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Delestrée N, Semizoglou E, Pagiazitis JG, Vukojicic A, Drobac E, Paushkin V, Mentis GZ. Serotonergic dysfunction impairs locomotor coordination in spinal muscular atrophy. Brain 2023; 146:4574-4593. [PMID: 37678880 PMCID: PMC10629775 DOI: 10.1093/brain/awad221] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2022] [Revised: 05/12/2023] [Accepted: 06/11/2023] [Indexed: 09/09/2023] Open
Abstract
Neuromodulation by serotonin regulates the activity of neuronal networks responsible for a wide variety of essential behaviours. Serotonin (or 5-HT) typically activates metabotropic G protein-coupled receptors, which in turn initiate second messenger signalling cascades and induce short and long-lasting behavioural effects. Serotonin is intricately involved in the production of locomotor activity and gait control for different motor behaviours. Although dysfunction of serotonergic neurotransmission has been associated with mood disorders and spasticity after spinal cord injury, whether and to what extent such dysregulation is implicated in movement disorders has not been firmly established. Here, we investigated whether serotonergic neuromodulation is affected in spinal muscular atrophy (SMA), a neurodegenerative disease caused by ubiquitous deficiency of the SMN protein. The hallmarks of SMA are death of spinal motor neurons, muscle atrophy and impaired motor control, both in human patients and mouse models of disease. We used a severe mouse model of SMA, that closely recapitulates the severe symptoms exhibited by type I SMA patients, the most common and most severe form of the disease. Together, with mouse genetics, optogenetics, physiology, morphology and behavioural analysis, we report severe dysfunction of serotonergic neurotransmission in the spinal cord of SMA mice, both at early and late stages of the disease. This dysfunction is followed by reduction of 5-HT synapses on vulnerable motor neurons. We demonstrate that motor neurons innervating axial and trunk musculature are preferentially affected, suggesting a possible cause for the proximo-distal progression of disease, and raising the possibility that it may underlie scoliosis in SMA patients. We also demonstrate that the 5-HT dysfunction is caused by SMN deficiency in serotonergic neurons in the raphe nuclei of the brainstem. The behavioural significance of the dysfunction in serotonergic neuromodulation is underlined by inter-limb discoordination in SMA mice, which is ameliorated when selective restoration of SMN in 5-HT neurons is achieved by genetic means. Our study uncovers an unexpected dysfunction of serotonergic neuromodulation in SMA and indicates that, if normal function is to be restored under disease conditions, 5-HT neuromodulation should be a key target for therapeutic approaches.
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Affiliation(s)
- Nicolas Delestrée
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA
- Department of Neurology, Columbia University, New York, NY 10032, USA
| | - Evangelia Semizoglou
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA
- Department of Neurology, Columbia University, New York, NY 10032, USA
| | - John G Pagiazitis
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA
- Department of Neurology, Columbia University, New York, NY 10032, USA
| | - Aleksandra Vukojicic
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA
- Department of Neurology, Columbia University, New York, NY 10032, USA
| | - Estelle Drobac
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA
- Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA
| | - Vasilissa Paushkin
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA
- Department of Neurology, Columbia University, New York, NY 10032, USA
| | - George Z Mentis
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA
- Department of Neurology, Columbia University, New York, NY 10032, USA
- Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA
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2
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Abstract
Loss of synapses on spinal motor neurons is a major feature of several neurodegenerative diseases; however, analyzing these premotor synapses is challenging because of their small size and high density. This protocol describes confocal and Stimulated Emission Depletion (STED) imaging of murine spinal premotor synapses and their segment-specific quantification by confocal microscopy. We detail the preparation of spinal cord segments, followed by image acquisition and analysis. This protocol enables in-depth analysis of pathological changes in spinal premotor synapses during neurodegeneration. For complete details on the use and execution of this protocol, please refer to Buettner et al. (2021). Dissection and sectioning of identified murine spinal cord segments Fluorescent labeling of spinal premotor synapses and motor neurons Confocal and super-resolution acquisition of individual premotor synapses Quantification of premotor synapses onto motor neurons
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Affiliation(s)
- Jannik M. Buettner
- Carl-Ludwig-Institute for Physiology, Leipzig University, 04103 Leipzig, Germany
| | - Toni Kirmann
- Carl-Ludwig-Institute for Physiology, Leipzig University, 04103 Leipzig, Germany
| | - George Z. Mentis
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA
- Depts. of Pathology and Cell Biology and Neurology, Columbia University, New York, NY 10032, USA
| | - Stefan Hallermann
- Carl-Ludwig-Institute for Physiology, Leipzig University, 04103 Leipzig, Germany
| | - Christian M. Simon
- Carl-Ludwig-Institute for Physiology, Leipzig University, 04103 Leipzig, Germany
- Corresponding author
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3
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Chalif JI, de Lourdes Martínez-Silva M, Pagiazitis JG, Murray AJ, Mentis GZ. Control of mammalian locomotion by ventral spinocerebellar tract neurons. Cell 2022; 185:328-344.e26. [PMID: 35063074 PMCID: PMC8852337 DOI: 10.1016/j.cell.2021.12.014] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2021] [Revised: 11/09/2021] [Accepted: 12/13/2021] [Indexed: 01/22/2023]
Abstract
Locomotion is a complex behavior required for animal survival. Vertebrate locomotion depends on spinal interneurons termed the central pattern generator (CPG), which generates activity responsible for the alternation of flexor and extensor muscles and the left and right side of the body. It is unknown whether multiple or a single neuronal type is responsible for the control of mammalian locomotion. Here, we show that ventral spinocerebellar tract neurons (VSCTs) drive generation and maintenance of locomotor behavior in neonatal and adult mice. Using mouse genetics, physiological, anatomical, and behavioral assays, we demonstrate that VSCTs exhibit rhythmogenic properties and neuronal circuit connectivity consistent with their essential role in the locomotor CPG. Importantly, optogenetic activation and chemogenetic silencing reveals that VSCTs are necessary and sufficient for locomotion. These findings identify VSCTs as critical components for mammalian locomotion and provide a paradigm shift in our understanding of neural control of complex behaviors.
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Affiliation(s)
- Joshua I. Chalif
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA,Dept. of Neurology, Columbia University, New York, NY 10032, USA
| | - María de Lourdes Martínez-Silva
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA,Dept. of Neurology, Columbia University, New York, NY 10032, USA
| | - John G. Pagiazitis
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA,Dept. of Neurology, Columbia University, New York, NY 10032, USA
| | - Andrew J. Murray
- Sainsbury Wellcome Centre, University College London, 25 Howland Street, London W1T 4JG, UK
| | - George Z. Mentis
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA,Dept. of Neurology, Columbia University, New York, NY 10032, USA,Dept. of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA,Corresponding author & Lead contact: Tel: +1-212-305-9846,
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4
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Chalif JI, Mentis GZ. Normal Development and Pathology of Motoneurons: Anatomy, Electrophysiological Properties, Firing Patterns and Circuit Connectivity. Adv Neurobiol 2022; 28:63-85. [PMID: 36066821 DOI: 10.1007/978-3-031-07167-6_3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
This chapter will provide an introduction into motoneuron anatomy, electrophysiological properties, firing patterns focusing on development and also describing several pathological conditions that affect mononeurons. It starts with a historical retrospective describing the early landmark work into motoneurons. The next section lays out the various types of motoneurons (alpha, beta, and gamma) and their subclasses (fast-twitch fatigable, fast-twitch fatigue-resistant, and slow-twitch fatigue resistant), highlighting the functional relevance of this classification scheme. The third section describes the development of motoneurons' passive and active electrophysiological properties. This section also defines the major terms one uses in describing how a neuron functions electrophysiologically. The electrophysiological aspects of a neuron is critical to understanding how it behaves within a circuit and contributes to behavior since the firing of an action potential is how neurons communicate with each other and with muscles. The electrophysiological changes of motoneurons over development underlies how their function changes over the lifetime of an organism. After describing the properties of individual motoneurons, the chapter then turns to revealing how motoneurons interact within complex neural circuits, with other motoneurons as well as sensory neurons, and how these circuits change over development. Finally, this chapter ends with highlighting some recent advances made in motoneuron pathology, focusing on spinal muscular atrophy, amyotrophic lateral sclerosis, and axotomy.
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Affiliation(s)
- Joshua I Chalif
- Departments of Neurology and Pathology & Cell Biology, Center for Motor Neuron Biology and Disease, Columbia University, New York, NY, USA
- Department of Neurosurgery, Brigham and Women's Hospital, Harvard University, Boston, MA, USA
| | - George Z Mentis
- Departments of Neurology and Pathology & Cell Biology, Center for Motor Neuron Biology and Disease, Columbia University, New York, NY, USA.
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5
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Kong L, Valdivia DO, Simon CM, Hassinan CW, Delestrée N, Ramos DM, Park JH, Pilato CM, Xu X, Crowder M, Grzyb CC, King ZA, Petrillo M, Swoboda KJ, Davis C, Lutz CM, Stephan AH, Zhao X, Weetall M, Naryshkin NA, Crawford TO, Mentis GZ, Sumner CJ. Impaired prenatal motor axon development necessitates early therapeutic intervention in severe SMA. Sci Transl Med 2021; 13:13/578/eabb6871. [PMID: 33504650 DOI: 10.1126/scitranslmed.abb6871] [Citation(s) in RCA: 45] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2020] [Accepted: 09/18/2020] [Indexed: 12/21/2022]
Abstract
Gene replacement and pre-mRNA splicing modifier therapies represent breakthrough gene targeting treatments for the neuromuscular disease spinal muscular atrophy (SMA), but mechanisms underlying variable efficacy of treatment are incompletely understood. Our examination of severe infantile onset human SMA tissues obtained at expedited autopsy revealed persistence of developmentally immature motor neuron axons, many of which are actively degenerating. We identified similar features in a mouse model of severe SMA, in which impaired radial growth and Schwann cell ensheathment of motor axons began during embryogenesis and resulted in reduced acquisition of myelinated axons that impeded motor axon function neonatally. Axons that failed to ensheath degenerated rapidly postnatally, specifically releasing neurofilament light chain protein into the blood. Genetic restoration of survival motor neuron protein (SMN) expression in mouse motor neurons, but not in Schwann cells or muscle, improved SMA motor axon development and maintenance. Treatment with small-molecule SMN2 splice modifiers beginning immediately after birth in mice increased radial growth of the already myelinated axons, but in utero treatment was required to restore axonal growth and associated maturation, prevent subsequent neonatal axon degeneration, and enhance motor axon function. Together, these data reveal a cellular basis for the fulminant neonatal worsening of patients with infantile onset SMA and identify a temporal window for more effective treatment. These findings suggest that minimizing treatment delay is critical to achieve optimal therapeutic efficacy.
