 University Avenue, Madison, WI 53706, USA
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36
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Klein DA, Patino A, Tresch MC. Flexibility of motor pattern generation across stimulation conditions by the neonatal rat spinal cord. J Neurophysiol 2010; 103:1580-90. [PMID: 20089814 DOI: 10.1152/jn.00961.2009] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Previous studies have demonstrated that "locomotor-like" rhythmic patterns can be evoked in the isolated neonatal rat spinal cord by several means, including pharmacological neuromodulation and electrical stimulation of various pathways. Recent studies have used stimulation of afferent pathways to evoke rhythmic patterns, relying on synaptic activation of interneuronal systems rather than global imposition of neuromodulatory state by pharmacological agents. We use the in vitro neonatal rat spinal cord with attached hindlimb to examine the muscle activation patterns evoked by stimulation of these different pathways and evaluate whether stimulation of these pathways all evoke the same patterns. We find that the patterns evoked by bath application of serotonin (5-HT) and N-methyl-D-aspartic acid (NMDA) consisted of alternation between hip flexors and extensors and similar alternation was observed in the patterns evoked by electrical stimulation of the cauda equina (CE) or contralateral fifth lumbar (L(5)) dorsal nerve root. In contrast, the knee extensor/hip flexor rectus femoris (RF) and knee flexor/hip extensor semitendinosus (ST) were activated differentially across stimulation conditions. In 5-HT/NMDA patterns, RF was active in late flexion and ST in late extension. In CE patterns, these two muscles switched places with RF typically active in late extension and ST active in flexion. In L(5) patterns, ST was activated in extension and RF was silent or weakly active during flexion. There were also systematic differences in the consistency of rhythms evoked by each stimulation method: patterns evoked by electrical stimulation of CE or L(5) were less consistently modulated with the rhythm when compared with 5-HT/NMDA-evoked patterns. All differences were preserved following deafferentation, demonstrating that they reflect intrinsic properties of spinal systems. These results highlight the intrinsic flexibility of motor pattern generation by spinal motor circuitry which is present from birth and provides important information to many studies examining spinal pattern generating networks.
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Affiliation(s)
- David A Klein
- Department of Biomedical Engineering, Northwestern University, Chicago, Illinois, USA
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37
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Dunbar MJ, Tran MA, Whelan PJ. Endogenous extracellular serotonin modulates the spinal locomotor network of the neonatal mouse. J Physiol 2009; 588:139-56. [PMID: 19884315 DOI: 10.1113/jphysiol.2009.177378] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Serotonin (5-HT) can potently activate and modulate spinal locomotor circuits in a variety of species. Many of these findings have been obtained by applying serotonin exogenously to the isolated spinal cord of in vitro preparations, which has the drawback of indiscriminately activating extrasynaptic receptors and neurons. To investigate the role of endogenously released serotonin in modulating locomotor networks, the selective serotonin reuptake inhibitor citalopram was used. Fictive locomotion was elicited by either electrical stimulation of the brainstem or the sacral 4 (S4) dorsal root. The addition of 20 microm of citalopram caudal to thoracic segment 5 (T5) had an overall inhibitory effect on the lumbar central pattern generator (CPG). Left-right and flexor-extensor coupling were significantly decreased, and there was also a phase shift in the flexor-extensor relationship. In addition, there was a significant decrease in burst amplitude. These effects were observed during both afferent and brainstem evoked fictive locomotion. When citalopram was added in the presence of 5-HT(1A) and 5-HT(1B) antagonists, the inhibitory effects were largely reversed. The remaining excitatory effects were mediated by 5-HT(7) and 5-HT(2) receptors. These results suggest that endogenous 5-HT release can modulate locomotor-like activity early in neonatal development.
