1
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Strohmer B, Najarro E, Ausborn J, Berg RW, Tolu S. Sparse Firing in a Hybrid Central Pattern Generator for Spinal Motor Circuits. Neural Comput 2024; 36:759-780. [PMID: 38658025 DOI: 10.1162/neco_a_01660] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2023] [Accepted: 01/02/2024] [Indexed: 04/26/2024]
Abstract
Central pattern generators are circuits generating rhythmic movements, such as walking. The majority of existing computational models of these circuits produce antagonistic output where all neurons within a population spike with a broad burst at about the same neuronal phase with respect to network output. However, experimental recordings reveal that many neurons within these circuits fire sparsely, sometimes as rarely as once within a cycle. Here we address the sparse neuronal firing and develop a model to replicate the behavior of individual neurons within rhythm-generating populations to increase biological plausibility and facilitate new insights into the underlying mechanisms of rhythm generation. The developed network architecture is able to produce sparse firing of individual neurons, creating a novel implementation for exploring the contribution of network architecture on rhythmic output. Furthermore, the introduction of sparse firing of individual neurons within the rhythm-generating circuits is one of the factors that allows for a broad neuronal phase representation of firing at the population level. This moves the model toward recent experimental findings of evenly distributed neuronal firing across phases among individual spinal neurons. The network is tested by methodically iterating select parameters to gain an understanding of how connectivity and the interplay of excitation and inhibition influence the output. This knowledge can be applied in future studies to implement a biologically plausible rhythm-generating circuit for testing biological hypotheses.
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Affiliation(s)
- Beck Strohmer
- Department of Electrical and Photonics Engineering, Technical University of Denmark, 2800 Lyngby, Denmark
| | - Elias Najarro
- Department of Digital Design, IT University of Copenhagen, DK-2300 Copenhagen, Denmark
| | - Jessica Ausborn
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA, U.S.A.
| | - Rune W Berg
- Department of Neuroscience, University of Copenhagen, DK-1165 Copenhagen, Denmark
| | - Silvia Tolu
- Department of Electrical and Photonics Engineering, Technical University of Denmark, 2800 Lyngby, Denmark
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2
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Gradwell MA, Ozeri-Engelhard N, Eisdorfer JT, Laflamme OD, Gonzalez M, Upadhyay A, Medlock L, Shrier T, Patel KR, Aoki A, Gandhi M, Abbas-Zadeh G, Oputa O, Thackray JK, Ricci M, George A, Yusuf N, Keating J, Imtiaz Z, Alomary SA, Bohic M, Haas M, Hernandez Y, Prescott SA, Akay T, Abraira VE. Multimodal sensory control of motor performance by glycinergic interneurons of the mouse spinal cord deep dorsal horn. Neuron 2024; 112:1302-1327.e13. [PMID: 38452762 DOI: 10.1016/j.neuron.2024.01.027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2023] [Revised: 10/31/2023] [Accepted: 01/26/2024] [Indexed: 03/09/2024]
Abstract
Sensory feedback is integral for contextually appropriate motor output, yet the neural circuits responsible remain elusive. Here, we pinpoint the medial deep dorsal horn of the mouse spinal cord as a convergence point for proprioceptive and cutaneous input. Within this region, we identify a population of tonically active glycinergic inhibitory neurons expressing parvalbumin. Using anatomy and electrophysiology, we demonstrate that deep dorsal horn parvalbumin-expressing interneuron (dPV) activity is shaped by convergent proprioceptive, cutaneous, and descending input. Selectively targeting spinal dPVs, we reveal their widespread ipsilateral inhibition onto pre-motor and motor networks and demonstrate their role in gating sensory-evoked muscle activity using electromyography (EMG) recordings. dPV ablation altered limb kinematics and step-cycle timing during treadmill locomotion and reduced the transitions between sub-movements during spontaneous behavior. These findings reveal a circuit basis by which sensory convergence onto dorsal horn inhibitory neurons modulates motor output to facilitate smooth movement and context-appropriate transitions.
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Affiliation(s)
- Mark A Gradwell
- Cell Biology and Neuroscience Department, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; W.M. Keck Center for Collaborative Neuroscience, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA
| | - Nofar Ozeri-Engelhard
- Cell Biology and Neuroscience Department, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; W.M. Keck Center for Collaborative Neuroscience, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; Neuroscience PhD program, Rutgers Robert Wood Johnson Medical School, Piscataway, NJ, USA
| | - Jaclyn T Eisdorfer
- Cell Biology and Neuroscience Department, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; W.M. Keck Center for Collaborative Neuroscience, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA
| | - Olivier D Laflamme
- Dalhousie PhD program, Dalhousie University, Halifax, NS, Canada; Department of Medical Neuroscience, Atlantic Mobility Action Project, Brain Repair Center, Dalhousie University, Halifax, NS, Canada
| | - Melissa Gonzalez
- Cell Biology and Neuroscience Department, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; W.M. Keck Center for Collaborative Neuroscience, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; Department of Biomedical Engineering, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA
| | - Aman Upadhyay
- Cell Biology and Neuroscience Department, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; W.M. Keck Center for Collaborative Neuroscience, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; Neuroscience PhD program, Rutgers Robert Wood Johnson Medical School, Piscataway, NJ, USA
| | - Laura Medlock
- Neurosciences & Mental Health, The Hospital for Sick Children, Toronto, ON, Canada; Institute of Biomedical Engineering, University of Toronto, Toronto, ON, Canada
| | - Tara Shrier
- Cell Biology and Neuroscience Department, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; W.M. Keck Center for Collaborative Neuroscience, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA
| | - Komal R Patel
- Cell Biology and Neuroscience Department, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; W.M. Keck Center for Collaborative Neuroscience, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA
| | - Adin Aoki
- Cell Biology and Neuroscience Department, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; W.M. Keck Center for Collaborative Neuroscience, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA
| | - Melissa Gandhi
- Cell Biology and Neuroscience Department, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; W.M. Keck Center for Collaborative Neuroscience, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA
| | - Gloria Abbas-Zadeh
- Cell Biology and Neuroscience Department, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; W.M. Keck Center for Collaborative Neuroscience, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA
| | - Olisemaka Oputa
- Cell Biology and Neuroscience Department, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; W.M. Keck Center for Collaborative Neuroscience, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA
| | - Joshua K Thackray
- Cell Biology and Neuroscience Department, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; W.M. Keck Center for Collaborative Neuroscience, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; Human Genetics Institute of New Jersey, Rutgers University, The State University of New Jersey, Piscataway, NJ, USA; Tourette International Collaborative Genetics Study (TIC Genetics)
| | - Matthew Ricci
- School of Computer Science and Engineering, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Arlene George
- Cell Biology and Neuroscience Department, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; W.M. Keck Center for Collaborative Neuroscience, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA
| | - Nusrath Yusuf
- Cell Biology and Neuroscience Department, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; W.M. Keck Center for Collaborative Neuroscience, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; Neuroscience PhD program, Rutgers Robert Wood Johnson Medical School, Piscataway, NJ, USA
| | - Jessica Keating
- Cell Biology and Neuroscience Department, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; W.M. Keck Center for Collaborative Neuroscience, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA
| | - Zarghona Imtiaz
- Cell Biology and Neuroscience Department, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; W.M. Keck Center for Collaborative Neuroscience, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA
| | - Simona A Alomary
- Cell Biology and Neuroscience Department, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; W.M. Keck Center for Collaborative Neuroscience, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA
| | - Manon Bohic
- Cell Biology and Neuroscience Department, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; W.M. Keck Center for Collaborative Neuroscience, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA
| | - Michael Haas
- Cell Biology and Neuroscience Department, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; W.M. Keck Center for Collaborative Neuroscience, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA
| | - Yurdiana Hernandez
- W.M. Keck Center for Collaborative Neuroscience, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA
| | - Steven A Prescott
- Neurosciences & Mental Health, The Hospital for Sick Children, Toronto, ON, Canada; Department of Physiology, University of Toronto, Toronto, ON, Canada
| | - Turgay Akay
- Department of Medical Neuroscience, Atlantic Mobility Action Project, Brain Repair Center, Dalhousie University, Halifax, NS, Canada
| | - Victoria E Abraira
- Cell Biology and Neuroscience Department, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA; W.M. Keck Center for Collaborative Neuroscience, Rutgers University, The State University of New Jersey, New Brunswick, NJ, USA.
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3
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Dougherty KJ. Distinguishing subtypes of spinal locomotor neurons to inform circuit function and dysfunction. Curr Opin Neurobiol 2023; 82:102763. [PMID: 37611531 PMCID: PMC10578609 DOI: 10.1016/j.conb.2023.102763] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2023] [Revised: 06/30/2023] [Accepted: 07/22/2023] [Indexed: 08/25/2023]
Abstract
Locomotion is a complex motor task executed by spinal neurons. Given the diversity of spinal cord neurons, linking neuronal cell type to function is a challenge. Molecular identification of broad spinal interneuronal classes provided a great advance. Recent studies have used other classifiers, including location, electrophysiological properties, and connectivity, in addition to gene profiling, to narrow the acuity with which groups of neurons can be related to specific functions. However, there are also functional populations without a clear identifier, as exemplified by rhythm generating neurons. Other considerations, including experience or plasticity, add a layer of complexity to the definition of functional subpopulations of spinal neurons, but spinal cord injury may provide insight.
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Affiliation(s)
- Kimberly J Dougherty
- Marion Murray Spinal Cord Research Center, Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA 19129, USA.
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4
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Hilscher MM, Mikulovic S, Perry S, Lundberg S, Kullander K. The alpha2 nicotinic acetylcholine receptor, a subunit with unique and selective expression in inhibitory interneurons associated with principal cells. Pharmacol Res 2023; 196:106895. [PMID: 37652281 DOI: 10.1016/j.phrs.2023.106895] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/19/2023] [Revised: 08/21/2023] [Accepted: 08/23/2023] [Indexed: 09/02/2023]
Abstract
Nicotinic acetylcholine receptors (nAChRs) play crucial roles in various human disorders, with the α7, α4, α6, and α3-containing nAChR subtypes extensively studied in relation to conditions such as Alzheimer's disease, Parkinson's disease, nicotine dependence, mood disorders, and stress disorders. In contrast, the α2-nAChR subunit has received less attention due to its more restricted expression and the scarcity of specific agonists and antagonists for studying its function. Nevertheless, recent research has shed light on the unique expression pattern of the Chrna2 gene, which encodes the α2-nAChR subunit, and its involvement in distinct populations of inhibitory interneurons. This review highlights the structure, pharmacology, localization, function, and disease associations of α2-containing nAChRs and points to the unique expression pattern of the Chrna2 gene and its role in different inhibitory interneuron populations. These populations, including the oriens lacunosum moleculare (OLM) cells in the hippocampus, Martinotti cells in the neocortex, and Renshaw cells in the spinal cord, share common features and contribute to recurrent inhibitory microcircuits. Thus, the α2-nAChR subunit's unique expression pattern in specific interneuron populations and its role in recurrent inhibitory microcircuits highlight its importance in various physiological processes. Further research is necessary to uncover the comprehensive functionality of α2-containing nAChRs, delineate their specific contributions to neuronal circuits, and investigate their potential as therapeutic targets for related disorders.
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Affiliation(s)
- Markus M Hilscher
- Department of Immunology, Genetics and Pathology, Uppsala University, IGP/BMC, Box 815, 751 08 Uppsala, Sweden; Department of Biochemistry and Biophysics, Science for Life Laboratory, Stockholm University, Solna, Sweden
| | - Sanja Mikulovic
- Department of Immunology, Genetics and Pathology, Uppsala University, IGP/BMC, Box 815, 751 08 Uppsala, Sweden; Leibniz Institute for Neurobiology, Cognition & Emotion Laboratory, Magdeburg, Germany; German Center for Mental Health(DZPG), Germany
| | - Sharn Perry
- Department of Immunology, Genetics and Pathology, Uppsala University, IGP/BMC, Box 815, 751 08 Uppsala, Sweden; Wicking Dementia Research and Education Centre, University of Tasmania, Hobart, Australia
| | - Stina Lundberg
- Department of Immunology, Genetics and Pathology, Uppsala University, IGP/BMC, Box 815, 751 08 Uppsala, Sweden
| | - Klas Kullander
- Department of Immunology, Genetics and Pathology, Uppsala University, IGP/BMC, Box 815, 751 08 Uppsala, Sweden.