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Affiliation(s)
- Lingling Kong
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - David O Valdivia
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Christian M Simon
- Center for Motor Neuron Biology and Disease, Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA
| | - Cera W Hassinan
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Nicolas Delestrée
- Center for Motor Neuron Biology and Disease, Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA
| | - Daniel M Ramos
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Jae Hong Park
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Celeste M Pilato
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Xixi Xu
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Melissa Crowder
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Chloe C Grzyb
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Zachary A King
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | | | - Kathryn J Swoboda
- Center for Genomic Medicine, Department of Neurology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA
| | - Crystal Davis
- Genetic Resource Science, The Jackson Laboratory, Bar Harbor, ME 04609, USA
| | - Cathleen M Lutz
- Genetic Resource Science, The Jackson Laboratory, Bar Harbor, ME 04609, USA
| | - Alexander H Stephan
- F. Hoffmann-La Roche Ltd., pRED, Pharma & Early Development, Roche Innovation Center Basel, Basel CH-4070, Switzerland
| | - Xin Zhao
- PTC Therapeutics, 100 Corporate Court, South Plainfield, NJ 07080, USA
| | - Marla Weetall
- PTC Therapeutics, 100 Corporate Court, South Plainfield, NJ 07080, USA
| | | | - Thomas O Crawford
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.,Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - George Z Mentis
- Center for Motor Neuron Biology and Disease, Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA.,Department of Neurology, Columbia University, New York, NY 10032, USA
| | - Charlotte J Sumner
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA. .,Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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6
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Van Alstyne M, Tattoli I, Delestree N, Recinos Y, Workman E, Shihabuddin LS, Zhang C, Mentis GZ, Pellizzoni L. Gain of toxic function by long-term AAV9-mediated SMN overexpression in the sensorimotor circuit. Nat Neurosci 2021; 24:930-940. [PMID: 33795885 PMCID: PMC8254787 DOI: 10.1038/s41593-021-00827-3] [Citation(s) in RCA: 83] [Impact Index Per Article: 27.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2020] [Accepted: 02/24/2021] [Indexed: 02/01/2023]
Abstract
The neurodegenerative disease spinal muscular atrophy (SMA) is caused by deficiency in the survival motor neuron (SMN) protein. Currently approved SMA treatments aim to restore SMN, but the potential for SMN expression beyond physiological levels is a unique feature of adeno-associated virus serotype 9 (AAV9)-SMN gene therapy. Here, we show that long-term AAV9-mediated SMN overexpression in mouse models induces dose-dependent, late-onset motor dysfunction associated with loss of proprioceptive synapses and neurodegeneration. Mechanistically, aggregation of overexpressed SMN in the cytoplasm of motor circuit neurons sequesters components of small nuclear ribonucleoproteins, leading to splicing dysregulation and widespread transcriptome abnormalities with prominent signatures of neuroinflammation and the innate immune response. Thus, long-term SMN overexpression interferes with RNA regulation and triggers SMA-like pathogenic events through toxic gain-of-function mechanisms. These unanticipated, SMN-dependent and neuron-specific liabilities warrant caution on the long-term safety of treating individuals with SMA with AAV9-SMN and the risks of uncontrolled protein expression by gene therapy.
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Affiliation(s)
- Meaghan Van Alstyne
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY, 10032,Department of Pathology and Cell Biology, Columbia University, New York, NY, 10032,Department of Neurology, Columbia University, New York, NY, 10032
| | - Ivan Tattoli
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY, 10032,Department of Pathology and Cell Biology, Columbia University, New York, NY, 10032
| | - Nicolas Delestree
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY, 10032,Department of Pathology and Cell Biology, Columbia University, New York, NY, 10032,Department of Neurology, Columbia University, New York, NY, 10032
| | - Yocelyn Recinos
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY, 10032,Department of Systems Biology, Columbia University, New York, NY 10032,Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032
| | - Eileen Workman
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY, 10032,Department of Pathology and Cell Biology, Columbia University, New York, NY, 10032
| | | | - Chaolin Zhang
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY, 10032,Department of Systems Biology, Columbia University, New York, NY 10032,Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032
| | - George Z. Mentis
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY, 10032,Department of Pathology and Cell Biology, Columbia University, New York, NY, 10032,Department of Neurology, Columbia University, New York, NY, 10032
| | - Livio Pellizzoni
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY, 10032,Department of Pathology and Cell Biology, Columbia University, New York, NY, 10032,Department of Neurology, Columbia University, New York, NY, 10032,Address correspondence to: Livio Pellizzoni, Center for Motor Neuron Biology and Disease, Department of Pathology and Cell Biology, Columbia University, 630 West 168TH Street, New York, NY, 10032. Phone: +1 212-305-3046;
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7
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Tosolini AP, Mentis GZ, Martin JH. Editorial: Dysfunction and Repair of Neural Circuits for Motor Control. Front Mol Neurosci 2021; 14:669824. [PMID: 33828459 PMCID: PMC8019806 DOI: 10.3389/fnmol.2021.669824] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2021] [Accepted: 02/26/2021] [Indexed: 12/03/2022] Open
Affiliation(s)
- Andrew Paul Tosolini
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, University College London, London, United Kingdom
| | - George Z Mentis
- Department of Pathology & Cell Biology and Neurology, Center for Motor Neuron Biology and Disease, Columbia University, New York, NY, United States
| | - John H Martin
- Department of Molecular, Cellular and Biomedical Sciences, Center for Discovery and Innovation, City University of New York School of Medicine, New York, NY, United States
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8
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Vukojicic A, Delestrée N, Fletcher EV, Pagiazitis JG, Sankaranarayanan S, Yednock TA, Barres BA, Mentis GZ. The Classical Complement Pathway Mediates Microglia-Dependent Remodeling of Spinal Motor Circuits during Development and in SMA. Cell Rep 2020; 29:3087-3100.e7. [PMID: 31801075 PMCID: PMC6937140 DOI: 10.1016/j.celrep.2019.11.013] [Citation(s) in RCA: 69] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2019] [Revised: 09/20/2019] [Accepted: 11/04/2019] [Indexed: 12/19/2022] Open
Abstract
Movement is an essential behavior requiring the assembly and refinement of spinal motor circuits. However, the mechanisms responsible for circuit refinement and synapse maintenance are poorly understood. Similarly, the molecular mechanisms by which gene mutations cause dysfunction and elimination of synapses in neurodegenerative diseases that occur during development are unknown. Here, we demonstrate that the complement protein C1q is required for the refinement of sensory-motor circuits during normal development, as well as for synaptic dysfunction and elimination in spinal muscular atrophy (SMA). C1q tags vulnerable SMA synapses, which triggers activation of the classical complement pathway leading to microglia-mediated elimination. Pharmacological inhibition of C1q or depletion of microglia rescues the number and function of synapses, conferring significant behavioral benefit in SMA mice. Thus, the classical complement pathway plays critical roles in the refinement of developing motor circuits, while its aberrant activation contributes to motor neuron disease.
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Affiliation(s)
- Aleksandra Vukojicic
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA; Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA
| | - Nicolas Delestrée
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA; Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA
| | - Emily V Fletcher
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA; Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA
| | - John G Pagiazitis
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA; Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA
| | | | - Ted A Yednock
- Annexon Biosciences, 180 Kimball Way, South San Francisco, CA 94080, USA
| | - Ben A Barres
- Department of Neurobiology, Stanford University, Palo Alto, CA, USA
| | - George Z Mentis
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA; Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA; Department of Neurology, Columbia University, New York, NY 10032, USA.
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9
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Simon CM, Van Alstyne M, Lotti F, Bianchetti E, Tisdale S, Watterson DM, Mentis GZ, Pellizzoni L. Stasimon Contributes to the Loss of Sensory Synapses and Motor Neuron Death in a Mouse Model of Spinal Muscular Atrophy. Cell Rep 2020; 29:3885-3901.e5. [PMID: 31851921 PMCID: PMC6956708 DOI: 10.1016/j.celrep.2019.11.058] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2019] [Revised: 10/08/2019] [Accepted: 11/14/2019] [Indexed: 12/31/2022] Open
Abstract
Reduced expression of the survival motor neuron (SMN) protein causes the neurodegenerative disease spinal muscular atrophy (SMA). Here, we show that adeno-associated virus serotype 9 (AAV9)-mediated delivery of Stasimon—a gene encoding an endoplasmic reticulum (ER)-resident transmembrane protein regulated by SMN—improves motor function in a mouse model of SMA through multiple mechanisms. In proprioceptive neurons, Stasimon overexpression prevents the loss of afferent synapses on motor neurons and enhances sensory-motor neurotransmission. In motor neurons, Stasimon suppresses neurodegeneration by reducing phosphorylation of the tumor suppressor p53. Moreover, Stasimon deficiency converges on SMA-related mechanisms of p53 upregulation to induce phosphorylation of p53 through activation of p38 mitogen-activated protein kinase (MAPK), and pharmacological inhibition of this kinase prevents motor neuron death in SMA mice. These findings identify Stasimon dysfunction induced by SMN deficiency as an upstream driver of distinct cellular cascades that lead to synaptic loss and motor neuron degeneration, revealing a dual contribution of Stasimon to motor circuit pathology in SMA. SMN deficiency causes motor circuit dysfunction in SMA. Simon et al. show that Stasimon—an ER-resident protein regulated by SMN—contributes to sensory synaptic loss and motor neuron death in SMA mice through distinct mechanisms. In motor neurons, Stasimon dysfunction induces p38 MAPK-mediated phosphorylation of p53 whose inhibition prevents neurodegeneration.
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Affiliation(s)
- Christian M Simon
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA; Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA
| | - Meaghan Van Alstyne
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA; Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA
| | - Francesco Lotti
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA; Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA
| | - Elena Bianchetti
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA; Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA
| | - Sarah Tisdale
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA; Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA
| | - D Martin Watterson
- Department of Pharmacology, Northwestern University, Chicago, IL 60611, USA
| | - George Z Mentis
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA; Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA; Department of Neurology, Columbia University, New York, NY 10032, USA
| | - Livio Pellizzoni
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA; Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA.