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Affiliation(s)
- Mary J Dunbar
- Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada T2N 4N1
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38
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Abstract
Hb9 interneurons (Hb9 INs) are putative components of the mouse spinal locomotor central pattern generator (CPG) and candidates for the rhythm-generating kernel. Studies in slices and hemisected spinal cords showed that Hb9 INs display TTX-resistant membrane potential oscillations, suggesting a role in rhythm generation. To further investigate the roles of Hb9 INs in the locomotor CPG, we used two-photon calcium imaging in the in vitro isolated whole neonatal mouse spinal cord preparation to record the activity of Hb9 INs, which were subsequently stained for unambiguous genetic identification. We elicited fictive locomotion by transmitter application or by electrically stimulating the caudal tip of the spinal cord. Although most Hb9 INs were rhythmically active during fictive locomotion, their activity was sparse and they failed to fire with each cycle of the episode. If Hb9 INs are the principal pacemakers of the CPG in the hemisegment in which they are located, they should direct the firing of motor neurons, with their activity preceding that of their ipsilateral segmental ventral roots. Instead, during each locomotor cycle, onset of Hb9 IN activity lagged behind the onset of the ipsilateral ventral root burst by a mean phase of 0.21 during electrical stimulation and 0.28 during transmitter application. Whole-cell recordings in intact and hemisected spinal cords confirmed the imaging results. Our data suggest that Hb9 INs participate in fictive locomotion, but the delayed onset of activity relative to ipsilateral motoneurons suggests that Hb9 INs are unlikely to be the sole intrasegmental rhythm-generating kernel of the CPG.
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Mandadi S, Nakanishi ST, Takashima Y, Dhaka A, Patapoutian A, McKemy DD, Whelan PJ. Locomotor networks are targets of modulation by sensory transient receptor potential vanilloid 1 and transient receptor potential melastatin 8 channels. Neuroscience 2009; 162:1377-97. [PMID: 19482068 DOI: 10.1016/j.neuroscience.2009.05.063] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2009] [Revised: 05/22/2009] [Accepted: 05/23/2009] [Indexed: 01/17/2023]
Abstract
It is well recognized that proprioceptive afferent inputs can control the timing and pattern of locomotion. C and Adelta afferents can also affect locomotion but an unresolved issue is the identity of the subsets of these afferents that encode defined modalities. Over the last decade, the transient receptor potential (TRP) ion channels have emerged as a family of non-selective cation conductances that can label specific subsets of afferents. We focus on a class of TRPs known as ThermoTRPs which are well known to be sensor receptors that transduce changes in heat and cold. ThermoTRPs are known to help encode somatosensation and painful stimuli, and receptors have been found on C and Adelta afferents with central projections onto dorsal horn laminae. Here we show, using in vitro neonatal mouse spinal cord preparations, that activation of both spinal and peripheral transient receptor potential vanilloid 1 (TRPV1) and transient receptor potential melastatin 8 (TRPM8) afferent terminals modulates central pattern generators (CPGs). Capsaicin or menthol and cooling modulated both sacrocaudal afferent (SCA) evoked and monoaminergic drug-induced rhythmic locomotor-like activity in spinal cords from wild type but not TRPV1-null (trpv1(-/-)) or TRPM8-null (trpm8(-/-)) mice, respectively. Capsaicin induced an initial increase in excitability of the lumbar motor networks, while menthol or cooling caused a decrease in excitability. Capsaicin and menthol actions on CPGs involved excitatory and inhibitory glutamatergic mechanisms, respectively. These results for the first time show that dedicated pathways of somatosensation and pain identified by TRPV1 or TRPM8 can target spinal locomotor CPGs.
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Affiliation(s)
- S Mandadi
- Hotchkiss Brain Institute, 3330 Hospital Drive Northwest, Calgary, AB, T2N 4N1 Canada
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40
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Cowley KC, Zaporozhets E, Joundi RA, Schmidt BJ. Contribution of Commissural Projections to Bulbospinal Activation of Locomotion in the In Vitro Neonatal Rat Spinal Cord. J Neurophysiol 2009; 101:1171-8. [DOI: 10.1152/jn.91212.2008] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Commissural projections are required for left-right coordination during locomotion. However, their role, if any, in rhythm production is unknown. This study uses the neonatal rat in vitro brain stem–spinal cord model to examine the rostrocaudal distribution of locomotor-related commissural projections and study whether commissural connections are needed for the generation of hindlimb rhythmic activity in response to electrical stimulation of the brain stem. Midsagittal lesions were made at a wide range of rostrocaudal levels. Locomotor-like activity persisted in some preparations despite midsagittal lesions extending from C1 to the mid-L1 level or from the conus medullaris to the T12/13 junction. In some preparations, midsagittal lesions throughout the entire spinal cord had no effect on locomotor-like activity if two or three contiguous segments remained intact. Those bridging segments had to include the T13 and/or L1 levels. These observations suggested that commissural projections in the thoracolumbar junction region were critical. However, locomotor-like activity was also elicited in preparations with limited midsagittal lesions focused on the thoracolumbar junction (T12 through L1 or L2 inclusive). In other experiments, locomotor-like activity was evoked by bath-applied 5-hydroxytryptamine (5-HT) and N-methyl-d-aspartate (NMDA). Appropriate side-to-side coordination was observed, even when only one segment remained bilaterally intact. Commissural projections traversing the thoracolumbar junction region were most effective. In combination, these results suggest that locomotor-related commissural projections are redundantly distributed along a bi-directional gradient that centers on the thoracolumbar junction. This commissural system not only provides a robust left-right coordinating mechanism but also supports locomotor rhythm generation in response to brain stem stimulation.