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5
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Minassian K, Bayart A, Lackner P, Binder H, Freundl B, Hofstoetter US. Rare phenomena of central rhythm and pattern generation in a case of complete spinal cord injury. Nat Commun 2023; 14:3276. [PMID: 37280242 DOI: 10.1038/s41467-023-39034-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2022] [Accepted: 05/26/2023] [Indexed: 06/08/2023] Open
Abstract
Lumbar central pattern generators (CPGs) control the basic rhythm and coordinate muscle activation underlying hindlimb locomotion in quadrupedal mammals. The existence and function of CPGs in humans have remained controversial. Here, we investigated a case of a male individual with complete thoracic spinal cord injury who presented with a rare form of self-sustained rhythmic spinal myoclonus in the legs and rhythmic activities induced by epidural electrical stimulation (EES). Analysis of muscle activation patterns suggested that the myoclonus tapped into spinal circuits that generate muscle spasms, rather than reflecting locomotor CPG activity as previously thought. The EES-induced patterns were fundamentally different in that they included flexor-extensor and left-right alternations, hallmarks of locomotor CPGs, and showed spontaneous errors in rhythmicity. These motor deletions, with preserved cycle frequency and period when rhythmic activity resumed, were previously reported only in animal studies and suggest a separation between rhythm generation and pattern formation. Spinal myoclonus and the EES-induced activity demonstrate that the human lumbar spinal cord contains distinct mechanisms for generating rhythmic multi-muscle patterns.
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Affiliation(s)
- Karen Minassian
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Aymeric Bayart
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Peter Lackner
- Neurological Center, Clinic Penzing, Vienna, Austria
- Department of Neurology, Clinic Floridsdorf, Vienna, Austria
| | | | | | - Ursula S Hofstoetter
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
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6
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Recabal-Beyer A, Tavakoli H, M M Senecal J, Stecina K, Nagy JI. Interrelationships between spinal sympathetic preganglionic neurons, autonomic systems and electrical synapses formed by connexin36-containing gap junctions. Neuroscience 2023:S0306-4522(23)00220-8. [PMID: 37225049 DOI: 10.1016/j.neuroscience.2023.05.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2022] [Revised: 04/24/2023] [Accepted: 05/14/2023] [Indexed: 05/26/2023]
Abstract
Spinal sympathetic preganglionic neurons (SPNs) are among the many neuronal populations in the mammalian central nervous system (CNS) where there is evidence for electrical coupling between cell pairs linked by gap junctions composed of connexin36 (Cx36). Understanding the organization of this coupling in relation to autonomic functions of spinal sympathetic systems requires knowledge of how these junctions are deployed among SPNs. Here, we document the distribution of immunofluorescence detection of Cx36 among SPNs identified by immunolabelling of their various markers, including choline acetyltransferase, nitric oxide and peripherin in adult and developing mouse and rat. In adult animals, labelling of Cx36 was exclusively punctate and dense concentrations of Cx36-puncta were distributed along the entire length of the spinal thoracic intermediolateral cell column (IML). These puncta were also seen in association with SPN dendritic processes in the lateral funiculus, the intercalated and central autonomic areas and those within and extending medially from the IML. All labelling for Cx36 was absent in spinal cords of Cx36 knockout mice. High densities of Cx36-puncta were already evident among clusters of SPNs in the IML of mouse and rat at postnatal days 10-12. In Cx36BAC::eGFP mice, eGFP reporter was absent in SPNs, thus representing false negative detection, but was localized to some glutamatergic and GABAergic synaptic terminals. Some eGFP+ terminals were found contacting SPN dendrites. These results indicate widespread Cx36 expression in SPNs, further supporting evidence of electrical coupling between these cells, and suggest that SPNs are innervated by neurons that themselves may be electrically coupled.
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Affiliation(s)
- A Recabal-Beyer
- Department of Physiology and Pathophysiology, Max Rady College of Medicine, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, Canada R3E 0J9
| | - H Tavakoli
- Department of Physiology and Pathophysiology, Max Rady College of Medicine, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, Canada R3E 0J9
| | - J M M Senecal
- Department of Physiology and Pathophysiology, Max Rady College of Medicine, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, Canada R3E 0J9
| | - K Stecina
- Department of Physiology and Pathophysiology, Max Rady College of Medicine, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, Canada R3E 0J9
| | - J I Nagy
- Department of Physiology and Pathophysiology, Max Rady College of Medicine, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, Canada R3E 0J9.
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7
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Barbay T, Pecchi E, Ducrocq M, Rouach N, Brocard F, Bos R. Astrocytic Kir4.1 channels regulate locomotion by orchestrating neuronal rhythmicity in the spinal network. Glia 2023; 71:1259-1277. [PMID: 36645018 DOI: 10.1002/glia.24337] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2022] [Revised: 12/22/2022] [Accepted: 01/02/2023] [Indexed: 01/17/2023]
Abstract
Neuronal rhythmogenesis in the spinal cord is correlated with variations in extracellular K+ levels ([K+ ]e ). Astrocytes play important role in [K+ ]e homeostasis and compute neuronal information. Yet it is unclear how neuronal oscillations are regulated by astrocytic K+ homeostasis. Here we identify the astrocytic inward-rectifying K+ channel Kir4.1 (a.k.a. Kcnj10) as a key molecular player for neuronal rhythmicity in the spinal central pattern generator (CPG). By combining two-photon calcium imaging with electrophysiology, immunohistochemistry and genetic tools, we report that astrocytes display Ca2+ transients before and during oscillations of neighboring neurons. Inhibition of astrocytic Ca2+ transients with BAPTA decreases the barium-sensitive Kir4.1 current responsible of K+ clearance. Finally, we show in mice that Kir4.1 knockdown in astrocytes progressively prevents neuronal oscillations and alters the locomotor pattern resulting in lower motor performances in challenging tasks. These data identify astroglial Kir4.1 channels as key regulators of neuronal rhythmogenesis in the CPG driving locomotion.
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Affiliation(s)
- Tony Barbay
- Aix Marseille Univ, CNRS, Institut de Neurosciences de la Timone (INT), UMR 7289, Marseille, France
| | - Emilie Pecchi
- Aix Marseille Univ, CNRS, Institut de Neurosciences de la Timone (INT), UMR 7289, Marseille, France
| | - Myriam Ducrocq
- Aix Marseille Univ, CNRS, Institut de Neurosciences de la Timone (INT), UMR 7289, Marseille, France
| | - Nathalie Rouach
- Center for Interdisciplinary Research in Biology, Collège de France, CNRS, INSERM, Labex Memolife, Université PSL, Paris, France
| | - Frédéric Brocard
- Aix Marseille Univ, CNRS, Institut de Neurosciences de la Timone (INT), UMR 7289, Marseille, France
| | - Rémi Bos
- Aix Marseille Univ, CNRS, Institut de Neurosciences de la Timone (INT), UMR 7289, Marseille, France
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Wilson AC, Sweeney LB. Spinal cords: Symphonies of interneurons across species. Front Neural Circuits 2023; 17:1146449. [PMID: 37180760 PMCID: PMC10169611 DOI: 10.3389/fncir.2023.1146449] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Accepted: 03/23/2023] [Indexed: 05/16/2023] Open
Abstract
Vertebrate movement is orchestrated by spinal inter- and motor neurons that, together with sensory and cognitive input, produce dynamic motor behaviors. These behaviors vary from the simple undulatory swimming of fish and larval aquatic species to the highly coordinated running, reaching and grasping of mice, humans and other mammals. This variation raises the fundamental question of how spinal circuits have changed in register with motor behavior. In simple, undulatory fish, exemplified by the lamprey, two broad classes of interneurons shape motor neuron output: ipsilateral-projecting excitatory neurons, and commissural-projecting inhibitory neurons. An additional class of ipsilateral inhibitory neurons is required to generate escape swim behavior in larval zebrafish and tadpoles. In limbed vertebrates, a more complex spinal neuron composition is observed. In this review, we provide evidence that movement elaboration correlates with an increase and specialization of these three basic interneuron types into molecularly, anatomically, and functionally distinct subpopulations. We summarize recent work linking neuron types to movement-pattern generation across fish, amphibians, reptiles, birds and mammals.
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Affiliation(s)
| | - Lora B. Sweeney
- Institute of Science and Technology Austria (IST Austria), Klosterneuburg, Lower Austria, Austria
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9
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Ren J, Gosgnach S. Localization of Rhythm Generating Components of the Mammalian Locomotor Central Pattern Generator. Neuroscience 2023; 513:28-37. [PMID: 36702374 DOI: 10.1016/j.neuroscience.2023.01.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2022] [Revised: 01/11/2023] [Accepted: 01/16/2023] [Indexed: 01/24/2023]
Abstract
Locomotor movements in mammals are generated by neural networks, situated in the spinal cord, known as central pattern generators (CPGs). Recently, significant strides have been made in the genetic identification of interneuronal components of the locomotor CPG and their specific function. Despite this progress, a population of interneurons that is required for locomotor rhythmogenesis has yet to be identified, and it has been suggested that subsets of interneurons belonging to several genetically-defined populations may be involved. In this study, rather than hunt for rhythmogenic neurons, we take a different approach and attempt to identify the specific region of the spinal cord in which they are located. Focal application of 5-hydroxytryptamine creatine sulfate complex (5-HT) and N-methyl-D-aspartate (NMDA) to the central canal of the rostral lumbar segments of newborn male and female mouse spinal cords quickly generates a robust pattern of fictive locomotion, while inhibition or ablation of neurons in this region disrupts the locomotor rhythm in both rostral and caudal lumbar segments. When applied to the central canal at caudal lumbar levels a higher volume of 5-HT and NMDA are required to elicit fictive locomotion, while inhibition of neurons surrounding the central canal at caudal levels again interrupts rhythmic activity at local segmental levels with minimal effects rostrally. The results of this study indicate that interneurons in the most medial laminae of the neonatal mouse spinal cord are both necessary and sufficient for the generation of locomotor activity, and suggests that this is the region where the rhythm generating core of the locomotor CPG resides.
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Affiliation(s)
- Jun Ren
- University of Alberta, Dept. of Physiology, 3-020M Katz Building, Edmonton, AL T6G 2E1, Canada
| | - Simon Gosgnach
- University of Alberta, Dept. of Physiology, 3-020M Katz Building, Edmonton, AL T6G 2E1, Canada.
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Transcription Factor Hb9 Is Expressed in Glial Cell Lineages in the Developing Mouse Spinal Cord. eNeuro 2022; 9:ENEURO.0214-22.2022. [PMID: 36265906 PMCID: PMC9636997 DOI: 10.1523/eneuro.0214-22.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2022] [Revised: 09/14/2022] [Accepted: 10/10/2022] [Indexed: 12/24/2022] Open
Abstract
Hb9 (Mnx1) is a transcription factor described as a spinal cord motor neuron (MN)-specific marker and critical factor for the postmitotic specification of these cells. To date, expression of Hb9 in other cell types has not been reported. We performed a fate-mapping approach to examine distributions of Hb9-expressing cells and their progeny ("Hb9-lineage cells") within the embryonic and adult spinal cord of Hb9cre;Ai14 mice. We found that Hb9-lineage cells are distributed in a gradient of increasing abundance throughout the rostrocaudal spinal cord axis during embryonic and postnatal stages. Furthermore, although the majority of Hb9-lineage cells at cervical spinal cord levels are MNs, at more caudal levels, Hb9-lineage cells include small-diameter dorsal horn neurons, astrocytes, and oligodendrocytes. In the peripheral nervous system, we observed a similar phenomenon with more abundant Hb9-lineage Schwann cells in muscles of the lower body versus upper body muscles. We cultured spinal cord progenitors in vitro and found that gliogenesis was increased by treatment with the caudalizing factor FGF-8B, while glial tdTomato expression was increased by treatment with both FGF-8B and GDF-11. Together, these observations suggest that early and transient expression of Hb9 in spinal cord neural progenitors may be induced by caudalizing factors such as FGF and GDF signaling. Furthermore, our work raises the possibility that early Hb9 expression may influence the development of spinal cord macroglia and Schwann cells, especially at caudal regions. Together, these findings highlight the importance of using caution when designing experiments using Hb9cre mice to perform spinal cord MN-specific manipulations.