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10
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Oskoui M, Kim DH, Mentis GZ, De Vivo DC. Transient hyperreflexia: An early diagnostic clue in later-onset spinal muscular atrophy. Neurol Clin Pract 2020; 10:e66-e67. [PMID: 33520420 DOI: 10.1212/cpj.0000000000000810] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2019] [Accepted: 12/26/2019] [Indexed: 11/15/2022]
Affiliation(s)
- Maryam Oskoui
- Departments of Pediatric and Neurology/Neurosurgery (MO) and Faculty of Medicine (DHK), McGill University, Montréal, QC, Canada; and Departments of Pathology and Cell Biology and Neurology (GZM), Center for Motor Neuron Biology and Disease (GZM, DCDV), and Departments of Neurology and Pediatrics (DCDV), Columbia University, New York
| | - Dong Hyun Kim
- Departments of Pediatric and Neurology/Neurosurgery (MO) and Faculty of Medicine (DHK), McGill University, Montréal, QC, Canada; and Departments of Pathology and Cell Biology and Neurology (GZM), Center for Motor Neuron Biology and Disease (GZM, DCDV), and Departments of Neurology and Pediatrics (DCDV), Columbia University, New York
| | - George Z Mentis
- Departments of Pediatric and Neurology/Neurosurgery (MO) and Faculty of Medicine (DHK), McGill University, Montréal, QC, Canada; and Departments of Pathology and Cell Biology and Neurology (GZM), Center for Motor Neuron Biology and Disease (GZM, DCDV), and Departments of Neurology and Pediatrics (DCDV), Columbia University, New York
| | - Darryl C De Vivo
- Departments of Pediatric and Neurology/Neurosurgery (MO) and Faculty of Medicine (DHK), McGill University, Montréal, QC, Canada; and Departments of Pathology and Cell Biology and Neurology (GZM), Center for Motor Neuron Biology and Disease (GZM, DCDV), and Departments of Neurology and Pediatrics (DCDV), Columbia University, New York
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11
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Hoang PT, Chalif JI, Bikoff JB, Jessell TM, Mentis GZ, Wichterle H. Subtype Diversification and Synaptic Specificity of Stem Cell-Derived Spinal Interneurons. Neuron 2019; 100:135-149.e7. [PMID: 30308166 DOI: 10.1016/j.neuron.2018.09.016] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2018] [Revised: 07/06/2018] [Accepted: 09/09/2018] [Indexed: 12/25/2022]
Abstract
Neuronal diversification is a fundamental step in the construction of functional neural circuits, but how neurons generated from single progenitor domains acquire diverse subtype identities remains poorly understood. Here we developed an embryonic stem cell (ESC)-based system to model subtype diversification of V1 interneurons, a class of spinal neurons comprising four clades collectively containing dozens of molecularly distinct neuronal subtypes. We demonstrate that V1 subtype diversity can be modified by extrinsic signals. Inhibition of Notch and activation of retinoid signaling results in a switch to MafA clade identity and enriches differentiation of Renshaw cells, a specialized MafA subtype that mediates recurrent inhibition of spinal motor neurons. We show that Renshaw cells are intrinsically programmed to migrate to species-specific laminae upon transplantation and to form subtype-specific synapses with motor neurons. Our results demonstrate that stem cell-derived neuronal subtypes can be used to investigate mechanisms underlying neuronal subtype specification and circuit assembly.
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Affiliation(s)
- Phuong T Hoang
- Departments of Pathology and Cell Biology, Neuroscience, Rehabilitation & Regenerative Medicine, and Neurology, Center for Motor Neuron Biology and Disease, Columbia Stem Cell Initiative, Columbia University Irving Medical Center, New York, NY 10032, USA
| | - Joshua I Chalif
- Departments of Pathology and Cell Biology and Neurology, Center for Motor Neuron Biology and Disease, Columbia University Irving Medical Center, New York, NY 10032, USA
| | - Jay B Bikoff
- Departments of Neuroscience and Biochemistry and Molecular Biophysics, Columbia University Irving Medical Center, New York, NY 10032, USA; Department of Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA
| | - Thomas M Jessell
- Departments of Neuroscience and Biochemistry and Molecular Biophysics, Columbia University Irving Medical Center, New York, NY 10032, USA
| | - George Z Mentis
- Departments of Pathology and Cell Biology and Neurology, Center for Motor Neuron Biology and Disease, Columbia University Irving Medical Center, New York, NY 10032, USA
| | - Hynek Wichterle
- Departments of Pathology and Cell Biology, Neuroscience, Rehabilitation & Regenerative Medicine, and Neurology, Center for Motor Neuron Biology and Disease, Columbia Stem Cell Initiative, Columbia University Irving Medical Center, New York, NY 10032, USA.
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12
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Van Alstyne M, Simon CM, Sardi SP, Shihabuddin LS, Mentis GZ, Pellizzoni L. Dysregulation of Mdm2 and Mdm4 alternative splicing underlies motor neuron death in spinal muscular atrophy. Genes Dev 2018; 32:1045-1059. [PMID: 30012555 PMCID: PMC6075148 DOI: 10.1101/gad.316059.118] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2018] [Accepted: 05/24/2018] [Indexed: 12/01/2022]
Abstract
Van Alstyne et al. show that loss of SMN-dependent regulation of Mdm2 and Mdm4 alternative splicing underlies p53-mediated death of motor neurons in SMA, establishing a causal link between snRNP dysfunction and neurodegeneration. Ubiquitous deficiency in the survival motor neuron (SMN) protein causes death of motor neurons—a hallmark of the neurodegenerative disease spinal muscular atrophy (SMA)—through poorly understood mechanisms. Here, we show that the function of SMN in the assembly of spliceosomal small nuclear ribonucleoproteins (snRNPs) regulates alternative splicing of Mdm2 and Mdm4, two nonredundant repressors of p53. Decreased inclusion of critical Mdm2 and Mdm4 exons is most prominent in SMA motor neurons and correlates with both snRNP reduction and p53 activation in vivo. Importantly, increased skipping of Mdm2 and Mdm4 exons regulated by SMN is necessary and sufficient to synergistically elicit robust p53 activation in wild-type mice. Conversely, restoration of full-length Mdm2 and Mdm4 suppresses p53 induction and motor neuron degeneration in SMA mice. These findings reveal that loss of SMN-dependent regulation of Mdm2 and Mdm4 alternative splicing underlies p53-mediated death of motor neurons in SMA, establishing a causal link between snRNP dysfunction and neurodegeneration.
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Affiliation(s)
- Meaghan Van Alstyne
- Center for Motor Neuron Biology and Disease, Columbia University, New York, New York 10032, USA.,Department of Pathology and Cell Biology, Columbia University, New York, New York 10032, USA
| | - Christian M Simon
- Center for Motor Neuron Biology and Disease, Columbia University, New York, New York 10032, USA.,Department of Pathology and Cell Biology, Columbia University, New York, New York 10032, USA
| | - S Pablo Sardi
- Neuroscience Therapeutic Area, Sanofi, Framingham, Massachusetts 01701, USA
| | | | - George Z Mentis
- Center for Motor Neuron Biology and Disease, Columbia University, New York, New York 10032, USA.,Department of Pathology and Cell Biology, Columbia University, New York, New York 10032, USA.,Department of Neurology, Columbia University, New York, New York 10032, USA
| | - Livio Pellizzoni
- Center for Motor Neuron Biology and Disease, Columbia University, New York, New York 10032, USA.,Department of Pathology and Cell Biology, Columbia University, New York, New York 10032, USA
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13
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Cantor S, Zhang W, Delestrée N, Remédio L, Mentis GZ, Burden SJ. Preserving neuromuscular synapses in ALS by stimulating MuSK with a therapeutic agonist antibody. eLife 2018; 7:34375. [PMID: 29460776 PMCID: PMC5837562 DOI: 10.7554/elife.34375] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2017] [Accepted: 02/02/2018] [Indexed: 12/22/2022] Open
Abstract
In amyotrophic lateral sclerosis (ALS) and animal models of ALS, including SOD1-G93A mice, disassembly of the neuromuscular synapse precedes motor neuron loss and is sufficient to cause a decline in motor function that culminates in lethal respiratory paralysis. We treated SOD1-G93A mice with an agonist antibody to MuSK, a receptor tyrosine kinase essential for maintaining neuromuscular synapses, to determine whether increasing muscle retrograde signaling would slow nerve terminal detachment from muscle. The agonist antibody, delivered after disease onset, slowed muscle denervation, promoting motor neuron survival, improving motor system output, and extending the lifespan of SOD1-G93A mice. These findings suggest a novel therapeutic strategy for ALS, using an antibody format with clinical precedence, which targets a pathway essential for maintaining attachment of nerve terminals to muscle. Amyotrophic lateral sclerosis – often shortened to ALS – is a disease that starts with difficulties moving and progresses to paralysis of many muscles, including those used for breathing. The disease is usually lethal, with patients rarely surviving more than a few years after diagnosis. There is no cure or effective treatment for the disease. It begins with the breakdown of the connections, or synapses, between the muscles and the nerve cells that connect with them. After this, the nerve cell itself breaks down. Many therapeutic approaches have focused on attempts to prevent the nerve cells from dying, but few target the initial degeneration of the synapse. Cantor et al. asked if intervening when the synapse has already begun to break down could slow the progression of the disease in mice with ALS. Their approach involved using an antibody to bind to a receptor protein called MuSK, which plays an important role in maintaining the synapse between muscle and nerve cell. The antibody boosted the receptor’s activity, helping to preserve synapses, including those that connect nerve cells to the diaphragm muscle. The experiments showed that the antibody treatment led to fewer synapses breaking down, and kept more of the nerve cells alive. Healthier connections between the nervous system and the diaphragm improved the function of this muscle. As a result, the mice given the antibody treatment had a slightly extended lifespan, compared with those given no treatment. The findings suggest a possible new way to develop treatments for ALS, which could be used in combination with other therapies, such as those aimed at improving the health of the nerve cells. Together, this could improve quality of life for the majority of patients with ALS. Similar strategies could be used to develop treatments to preserve synapses in other neurodegenerative diseases, such as Alzheimer’s, Parkinson’s and Huntington’s disease, as well as some kinds of dementia. Preserving synapses early on, before the significant loss of nerve cells, could help to slow the progression of these diseases, improve the patients' quality of life and extend their lifespans too.