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41
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Anglister L, Etlin A, Finkel E, Durrant A, Lev-Tov A. Cholinesterases in development and disease. Chem Biol Interact 2008; 175:92-100. [DOI: 10.1016/j.cbi.2008.04.046] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2007] [Revised: 04/22/2008] [Accepted: 04/23/2008] [Indexed: 01/30/2023]
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42
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Gordon IT, Dunbar MJ, Vanneste KJ, Whelan PJ. Interaction between developing spinal locomotor networks in the neonatal mouse. J Neurophysiol 2008; 100:117-28. [PMID: 18436636 DOI: 10.1152/jn.00829.2007] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
At birth, thoracosacral spinal cord networks in mouse can produce a coordinated locomotor-like pattern. In contrast, less is known about the cervicothoracic networks that generate forelimb locomotion. Here we show that cervical networks can produce coordinated rhythmic patterns in the brain stem-spinal cord preparation of the mouse. Segmentally the C5 and C8 neurograms were each found to be alternating left-right, and the ipsilateral C5 and C8 neurograms also alternated. Collectively these patterns were suggestive of locomotor-like activity. This pattern was not dependent on the presence of thoracosacral segments because they could be evoked following a complete transection of the spinal cord at T5. We next demonstrated that activation of thoracosacral networks either pharmacologically or by stimulation of sacrocaudal afferents could produce rhythmic activity within the C5 and C8 neurograms. On the other hand, pharmacological activation of cervical networks did not evoke alternating cervical rhythmic activity either in isolated cervicothoracic or -sacral preparations. Under these conditions, we found that activation of cervicothoracic networks could alter the timing of thoracosacral locomotor-like patterns. When thoracosacral networks were not activated pharmacologically but received rhythmic drive from cervicothoracic networks, a pattern of slow bursts with superimposed fast synchronous oscillations became the dominant lumbar neurogram pattern. Our data suggest that in neonatal mice the cervical CPG is capable of producing coordinated rhythmic patterns in the absence of input from lumbar segments, but caudorostral drive contributes to cervical patterns and rhythm stability.
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Affiliation(s)
- Ian T Gordon
- Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada
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43
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Ivanenko YP, Poppele RE, Lacquaniti F. Distributed neural networks for controlling human locomotion: lessons from normal and SCI subjects. Brain Res Bull 2008; 78:13-21. [PMID: 19070781 DOI: 10.1016/j.brainresbull.2008.03.018] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2007] [Revised: 03/02/2008] [Accepted: 03/25/2008] [Indexed: 10/22/2022]
Abstract
The control of human locomotion engages various brain structures and numerous muscles. Even though the hypothetical central pattern generator (CPG) and sensory feedback can sustain the basic locomotor rhythm, the resultant motor output is highly adaptable and context-dependent. Indeed, while the temporal architecture of the locomotor output (basic EMG components) is relatively conserved across subjects and conditions, the spatial architecture (muscle activations) shows considerable non-linear changes with walking speed, level of body unloading or the direction of progression. Even so, leg kinematics are remarkably similar in all cases. Spinal cord injured (SCI) patients may learn new motor patterns with training rather than re-activate normal motor patterns, and such locomotor improvements may not transfer to untrained tasks. Redundancy in the neuromuscular system or malfunctioning of injured 'elements' may often result in motor equivalent compensatory solutions. Injured pathways can partially recover while uninjured pathways can augment or modify their activity. As a result, the reconstructed spatiotemporal maps of motor neuron activity in SCI patients might be quite different from those of healthy subjects but they nevertheless achieve nearly normal foot kinematics. Kinematics training may thus provide a more successful rehabilitation than training based on reconstructing normal muscle activation patterns. Taken together, recent data support the idea of plasticity and distributed networks for controlling human locomotion. A new generation of robotic devices takes advantage of this by providing the opportunity for patients to generate and correct limb movements rather than just adapting muscle activation to the fixed kinematic template imposed by a gait orthosis.