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11
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Garcia-Ramirez DL, Singh S, McGrath JR, Ha NT, Dougherty KJ. Identification of adult spinal Shox2 neuronal subpopulations based on unbiased computational clustering of electrophysiological properties. Front Neural Circuits 2022; 16:957084. [PMID: 35991345 PMCID: PMC9385948 DOI: 10.3389/fncir.2022.957084] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2022] [Accepted: 07/08/2022] [Indexed: 11/13/2022] Open
Abstract
Spinal cord neurons integrate sensory and descending information to produce motor output. The expression of transcription factors has been used to dissect out the neuronal components of circuits underlying behaviors. However, most of the canonical populations of interneurons are heterogeneous and require additional criteria to determine functional subpopulations. Neurons expressing the transcription factor Shox2 can be subclassified based on the co-expression of the transcription factor Chx10 and each subpopulation is proposed to have a distinct connectivity and different role in locomotion. Adult Shox2 neurons have recently been shown to be diverse based on their firing properties. Here, in order to subclassify adult mouse Shox2 neurons, we performed multiple analyses of data collected from whole-cell patch clamp recordings of visually-identified Shox2 neurons from lumbar spinal slices. A smaller set of Chx10 neurons was included in the analyses for validation. We performed k-means and hierarchical unbiased clustering approaches, considering electrophysiological variables. Unlike the categorizations by firing type, the clusters displayed electrophysiological properties that could differentiate between clusters of Shox2 neurons. The presence of clusters consisting exclusively of Shox2 neurons in both clustering techniques suggests that it is possible to distinguish Shox2+Chx10- neurons from Shox2+Chx10+ neurons by electrophysiological properties alone. Computational clusters were further validated by immunohistochemistry with accuracy in a small subset of neurons. Thus, unbiased cluster analysis using electrophysiological properties is a tool that can enhance current interneuronal subclassifications and can complement groupings based on transcription factor and molecular expression.
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Affiliation(s)
| | | | | | | | - Kimberly J. Dougherty
- Department of Neurobiology and Anatomy, Marion Murray Spinal Cord Research Center, Drexel University College of Medicine, Philadelphia, PA, United States
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12
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Genç B, Jara JH, Sanchez SS, Lagrimas AKB, Gözütok Ö, Koçak N, Zhu Y, Hande Özdinler P. Upper motor neurons are a target for gene therapy and UCHL1 is necessary and sufficient to improve cellular integrity of diseased upper motor neurons. Gene Ther 2022; 29:178-192. [PMID: 34853443 PMCID: PMC9018479 DOI: 10.1038/s41434-021-00303-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2021] [Revised: 10/25/2021] [Accepted: 10/26/2021] [Indexed: 12/15/2022]
Abstract
There are no effective cures for upper motor neuron (UMN) diseases, such as amyotrophic lateral sclerosis (ALS), primary lateral sclerosis, and hereditary spastic paraplegia. Here, we show UMN loss occurs independent of spinal motor neuron degeneration and that UMNs are indeed effective cellular targets for gene therapy, which offers a potential solution especially for UMN disease patients. UCHL1 (ubiquitin C-terminal hydrolase-L1) is a deubiquitinating enzyme crucial for maintaining free ubiquitin levels. Corticospinal motor neurons (CSMN, a.k.a UMNs in mice) show early, selective, and profound degeneration in Uchl1nm3419 (UCHL1-/-) mice, which lack all UCHL1 function. When UCHL1 activity is ablated only from spinal motor neurons, CSMN remained intact. However, restoring UCHL1 specifically in CSMN of UCHL1-/- mice via directed gene delivery was sufficient to improve CSMN integrity to the healthy control levels. In addition, when UCHL1 gene was delivered selectively to CSMN that are diseased due to misfolded SOD1 toxicity and TDP-43 pathology via AAV-mediated retrograde transduction, the disease causing misfolded SOD1 and mutant human TDP-43 were reduced in hSOD1G93A and prpTDP-43A315T models, respectively. Diseased CSMN retained their neuronal integrity and cytoarchitectural stability in two different mouse models that represent two distinct causes of neurodegeneration in ALS.
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Affiliation(s)
- Barış Genç
- Davee Department of Neurology and Clinical Neurological Sciences, Northwestern University, Feinberg School of Medicine, Chicago, IL, 60611, USA
| | - Javier H Jara
- Davee Department of Neurology and Clinical Neurological Sciences, Northwestern University, Feinberg School of Medicine, Chicago, IL, 60611, USA
| | - Santana S Sanchez
- Davee Department of Neurology and Clinical Neurological Sciences, Northwestern University, Feinberg School of Medicine, Chicago, IL, 60611, USA
| | - Amiko K B Lagrimas
- Davee Department of Neurology and Clinical Neurological Sciences, Northwestern University, Feinberg School of Medicine, Chicago, IL, 60611, USA
| | - Öge Gözütok
- Davee Department of Neurology and Clinical Neurological Sciences, Northwestern University, Feinberg School of Medicine, Chicago, IL, 60611, USA
| | - Nuran Koçak
- Davee Department of Neurology and Clinical Neurological Sciences, Northwestern University, Feinberg School of Medicine, Chicago, IL, 60611, USA
| | - Yongling Zhu
- Departments of Ophthalmology and Physiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, 60611, USA
| | - P Hande Özdinler
- Davee Department of Neurology and Clinical Neurological Sciences, Northwestern University, Feinberg School of Medicine, Chicago, IL, 60611, USA.
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13
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Catela C, Chen Y, Weng Y, Wen K, Kratsios P. Control of spinal motor neuron terminal differentiation through sustained Hoxc8 gene activity. eLife 2022; 11:70766. [PMID: 35315772 PMCID: PMC8940177 DOI: 10.7554/elife.70766] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2021] [Accepted: 03/12/2022] [Indexed: 12/30/2022] Open
Abstract
Spinal motor neurons (MNs) constitute cellular substrates for several movement disorders. Although their early development has received much attention, how spinal MNs become and remain terminally differentiated is poorly understood. Here, we determined the transcriptome of mouse MNs located at the brachial domain of the spinal cord at embryonic and postnatal stages. We identified novel transcription factors (TFs) and terminal differentiation genes (e.g. ion channels, neurotransmitter receptors, adhesion molecules) with continuous expression in MNs. Interestingly, genes encoding homeodomain TFs (e.g. HOX, LIM), previously implicated in early MN development, continue to be expressed postnatally, suggesting later functions. To test this idea, we inactivated Hoxc8 at successive stages of mouse MN development and observed motor deficits. Our in vivo findings suggest that Hoxc8 is not only required to establish, but also maintain expression of several MN terminal differentiation markers. Data from in vitro generated MNs indicate Hoxc8 acts directly and is sufficient to induce expression of terminal differentiation genes. Our findings dovetail recent observations in Caenorhabditis elegans MNs, pointing toward an evolutionarily conserved role for Hox in neuronal terminal differentiation.
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Affiliation(s)
- Catarina Catela
- Department of Neurobiology, University of Chicago, Chicago, United States.,University of Chicago Neuroscience Institute, Chicago, United States
| | - Yihan Chen
- Department of Neurobiology, University of Chicago, Chicago, United States.,University of Chicago Neuroscience Institute, Chicago, United States
| | - Yifei Weng
- Department of Neurobiology, University of Chicago, Chicago, United States.,University of Chicago Neuroscience Institute, Chicago, United States
| | - Kailong Wen
- Department of Neurobiology, University of Chicago, Chicago, United States.,University of Chicago Neuroscience Institute, Chicago, United States
| | - Paschalis Kratsios
- Department of Neurobiology, University of Chicago, Chicago, United States.,University of Chicago Neuroscience Institute, Chicago, United States
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14
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Recabal-Beyer AJ, Senecal JMM, Senecal JEM, Lynn BD, Nagy JI. On the Organization of Connexin36 Expression in Electrically Coupled Cholinergic V0c Neurons (Partition Cells) in the Spinal Cord and Their C-terminal Innervation of Motoneurons. Neuroscience 2022; 485:91-115. [PMID: 35090881 DOI: 10.1016/j.neuroscience.2022.01.015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2021] [Revised: 01/07/2022] [Accepted: 01/19/2022] [Indexed: 12/13/2022]
Abstract
Large cholinergic neurons (V0c neurons; aka, partition cells) in the spinal cord project profusely to motoneurons on which they form C-terminal contacts distinguished by their specialized postsynaptic subsurface cisterns (SSCs). The V0c neurons are known to be rhythmically active during locomotion and release of acetylcholine (ACh) from their terminals is known to modulate the excitability of motoneurons in what appears to be a task-dependent manner. Here, we present evidence that a subpopulation of V0c neurons express the gap junction forming protein connexin36 (Cx36), indicating that they are coupled by electrical synapses. Based on immunofluorescence imaging and the use of Cx36BAC-enhanced green fluorescent protein (eGFP) mice in which C-terminals immunolabelled for their marker vesicular acetylcholine transporter (vAChT) are also labelled for eGFP, we found a heterogeneous distribution of eGFP+ C-terminals on motoneurons at cervical, thoracic and lumber spinal levels. The density of C-terminals on motoneurons varied as did the proportion of those that were eGFP+ vs. eGFP-. We present evidence that fast vs. slow motoneurons have a greater abundance of these terminals and fast motoneurons also have the highest density that were eGFP+. Thus, our results indicate that a subpopulation of V0c neurons projects preferentially to fast motoneurons, suggesting that the capacity for synchronous activity conferred by electrical synapses among networks of coupled V0c neurons enhances their dynamic capabilities for synchronous regulation of motoneuron excitability during high muscle force generation. The eGFP+ vs. eGFP- V0c neurons were more richly innervated by serotonergic terminals, suggesting their greater propensity for regulation by descending serotonergic systems.
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Affiliation(s)
- A J Recabal-Beyer
- Department of Physiology and Pathophysiology, Rady Faculty of Health Sciences, Max Rady College of Medicine, University of Manitoba, Winnipeg, Canada
| | - J M M Senecal
- Department of Physiology and Pathophysiology, Rady Faculty of Health Sciences, Max Rady College of Medicine, University of Manitoba, Winnipeg, Canada
| | - J E M Senecal
- Department of Physiology and Pathophysiology, Rady Faculty of Health Sciences, Max Rady College of Medicine, University of Manitoba, Winnipeg, Canada
| | - B D Lynn
- Department of Physiology and Pathophysiology, Rady Faculty of Health Sciences, Max Rady College of Medicine, University of Manitoba, Winnipeg, Canada
| | - J I Nagy
- Department of Physiology and Pathophysiology, Rady Faculty of Health Sciences, Max Rady College of Medicine, University of Manitoba, Winnipeg, Canada.
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15
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Vargova I, Kriska J, Kwok JCF, Fawcett JW, Jendelova P. Long-Term Cultures of Spinal Cord Interneurons. Front Cell Neurosci 2022; 16:827628. [PMID: 35197829 PMCID: PMC8859857 DOI: 10.3389/fncel.2022.827628] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2021] [Accepted: 01/12/2022] [Indexed: 11/25/2022] Open
Abstract
Spinal cord interneurons (SpINs) are highly diverse population of neurons that play a significant role in circuit reorganization and spontaneous recovery after spinal cord injury. Regeneration of SpIN axons across rodent spinal injuries has been demonstrated after modification of the environment and neurotrophin treatment, but development of methods to enhance the intrinsic regenerative ability of SpINs is needed. There is a lack of described in vitro models of spinal cord neurons in which to develop new regeneration treatments. For this reason, we developed a new model of mouse primary spinal cord neuronal culture in which to analyze maturation, morphology, physiology, connectivity and regeneration of identified interneurons. Isolated from E14 mice, the neurons mature over 15 days in vitro, demonstrated by expression of maturity markers, electrophysiological patch-clamp recordings, and formation of synapses. The neurons express markers of SpINs, including Tlx3, Lmx1b, Lbx1, Chx10, and Pax2. The neurons demonstrate distinct morphologies and some form perineuronal nets in long-term cultivation. Live neurons in various maturation stages were axotomized, using a 900 nm multiphoton laser and their fate was observed overnight. The percentage of axons that regenerated declined with neuronal maturity. This model of SpINs will be a valuable tool in future regenerative, developmental, and functional studies alongside existing models using cortical or hippocampal neurons.