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Affiliation(s)
- Sarah Cantor
- Molecular Neurobiology Program, Helen L. and Martin S. Kimmel Center for Biology and Medicine at the Skirball Institute of Biomolecular Medicine, NYU Medical School, New York, United States
| | - Wei Zhang
- Molecular Neurobiology Program, Helen L. and Martin S. Kimmel Center for Biology and Medicine at the Skirball Institute of Biomolecular Medicine, NYU Medical School, New York, United States
| | - Nicolas Delestrée
- Center for Motor Neuron Biology and Disease and Departments of Pathology and Cell Biology and Neurology, Columbia University, New York, United States
| | - Leonor Remédio
- Molecular Neurobiology Program, Helen L. and Martin S. Kimmel Center for Biology and Medicine at the Skirball Institute of Biomolecular Medicine, NYU Medical School, New York, United States
| | - George Z Mentis
- Center for Motor Neuron Biology and Disease and Departments of Pathology and Cell Biology and Neurology, Columbia University, New York, United States
| | - Steven J Burden
- Molecular Neurobiology Program, Helen L. and Martin S. Kimmel Center for Biology and Medicine at the Skirball Institute of Biomolecular Medicine, NYU Medical School, New York, United States
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14
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Fletcher EV, Simon CM, Pagiazitis JG, Chalif JI, Vukojicic A, Drobac E, Wang X, Mentis GZ. Reduced sensory synaptic excitation impairs motor neuron function via Kv2.1 in spinal muscular atrophy. Nat Neurosci 2017; 20:905-916. [PMID: 28504671 PMCID: PMC5487291 DOI: 10.1038/nn.4561] [Citation(s) in RCA: 85] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Accepted: 04/04/2017] [Indexed: 12/30/2022]
Abstract
Behavioral deficits in neurodegenerative diseases are often attributed to the selective dysfunction of vulnerable neurons via cell-autonomous mechanisms. Although vulnerable neurons are embedded in neuronal circuits, the contribution of their synaptic partners to the disease process is largely unknown. Here, we show that in a mouse model of spinal muscular atrophy (SMA), a reduction in proprioceptive synaptic drive leads to motor neuron dysfunction and motor behavior impairments. In SMA mice or after the blockade of proprioceptive synaptic transmission we observed a decrease in the motor neuron firing which could be explained by the reduction in the expression of the potassium channel Kv2.1 at the surface of motor neurons. Increasing neuronal activity pharmacologically by chronic exposure in vivo led to a normalization of Kv2.1 expression and an improvement in motor function. Our results demonstrate a key role of excitatory synaptic drive in shaping the function of motor neurons during development and the contribution of its disruption to a neurodegenerative disease.
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Affiliation(s)
- Emily V Fletcher
- Center for Motor Neuron Biology and Disease, Columbia University, New York, New York, USA.,Department of Pathology and Cell Biology, Columbia University, New York, New York, USA
| | - Christian M Simon
- Center for Motor Neuron Biology and Disease, Columbia University, New York, New York, USA.,Department of Pathology and Cell Biology, Columbia University, New York, New York, USA
| | - John G Pagiazitis
- Center for Motor Neuron Biology and Disease, Columbia University, New York, New York, USA.,Department of Pathology and Cell Biology, Columbia University, New York, New York, USA
| | - Joshua I Chalif
- Center for Motor Neuron Biology and Disease, Columbia University, New York, New York, USA.,Department of Pathology and Cell Biology, Columbia University, New York, New York, USA
| | - Aleksandra Vukojicic
- Center for Motor Neuron Biology and Disease, Columbia University, New York, New York, USA.,Department of Pathology and Cell Biology, Columbia University, New York, New York, USA
| | - Estelle Drobac
- Center for Motor Neuron Biology and Disease, Columbia University, New York, New York, USA.,Department of Pathology and Cell Biology, Columbia University, New York, New York, USA
| | - Xiaojian Wang
- Center for Motor Neuron Biology and Disease, Columbia University, New York, New York, USA.,Department of Pathology and Cell Biology, Columbia University, New York, New York, USA
| | - George Z Mentis
- Center for Motor Neuron Biology and Disease, Columbia University, New York, New York, USA.,Department of Pathology and Cell Biology, Columbia University, New York, New York, USA.,Department of Neurology, Columbia University, New York, New York, USA
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15
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Remédio L, Gribble KD, Lee JK, Kim N, Hallock PT, Delestrée N, Mentis GZ, Froemke RC, Granato M, Burden SJ. Diverging roles for Lrp4 and Wnt signaling in neuromuscular synapse development during evolution. Genes Dev 2017; 30:1058-69. [PMID: 27151977 PMCID: PMC4863737 DOI: 10.1101/gad.279745.116] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2016] [Accepted: 03/31/2016] [Indexed: 11/25/2022]
Abstract
In this study, Remédio et al. use mice and zebrafish to show that muscle prepatterning in mammals and zebrafish is established by different mechanisms. Their findings demonstrate that Agrin/Lrp4/MuSK signaling plays an essential role in neuromuscular synapse formation in both fish and mammals, whereas Wnt signaling is dispensable. Motor axons approach muscles that are prepatterned in the prospective synaptic region. In mice, prepatterning of acetylcholine receptors requires Lrp4, a LDLR family member, and MuSK, a receptor tyrosine kinase. Lrp4 can bind and stimulate MuSK, strongly suggesting that association between Lrp4 and MuSK, independent of additional ligands, initiates prepatterning in mice. In zebrafish, Wnts, which bind the Frizzled (Fz)-like domain in MuSK, are required for prepatterning, suggesting that Wnts may contribute to prepatterning and neuromuscular development in mammals. We show that prepatterning in mice requires Lrp4 but not the MuSK Fz-like domain. In contrast, prepatterning in zebrafish requires the MuSK Fz-like domain but not Lrp4. Despite these differences, neuromuscular synapse formation in zebrafish and mice share similar mechanisms, requiring Lrp4, MuSK, and neuronal Agrin but not the MuSK Fz-like domain or Wnt production from muscle. Our findings demonstrate that evolutionary divergent mechanisms establish muscle prepatterning in zebrafish and mice.
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Affiliation(s)
- Leonor Remédio
- Molecular Neurobiology Program, Helen L. and Martin S. Kimmel Center for Biology and Medicine at the Skirball Institute of Biomolecular Medicine, New York University Medical School, New York, New York 10016, USA
| | - Katherine D Gribble
- Department of Cell and Developmental Biology, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania 19104, USA
| | - Jennifer K Lee
- Molecular Neurobiology Program, Helen L. and Martin S. Kimmel Center for Biology and Medicine at the Skirball Institute of Biomolecular Medicine, New York University Medical School, New York, New York 10016, USA
| | - Natalie Kim
- Molecular Neurobiology Program, Helen L. and Martin S. Kimmel Center for Biology and Medicine at the Skirball Institute of Biomolecular Medicine, New York University Medical School, New York, New York 10016, USA
| | - Peter T Hallock
- Molecular Neurobiology Program, Helen L. and Martin S. Kimmel Center for Biology and Medicine at the Skirball Institute of Biomolecular Medicine, New York University Medical School, New York, New York 10016, USA
| | - Nicolas Delestrée
- Center for Motor Neuron Biology and Disease, Columbia University, New York, New York 10032, USA; Department of Pathology and Cell Biology, Columbia University, New York, New York 10032, USA; Department of Neurology, Columbia University, New York, New York 10032, USA
| | - George Z Mentis
- Center for Motor Neuron Biology and Disease, Columbia University, New York, New York 10032, USA; Department of Pathology and Cell Biology, Columbia University, New York, New York 10032, USA; Department of Neurology, Columbia University, New York, New York 10032, USA
| | - Robert C Froemke
- Molecular Neurobiology Program, Helen L. and Martin S. Kimmel Center for Biology and Medicine at the Skirball Institute of Biomolecular Medicine, New York University Medical School, New York, New York 10016, USA
| | - Michael Granato
- Department of Cell and Developmental Biology, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania 19104, USA
| | - Steven J Burden
- Molecular Neurobiology Program, Helen L. and Martin S. Kimmel Center for Biology and Medicine at the Skirball Institute of Biomolecular Medicine, New York University Medical School, New York, New York 10016, USA
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16
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Simon CM, Janas AM, Lotti F, Tapia JC, Pellizzoni L, Mentis GZ. A Stem Cell Model of the Motor Circuit Uncouples Motor Neuron Death from Hyperexcitability Induced by SMN Deficiency. Cell Rep 2016; 16:1416-1430. [PMID: 27452470 PMCID: PMC4972669 DOI: 10.1016/j.celrep.2016.06.087] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2016] [Revised: 05/06/2016] [Accepted: 06/24/2016] [Indexed: 12/13/2022] Open
Abstract
In spinal muscular atrophy, a neurodegenerative disease caused by ubiquitous deficiency in the survival motor neuron (SMN) protein, sensory-motor synaptic dysfunction and increased excitability precede motor neuron (MN) loss. Whether central synaptic dysfunction and MN hyperexcitability are cell-autonomous events or they contribute to MN death is unknown. We addressed these issues using a stem-cell-based model of the motor circuit consisting of MNs and both excitatory and inhibitory interneurons (INs) in which SMN protein levels are selectively depleted. We show that SMN deficiency induces selective MN death through cell-autonomous mechanisms, while hyperexcitability is a non-cell-autonomous response of MNs to defects in pre-motor INs, leading to loss of glutamatergic synapses and reduced excitation. Findings from our in vitro model suggest that dysfunction and loss of MNs result from differential effects of SMN deficiency in distinct neurons of the motor circuit and that hyperexcitability does not trigger MN death.
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Affiliation(s)
- Christian M Simon
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA; Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA
| | - Anna M Janas
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA; Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA
| | - Francesco Lotti
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA; Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA
| | - Juan Carlos Tapia
- Department of Neuroscience, Columbia University, New York, NY 10032, USA
| | - Livio Pellizzoni
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA; Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA.
| | - George Z Mentis
- Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA; Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA; Department of Neurology, Columbia University, New York, NY 10032, USA.
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17
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Bikoff JB, Gabitto MI, Rivard AF, Drobac E, Machado TA, Miri A, Brenner-Morton S, Famojure E, Diaz C, Alvarez FJ, Mentis GZ, Jessell TM. Spinal Inhibitory Interneuron Diversity Delineates Variant Motor Microcircuits. Cell 2016; 165:207-219. [PMID: 26949184 DOI: 10.1016/j.cell.2016.01.027] [Citation(s) in RCA: 167] [Impact Index Per Article: 20.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2015] [Revised: 11/30/2015] [Accepted: 01/15/2016] [Indexed: 12/11/2022]
Abstract
Animals generate movement by engaging spinal circuits that direct precise sequences of muscle contraction, but the identity and organizational logic of local interneurons that lie at the core of these circuits remain unresolved. Here, we show that V1 interneurons, a major inhibitory population that controls motor output, fractionate into highly diverse subsets on the basis of the expression of 19 transcription factors. Transcriptionally defined V1 subsets exhibit distinct physiological signatures and highly structured spatial distributions with mediolateral and dorsoventral positional biases. These positional distinctions constrain patterns of input from sensory and motor neurons and, as such, suggest that interneuron position is a determinant of microcircuit organization. Moreover, V1 diversity indicates that different inhibitory microcircuits exist for motor pools controlling hip, ankle, and foot muscles, revealing a variable circuit architecture for interneurons that control limb movement.