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Affiliation(s)
- Y P Ivanenko
- Department of Neuromotor Physiology, IRCCS Fondazione Santa Lucia, Rome, Italy.
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44
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Gordon IT, Whelan PJ. Brainstem modulation of locomotion in the neonatal mouse spinal cord. J Physiol 2008; 586:2487-97. [PMID: 18372309 DOI: 10.1113/jphysiol.2007.148320] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
During development, descending projections to the spinal cord are immature. Available data suggest that even though these projections are not fully formed, they contribute to activation of spinal circuitry and promote development of network function. Here we examine the modulation of sacrocaudal afferent-evoked locomotor activity by descending pathways. We first examined the effects of brainstem transection on the afferent evoked locomotor-like rhythm using an isolated brainstem-spinal cord preparation of the mouse. Transection increased the frequency and stability of the locomotor-like rhythm while the phase remained unchanged. We then made histologically verified lesions of the ventrolateral funiculus and observed similar effects on the stability and frequency of the locomotor rhythm. We next tested whether these effects were due to downstream effects of the transection. A split-bath was constructed between the brainstem and spinal cord. Neural activity was suppressed in the brainstem compartment using cooled high sucrose solutions. This manipulation led to a reversible change in frequency and stability that mirrored our findings using lesion approaches. Our findings suggest that spontaneous brainstem activity contributes to the ongoing modulation of afferent-evoked locomotor patterns during early postnatal development. Our work suggests that some of the essential circuits necessary to modulate and control locomotion are at least partly functional before the onset of weight-bearing locomotion.
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Affiliation(s)
- Ian T Gordon
- Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada
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45
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Abstract
A network of spinal neurons known as central pattern generator (CPG) produces the rhythmic motor patterns required for coordinated swimming, walking, and running in mammals. Because the output of this network varies with time, its analysis cannot be performed by statistical methods that assume data stationarity. The present work uses short-time Fourier (STFT) and wavelet-transform (WT) algorithms to analyze the nonstationary rhythmic signals produced in isolated spinal cords of neonatal rats during activation of the CPGs. The STFT algorithm divides the time series into consecutive overlapping or nonoverlapping windows and repeatedly applies the Fourier transform across the signal. The WT algorithm decomposes the signal using a family of wavelets varying in scale, resulting in a set of wavelet coefficients presented onto a continuous frequency range over time. Our studies revealed that a Morlet WT algorithm was the tool of choice for analyzing the CPG output. Cross-WT and wavelet coherence were used to determine interrelations between pairs of time series in time and frequency domain, while determining the critical values for statistical significance of the coherence spectra using Monte Carlo simulations of white-noise series. The ability of the cross-Morlet WT and cross-WT coherence algorithms to efficiently extract the rhythmic parameters of complex nonstationary output of spinal pattern generators over a wide range of frequencies with time is demonstrated in this work under different experimental conditions. This ability can be exploited to create a quantitative dynamic portrait of experimental and clinical data under various physiological and pathological conditions.