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Affiliation(s)
- Ingrid Vargova
- Department of Neuroregeneration, Institute of Experimental Medicine, Czech Academy of Sciences, Prague, Czechia
- Second Faculty of Medicine, Charles University, Prague, Czechia
| | - Jan Kriska
- Department of Cellular Neurophysiology, Institute of Experimental Medicine, Czech Academy of Sciences, Prague, Czechia
| | - Jessica C. F. Kwok
- The Center for Reconstructive Neuroscience, Institute of Experimental Medicine, Czech Academy of Sciences, Prague, Czechia
- Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
| | - James W. Fawcett
- The Center for Reconstructive Neuroscience, Institute of Experimental Medicine, Czech Academy of Sciences, Prague, Czechia
- John van Geest Centre for Brain Repair, Department of Clinical Neurosciences, University of Cambridge, Cambridge, United Kingdom
| | - Pavla Jendelova
- Department of Neuroregeneration, Institute of Experimental Medicine, Czech Academy of Sciences, Prague, Czechia
- Second Faculty of Medicine, Charles University, Prague, Czechia
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16
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Sharples SA, Parker J, Vargas A, Milla-Cruz JJ, Lognon AP, Cheng N, Young L, Shonak A, Cymbalyuk GS, Whelan PJ. Contributions of h- and Na+/K+ Pump Currents to the Generation of Episodic and Continuous Rhythmic Activities. Front Cell Neurosci 2022; 15:715427. [PMID: 35185470 PMCID: PMC8855656 DOI: 10.3389/fncel.2021.715427] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2021] [Accepted: 12/29/2021] [Indexed: 12/31/2022] Open
Abstract
Developing spinal motor networks produce a diverse array of outputs, including episodic and continuous patterns of rhythmic activity. Variation in excitability state and neuromodulatory tone can facilitate transitions between episodic and continuous rhythms; however, the intrinsic mechanisms that govern these rhythms and their transitions are poorly understood. Here, we tested the capacity of a single central pattern generator (CPG) circuit with tunable properties to generate multiple outputs. To address this, we deployed a computational model composed of an inhibitory half-center oscillator (HCO). Following predictions of our computational model, we tested the contributions of key properties to the generation of an episodic rhythm produced by isolated spinal cords of the newborn mouse. The model recapitulates the diverse state-dependent rhythms evoked by dopamine. In the model, episodic bursting depended predominantly on the endogenous oscillatory properties of neurons, with Na+/K+ ATPase pump (IPump) and hyperpolarization-activated currents (Ih) playing key roles. Modulation of either IPump or Ih produced transitions between episodic and continuous rhythms and silence. As maximal activity of IPump decreased, the interepisode interval and period increased along with a reduction in episode duration. Decreasing maximal conductance of Ih decreased episode duration and increased interepisode interval. Pharmacological manipulations of Ih with ivabradine, and IPump with ouabain or monensin in isolated spinal cords produced findings consistent with the model. Our modeling and experimental results highlight key roles of Ih and IPump in producing episodic rhythms and provide insight into mechanisms that permit a single CPG to produce multiple patterns of rhythmicity.
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Affiliation(s)
- Simon A. Sharples
- School of Psychology and Neuroscience, University of St Andrews, St Andrews, United Kingdom
- Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada
- Department of Neuroscience, University of Calgary, Calgary, AB, Canada
| | - Jessica Parker
- Neuroscience Institute, Georgia State University, Atlanta, GA, United States
| | - Alex Vargas
- Neuroscience Institute, Georgia State University, Atlanta, GA, United States
| | - Jonathan J. Milla-Cruz
- Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada
- Department of Comparative Biology and Experimental Medicine, University of Calgary, Calgary, AB, Canada
| | - Adam P. Lognon
- Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada
- Department of Neuroscience, University of Calgary, Calgary, AB, Canada
| | - Ning Cheng
- Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada
- Department of Comparative Biology and Experimental Medicine, University of Calgary, Calgary, AB, Canada
| | - Leanne Young
- Department of Comparative Biology and Experimental Medicine, University of Calgary, Calgary, AB, Canada
| | - Anchita Shonak
- Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada
- Department of Neuroscience, University of Calgary, Calgary, AB, Canada
| | - Gennady S. Cymbalyuk
- Neuroscience Institute, Georgia State University, Atlanta, GA, United States
- Department of Physics and Astronomy, Georgia State University, Atlanta, GA, United States
- Gennady S. Cymbalyuk,
| | - Patrick J. Whelan
- Hotchkiss Brain Institute, University of Calgary, Calgary, AB, Canada
- Department of Neuroscience, University of Calgary, Calgary, AB, Canada
- Department of Comparative Biology and Experimental Medicine, University of Calgary, Calgary, AB, Canada
- *Correspondence: Patrick J. Whelan,
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17
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Falgairolle M, O'Donovan MJ. Motoneuronal Regulation of Central Pattern Generator and Network Function. ADVANCES IN NEUROBIOLOGY 2022; 28:259-280. [PMID: 36066829 DOI: 10.1007/978-3-031-07167-6_11] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
This chapter reviews recent work showing that vertebrate motoneurons can trigger spontaneous rhythmic activity in the developing spinal cord and can modulate the function of several different central pattern generators later in development. In both the embryonic chick and the fetal mouse spinal cords, antidromic activation of motoneurons can trigger bouts of rhythmic activity. In the neonatal mouse, optogenetic manipulation of motoneuron firing can modulate the frequency of fictive locomotion activated by a drug cocktail. In adult animals, motoneurons have been shown to regulate swimming in the zebrafish, and vocalization in fish and frogs. We discuss the significance of these findings and the degree to which motoneurons may be considered a part of these central pattern generators.
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18
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Sharples SA, Miles GB. Maturation of persistent and hyperpolarization-activated inward currents shapes the differential activation of motoneuron subtypes during postnatal development. eLife 2021; 10:e71385. [PMID: 34783651 PMCID: PMC8641952 DOI: 10.7554/elife.71385] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2021] [Accepted: 11/15/2021] [Indexed: 12/15/2022] Open
Abstract
The size principle underlies the orderly recruitment of motor units; however, motoneuron size is a poor predictor of recruitment amongst functionally defined motoneuron subtypes. Whilst intrinsic properties are key regulators of motoneuron recruitment, the underlying currents involved are not well defined. Whole-cell patch-clamp electrophysiology was deployed to study intrinsic properties, and the underlying currents, that contribute to the differential activation of delayed and immediate firing motoneuron subtypes. Motoneurons were studied during the first three postnatal weeks in mice to identify key properties that contribute to rheobase and may be important to establish orderly recruitment. We find that delayed and immediate firing motoneurons are functionally homogeneous during the first postnatal week and are activated based on size, irrespective of subtype. The rheobase of motoneuron subtypes becomes staggered during the second postnatal week, which coincides with the differential maturation of passive and active properties, particularly persistent inward currents. Rheobase of delayed firing motoneurons increases further in the third postnatal week due to the development of a prominent resting hyperpolarization-activated inward current. Our results suggest that motoneuron recruitment is multifactorial, with recruitment order established during postnatal development through the differential maturation of passive properties and sequential integration of persistent and hyperpolarization-activated inward currents.
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Affiliation(s)
- Simon A Sharples
- School of Psychology and Neuroscience, University of St AndrewsSt AndrewsUnited Kingdom
| | - Gareth B Miles
- School of Psychology and Neuroscience, University of St AndrewsSt AndrewsUnited Kingdom
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19
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Lemieux M, Thiry L, Laflamme OD, Bretzner F. Role of DSCAM in the Development of Neural Control of Movement and Locomotion. Int J Mol Sci 2021; 22:ijms22168511. [PMID: 34445216 PMCID: PMC8395195 DOI: 10.3390/ijms22168511] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Revised: 08/02/2021] [Accepted: 08/04/2021] [Indexed: 11/30/2022] Open
Abstract
Locomotion results in an alternance of flexor and extensor muscles between left and right limbs generated by motoneurons that are controlled by the spinal interneuronal circuit. This spinal locomotor circuit is modulated by sensory afferents, which relay proprioceptive and cutaneous inputs that inform the spatial position of limbs in space and potential contacts with our environment respectively, but also by supraspinal descending commands of the brain that allow us to navigate in complex environments, avoid obstacles, chase prey, or flee predators. Although signaling pathways are important in the establishment and maintenance of motor circuits, the role of DSCAM, a cell adherence molecule associated with Down syndrome, has only recently been investigated in the context of motor control and locomotion in the rodent. DSCAM is known to be involved in lamination and delamination, synaptic targeting, axonal guidance, dendritic and cell tiling, axonal fasciculation and branching, programmed cell death, and synaptogenesis, all of which can impact the establishment of motor circuits during development, but also their maintenance through adulthood. We discuss herein how DSCAM is important for proper motor coordination, especially for breathing and locomotion.
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Affiliation(s)
- Maxime Lemieux
- Centre de Recherche du Centre Hospitalier Universitaire de Québec, CHUL-Neurosciences P09800, 2705 boul. Laurier, Québec, QC G1V 4G2, Canada; (M.L.); (L.T.); (O.D.L.)
| | - Louise Thiry
- Centre de Recherche du Centre Hospitalier Universitaire de Québec, CHUL-Neurosciences P09800, 2705 boul. Laurier, Québec, QC G1V 4G2, Canada; (M.L.); (L.T.); (O.D.L.)
| | - Olivier D. Laflamme
- Centre de Recherche du Centre Hospitalier Universitaire de Québec, CHUL-Neurosciences P09800, 2705 boul. Laurier, Québec, QC G1V 4G2, Canada; (M.L.); (L.T.); (O.D.L.)
| | - Frédéric Bretzner
- Centre de Recherche du Centre Hospitalier Universitaire de Québec, CHUL-Neurosciences P09800, 2705 boul. Laurier, Québec, QC G1V 4G2, Canada; (M.L.); (L.T.); (O.D.L.)
- Department of Psychiatry and Neurosciences, Faculty of Medicine, Université Laval, Québec, QC G1V 4G2, Canada
- Correspondence:
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20
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Elimination of glutamatergic transmission from Hb9 interneurons does not impact treadmill locomotion. Sci Rep 2021; 11:16008. [PMID: 34362940 PMCID: PMC8346588 DOI: 10.1038/s41598-021-95143-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2021] [Accepted: 07/20/2021] [Indexed: 11/08/2022] Open
Abstract
The spinal cord contains neural circuits that can produce the rhythm and pattern of locomotor activity. It has previously been postulated that a population of glutamatergic neurons, termed Hb9 interneurons, contributes to locomotor rhythmogenesis. These neurons were identified by their expression of the homeobox gene, Hb9, which is also expressed in motor neurons. We developed a mouse line in which Cre recombinase activity is inducible in neurons expressing Hb9. We then used this line to eliminate vesicular glutamate transporter 2 from Hb9 interneurons, and found that there were no deficits in treadmill locomotion. We conclude that glutamatergic neurotransmission by Hb9 interneurons is not required for locomotor behaviour. The role of these neurons in neural circuits remains elusive.
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21
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Garcia-Ramirez DL, Ha NT, Bibu S, Stachowski NJ, Dougherty KJ. Spinal Cord Injury Alters Spinal Shox2 Interneurons by Enhancing Excitatory Synaptic Input and Serotonergic Modulation While Maintaining Intrinsic Properties in Mouse. J Neurosci 2021; 41:5833-5848. [PMID: 34006587 PMCID: PMC8265802 DOI: 10.1523/jneurosci.1576-20.2021] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2020] [Revised: 05/03/2021] [Accepted: 05/05/2021] [Indexed: 12/11/2022] Open
Abstract
Neural circuitry generating locomotor rhythm and pattern is located in the spinal cord. Most spinal cord injuries (SCIs) occur above the level of spinal locomotor neurons; therefore, these circuits are a target for improving motor function after SCI. Despite being relatively intact below the injury, locomotor circuitry undergoes substantial plasticity with the loss of descending control. Information regarding cell type-specific plasticity within locomotor circuits is limited. Shox2 interneurons (INs) have been linked to locomotor rhythm generation and patterning, making them a potential therapeutic target for the restoration of locomotion after SCI. The goal of the present study was to identify SCI-induced plasticity at the level of Shox2 INs in a complete thoracic transection model in adult male and female mice. Whole-cell patch-clamp recordings of Shox2 INs revealed minimal changes in intrinsic excitability properties after SCI. However, afferent stimulation resulted in mixed excitatory and inhibitory input to Shox2 INs in uninjured mice which became predominantly excitatory after SCI. Shox2 INs were differentially modulated by serotonin (5-HT) in a concentration-dependent manner in uninjured conditions but following SCI, 5-HT predominantly depolarized Shox2 INs. 5-HT7 receptors mediated excitatory effects on Shox2 INs from both uninjured and SCI mice, but activation of 5-HT2B/2C receptors enhanced excitability of Shox2 INs only after SCI. Overall, SCI alters sensory afferent input pathways to Shox2 INs and 5-HT modulation of Shox2 INs to enhance excitatory responses. Our findings provide relevant information regarding the locomotor circuitry response to SCI that could benefit strategies to improve locomotion after SCI.SIGNIFICANCE STATEMENT Current therapies to gain locomotor control after spinal cord injury (SCI) target spinal locomotor circuitry. Improvements in therapeutic strategies will require a better understanding of the SCI-induced plasticity within specific locomotor elements and their controllers, including sensory afferents and serotonergic modulation. Here, we demonstrate that excitability and intrinsic properties of Shox2 interneurons, which contribute to the generation of the locomotor rhythm and pattering, remain intact after SCI. However, SCI induces plasticity in both sensory afferent pathways and serotonergic modulation, enhancing the activation and excitation of Shox2 interneurons. Our findings will impact future strategies looking to harness these changes with the ultimate goal of restoring functional locomotion after SCI.