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Affiliation(s)
- Jay B Bikoff
- Howard Hughes Medical Institute, Columbia University, New York, NY 10032, USA; Kavli Institute for Brain Science, Columbia University, New York, NY 10032, USA; Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10032, USA; Departments of Neuroscience and Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA.
| | - Mariano I Gabitto
- Howard Hughes Medical Institute, Columbia University, New York, NY 10032, USA; Kavli Institute for Brain Science, Columbia University, New York, NY 10032, USA; Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10032, USA; Departments of Neuroscience and Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Andre F Rivard
- Department of Physiology, Emory University School of Medicine, Atlanta, GA 30319, USA
| | - Estelle Drobac
- Center for Motor Neuron Biology and Disease, Departments of Pathology and Cell Biology and Neurology, Columbia University, New York, NY 10032, USA
| | - Timothy A Machado
- Howard Hughes Medical Institute, Columbia University, New York, NY 10032, USA; Kavli Institute for Brain Science, Columbia University, New York, NY 10032, USA; Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10032, USA; Departments of Neuroscience and Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Andrew Miri
- Howard Hughes Medical Institute, Columbia University, New York, NY 10032, USA; Kavli Institute for Brain Science, Columbia University, New York, NY 10032, USA; Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10032, USA; Departments of Neuroscience and Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Susan Brenner-Morton
- Howard Hughes Medical Institute, Columbia University, New York, NY 10032, USA; Kavli Institute for Brain Science, Columbia University, New York, NY 10032, USA; Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10032, USA; Departments of Neuroscience and Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Erica Famojure
- Howard Hughes Medical Institute, Columbia University, New York, NY 10032, USA; Kavli Institute for Brain Science, Columbia University, New York, NY 10032, USA; Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10032, USA; Departments of Neuroscience and Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Carolyn Diaz
- Howard Hughes Medical Institute, Columbia University, New York, NY 10032, USA; Kavli Institute for Brain Science, Columbia University, New York, NY 10032, USA; Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10032, USA; Departments of Neuroscience and Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Francisco J Alvarez
- Department of Physiology, Emory University School of Medicine, Atlanta, GA 30319, USA
| | - George Z Mentis
- Center for Motor Neuron Biology and Disease, Departments of Pathology and Cell Biology and Neurology, Columbia University, New York, NY 10032, USA
| | - Thomas M Jessell
- Howard Hughes Medical Institute, Columbia University, New York, NY 10032, USA; Kavli Institute for Brain Science, Columbia University, New York, NY 10032, USA; Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10032, USA; Departments of Neuroscience and Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA.
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18
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Sharma A, Lyashchenko AK, Lu L, Nasrabady SE, Elmaleh M, Mendelsohn M, Nemes A, Tapia JC, Mentis GZ, Shneider NA. ALS-associated mutant FUS induces selective motor neuron degeneration through toxic gain of function. Nat Commun 2016; 7:10465. [PMID: 26842965 PMCID: PMC4742863 DOI: 10.1038/ncomms10465] [Citation(s) in RCA: 225] [Impact Index Per Article: 28.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2015] [Accepted: 12/14/2015] [Indexed: 12/13/2022] Open
Abstract
Mutations in FUS cause amyotrophic lateral sclerosis (ALS), including some of the most aggressive, juvenile-onset forms of the disease. FUS loss-of-function and toxic gain-of-function mechanisms have been proposed to explain how mutant FUS leads to motor neuron degeneration, but neither has been firmly established in the pathogenesis of ALS. Here we characterize a series of transgenic FUS mouse lines that manifest progressive, mutant-dependent motor neuron degeneration preceded by early, structural and functional abnormalities at the neuromuscular junction. A novel, conditional FUS knockout mutant reveals that postnatal elimination of FUS has no effect on motor neuron survival or function. Moreover, endogenous FUS does not contribute to the onset of the ALS phenotype induced by mutant FUS. These findings demonstrate that FUS-dependent motor degeneration is not due to loss of FUS function, but to the gain of toxic properties conferred by ALS mutations. The mechanism by which FUS mutations cause familial ALS remains unclear. Here, the authors use mouse transgenic models to show that a toxic gain-of-function underlies motor neuron degeneration, and that the toxicity of mutant FUS does not depend on a loss or excess of FUS activity.
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Affiliation(s)
- Aarti Sharma
- Department of Neurology, Center for Motor Neuron Biology and Disease, Columbia University, 630 W 168th Street, P&S Building, Room 5-423, New York, New York 10032, USA
| | - Alexander K Lyashchenko
- Department of Neurology, Center for Motor Neuron Biology and Disease, Columbia University, 630 W 168th Street, P&S Building, Room 5-423, New York, New York 10032, USA
| | - Lei Lu
- Department of Neurology, Center for Motor Neuron Biology and Disease, Columbia University, 630 W 168th Street, P&S Building, Room 5-423, New York, New York 10032, USA
| | - Sara Ebrahimi Nasrabady
- Department of Pathology and Cell Biology, Center for Motor Neuron Biology and Disease, Columbia University, New York, New York 10032, USA
| | - Margot Elmaleh
- Department of Neurology, Center for Motor Neuron Biology and Disease, Columbia University, 630 W 168th Street, P&S Building, Room 5-423, New York, New York 10032, USA
| | - Monica Mendelsohn
- Department of Pathology and Cell Biology, Center for Motor Neuron Biology and Disease, Columbia University, New York, New York 10032, USA
| | - Adriana Nemes
- Department of Neuroscience, Howard Hughes Medical Institute, Columbia University, New York, New York 10032, USA
| | - Juan Carlos Tapia
- Department of Neuroscience, Columbia University, New York, New York 10032, USA
| | - George Z Mentis
- Department of Pathology and Cell Biology, Center for Motor Neuron Biology and Disease, Columbia University, New York, New York 10032, USA
| | - Neil A Shneider
- Department of Neurology, Center for Motor Neuron Biology and Disease, Columbia University, 630 W 168th Street, P&S Building, Room 5-423, New York, New York 10032, USA
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19
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Mendelsohn AI, Simon CM, Abbott LF, Mentis GZ, Jessell TM. Activity Regulates the Incidence of Heteronymous Sensory-Motor Connections. Neuron 2015; 87:111-23. [PMID: 26094608 DOI: 10.1016/j.neuron.2015.05.045] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2015] [Revised: 04/23/2015] [Accepted: 05/26/2015] [Indexed: 12/19/2022]
Abstract
The construction of spinal sensory-motor circuits involves the selection of appropriate synaptic partners and the allocation of precise synaptic input densities. Many aspects of spinal sensory-motor selectivity appear to be preserved when peripheral sensory activation is blocked, which has led to a view that sensory-motor circuits are assembled in an activity-independent manner. Yet it remains unclear whether activity-dependent refinement has a role in the establishment of connections between sensory afferents and those motor pools that have synergistic biomechanical functions. We show here that genetically abolishing central sensory-motor neurotransmission leads to a selective enhancement in the number and density of such "heteronymous" connections, whereas other aspects of sensory-motor connectivity are preserved. Spike-timing-dependent synaptic refinement represents one possible mechanism for the changes in connectivity observed after activity blockade. Our findings therefore reveal that sensory activity does have a limited and selective role in the establishment of patterned monosynaptic sensory-motor connections.
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Affiliation(s)
- Alana I Mendelsohn
- Howard Hughes Medical Institute, Kavli Institute for Brain Science, Zuckerman Mind Brain Behavior Institute, Departments of Neuroscience and Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Christian M Simon
- Center for Motor Neuron Biology and Disease, Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA
| | - L F Abbott
- Center for Theoretical Neuroscience, Departments of Physiology and Neuroscience, Columbia University, New York, NY 10032, USA
| | - George Z Mentis
- Center for Motor Neuron Biology and Disease, Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA
| | - Thomas M Jessell
- Howard Hughes Medical Institute, Kavli Institute for Brain Science, Zuckerman Mind Brain Behavior Institute, Departments of Neuroscience and Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA.
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Fletcher EV, Mentis GZ. The Intrinsic Hyperexcitability of SMA Motor Neurons is a Result of Dysfunctional Spinal Circuitry. Biophys J 2013. [DOI: 10.1016/j.bpj.2012.11.896] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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Lotti F, Imlach WL, Saieva L, Beck ES, Hao LT, Li DK, Jiao W, Mentis GZ, Beattie CE, McCabe BD, Pellizzoni L. An SMN-dependent U12 splicing event essential for motor circuit function. Cell 2012; 151:440-54. [PMID: 23063131 DOI: 10.1016/j.cell.2012.09.012] [Citation(s) in RCA: 207] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2011] [Revised: 06/16/2012] [Accepted: 09/10/2012] [Indexed: 01/06/2023]
Abstract
Spinal muscular atrophy (SMA) is a motor neuron disease caused by deficiency of the ubiquitous survival motor neuron (SMN) protein. To define the mechanisms of selective neuronal dysfunction in SMA, we investigated the role of SMN-dependent U12 splicing events in the regulation of motor circuit activity. We show that SMN deficiency perturbs splicing and decreases the expression of a subset of U12 intron-containing genes in mammalian cells and Drosophila larvae. Analysis of these SMN target genes identifies Stasimon as a protein required for motor circuit function. Restoration of Stasimon expression in the motor circuit corrects defects in neuromuscular junction transmission and muscle growth in Drosophila SMN mutants and aberrant motor neuron development in SMN-deficient zebrafish. These findings directly link defective splicing of critical neuronal genes induced by SMN deficiency to motor circuit dysfunction, establishing a molecular framework for the selective pathology of SMA.