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Affiliation(s)
- Y Mor
- Department of Anatomy and Cell Biology, The Hebrew University Medical School, Jerusalem 91010, Israel
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46
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Blivis D, Mentis GZ, O'donovan MJ, Lev-Tov A. Differential Effects of Opioids on Sacrocaudal Afferent Pathways and Central Pattern Generators in the Neonatal Rat Spinal Cord. J Neurophysiol 2007; 97:2875-86. [PMID: 17287435 DOI: 10.1152/jn.01313.2006] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The effects of opioids on sacrocaudal afferent (SCA) pathways and the pattern-generating circuitry of the thoracolumbar and sacrocaudal segments of the spinal cord were studied in isolated spinal cord and brain stem-spinal cord preparations of the neonatal rat. The locomotor and tail moving rhythm produced by activation of nociceptive and nonnociceptive sacrocaudal afferents was completely blocked by specific application of the μ-opioid receptor agonist [d-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin acetate salt (DAMGO) to the sacrocaudal but not the thoracolumbar segments of the spinal cord. The rhythmic activity could be restored after addition of the opioid receptor antagonist naloxone to the experimental chamber. The opioid block of the SCA-induced rhythm is not due to impaired rhythmogenic capacity of the spinal cord because a robust rhythmic activity could be initiated in the thoracolumbar and sacrocaudal segments in the presence of DAMGO, either by stimulation of the ventromedial medulla or by bath application of N-methyl-d-aspartate/serotonin. We suggest that the opioid block of the SCA-induced rhythm involves suppression of synaptic transmission through sacrocaudal interneurons interposed between SCA and the pattern-generating circuitry. The expression of μ opioid receptors in several groups of dorsal, intermediate and ventral horn interneurons in the sacrocaudal segments of the cord, documented in this study, provides an anatomical basis for this suggestion.
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MESH Headings
- Afferent Pathways/drug effects
- Analgesics, Opioid/pharmacology
- Animals
- Animals, Newborn/physiology
- Brain Stem/drug effects
- Brain Stem/physiology
- Data Interpretation, Statistical
- Electric Stimulation
- Electrophysiology
- Enkephalin, Ala(2)-MePhe(4)-Gly(5)-/pharmacology
- Excitatory Postsynaptic Potentials/drug effects
- Immunohistochemistry
- Instinct
- Locomotion/physiology
- Microscopy, Confocal
- Movement/physiology
- Naloxone/pharmacology
- Narcotic Antagonists/pharmacology
- Rats
- Receptors, Opioid, mu/agonists
- Receptors, Opioid, mu/genetics
- Receptors, Opioid, mu/physiology
- Spinal Cord/drug effects
- Spinal Cord/physiology
- Tail/innervation
- Tail/physiology
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Affiliation(s)
- D Blivis
- Dept. of Anatomy and Cell Biology, The Hebrew University Medical School, Jerusalem, 91010, Israel
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47
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Abstract
The question of how the central nervous system coordinates muscle activity is central to an understanding of motor control. The authors argue that motor programs may be considered as a characteristic timing of muscle activations linked to specific kinematic events. In particular, muscle activity occurring during human locomotion can be accounted for by five basic temporal components in a variety of locomotion conditions. Spatiotemporal maps of spinal cord motoneuron activation also show discrete periods of activity. Furthermore, the coordination of locomotion with voluntary tasks is accomplished through a superposition of motor programs or activation timings that are separately associated with each task. As a consequence, the selection of muscle synergies appears to be downstream from the processes that generate activation timings.
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Affiliation(s)
- Yuri P Ivanenko
- Department of Neuromotor Physiology, IRCCS Fondazione Santa Lucia, Rome, Italy.
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48
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Gordon IT, Whelan PJ. Monoaminergic control of cauda-equina-evoked locomotion in the neonatal mouse spinal cord. J Neurophysiol 2006; 96:3122-9. [PMID: 16956991 DOI: 10.1152/jn.00606.2006] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Monoaminergic projections are among the first supraspinal inputs to innervate spinal networks. Little is known regarding the role of monoamines in modulating ongoing locomotor patterns evoked by endogenous release of neurotransmitter. Here we activate a locomotor-like rhythm by electrical stimulation of afferents and then test the modulatory effects of monoamines on the frequency, pattern, and quality of the rhythm. Stimulation of the cauda equina induced a rhythm consisting of left-right and ipsilateral alternation indicative of locomotor-like activity. First, we examined the effects of noradrenaline (NA), serotonin (5-HT), or dopamine (DA) at dose levels that did not elicit locomotor activity. Bath application of NA and DA resulted in a depression of the cauda-equina-evoked rhythm. Conversely, bath-applied 5-HT increased both the amplitude and cycle period of the evoked rhythm, an effect that was mimicked by the addition of 5-HT(2) agonists to the bath. Application of 5-HT(7) agonists disrupted the evoked rhythmic behavior. Next, we examined the effects of NA alpha(1) and alpha(2) agonists and found that the suppressive effects of NA on the rhythm could be reproduced by adding the alpha(2) agonist, clonidine, to the bath. In contrast, bath applying the alpha(1) agonist, phenylephrine, increased the amplitude and duration of the cycle period. Finally, the suppressive effects of DA were not replicated by the administration of D(1), D(2), or D(3) agonists although application of NA alpha(2) antagonists reversed the effects of DA. Application of D(1) agonists, increased the amplitude of the bursts but did not affect the cycle period. Our results indicate that monoamines can control the expression, pattern, and timing of cauda-equina-evoked locomotor patterns in developing mice.