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Affiliation(s)
- D Leonardo Garcia-Ramirez
- Marion Murray Spinal Cord Research Center, Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129
| | - Ngoc T Ha
- Marion Murray Spinal Cord Research Center, Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129
| | - Steve Bibu
- Marion Murray Spinal Cord Research Center, Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129
| | - Nicholas J Stachowski
- Marion Murray Spinal Cord Research Center, Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129
| | - Kimberly J Dougherty
- Marion Murray Spinal Cord Research Center, Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129
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22
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Recent Insights into the Rhythmogenic Core of the Locomotor CPG. Int J Mol Sci 2021; 22:ijms22031394. [PMID: 33573259 PMCID: PMC7866530 DOI: 10.3390/ijms22031394] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2020] [Revised: 01/19/2021] [Accepted: 01/25/2021] [Indexed: 01/10/2023] Open
Abstract
In order for locomotion to occur, a complex pattern of muscle activation is required. For more than a century, it has been known that the timing and pattern of stepping movements in mammals are generated by neural networks known as central pattern generators (CPGs), which comprise multiple interneuron cell types located entirely within the spinal cord. A genetic approach has recently been successful in identifying several populations of spinal neurons that make up this neural network, as well as the specific role they play during stepping. In spite of this progress, the identity of the neurons responsible for generating the locomotor rhythm and the manner in which they are interconnected have yet to be deciphered. In this review, we summarize key features considered to be expressed by locomotor rhythm-generating neurons and describe the different genetically defined classes of interneurons which have been proposed to be involved.
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23
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Lee B, Cho Y. Experimental Model Systems for Understanding Human Axonal Injury Responses. Int J Mol Sci 2021; 22:E474. [PMID: 33418850 PMCID: PMC7824864 DOI: 10.3390/ijms22020474] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2020] [Revised: 12/03/2020] [Accepted: 12/30/2020] [Indexed: 12/26/2022] Open
Abstract
Neurons are structurally unique and have dendrites and axons that are vulnerable to injury. Some neurons in the peripheral nervous system (PNS) can regenerate their axons after injuries. However, most neurons in the central nervous system (CNS) fail to do so, resulting in irreversible neurological disorders. To understand the mechanisms of axon regeneration, various experimental models have been utilized in vivo and in vitro. Here, we collate the key experimental models that revealed the important mechanisms regulating axon regeneration and degeneration in different systems. We also discuss the advantages of experimenting with the rodent model, considering the application of these findings in understanding human diseases and for developing therapeutic methods.
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Affiliation(s)
| | - Yongcheol Cho
- Laboratory of Axon Regeneration & Degeneration, Department of Life Sciences, Korea University, Anam-ro 145, Seongbuk-gu, Seoul 02841, Korea;
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24
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Shevtsova NA, Ha NT, Rybak IA, Dougherty KJ. Neural Interactions in Developing Rhythmogenic Spinal Networks: Insights From Computational Modeling. Front Neural Circuits 2020; 14:614615. [PMID: 33424558 PMCID: PMC7787004 DOI: 10.3389/fncir.2020.614615] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2020] [Accepted: 11/17/2020] [Indexed: 11/13/2022] Open
Abstract
The mechanisms involved in generation of rhythmic locomotor activity in the mammalian spinal cord remain poorly understood. These mechanisms supposedly rely on both intrinsic properties of constituting neurons and interactions between them. A subset of Shox2 neurons was suggested to contribute to generation of spinal locomotor activity, but the possible cellular basis for rhythmic bursting in these neurons remains unknown. Ha and Dougherty (2018) recently revealed the presence of bidirectional electrical coupling between Shox2 neurons in neonatal spinal cords, which can be critically involved in neuronal synchronization and generation of populational bursting. Gap junctional connections found between functionally-related Shox2 interneurons decrease with age, possibly being replaced by increasing interactions through chemical synapses. Here, we developed a computational model of a heterogeneous population of neurons sparsely connected by electrical or/and chemical synapses and investigated the dependence of frequency of populational bursting on the type and strength of neuronal interconnections. The model proposes a mechanistic explanation that can account for the emergence of a synchronized rhythmic activity in the neuronal population and provides insights into the possible role of gap junctional coupling between Shox2 neurons in the spinal mechanisms for locomotor rhythm generation.
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Affiliation(s)
| | | | - Ilya A. Rybak
- Department of Neurobiology and Anatomy, College of Medicine, Drexel University, Philadelphia, PA, United States
| | - Kimberly J. Dougherty
- Department of Neurobiology and Anatomy, College of Medicine, Drexel University, Philadelphia, PA, United States
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25
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Differential dopamine modulation of spinal reflex amplitudes is associated with the presence or absence of the autonomic nervous system. Neurosci Lett 2020; 742:135514. [PMID: 33227368 DOI: 10.1016/j.neulet.2020.135514] [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: 05/05/2020] [Revised: 11/12/2020] [Accepted: 11/16/2020] [Indexed: 11/22/2022]
Abstract
The spinal cord contains a highly collateralized network of descending dopamine (DA) fibers that stem from the dorso-posterior hypothalamic A11 region in the brain, however, the modulatory actions of DA have generally only been assessed in lumbar segments L2-L5. In contrast to these exclusively sensorimotor segments, spinal cords segments T1-L2 and, in mouse, L6-S2, additionally contain the intermediolateral (IML) nucleus, the origin of autonomic nervous system (ANS). Here, we tested if the different spinal circuits in sensorimotor and IML-containing segments react differently to the modulation of the monosynaptic reflex (MSR) by DA. Bath-application of DA (1 μM) led to a decrease of MSR amplitude in L3-L5 segments; however, in IML-containing segments (T10-L2, and S1/2) the MSR response was facilitated. We did not observe any difference in the response between thoracic (sympathetic) and lumbosacral (parasympathetic) segments. Application of the D2-receptor agonists bromocriptine or quinpirole mimicked the effects of DA, while blocking D2 receptor pathways with raclopride or application with the D1-receptor agonist SKF 38393 led to an increase of the MSR in L3-L5 segments and a decrease of the MSR in IML-containing segments. In contrast, in the presence of the gap-junction blockers, carbenoloxone and quinine, DA modulatory actions in IML-containing segments were similar to those of sensorimotor L3-L5 segments. We suggest that DA modulates MSR amplitudes in the spinal cord in a segment-specific manner, and that the differential outcome observed in ANS segments may be a result of gap junctions in the IML.
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26
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The M-current works in tandem with the persistent sodium current to set the speed of locomotion. PLoS Biol 2020; 18:e3000738. [PMID: 33186352 PMCID: PMC7688130 DOI: 10.1371/journal.pbio.3000738] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2020] [Revised: 11/25/2020] [Accepted: 10/13/2020] [Indexed: 01/20/2023] Open
Abstract
The central pattern generator (CPG) for locomotion is a set of pacemaker neurons endowed with inherent bursting driven by the persistent sodium current (INaP). How they proceed to regulate the locomotor rhythm remained unknown. Here, in neonatal rodents, we identified a persistent potassium current critical in regulating pacemakers and locomotion speed. This current recapitulates features of the M-current (IM): a subthreshold noninactivating outward current blocked by 10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone dihydrochloride (XE991) and enhanced by N-(2-chloro-5-pyrimidinyl)-3,4-difluorobenzamide (ICA73). Immunostaining and mutant mice highlight an important role of Kv7.2-containing channels in mediating IM. Pharmacological modulation of IM regulates the emergence and the frequency regime of both pacemaker and CPG activities and controls the speed of locomotion. Computational models captured these results and showed how an interplay between IM and INaP endows the locomotor CPG with rhythmogenic properties. Overall, this study provides fundamental insights into how IM and INaP work in tandem to set the speed of locomotion.
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27
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Smith CC, Brownstone RM. Spinal motoneuron firing properties mature from rostral to caudal during postnatal development of the mouse. J Physiol 2020; 598:5467-5485. [PMID: 32851667 PMCID: PMC8436765 DOI: 10.1113/jp280274] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2020] [Accepted: 08/24/2020] [Indexed: 12/16/2022] Open
Abstract
Key points Many mammals are born with immature motor systems that develop through a critical period of postnatal development. In rodents, postnatal maturation of movement occurs from rostral to caudal, correlating with maturation of descending supraspinal and local spinal circuits. We asked whether development of fundamental electrophysiological properties of spinal motoneurons follows the same rostro‐caudal sequence. We show that in both regions, repetitive firing parameters increase and excitability decreases with development; however, these characteristics mature earlier in cervical motoneurons. We suggest that in addition to autonomous mechanisms, motoneuron development depends on activity resulting from their circuit milieu.
Abstract Altricial mammals are born with immature nervous systems comprised of circuits that do not yet have the neuronal properties and connectivity required to produce future behaviours. During the critical period of postnatal development, neuronal properties are tuned to participate in functional circuits. In rodents, cervical motoneurons are born prior to lumbar motoneurons, and spinal cord development follows a sequential rostro‐caudal pattern. Here we asked whether birth order is reflected in the postnatal development of electrophysiological properties. We show that motoneurons of both regions have similar properties at birth and follow the same developmental profile, with maximal firing increasing and excitability decreasing into the third postnatal week. However, these maturative processes occur in cervical motoneurons prior to lumbar motoneurons, correlating with the maturation of premotor descending and local spinal systems. These results suggest that motoneuron properties do not mature by cell autonomous mechanisms alone, but also depend on developing premotor circuits. Many mammals are born with immature motor systems that develop through a critical period of postnatal development. In rodents, postnatal maturation of movement occurs from rostral to caudal, correlating with maturation of descending supraspinal and local spinal circuits. We asked whether development of fundamental electrophysiological properties of spinal motoneurons follows the same rostro‐caudal sequence. We show that in both regions, repetitive firing parameters increase and excitability decreases with development; however, these characteristics mature earlier in cervical motoneurons. We suggest that in addition to autonomous mechanisms, motoneuron development depends on activity resulting from their circuit milieu.
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Affiliation(s)
- Calvin C Smith
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, University College London, London, UK
| | - Robert M Brownstone
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, University College London, London, UK
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28
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Domínguez-Rodríguez LE, Stecina K, García-Ramírez DL, Mena-Avila E, Milla-Cruz JJ, Martínez-Silva L, Zhang M, Hultborn H, Quevedo JN. Candidate Interneurons Mediating the Resetting of the Locomotor Rhythm by Extensor Group I Afferents in the Cat. Neuroscience 2020; 450:96-112. [PMID: 32946952 DOI: 10.1016/j.neuroscience.2020.09.017] [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: 05/18/2020] [Revised: 08/07/2020] [Accepted: 09/04/2020] [Indexed: 10/23/2022]
Abstract
Sensory information arising from limb movements controls the spinal locomotor circuitry to adapt the motor pattern to demands of the environment. Stimulation of extensor group (gr) I afferents during fictive locomotion in decerebrate cats prolongs the ongoing extension, and terminates ongoing flexion with an initiation of the subsequent extension, i. e. "resetting to extension". Moreover, instead of the classical Ib non-reciprocal inhibition, stimulation of extensor gr I afferents produces a polysynaptic excitation in extensor motoneurons with latencies (∼3.5-4.0 ms) compatible with 3 interposed interneurons. We assume that some interneurons in this pathway actually belong to the rhythm-generating layer of the locomotor Central Pattern Generator (CPG), since their activity was correlated to a resetting of the rhythm. In the present work fictive locomotion was (mostly) induced by i.v. injection of nialamide followed by l-DOPA in paralyzed cats following decerebration and spinalization at C1 level. In some experiments, we extended previous observations during fictive locomotion on the emergence and locomotor state-dependence of polysynaptic excitatory postsynaptic potentials from extensor gr I afferents to ankle extensor motoneurons. However, the main focus was to record location and properties of interneurons (n = 62) that (i) were active during the extensor phase of fictive locomotion and (ii) received short-latency excitation (mono-, di- or polysynaptic) from extensor gr I afferents. We conclude that the interneurons recorded fulfill the characteristics to belong to the neuronal pathway activated by extensor gr I afferents during locomotion, and may contribute to the 'resetting to extension' as part of the locomotor CPG.