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Affiliation(s)
- Francesco Lotti
- Department of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA
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22
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Siembab VC, Smith CA, Zagoraiou L, Berrocal MC, Mentis GZ, Alvarez FJ. Target selection of proprioceptive and motor axon synapses on neonatal V1-derived Ia inhibitory interneurons and Renshaw cells. J Comp Neurol 2011; 518:4675-701. [PMID: 20963823 DOI: 10.1002/cne.22441] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The diversity of premotor interneurons in the mammalian spinal cord is generated from a few phylogenetically conserved embryonic classes of interneurons (V0, V1, V2, V3). Their mechanisms of diversification remain unresolved, although these are clearly important to understand motor circuit assembly in the spinal cord. Some Ia inhibitory interneurons (IaINs) and all Renshaw cells (RCs) derive from embryonic V1 interneurons; however, in adult they display distinct functional properties and synaptic inputs, for example proprioceptive inputs preferentially target IaINs, while motor axons target RCs. Previously, we found that both inputs converge on RCs in neonates, raising the possibility that proprioceptive (VGLUT1-positive) and motor axon synapses (VAChT-positive) initially target several different V1 interneurons populations and then become selected or deselected postnatally. Alternatively, specific inputs might precisely connect only with predefined groups of V1 interneurons. To test these hypotheses we analyzed synaptic development on V1-derived IaINs and compared them to RCs of the same age and spinal cord levels. V1-interneurons were labeled using genetically encoded lineage markers in mice. The results show that although neonatal V1-derived IaINs and RCs are competent to receive proprioceptive synapses, these synapses preferentially target the proximal somato-dendritic regions of IaINs and postnatally proliferate on IaINs, but not on RCs. In contrast, cholinergic synapses on RCs are specifically derived from motor axons, while on IaINs they originate from Pitx2 V0c interneurons. Thus, motor, proprioceptive, and even some interneuron inputs are biased toward specific subtypes of V1-interneurons. Postnatal strengthening of these inputs is later superimposed on this initial preferential targeting.
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Affiliation(s)
- Valerie C Siembab
- Department of Neuroscience, Cell Biology and Physiology, Boonshoft School of Medicine, Wright State University, Dayton, Ohio 45435, USA
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Mentis GZ, Blivis D, Liu W, Drobac E, Crowder ME, Kong L, Alvarez FJ, Sumner CJ, O'Donovan MJ. Early functional impairment of sensory-motor connectivity in a mouse model of spinal muscular atrophy. Neuron 2011; 69:453-67. [PMID: 21315257 DOI: 10.1016/j.neuron.2010.12.032] [Citation(s) in RCA: 269] [Impact Index Per Article: 20.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/11/2010] [Indexed: 01/12/2023]
Abstract
To define alterations of neuronal connectivity that occur during motor neuron degeneration, we characterized the function and structure of spinal circuitry in spinal muscular atrophy (SMA) model mice. SMA motor neurons show reduced proprioceptive reflexes that correlate with decreased number and function of synapses on motor neuron somata and proximal dendrites. These abnormalities occur at an early stage of disease in motor neurons innervating proximal hindlimb muscles and medial motor neurons innervating axial muscles, but only at end-stage disease in motor neurons innervating distal hindlimb muscles. Motor neuron loss follows afferent synapse loss with the same temporal and topographical pattern. Trichostatin A, which improves motor behavior and survival of SMA mice, partially restores spinal reflexes, illustrating the reversibility of these synaptic defects. Deafferentation of motor neurons is an early event in SMA and may be a primary cause of motor dysfunction that is amenable to therapeutic intervention.
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Affiliation(s)
- George Z Mentis
- Section on Developmental Biology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA.
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Siembab VC, Smith CA, Zagoraiou L, Berrocal MC, Mentis GZ, Alvarez FJ. Target selection of proprioceptive and motor axon synapses on neonatal V1-derived Ia inhibitory interneurons and Renshaw cells. J Comp Neurol 2010. [DOI: 10.1002/cne.22537] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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O'Donovan MJ, Bonnot A, Mentis GZ, Chub N, Pujala A, Alvarez FJ. Mechanisms of excitation of spinal networks by stimulation of the ventral roots. Ann N Y Acad Sci 2010; 1198:63-71. [PMID: 20536921 DOI: 10.1111/j.1749-6632.2010.05535.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
It has recently been demonstrated that motoneurons in neonatal rodents release an excitatory amino acid, in addition to acetylcholine, from their central terminals onto Renshaw cells. Although the function of this amino acid release is not understood, it may mediate the excitatory actions of motor axon stimulation on spinal motor networks. Stimulation of motor axons in the ventral roots or muscle nerves can activate the locomotor central pattern generator or entrain bursting in the disinhibited cord. Both of these effects persist in the presence of cholinergic antagonists and are abolished or diminished by ionotropic and metabotropic glutamate antagonists. Calcium imaging in the disinhibited cord shows that a ventral root stimulus evokes ventrolateral activity initially, which subsequently propagates to the rest of the cord. This finding suggests that excitatory interneurons excited by motoneuron recurrent collaterals are located in this region. However, motoneurons do not exhibit short latency excitatory potentials in response to ventral root stimulation indicating that the excitatory effects are mediated polysynaptically. We discuss the significance of these findings.
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Mentis GZ, Alvarez FJ, Shneider NA, Siembab VC, O'Donovan MJ. Mechanisms regulating the specificity and strength of muscle afferent inputs in the spinal cord. Ann N Y Acad Sci 2010; 1198:220-30. [PMID: 20536937 DOI: 10.1111/j.1749-6632.2010.05538.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
We investigated factors controlling the development of connections between muscle spindle afferents, spinal motor neurons, and inhibitory Renshaw cells. Several mutants were examined to establish the role of muscle spindles, muscle spindle-derived NT3, and excess NT3 in determining the specificity and strength of these connections. The findings suggest that although spindle-derived factors are not necessary for the initial formation and specificity of the synapses, spindle-derived NT3 seems necessary for strengthening homonymous connections between Ia afferents and motor neurons during the second postnatal week. We also found evidence for functional monosynaptic connections between sensory afferents and neonatal Renshaw cells although the density of these synapses decreases at P15. We conclude that muscle spindle synapses are weakened on Renshaw cells while they are strengthened on motor neurons. Interestingly, the loss of sensory synapses on Renshaw cells was reversed in mice overexpressing NT3 in the periphery, suggesting that different levels of NT3 are required for functional maintenance and strengthening of spindle afferent inputs on motor neurons and Renshaw cells.
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Affiliation(s)
- George Z Mentis
- Developmental Neurobiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA.
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Ziskind-Conhaim L, Mentis GZ, Wiesner EP, Titus DJ. Synaptic integration of rhythmogenic neurons in the locomotor circuitry: the case of Hb9 interneurons. Ann N Y Acad Sci 2010; 1198:72-84. [PMID: 20536922 DOI: 10.1111/j.1749-6632.2010.05533.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Innovative molecular and genetic techniques have recently led to the identification of genetically defined populations of ipsilaterally projecting excitatory interneurons with probable functions in the rhythm-generating kernel of the central pattern generators (CPGs). The role of interneuronal populations in specific motor function is determined by their synaptic inputs, intrinsic properties, and target neurons. In this review we examine whether Hb9-expressing interneurons (Hb9 INs) fulfill a set of criteria that are the hallmarks of rhythm generators in the locomotor circuitry. Induced locomotor-like activity in this distinct population of ventral interneurons is in phase with bursts of motor activity, raising the possibility that they are part of the locomotor generator. To increase our understanding of the integrative function of Hb9 INs in the locomotor CPG, we investigated the cellular mechanisms underlying their rhythmic activity and examined the properties of synaptic inputs from low-threshold afferents and possible synaptic contacts with segmental motoneurons. Our findings suggest that the rhythmogenic Hb9 INs are integral components of the sensorimotor circuitry that regulate locomotor-like activity in the spinal cord.
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Affiliation(s)
- Lea Ziskind-Conhaim
- Department of Physiology and Center for Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA.
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Hinckley CA, Wiesner EP, Mentis GZ, Titus DJ, Ziskind-Conhaim L. Sensory modulation of locomotor-like membrane oscillations in Hb9-expressing interneurons. J Neurophysiol 2010; 103:3407-23. [PMID: 20393069 DOI: 10.1152/jn.00996.2009] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The central pattern generator can generate locomotor-like rhythmic activity in the spinal cord in the absence of descending and peripheral inputs, but the motor pattern is regulated by feedback from peripheral sensory inputs that adjust motor outputs to external stimuli. To elucidate the possible role of Hb9-expressing interneurons (Hb9 INs) in the locomotor circuitry, we investigated whether their induced oscillatory activity is modulated by low-threshold afferents in the isolated spinal cords of neonatal Hb9:eGFP transgenic mice. Low-intensity stimulation of segmental afferents generated short-latency, monosynaptic excitatory responses in 62% of Hb9 INs. These were associated with longer-latency (approximately 13 ms) excitatory postsynaptic currents that were evoked in all Hb9 INs, probably by slow conducting afferents that synapse directly onto them. Concomitant morphological analysis confirmed that afferent axons with immunoreactive expression of vesicular glutamate transporter-1 and parvalbumin, presumably from primary afferents, contacted somata and dendrites of all Hb9 INs. Most of the putative synaptic contacts were on distal dendrites that extended to an area with profuse afferent projections. We next examined whether low-threshold afferents in upper (flexor-related) and lower (extensor-related) lumbar segments altered the timing of neurochemically induced locomotor-like rhythms in Hb9 INs and motoneurons. Excitation of flexor-related afferents during the flexor phase delayed the onset of subsequent cycles in both Hb9 INs and segmental motoneurons while maintaining the phase relationship between them. The in-phase correlation between voltage oscillations in Hb9 INs and motor bursts also persisted during the two- to threefold increase in cycle period triggered by extensor-related afferents. Our findings that low-threshold, presumably muscle afferents, synapse directly onto these interneurons and perturb their induced locomotor-like membrane oscillations in a pattern that remains phase-locked with motor bursts support the hypothesis that Hb9 INs are part of the sensorimotor circuitry that regulates the pattern of locomotor rhythms in the isolated cord.
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Affiliation(s)
- Christopher A Hinckley
- Department of Physiology, University of Wisconsin School of Medicine, 1300 University Avenue, Madison, WI 53706, USA
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Abstract
This unit describes methods for loading ion- and voltage-sensitive dyes into neurons, with a particular focus on the spinal cord as a model system. In addition, we describe the use of these dyes to visualize neural activity. Although the protocols described here concern spinal networks in culture or an intact in vitro preparation, they can be, and have been, widely used in other parts of the nervous system.
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Affiliation(s)
- Douglas R Fields
- Section on Nervous System Development and Plasticity, National Institute of Child Health and Human Development (NICHD), NIH, Bethesda, Maryland, USA
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O'Donovan MJ, Bonnot A, Mentis GZ, Arai Y, Chub N, Shneider NA, Wenner P. Imaging the spatiotemporal organization of neural activity in the developing spinal cord. Dev Neurobiol 2008; 68:788-803. [PMID: 18383543 DOI: 10.1002/dneu.20620] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
In this review, we discuss the use of imaging to visualize the spatiotemporal organization of network activity in the developing spinal cord of the chick embryo and the neonatal mouse. We describe several different methods for loading ion- and voltage-sensitive dyes into spinal neurons and consider the advantages and limitations of each one. We review work in the chick embryo, suggesting that motoneurons play a critical role in the initiation of each cycle of spontaneous network activity and describe how imaging has been used to identify a class of spinal interneuron that appears to be the avian homolog of mammalian Renshaw cells or 1a-inhibitory interneurons. Imaging of locomotor-like activity in the neonatal mouse revealed a wave-like activation of motoneurons during each cycle of discharge. We discuss the significance of this finding and its implications for understanding how locomotor-like activity is coordinated across different segments of the cord. In the last part of the review, we discuss some of the exciting new prospects for the future.