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Affiliation(s)
- Ian T Gordon
- HSC 2119, Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta T2N4N1, Canada
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49
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Ivanenko YP, Poppele RE, Lacquaniti F. Spinal Cord Maps of Spatiotemporal Alpha-Motoneuron Activation in Humans Walking at Different Speeds. J Neurophysiol 2006; 95:602-18. [PMID: 16282202 DOI: 10.1152/jn.00767.2005] [Citation(s) in RCA: 135] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Functional MRI (fMRI) imaging of motoneuron activity in the human spinal cord is still in its infancy, and it will remain difficult to apply to walking. Here we present a viable alternative for documenting the spatiotemporal maps of α-motorneuron (MN) activity in the human spinal cord during walking, similar to the method recently reported for the cat. We recorded EMG activity from 16 to 32 ipsilateral limb and trunk muscles in 13 healthy subjects walking on a treadmill at different speeds (1–7 km/h) and mapped the recorded patterns onto the spinal cord in approximate rostrocaudal locations of the motoneuron pools. This approach can provide information about pattern generator output during locomotion in terms of segmental control rather than in terms of individual muscle control. A striking feature we found is that nearly every spinal segment undergoes at least two cycles of activation in the step cycle, thus supporting the idea of half-center oscillators controlling MN activation at any segmental level. The resulting spatiotemporal map patterns seem highly stereotyped over the range of walking speeds studied, although there were also some systematic redistributions of MN activity with speed. Bursts of MN activity were either temporally aligned across several spinal segments or switched between different segments. For example, the center of mass of MN activity in the lumbosacral levels generally shifted from rostral to caudal positions in two cycles for each step, revealing four major activation foci: two in the upper lumbar segments and two in the sacral segments. The results are consistent with the presence of at least two and possibly more pattern generators controlling the activation of lumbosacral MNs.
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Affiliation(s)
- Y P Ivanenko
- Department of Neuromotor Physiology, Scientific Institute Foundation Santa Lucia, Rome, Italy.
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50
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Cazalets JR. Metachronal propagation of motoneurone burst activation in isolated spinal cord of newborn rat. J Physiol 2005; 568:583-97. [PMID: 16081478 PMCID: PMC1474724 DOI: 10.1113/jphysiol.2005.086850] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Adequate locomotor and postural activity in mammals results from the coordinated activation of assemblies of spinal cord networks. In order to assess the global functioning of spinal circuitry, multisite recordings were made from an isolated spinal cord preparation of the newborn rat. Motor activity, elicited in a disinhibited network by bath-applying strychnine (glycinergic blocker) and bicuculline (GABAergic blocker), consisted of slow spontaneous bursting. Under these conditions, the recorded bursts were coordinated in 1: 1 relationships at all segmental levels. For each cycle, a leading segment initiated the activity that then propagated in a metachronal way through adjacent segments along the length of spinal cord. There was both regional non-linearity and directional asymmetry in this burst propagation: motor bursts propagated most rapidly in the thoracic spinal cord and the rostro-caudal wave travelled faster than the caudo-rostral one. Propagation involved both long projecting fibres and local intersegmental connections. These results suggest that the mammalian spinal cord contains propriospinal pathways subserving a metachronal transmission of motor information and that normally it may be involved in coordinating various parts of the body. The simple model developed here could be useful in unravelling more general mechanisms of neuronal circuit coupling.
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