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Affiliation(s)
| | - K Stecina
- Spinal Cord Research Centre, University of Manitoba, Winnipeg, Canada; Dept. of Neuroscience, University of Copenhagen, Denmark
| | - D L García-Ramírez
- Dept. of Physiology, Biophysics and Neuroscience, CINVESTAV del IPN, Mexico City, Mexico; Department of Neurobiology & Anatomy, Drexel University College of Medicine, Philadelphia, PA, USA
| | - E Mena-Avila
- Dept. of Physiology, Biophysics and Neuroscience, CINVESTAV del IPN, Mexico City, Mexico
| | - J J Milla-Cruz
- Dept. of Physiology, Biophysics and Neuroscience, CINVESTAV del IPN, Mexico City, Mexico
| | - L Martínez-Silva
- Dept. of Physiology, Biophysics and Neuroscience, CINVESTAV del IPN, Mexico City, Mexico; Department of Pathology and Cell Biology, Columbia University, New York, NY, USA
| | - M Zhang
- Dept. of Neuroscience, University of Copenhagen, Denmark; Inst. of Molecular Medicine, Medical Faculty, University of Southern Denmark, Odense, Denmark
| | - H Hultborn
- Dept. of Neuroscience, University of Copenhagen, Denmark.
| | - J N Quevedo
- Dept. of Physiology, Biophysics and Neuroscience, CINVESTAV del IPN, Mexico City, Mexico.
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29
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Le Gal JP, Colnot E, Cardoit L, Bacqué-Cazenave J, Thoby-Brisson M, Juvin L, Morin D. Modulation of respiratory network activity by forelimb and hindlimb locomotor generators. Eur J Neurosci 2020; 52:3181-3195. [PMID: 32150780 DOI: 10.1111/ejn.14717] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2019] [Revised: 02/05/2020] [Accepted: 03/03/2020] [Indexed: 01/22/2023]
Abstract
Early at the onset of exercise, breathing rate accelerates in order to anticipate the increasing metabolic demand resulting from the extra effort produced. Accordingly, the respiratory neural networks are the target of various input signals originating either centrally or peripherally. For example, during locomotion, the activation of muscle sensory afferents is able to entrain and thereby increase the frequency of spontaneous respiratory rhythmogenesis. Moreover, the lumbar spinal networks engaged in generating hindlimb locomotor rhythms are also capable of activating the medullary respiratory generators through an ascending excitatory command. However, in the context of quadrupedal locomotion, the influence of other spinal cord regions, such as cervical and thoracic segments, remains unknown. Using isolated brainstem-spinal cord preparations from neonatal rats and mice, we show that cervicothoracic circuitry may also contribute to locomotion-induced acceleration of respiratory cycle frequency. As previously observed for the hindlimb CPGs, the pharmacological activation of forelimb locomotor networks produces episodes of fictive locomotion that in turn increase the ongoing respiratory rhythm. Thoracic neuronal circuitry may also participate indirectly in this modulation via the activation of both cervical and lumbar CPG neurons. Furthermore, using light stimulation of CHR2-expressing glutamatergic neurons, we found that the modulation of the respiratory rate during locomotion involves lumbar glutamatergic circuitry. Our results demonstrate that during locomotion, the respiratory rhythm-generating networks receive excitatory ascending inputs from the spinal circuits responsible for generating and coordinating fore- and hindlimb movements. This constitutes a distributed central mechanism that contributes to matching breathing rate to the speed of locomotion.
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Affiliation(s)
- Jean-Patrick Le Gal
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, Unité Mixte de Recherche, Centre National de la Recherche Scientifique, Université de Bordeaux, Bordeaux, France
| | - Eloïse Colnot
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, Unité Mixte de Recherche, Centre National de la Recherche Scientifique, Université de Bordeaux, Bordeaux, France
| | - Laura Cardoit
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, Unité Mixte de Recherche, Centre National de la Recherche Scientifique, Université de Bordeaux, Bordeaux, France
| | - Julien Bacqué-Cazenave
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, Unité Mixte de Recherche, Centre National de la Recherche Scientifique, Université de Bordeaux, Bordeaux, France
| | - Muriel Thoby-Brisson
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, Unité Mixte de Recherche, Centre National de la Recherche Scientifique, Université de Bordeaux, Bordeaux, France
| | - Laurent Juvin
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, Unité Mixte de Recherche, Centre National de la Recherche Scientifique, Université de Bordeaux, Bordeaux, France
| | - Didier Morin
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, Unité Mixte de Recherche, Centre National de la Recherche Scientifique, Université de Bordeaux, Bordeaux, France
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30
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Song J, Pallucchi I, Ausborn J, Ampatzis K, Bertuzzi M, Fontanel P, Picton LD, El Manira A. Multiple Rhythm-Generating Circuits Act in Tandem with Pacemaker Properties to Control the Start and Speed of Locomotion. Neuron 2020; 105:1048-1061.e4. [PMID: 31982322 DOI: 10.1016/j.neuron.2019.12.030] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2019] [Revised: 11/18/2019] [Accepted: 12/26/2019] [Indexed: 10/25/2022]
Abstract
In vertebrates, specific command centers in the brain can selectively drive slow-explorative or fast-speed locomotion. However, it remains unclear how the locomotor central pattern generator (CPG) processes descending drive into coordinated locomotion. Here, we reveal, in adult zebrafish, a logic of the V2a interneuron rhythm-generating circuits involving recurrent and hierarchical connectivity that acts in tandem with pacemaker properties to provide an ignition and gear-shift mechanism to start locomotion and change speed. A comprehensive mapping of synaptic connections reveals three recurrent circuit modules engaged sequentially to increase locomotor speed. The connectivity between V2a interneurons of different modules displayed a clear asymmetry in favor of connections from faster to slower modules. The interplay between V2a interneuron pacemaker properties and their organized connectivity provides a mechanism for locomotor initiation and speed control. Thus, our results provide mechanistic insights into how the spinal CPG transforms descending drive into locomotion and align its speed with the initial intention.
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Affiliation(s)
- Jianren Song
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden; Center of Translational Medicine, Tongji Hospital, Tongji University School of Medicine, Shanghai 200065, China
| | - Irene Pallucchi
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden
| | - Jessica Ausborn
- Department of Neurobiology and Anatomy, College of Medicine, Drexel University, Philadelphia, PA, USA
| | | | - Maria Bertuzzi
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden
| | - Pierre Fontanel
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden
| | - Laurence D Picton
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden
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31
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Hachoumi L, Sillar KT. Developmental stage-dependent switching in the neuromodulation of vertebrate locomotor central pattern generator networks. Dev Neurobiol 2019; 80:42-57. [PMID: 31705739 DOI: 10.1002/dneu.22725] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2019] [Revised: 09/24/2019] [Accepted: 11/05/2019] [Indexed: 12/27/2022]
Abstract
Neuromodulation plays important and stage-dependent roles in regulating locomotor central pattern (CPG) outputs during vertebrate motor system development. Dopamine, serotonin and nitric oxide are three neuromodulators that potently influence CPG outputs in the development of Xenopus frog tadpole locomotion. However, their roles switch from predominantly inhibitory early in development to mainly excitatory at later stages. In this review, we compare the stage-dependent switching in neuromodulation in Xenopus with other vertebrate systems, notably the mouse and the zebrafish, and highlight features that appear to be phylogenetically conserved.
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Affiliation(s)
- Lamia Hachoumi
- School of Psychology and Neuroscience, University of St Andrews, St Andrews, UK
| | - Keith T Sillar
- School of Psychology and Neuroscience, University of St Andrews, St Andrews, UK
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32
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Bubnys A, Kandel H, Kao LM, Pfaff D, Tabansky I. Hindbrain V2a Neurons Pattern Rhythmic Activity of Motor Neurons in a Reticulospinal Coculture. Front Neurosci 2019; 13:1077. [PMID: 31680817 PMCID: PMC6811747 DOI: 10.3389/fnins.2019.01077] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2019] [Accepted: 09/24/2019] [Indexed: 11/19/2022] Open
Abstract
As the capacity to isolate distinct neuronal cell types has advanced over the past several decades, new two- and three-dimensional in vitro models of the interactions between different brain regions have expanded our understanding of human neurobiology and the origins of disease. These cultures develop distinctive patterns of activity, but the extent that these patterns are determined by the molecular identity of individual cell types versus the specific pattern of network connectivity is unclear. To address the question of how individual cell types interact in vitro, we developed a simplified culture using two excitatory neuronal subtypes known to participate in the in vivo reticulospinal circuit: HB9+ spinal motor neurons and Chx10+ hindbrain V2a neurons. Here, we report the emergence of cell type-specific patterns of activity in culture; on their own, Chx10+ neurons developed regular, synchronized bursts of activity that recruited neurons across the entire culture, whereas HB9+ neuron activity consisted of an irregular pattern. When these two subtypes were cocultured, HB9+ neurons developed synchronized network bursts that were precisely correlated with Chx10+ neuron activity, thereby recreating an aspect of Chx10+ neurons' role in driving motor activity. These bursts were dependent on AMPA receptors. Our results demonstrate that the molecular classification of the neurons comprising in vitro networks is a crucial determinant of their activity. It is therefore possible to improve both the reproducibility and the applicability of in vitro neurobiological and disease models by carefully controlling the constituent mixtures of neuronal subtypes.
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Affiliation(s)
- Adele Bubnys
- Laboratory of Neurobiology and Behavior, The Rockefeller University, New York, NY, United States
| | - Hagar Kandel
- Laboratory of Neurobiology and Behavior, The Rockefeller University, New York, NY, United States
| | - Lee Ming Kao
- Laboratory of Neurobiology and Behavior, The Rockefeller University, New York, NY, United States
| | - Donald Pfaff
- Laboratory of Neurobiology and Behavior, The Rockefeller University, New York, NY, United States
| | - Inna Tabansky
- Laboratory of Neurobiology and Behavior, The Rockefeller University, New York, NY, United States
- Feinstein Institute for Medical Research, Manhasset, NY, United States
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33
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Brettle M, Stefen H, Djordjevic A, Fok SYY, Chan JW, van Hummel A, van der Hoven J, Przybyla M, Volkerling A, Ke YD, Delerue F, Ittner LM, Fath T. Developmental Expression of Mutant PFN1 in Motor Neurons Impacts Neuronal Growth and Motor Performance of Young and Adult Mice. Front Mol Neurosci 2019; 12:231. [PMID: 31611772 PMCID: PMC6776973 DOI: 10.3389/fnmol.2019.00231] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2019] [Accepted: 09/10/2019] [Indexed: 12/11/2022] Open
Abstract
Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease with limited treatment and no cure. Mutations in profilin 1 were identified as a cause of familial ALS (fALS) in 2012. We investigated the functional impact of mutant profilin 1 expression in spinal cords during mouse development. We developed a novel mouse model with the expression of profilin 1 C71G under the control of the Hb9 promoter, targeting expression to α-motor neurons in the spinal cord during development. Embryos of transgenic mice showed evidence of a significant reduction of brachial nerve diameter and a loss of Mendelian inheritance. Despite the lack of transgene expression, adult mice presented with significant motor deficits. Transgenic mice had a significant reduction in the number of motor neurons in the spinal cord. Further analysis of these motor neurons in aged transgenic mice revealed reduced levels of TDP-43 and ChAT expression. Although profilin 1 C71G was only expressed during development, adult mice presented with some ALS-associated pathology and motor symptoms. This study highlights the effect of profilin 1 during neurodevelopment and the impact that this may have in later ALS.