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Affiliation(s)
- Michael J O'Donovan
- National Institute of Neurological Disorder and Stroke, NIH, Bethesda, Maryland 20892, USA.
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Mentis GZ, Díaz E, Moran LB, Navarrete R. Early alterations in the electrophysiological properties of rat spinal motoneurones following neonatal axotomy. J Physiol 2007; 582:1141-61. [PMID: 17510183 PMCID: PMC2075252 DOI: 10.1113/jphysiol.2007.133488] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Revised: 03/27/2007] [Accepted: 05/17/2007] [Indexed: 12/15/2022] Open
Abstract
Early in development, motoneurones are critically dependent on their target muscles for survival and differentiation. Previous studies have shown that neonatal axotomy causes massive motoneurone death and abnormal function in the surviving motoneurones. We have investigated the electrophysiological and morphological properties of motoneurones innervating the flexor tibialis anterior (TA) muscle during the first week after a neonatal axotomy, at a time when the motoneurones would be either in the process of degeneration or attempting to reinnervate their target muscles. We found that a large number ( approximately 75%) of TA motoneurones died within 3 weeks after neonatal axotomy. Intracellular recordings revealed a marked increase in motoneurone excitability, as indicated by changes in passive and active membrane electrical properties. These changes were associated with a shift in the motoneurone firing pattern from a predominantly phasic pattern to a tonic pattern. Morphologically, the dendritic tree of the physiologically characterized axotomized cells was significantly reduced compared with age-matched normal motoneurones. These data demonstrate that motoneurone electrical properties are profoundly altered shortly after neonatal axotomy. In a subpopulation of the axotomized cells, abnormally high motoneurone excitability (input resistance significantly higher compared with control cells) was associated with a severe truncation of the dendritic arbor, suggesting that this excitability may represent an early electrophysiological correlate of motoneurone degeneration.
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Affiliation(s)
- George Z Mentis
- Division of Neuroscience and Mental Health, Department of Cellular & Molecular Neuroscience, Imperial College London, Fulham Palace Road, London W6 8RF, UK.
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Personius KE, Chang Q, Mentis GZ, O'Donovan MJ, Balice-Gordon RJ. Reduced gap junctional coupling leads to uncorrelated motor neuron firing and precocious neuromuscular synapse elimination. Proc Natl Acad Sci U S A 2007; 104:11808-13. [PMID: 17609378 PMCID: PMC1913899 DOI: 10.1073/pnas.0703357104] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2007] [Indexed: 11/18/2022] Open
Abstract
During late embryonic and early postnatal life, neuromuscular junctions undergo synapse elimination that is modulated by patterns of motor neuron activity. Here, we test the hypothesis that reduced spinal neuron gap junctional coupling decreases temporally correlated motor neuron activity that, in turn, modulates neuromuscular synapse elimination, by using mutant mice lacking connexin 40 (Cx40), a developmentally regulated gap junction protein expressed in motor and other spinal neurons. In Cx40-/- mice, electrical coupling among lumbar motor neurons, measured by whole-cell recordings, was reduced, and single motor unit recordings in awake, behaving neonates showed that temporally correlated motor neuron activity was also reduced. Immunostaining and intracellular recording showed that the neuromuscular synapse elimination was accelerated in muscles from Cx40-/- mice compared with WT littermates. Our work shows that gap junctional coupling modulates neuronal activity patterns that, in turn, mediate synaptic competition, a process that shapes synaptic circuitry in the developing brain.
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Affiliation(s)
- Kirkwood E. Personius
- *Department of Rehabilitation Science, School of Public Health and Health Professions, University at Buffalo, the State University of New York, Buffalo, NY 14214-3079
| | - Qiang Chang
- Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6074; and
| | - George Z. Mentis
- The Porter Neuroscience Center, National Institutes of Health, Bethesda, MD 20892-3701
| | - Michael J. O'Donovan
- The Porter Neuroscience Center, National Institutes of Health, Bethesda, MD 20892-3701
| | - Rita J. Balice-Gordon
- Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6074; and
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Jean-Xavier C, Mentis GZ, O'Donovan MJ, Cattaert D, Vinay L. Dual personality of GABA/glycine-mediated depolarizations in immature spinal cord. Proc Natl Acad Sci U S A 2007; 104:11477-82. [PMID: 17592145 PMCID: PMC2040923 DOI: 10.1073/pnas.0704832104] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The inhibitory action of glycine and GABA in adult neurons consists of both shunting incoming excitations and moving the membrane potential away from the action potential (AP) threshold. By contrast, in immature neurons, inhibitory postsynaptic potentials (IPSPs) are depolarizing; it is generally accepted that, despite their depolarizing action, these IPSPs are inhibitory because of the shunting action of the Cl(-) conductance increase. Here we investigated the integration of depolarizing IPSPs (dIPSPs) with excitatory inputs in the neonatal rodent spinal cord by means of both intracellular recordings from lumbar motoneurons and a simulation using the compartment model program "Neuron." We show that the ability of IPSPs to suppress suprathreshold excitatory events depends on E(Cl) and the location of inhibitory synapses. The depolarization outlasts the conductance changes and spreads electrotonically in the somatodendritic tree, whereas the shunting effect is restricted and local. As a consequence, dIPSPs facilitated AP generation by subthreshold excitatory events in the late phase of the response. The window of facilitation became wider as E(Cl) was more depolarized and started earlier as inhibitory synapses were moved away from the excitatory input. GAD65/67 immunohistochemistry demonstrated the existence of distal inhibitory synapses on motoneurons in the neonatal rodent spinal cord. This study demonstrates that small dIPSPs can either inhibit or facilitate excitatory inputs depending on timing and location. Our results raise the possibility that inhibitory synapses exert a facilitatory action on distant excitatory inputs and slight changes of E(Cl) may have important consequences for network processing.
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Affiliation(s)
- Céline Jean-Xavier
- *Laboratoire Plasticité et Physio-Pathologie de la Motricité, Centre National de la Recherche Scientifique, Aix-Marseille Université, 31 Chemin Joseph Aiguier, F-13402 Marseille Cedex 20, France
| | - George Z. Mentis
- Laboratory of Neural Control, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892
| | - Michael J. O'Donovan
- Laboratory of Neural Control, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892
| | - Daniel Cattaert
- Laboratoire de Neurobiologie des Réseaux, Centre National de la Recherche Scientifique, Université de Bordeaux, 1 Avenue des Facultés, 33405 Talence Cedex, France; and
| | - Laurent Vinay
- *Laboratoire Plasticité et Physio-Pathologie de la Motricité, Centre National de la Recherche Scientifique, Aix-Marseille Université, 31 Chemin Joseph Aiguier, F-13402 Marseille Cedex 20, France
- To whom correspondence should be addressed. E-mail:
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Arai Y, Mentis GZ, Wu JY, O'Donovan MJ. Ventrolateral origin of each cycle of rhythmic activity generated by the spinal cord of the chick embryo. PLoS One 2007; 2:e417. [PMID: 17479162 PMCID: PMC1855078 DOI: 10.1371/journal.pone.0000417] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2006] [Accepted: 03/15/2007] [Indexed: 11/19/2022] Open
Abstract
Background The mechanisms responsible for generating rhythmic motor activity in the developing spinal cord of the chick embryo are poorly understood. Here we investigate whether the activity of motoneurons occurs before other neuronal populations at the beginning of each cycle of rhythmic discharge. Methodology/Principal Findings The spatiotemporal organization of neural activity in transverse slices of the lumbosacral cord of the chick embryo (E8-E11) was investigated using intrinsic and voltage-sensitive dye (VSD) imaging. VSD signals accompanying episodes of activity comprised a rhythmic decrease in light transmission that corresponded to each cycle of electrical activity recorded from the ipsilateral ventral root. The rhythmic signals were widely synchronized across the cord face, and the largest signal amplitude was in the ventrolateral region where motoneurons are located. In unstained slices we recorded two classes of intrinsic signal. In the first, an episode of rhythmic activity was accompanied by a slow decrease in light transmission that peaked in the dorsal horn and decayed dorsoventrally. Superimposed on this signal was a much smaller rhythmic increase in transmission that was coincident with each cycle of discharge and whose amplitude and spatial distribution was similar to that of the VSD signals. At the onset of a spontaneously occurring episode and each subsequent cycle, both the intrinsic and VSD signals originated within the lateral motor column and spread medially and then dorsally. By contrast, following a dorsal root stimulus, the optical signals originated within the dorsal horn and traveled ventrally to reach the lateral motor column. Conclusions/Significance These findings suggest that motoneuron activity contributes to the initiation of each cycle of rhythmic activity, and that motoneuron and/or R-interneuron synapses are a plausible site for the activity-dependent synaptic depression that modeling studies have identified as a critical mechanism for cycling within an episode.
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Affiliation(s)
- Yoshiyasu Arai
- Laboratory of Neural Control, Section on Developmental Neurobiology, National Institute of Neurological Disorders and Stroke (NINDS), National Institutes of Health (NIH), Bethesda, Maryland, United States of America
| | - George Z. Mentis
- Laboratory of Neural Control, Section on Developmental Neurobiology, National Institute of Neurological Disorders and Stroke (NINDS), National Institutes of Health (NIH), Bethesda, Maryland, United States of America
| | - Jiang-young Wu
- Laboratory of Neural Control, Section on Developmental Neurobiology, National Institute of Neurological Disorders and Stroke (NINDS), National Institutes of Health (NIH), Bethesda, Maryland, United States of America
- Department of Physiology and Biophysics, Georgetown University, Washington, D. C., United States of America
| | - Michael J. O'Donovan
- Laboratory of Neural Control, Section on Developmental Neurobiology, National Institute of Neurological Disorders and Stroke (NINDS), National Institutes of Health (NIH), Bethesda, Maryland, United States of America
- * To whom correspondence should be addressed. E-mail:
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Blivis D, Mentis GZ, O'donovan MJ, Lev-Tov A. Differential Effects of Opioids on Sacrocaudal Afferent Pathways and Central Pattern Generators in the Neonatal Rat Spinal Cord. J Neurophysiol 2007; 97:2875-86. [PMID: 17287435 DOI: 10.1152/jn.01313.2006] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The effects of opioids on sacrocaudal afferent (SCA) pathways and the pattern-generating circuitry of the thoracolumbar and sacrocaudal segments of the spinal cord were studied in isolated spinal cord and brain stem-spinal cord preparations of the neonatal rat. The locomotor and tail moving rhythm produced by activation of nociceptive and nonnociceptive sacrocaudal afferents was completely blocked by specific application of the μ-opioid receptor agonist [d-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin acetate salt (DAMGO) to the sacrocaudal but not the thoracolumbar segments of the spinal cord. The rhythmic activity could be restored after addition of the opioid receptor antagonist naloxone to the experimental chamber. The opioid block of the SCA-induced rhythm is not due to impaired rhythmogenic capacity of the spinal cord because a robust rhythmic activity could be initiated in the thoracolumbar and sacrocaudal segments in the presence of DAMGO, either by stimulation of the ventromedial medulla or by bath application of N-methyl-d-aspartate/serotonin. We suggest that the opioid block of the SCA-induced rhythm involves suppression of synaptic transmission through sacrocaudal interneurons interposed between SCA and the pattern-generating circuitry. The expression of μ opioid receptors in several groups of dorsal, intermediate and ventral horn interneurons in the sacrocaudal segments of the cord, documented in this study, provides an anatomical basis for this suggestion.