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Affiliation(s)
- Merryn Brettle
- School of Medical Sciences, Faculty of Medicine, UNSW Sydney, Randwick, NSW, Australia.,Biomedical Imaging Facility, Mark Wainwright Analytical Centre, UNSW Sydney, Randwick, NSW, Australia
| | - Holly Stefen
- Dementia Research Centre and Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia
| | - Aleksandra Djordjevic
- School of Medical Sciences, Faculty of Medicine, UNSW Sydney, Randwick, NSW, Australia
| | - Sandra Y Y Fok
- School of Medical Sciences, Faculty of Medicine, UNSW Sydney, Randwick, NSW, Australia.,Biomedical Imaging Facility, Mark Wainwright Analytical Centre, UNSW Sydney, Randwick, NSW, Australia
| | - Josephine W Chan
- School of Medical Sciences, Faculty of Medicine, UNSW Sydney, Randwick, NSW, Australia
| | - Annika van Hummel
- Dementia Research Centre and Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia
| | - Julia van der Hoven
- Dementia Research Centre and Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia
| | - Magdalena Przybyla
- Dementia Research Centre and Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia
| | - Alexander Volkerling
- School of Medical Sciences, Faculty of Medicine, UNSW Sydney, Randwick, NSW, Australia
| | - Yazi D Ke
- Dementia Research Centre and Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia
| | - Fabien Delerue
- Dementia Research Centre and Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia
| | - Lars M Ittner
- Dementia Research Centre and Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia
| | - Thomas Fath
- School of Medical Sciences, Faculty of Medicine, UNSW Sydney, Randwick, NSW, Australia.,Dementia Research Centre and Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia
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34
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Sp1-regulated expression of p11 contributes to motor neuron degeneration by membrane insertion of TASK1. Nat Commun 2019; 10:3784. [PMID: 31439839 PMCID: PMC6706379 DOI: 10.1038/s41467-019-11637-4] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2018] [Accepted: 07/25/2019] [Indexed: 01/18/2023] Open
Abstract
Disruption in membrane excitability contributes to malfunction and differential vulnerability of specific neuronal subpopulations in a number of neurological diseases. The adaptor protein p11, and background potassium channel TASK1, have overlapping distributions in the CNS. Here, we report that the transcription factor Sp1 controls p11 expression, which impacts on excitability by hampering functional expression of TASK1. In the SOD1-G93A mouse model of ALS, Sp1-p11-TASK1 dysregulation contributes to increased excitability and vulnerability of motor neurons. Interference with either Sp1 or p11 is neuroprotective, delaying neuron loss and prolonging lifespan in this model. Nitrosative stress, a potential factor in human neurodegeneration, stimulated Sp1 expression and human p11 promoter activity, at least in part, through a Sp1-binding site. Disruption of Sp1 or p11 also has neuroprotective effects in a traumatic model of motor neuron degeneration. Together our work suggests the Sp1-p11-TASK1 pathway is a potential target for treatment of degeneration of motor neurons. The adaptor protein p11 and K+ channel TASK1 have overlapping distributions in the CNS. Here, the authors demonstrate that the transcription factor Sp1 regulates p11 levels, which in turn affects intrinsic membrane properties and can contribute to degeneration of motor neurons in disease and injury models.
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35
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Steuer I, Guertin PA. Central pattern generators in the brainstem and spinal cord: an overview of basic principles, similarities and differences. Rev Neurosci 2019; 30:107-164. [PMID: 30543520 DOI: 10.1515/revneuro-2017-0102] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2017] [Accepted: 03/30/2018] [Indexed: 12/11/2022]
Abstract
Central pattern generators (CPGs) are generally defined as networks of neurons capable of enabling the production of central commands, specifically controlling stereotyped, rhythmic motor behaviors. Several CPGs localized in brainstem and spinal cord areas have been shown to underlie the expression of complex behaviors such as deglutition, mastication, respiration, defecation, micturition, ejaculation, and locomotion. Their pivotal roles have clearly been demonstrated although their organization and cellular properties remain incompletely characterized. In recent years, insightful findings about CPGs have been made mainly because (1) several complementary animal models were developed; (2) these models enabled a wide variety of techniques to be used and, hence, a plethora of characteristics to be discovered; and (3) organizations, functions, and cell properties across all models and species studied thus far were generally found to be well-preserved phylogenetically. This article aims at providing an overview for non-experts of the most important findings made on CPGs in in vivo animal models, in vitro preparations from invertebrate and vertebrate species as well as in primates. Data about CPG functions, adaptation, organization, and cellular properties will be summarized with a special attention paid to the network for locomotion given its advanced level of characterization compared with some of the other CPGs. Similarities and differences between these networks will also be highlighted.
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Affiliation(s)
- Inge Steuer
- Neuroscience Unit, Laval University Medical Center (CHUL - CHU de Québec), 2705 Laurier Blvd, Quebec City, Quebec G1V 4G2, Canada
| | - Pierre A Guertin
- Neuroscience Unit, Laval University Medical Center (CHUL - CHU de Québec), 2705 Laurier Blvd, Quebec City, Quebec G1V 4G2, Canada
- Faculty of Medicine, Department of Psychiatry and Neurosciences, Laval University, Quebec City, Quebec G1V 0A6, Canada
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Radosevic M, Willumsen A, Petersen PC, Lindén H, Vestergaard M, Berg RW. Decoupling of timescales reveals sparse convergent CPG network in the adult spinal cord. Nat Commun 2019; 10:2937. [PMID: 31270315 PMCID: PMC6610135 DOI: 10.1038/s41467-019-10822-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2018] [Accepted: 06/04/2019] [Indexed: 12/12/2022] Open
Abstract
During the generation of rhythmic movements, most spinal neurons receive an oscillatory synaptic drive. The neuronal architecture underlying this drive is unknown, and the corresponding network size and sparseness have not yet been addressed. If the input originates from a small central pattern generator (CPG) with dense divergent connectivity, it will induce correlated input to all receiving neurons, while sparse convergent wiring will induce a weak correlation, if any. Here, we use pairwise recordings of spinal neurons to measure synaptic correlations and thus infer the wiring architecture qualitatively. A strong correlation on a slow timescale implies functional relatedness and a common source, which will also cause correlation on fast timescale due to shared synaptic connections. However, we consistently find marginal coupling between slow and fast correlations regardless of neuronal identity. This suggests either sparse convergent connectivity or a CPG network with recurrent inhibition that actively decorrelates common input.
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Affiliation(s)
- Marija Radosevic
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200, Copenhagen N, Denmark
| | - Alex Willumsen
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200, Copenhagen N, Denmark
| | - Peter C Petersen
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200, Copenhagen N, Denmark
- Neuroscience Institute, New York University, New York, NY, 10016, USA
| | - Henrik Lindén
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200, Copenhagen N, Denmark
| | - Mikkel Vestergaard
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200, Copenhagen N, Denmark
- Department of Neuroscience, Max Delbrück Center for Molecular Medicine (MDC), 13125, Berlin-Buch, Germany
| | - Rune W Berg
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3, DK-2200, Copenhagen N, Denmark.
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Dougherty KJ, Ha NT. The rhythm section: An update on spinal interneurons setting the beat for mammalian locomotion. CURRENT OPINION IN PHYSIOLOGY 2019; 8:84-93. [PMID: 31179403 PMCID: PMC6550992 DOI: 10.1016/j.cophys.2019.01.004] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
To initiate and support locomotion, rhythm generating neurons in the spinal central pattern generator convert descending input into a rhythmic signal which is conveyed to downstream neurons, leading to the recruitment of motor neurons and activation of muscles. Although two genetically-defined neuronal populations have been linked to rhythm generation, a single all-inclusive rhythm generating population has yet to be identified. Here, we consolidate recent work aimed at identifying rhythm generating neurons, summarize the evidence for the involvement of two neuronal populations in rhythm generation, describe the challenges in identifying a marker for rhythm generating neurons, and discuss potential directions to take in integrating spinal rhythm generating neurons into recently identified speed-dependent locomotor circuits.
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Affiliation(s)
- Kimberly J. Dougherty
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA 19129, USA
| | - Ngoc T. Ha
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, PA 19129, USA
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Li WC, Soffe SR. Stimulation of Single, Possible CHX10 Hindbrain Neurons Turns Swimming On and Off in Young Xenopus Tadpoles. Front Cell Neurosci 2019; 13:47. [PMID: 30873004 PMCID: PMC6401594 DOI: 10.3389/fncel.2019.00047] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2018] [Accepted: 02/01/2019] [Indexed: 11/13/2022] Open
Abstract
Vertebrate central pattern generators (CPGs) controlling locomotion contain neurons which provide the excitation that drives and maintains network rhythms. In a simple vertebrate, the developing Xenopus tadpole, we study the role of excitatory descending neurons with ipsilateral projecting axons (descending interneurons, dINs) in the control of swimming rhythms. In tadpoles with both intact central nervous system (CNS) and transections in the hindbrain, exciting some individual dINs in the caudal hindbrain region could start swimming repeatedly. Analyses indicated the recruitment of additional dINs immediately after such evoked dIN spiking and prior to swimming. Excitation of dINs can therefore be sufficient for the initiation of swimming. These "powerful" dINs all possessed both ascending and descending axons. However, their axon projection lengths were not different from those of other excitatory dINs at similar locations. The dorsoventral position of dINs, as a population, significantly better matched that of cells marked by immunocytochemistry for the transcription factor CHX10 than other known neuron types in the ventral hindbrain and spinal cord. The comparison suggests that the excitatory interneurons including dINs are CHX10-positive, in agreement with CHX10 as a marker for excitatory neurons with ipsilateral projections in the spinal cord and brainstem of other vertebrates. Overall, our results further demonstrate the key importance of dINs in driving tadpole swimming rhythms.
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Affiliation(s)
- Wen-Chang Li
- School of Psychology and Neuroscience, University of St Andrews, St Andrews, United Kingdom
| | - Stephen R Soffe
- School of Biological Sciences, Tyndall Avenue, University of Bristol, Bristol, United Kingdom
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Ha NT, Dougherty KJ. Spinal Shox2 interneuron interconnectivity related to function and development. eLife 2018; 7:42519. [PMID: 30596374 PMCID: PMC6333440 DOI: 10.7554/elife.42519] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2018] [Accepted: 12/27/2018] [Indexed: 12/25/2022] Open
Abstract
Neuronal networks generating hindlimb locomotion are located in the spinal cord. The mechanisms underlying spinal rhythmogenesis are unknown but network activity and interconnectivity of excitatory interneurons likely play prominent roles. Here, we investigate interconnectivity within the Shox2 interneuron population, a subset of which has been suggested to be involved in locomotor rhythm generation, using paired recordings in isolated spinal cords or slices from transgenic mice. Sparse unidirectional connections consistent with chemical synaptic transmission and prominent bidirectional connections mediated by electrical synapses were present within distinct subsets of Shox2 interneurons. Moreover, bidirectional electrical connections were preferentially found between functionally-related Shox2 interneurons. Though prevalent in neonatal mice, electrical coupling began to decline in incidence and strength in mice ~ 3 weeks of age. Overall, our data suggest that gap junctional coupling promotes synchronization of Shox2 interneurons, and may be implicated in locomotor rhythmicity in developing mice.
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Affiliation(s)
- Ngoc T Ha
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, United States
| | - Kimberly J Dougherty
- Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, United States
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Characterization of Dmrt3-Derived Neurons Suggest a Role within Locomotor Circuits. J Neurosci 2018; 39:1771-1782. [PMID: 30578339 DOI: 10.1523/jneurosci.0326-18.2018] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2018] [Revised: 11/27/2018] [Accepted: 12/10/2018] [Indexed: 11/21/2022] Open
Abstract
Neuronal networks within the spinal cord, collectively known as the central pattern generator (CPG), coordinate rhythmic movements underlying locomotion. The transcription factor doublesex and mab-3-related transcription factor 3 (DMRT3) is involved in the differentiation of the dorsal interneuron 6 class of spinal cord interneurons. In horses, a non-sense mutation in the Dmrt3 gene has major effects on gaiting ability, whereas mice lacking the Dmrt3 gene display impaired locomotor activity. Although the Dmrt3 gene is necessary for normal spinal network formation and function in mice, a direct role for Dmrt3-derived neurons in locomotor-related activities has not been demonstrated. Here we present the characteristics of the Dmrt3-derived spinal cord interneurons. Using transgenic mice of both sexes, we characterized interneurons labeled by their expression of Cre driven by the endogenous Dmrt3 promoter. We used molecular, retrograde tracing and electrophysiological techniques to examine the anatomical, morphological, and electrical properties of the Dmrt3-Cre neurons. We demonstrate that inhibitory Dmrt3-Cre neurons receive extensive synaptic inputs, innervate surrounding CPG neurons, intrinsically regulate CPG neuron's electrical activity, and are rhythmically active during fictive locomotion, bursting at frequencies independent to the ventral root output. The present study provides novel insights on the character of spinal Dmrt3-derived neurons, data demonstrating that these neurons participate in locomotor coordination.SIGNIFICANCE STATEMENT In this work, we provide evidence for a role of the Dmrt3 interneurons in spinal cord locomotor circuits as well as molecular and functional insights on the cellular and microcircuit level of the Dmrt3-expressing neurons in the spinal cord. Dmrt3 neurons provide the first example of an interneuron population displaying different oscillation frequencies. This study presents novel findings on an under-reported population of spinal cord neurons, which will aid in deciphering the locomotor network and will facilitate the design and development of therapeutics for spinal cord injury and motor disorders.
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Orexinergic Modulation of Spinal Motor Activity in the Neonatal Mouse Spinal Cord. eNeuro 2018; 5:eN-NWR-0226-18. [PMID: 30417080 PMCID: PMC6223113 DOI: 10.1523/eneuro.0226-18.2018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2018] [Revised: 10/15/2018] [Accepted: 10/20/2018] [Indexed: 11/21/2022] Open
Abstract
The role of orexin during development, and especially in terms of spinal cord function, is not well understood. It is for this reason that we focused on the network actions of orexin during the first week of development. We found that orexinergic fibers were present in the lumbar spinal cord of postnatal day 0 (P0) to P3 mice. The fibers were expressed mainly in the dorsal horn, but occasional fibers were observed in the ventral horn. Both orexin (OX) A and OXB increased the motoneurons (MNs) tonic neurogram discharge. However, only OXA was found to significantly increase spontaneous bursting activity and the frequency of fictive locomotor bursts. We show that OXA is able to act directly on MNs. To test the contribution of the recurrent MN collaterals, we blocked the nicotinic cholinergic drive and observed that OXA retained its ability to increase fictive locomotor activity. Additionally, we recorded neurograms from ventral lateral funiculi, where OXA had no effect on population discharge. These effects were also confirmed by recording from descending commissural interneurons via patch recordings. The loci of the effects of OXA were further investigated in a dorsal horn-removed preparation where OXA also shows an increase in the discharge from ventral root neurograms but no increase in the frequency of spontaneous or fictive locomotion burst activity. In summary, multiple lines of evidence from our work demonstrate the robust effects of orexins on spinal cord networks and MNs at the time of birth.
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Chopek JW, Nascimento F, Beato M, Brownstone RM, Zhang Y. Sub-populations of Spinal V3 Interneurons Form Focal Modules of Layered Pre-motor Microcircuits. Cell Rep 2018; 25:146-156.e3. [PMID: 30282024 PMCID: PMC6180347 DOI: 10.1016/j.celrep.2018.08.095] [Citation(s) in RCA: 54] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2018] [Revised: 07/25/2018] [Accepted: 08/30/2018] [Indexed: 12/26/2022] Open
Abstract
Layering of neural circuits facilitates the separation of neurons with high spatial sensitivity from those that play integrative temporal roles. Although anatomical layers are readily identifiable in the brain, layering is not structurally obvious in the spinal cord. But computational studies of motor behaviors have led to the concept of layered processing in the spinal cord. It has been postulated that spinal V3 interneurons (INs) play multiple roles in locomotion, leading us to investigate whether they form layered microcircuits. Using patch-clamp recordings in combination with holographic glutamate uncaging, we demonstrate focal, layered modules, in which ventromedial V3 INs form synapses with one another and with ventrolateral V3 INs, which in turn form synapses with ipsilateral motoneurons. Motoneurons, in turn, provide recurrent excitatory, glutamatergic input to V3 INs. Thus, ventral V3 interneurons form layered microcircuits that could function to ensure well-timed, spatially specific movements.
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Affiliation(s)
- Jeremy W Chopek
- Department of Medical Neuroscience, Faculty of Medicine, Dalhousie University, Halifax, NS B3H 4R2, Canada; Sobell Department of Neuromuscular Diseases, Institute of Neurology, University College London, London WC1N 3BG, UK
| | - Filipe Nascimento
- Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, UK
| | - Marco Beato
- Department of Neuroscience, Physiology and Pharmacology, University College London, London WC1E 6BT, UK
| | - Robert M Brownstone
- Sobell Department of Neuromuscular Diseases, Institute of Neurology, University College London, London WC1N 3BG, UK.
| | - Ying Zhang
- Department of Medical Neuroscience, Faculty of Medicine, Dalhousie University, Halifax, NS B3H 4R2, Canada.
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Duysens J, Forner-Cordero A. Walking with perturbations: a guide for biped humans and robots. BIOINSPIRATION & BIOMIMETICS 2018; 13:061001. [PMID: 30109860 DOI: 10.1088/1748-3190/aada54] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
This paper provides an update on the neural control of bipedal walking in relation to bioinspired models and robots. It is argued that most current models or robots are based on the construct of a symmetrical central pattern generator (CPG). However, new evidence suggests that CPG functioning is basically asymmetrical with its flexor half linked more tightly to the rhythm generator. The stability of bipedal gait, which is an important problem for robots and biological systems, is also addressed. While it is not possible to determine how biological biped systems guarantee stability, robot solutions can be useful to propose new hypotheses for biology. In the second part of this review, the focus is on gait perturbations, which is an important topic in robotics in view of the frequent falls of robots when faced with perturbations. From the human physiology it is known that the initial reaction often consists of a brief interruption followed by an adequate response. For instance, the successful recovery from a trip is achieved using some basic reactions (termed elevating and lowering strategies), that depend on the phase of the step cycle of the trip occurrence. Reactions to stepping unexpectedly in a hole depend on comparing expected and real feedback. Implementation of these ideas in models and robotics starts to emerge, with the most advanced robots being able to learn how to fall safely and how to deal with complicated disturbances such as provided by walking on a split-belt.
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Affiliation(s)
- Jacques Duysens
- Biomechatronics Lab., Mechatronics Department, Escola Politécnica da Universidade de São Paulo, Av. Prof. Mello Moraes, 2231, Cidade Universitária 05508-030, São Paulo-SP, Brasil. Department of Kinesiology, FaBeR, Katholieke Universiteit Leuven, Leuven, Belgium
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Dopamine Pumping Up Spinal Locomotor Network Function. J Neurosci 2018; 37:3103-3105. [PMID: 28330979 DOI: 10.1523/jneurosci.0019-17.2017] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2017] [Revised: 02/06/2017] [Accepted: 02/16/2017] [Indexed: 01/11/2023] Open
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Delineating the Diversity of Spinal Interneurons in Locomotor Circuits. J Neurosci 2017; 37:10835-10841. [PMID: 29118212 DOI: 10.1523/jneurosci.1829-17.2017] [Citation(s) in RCA: 65] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2017] [Revised: 09/27/2017] [Accepted: 10/11/2017] [Indexed: 11/21/2022] Open
Abstract
Locomotion is common to all animals and is essential for survival. Neural circuits located in the spinal cord have been shown to be necessary and sufficient for the generation and control of the basic locomotor rhythm by activating muscles on either side of the body in a specific sequence. Activity in these neural circuits determines the speed, gait pattern, and direction of movement, so the specific locomotor pattern generated relies on the diversity of the neurons within spinal locomotor circuits. Here, we review findings demonstrating that developmental genetics can be used to identify populations of neurons that comprise these circuits and focus on recent work indicating that many of these populations can be further subdivided into distinct subtypes, with each likely to play complementary functions during locomotion. Finally, we discuss data describing the manner in which these populations interact with each other to produce efficient, task-dependent locomotion.
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Ziskind-Conhaim L, Hochman S. Diversity of molecularly defined spinal interneurons engaged in mammalian locomotor pattern generation. J Neurophysiol 2017; 118:2956-2974. [PMID: 28855288 DOI: 10.1152/jn.00322.2017] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2017] [Revised: 08/29/2017] [Accepted: 08/30/2017] [Indexed: 01/18/2023] Open
Abstract
Mapping the expression of transcription factors in the mouse spinal cord has identified ten progenitor domains, four of which are cardinal classes of molecularly defined, ventrally located interneurons that are integrated in the locomotor circuitry. This review focuses on the properties of these interneuronal populations and their contribution to hindlimb locomotor central pattern generation. Interneuronal populations are categorized based on their excitatory or inhibitory functions and their axonal projections as predictors of their role in locomotor rhythm generation and coordination. The synaptic connectivity and functions of these interneurons in the locomotor central pattern generators (CPGs) have been assessed by correlating their activity patterns with motor output responses to rhythmogenic neurochemicals and sensory and descending fibers stimulations as well as analyzing kinematic gait patterns in adult mice. The observed complex organization of interneurons in the locomotor CPG circuitry, some with seemingly similar physiological functions, reflects the intricate repertoire associated with mammalian motor control and is consistent with high transcriptional heterogeneity arising from cardinal interneuronal classes. This review discusses insights derived from recent studies to describe innovative approaches and limitations in experimental model systems and to identify missing links in current investigational enterprise.
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Affiliation(s)
- Lea Ziskind-Conhaim
- Department of Neuroscience, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin; and
| | - Shawn Hochman
- Department of Physiology, Emory University School of Medicine, Atlanta, Georgia
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Spinal Hb9::Cre-derived excitatory interneurons contribute to rhythm generation in the mouse. Sci Rep 2017; 7:41369. [PMID: 28128321 PMCID: PMC5269678 DOI: 10.1038/srep41369] [Citation(s) in RCA: 54] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2016] [Accepted: 12/20/2016] [Indexed: 11/14/2022] Open
Abstract
Rhythm generating neurons are thought to be ipsilaterally-projecting excitatory neurons in the thoracolumbar mammalian spinal cord. Recently, a subset of Shox2 interneurons (Shox2 non-V2a INs) was found to fulfill these criteria and make up a fraction of the rhythm-generating population. Here we use Hb9::Cre mice to genetically manipulate Hb9::Cre-derived excitatory interneurons (INs) in order to determine the role of these INs in rhythm generation. We demonstrate that this line captures a consistent population of spinal INs which is mixed with respect to neurotransmitter phenotype and progenitor domain, but does not overlap with the Shox2 non-V2a population. We also show that Hb9::Cre-derived INs include the comparatively small medial population of INs which continues to express Hb9 postnatally. When excitatory neurotransmission is selectively blocked by deleting Vglut2 from Hb9::Cre-derived INs, there is no difference in left-right and/or flexor-extensor phasing between these cords and controls, suggesting that excitatory Hb9::Cre-derived INs do not affect pattern generation. In contrast, the frequencies of locomotor activity are significantly lower in cords from Hb9::Cre-Vglut2Δ/Δ mice than in cords from controls. Collectively, our findings indicate that excitatory Hb9::Cre-derived INs constitute a distinct population of neurons that participates in the rhythm generating kernel for spinal locomotion.
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48
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Kusakabe TG. Identifying Vertebrate Brain Prototypes in Deuterostomes. DIVERSITY AND COMMONALITY IN ANIMALS 2017. [DOI: 10.1007/978-4-431-56469-0_7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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49
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Arshavsky YI. Neurons versus Networks: The Interplay between Individual Neurons and Neural Networks in Cognitive Functions. Neuroscientist 2016; 23:341-355. [PMID: 27660240 DOI: 10.1177/1073858416670124] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The main paradigm of cognitive neuroscience is the connectionist concept postulating that the higher nervous activity is performed through interactions of neurons forming complex networks, whereas the function of individual neurons is restricted to generating electrical potentials and transmitting signals to other cells. In this article, I describe the observations from three fields-neurolinguistics, physiology of memory, and sensory perception-that can hardly be explained within the constraints of a purely connectionist concept. Rather, these examples suggest that cognitive functions are determined by specific properties of individual neurons and, therefore, are likely to be accomplished primarily at the intracellular level. This view is supported by the recent discovery that the brain's ability to create abstract concepts of particular individuals, animals, or places is performed by neurons ("concept cells") sparsely distributed in the medial temporal lobe.
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Affiliation(s)
- Yuri I Arshavsky
- 1 BioCircuits Institute, University of California San Diego, La Jolla, CA, USA
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50
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Modeling ALS with motor neurons derived from human induced pluripotent stem cells. Nat Neurosci 2016; 19:542-53. [PMID: 27021939 DOI: 10.1038/nn.4273] [Citation(s) in RCA: 185] [Impact Index Per Article: 23.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2015] [Accepted: 02/22/2016] [Indexed: 02/08/2023]
Abstract
Directing the differentiation of induced pluripotent stem cells into motor neurons has allowed investigators to develop new models of amyotrophic lateral sclerosis (ALS). However, techniques vary between laboratories and the cells do not appear to mature into fully functional adult motor neurons. Here we discuss common developmental principles of both lower and upper motor neuron development that have led to specific derivation techniques. We then suggest how these motor neurons may be matured further either through direct expression or administration of specific factors or coculture approaches with other tissues. Ultimately, through a greater understanding of motor neuron biology, it will be possible to establish more reliable models of ALS. These in turn will have a greater chance of validating new drugs that may be effective for the disease.
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