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MESH Headings
- Afferent Pathways/drug effects
- Analgesics, Opioid/pharmacology
- Animals
- Animals, Newborn/physiology
- Brain Stem/drug effects
- Brain Stem/physiology
- Data Interpretation, Statistical
- Electric Stimulation
- Electrophysiology
- Enkephalin, Ala(2)-MePhe(4)-Gly(5)-/pharmacology
- Excitatory Postsynaptic Potentials/drug effects
- Immunohistochemistry
- Instinct
- Locomotion/physiology
- Microscopy, Confocal
- Movement/physiology
- Naloxone/pharmacology
- Narcotic Antagonists/pharmacology
- Rats
- Receptors, Opioid, mu/agonists
- Receptors, Opioid, mu/genetics
- Receptors, Opioid, mu/physiology
- Spinal Cord/drug effects
- Spinal Cord/physiology
- Tail/innervation
- Tail/physiology
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Affiliation(s)
- D Blivis
- Dept. of Anatomy and Cell Biology, The Hebrew University Medical School, Jerusalem, 91010, Israel
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36
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Abstract
The mechanisms that diversify adult interneurons from a few pools of embryonic neurons are unknown. Renshaw cells, Ia inhibitory interneurons (IaINs), and possibly other types of mammalian spinal interneurons have common embryonic origins within the V1 group. However, in contrast to IaINs and other V1-derived interneurons, adult Renshaw cells receive motor axon synapses and lack proprioceptive inputs. Here, we investigated how this specific pattern of connectivity emerges during the development of Renshaw cells. Tract tracing and immunocytochemical markers [parvalbumin and vesicular glutamate transporter 1 (VGLUT1)] showed that most embryonic (embryonic day 18) Renshaw cells lack dorsal root inputs, but more than half received dorsal root synapses by postnatal day 0 (P0) and this input spread to all Renshaw cells by P10-P15. Electrophysiological recordings in neonates indicated that this input is functional and evokes Renshaw cell firing. VGLUT1-IR bouton density on Renshaw cells increased until P15 but thereafter decreased because of limited synapse proliferation coupled with the enlargement of Renshaw cell dendrites. In parallel, Renshaw cell postsynaptic densities apposed to VGLUT1-IR synapses became smaller in adult compared with P15. In contrast, vesicular acetylcholine transporter-IR motor axon synapses contact embryonic Renshaw cells and proliferate postnatally matching Renshaw cell growth. Like other V1 neurons, Renshaw cells are thus competent to receive sensory synapses. However, after P15, these sensory inputs appear deselected through arrested proliferation and synapse weakening. Thus, Renshaw cells shift from integrating sensory and motor inputs in neonates to predominantly motor inputs in adult. Similar synaptic weight shifts on interneurons may be involved in the maturation of motor reflexes and locomotor circuitry.
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Affiliation(s)
- George Z. Mentis
- Laboratory of Neural Control, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892
| | - Valerie C. Siembab
- Department of Neurosciences, Cell Biology, and Physiology, Wright State University, Dayton, Ohio 45435, and
| | - Ricardo Zerda
- Department of Neurosciences, Cell Biology, and Physiology, Wright State University, Dayton, Ohio 45435, and
| | - Michael J. O'Donovan
- Laboratory of Neural Control, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892
| | - Francisco J. Alvarez
- Department of Neurosciences, Cell Biology, and Physiology, Wright State University, Dayton, Ohio 45435, and
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37
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Mentis GZ, Gravell M, Hamilton R, Shneider NA, O'Donovan MJ, Schubert M. Transduction of motor neurons and muscle fibers by intramuscular injection of HIV-1-based vectors pseudotyped with select rabies virus glycoproteins. J Neurosci Methods 2006; 157:208-17. [PMID: 16725205 DOI: 10.1016/j.jneumeth.2006.04.011] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2005] [Revised: 03/21/2006] [Accepted: 04/12/2006] [Indexed: 11/22/2022]
Abstract
For studies of motor neuron function or for therapeutic purposes, novel pseudotype HIV-1-based vectors were developed that are capable of expressing transgenes in motor neurons following injection into mouse hind limb muscles. To specifically target motor neurons, glycoproteins from two rabies virus (RV) isolates, the mouse-brain adapted challenge virus 24 (CVS-24) variants, CVS-N2c and CVS-B2c were evaluated for pseudotype formation with an HIV-1-based vector. Both RV glycoproteins incorporated into vector envelopes, and both pseudotypes yielded high titers with Hek293T and cortical plate neuron cultures. Increased neuronotropism by the CVS-N2c pseudotype was not observed, suggesting that vector tropism is not solely determined by the fusogenic viral glycoprotein. Vector injection into hind limb muscles resulted in EYFP reporter gene expression in the injected muscle fibers and in spinal cord motor neurons innervating the same muscle, indicating retrograde vector transport. Intramuscular vector injections into the soleus and tibialis anterior muscles transduced 26% and 16% of all motor neurons in each motor nucleus, respectively. These transduction efficiencies may allow novel approaches to functional studies of the motor system and the treatment of neuromuscular disease.
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Affiliation(s)
- George Z Mentis
- Developmental Neurobiology Section, Basic Neuroscience Program, National Institutes of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892-3700, USA.
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38
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Chub N, Mentis GZ, O'donovan MJ. Chloride-sensitive MEQ fluorescence in chick embryo motoneurons following manipulations of chloride and during spontaneous network activity. J Neurophysiol 2005; 95:323-30. [PMID: 16192339 DOI: 10.1152/jn.00162.2005] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Intracellular Cl(-) ([Cl(-)](in)) homeostasis is thought to be an important regulator of spontaneous activity in the spinal cord of the chick embryo. We investigated this idea by visualizing the variations of [Cl(-)](in) in motoneurons retrogradely labeled with the Cl-sensitive dye 6-methoxy-N-ethylquinolinium iodide (MEQ) applied to cut muscle nerves in the isolated E10-E12 spinal cord. This labeling procedure obviated the need for synthesizing the reduced, cell-permeable dihydro-MEQ (DiH-MEQ). The specificity of motoneuron labeling was confirmed using retrograde co-labeling with Texas Red Dextran and immunocytochemistry for choline acetyltransferase (ChAT). In MEQ-labeled motoneurons, the GABA(A) receptor agonist isoguvacine (100 muM) increased somatic and dendritic fluorescence by 7.4 and 16.7%, respectively. The time course of this fluorescence change mirrored that of the depolarization recorded from the axons of the labeled motoneurons. Blockade of the inward Na(+)/K(-)/2Cl(-) co-transporter (NKCC1) with bumetanide (20 microM) or with a low-Na(+) bath solution (12 mM), increased MEQ fluorescence by 5.3 and 11.4%, respectively, consistent with a decrease of [Cl(-)](in). After spontaneous episodes of activity, MEQ fluorescence increased and then declined to the pre-episode level during the interepisode interval. The largest fluorescence changes occurred over motoneuron dendrites (19.7%) with significantly smaller changes (5.2%) over somata. Collectively, these results show that retrogradely loaded MEQ can be used to detect [Cl(-)](in) in motoneurons, that the bumetanide-sensitive NKCC1 co-transporter is at least partially responsible for the elevated [Cl(-)](in) of developing motoneurons, and that dendritic [Cl(-)](in) decreases during spontaneous episodes and recovers during the inter-episode interval, presumably due to the action of NKCC1.
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Affiliation(s)
- Nikolai Chub
- Laboratory of Neural Control, NINDS/NIH, Rm. 3BC911, 35 Convent Dr., Bethesda, MD 20892-3700, USA.
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39
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Mentis GZ, Alvarez FJ, Bonnot A, Richards DS, Gonzalez-Forero D, Zerda R, O'Donovan MJ. Noncholinergic excitatory actions of motoneurons in the neonatal mammalian spinal cord. Proc Natl Acad Sci U S A 2005; 102:7344-9. [PMID: 15883359 PMCID: PMC1091756 DOI: 10.1073/pnas.0502788102] [Citation(s) in RCA: 138] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2005] [Indexed: 11/18/2022] Open
Abstract
Mammalian spinal motoneurons are considered to be output elements of the spinal cord that generate exclusively cholinergic actions on Renshaw cells, their intraspinal synaptic targets. Here, we show that antidromic stimulation of motor axons evokes depolarizing monosynaptic potentials in Renshaw cells that are depressed, but not abolished, by cholinergic antagonists. This residual potential was abolished by 2-amino-5-phosphonovaleric acid and 6-cyano-7-nitroquinoxaline-2,3-dione. In the presence of cholinergic antagonists, motor axon stimulation triggered locomotor-like activity that was blocked by 2-amino-5-phosphonovaleric acid. Some cholinergic motoneuronal terminals on both Renshaw cells and motoneurons were enriched in glutamate, but none expressed vesicular glutamate transporters. Our results raise the possibility that motoneurons release an excitatory amino acid in addition to acetylcholine and that they may be more directly involved in the genesis of mammalian locomotion than previously believed.
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Affiliation(s)
- George Z Mentis
- Laboratory of Neural Control, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892, USA.
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40
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O'Donovan MJ, Bonnot A, Wenner P, Mentis GZ. Calcium imaging of network function in the developing spinal cord. Cell Calcium 2005; 37:443-50. [PMID: 15820392 DOI: 10.1016/j.ceca.2005.01.012] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2004] [Accepted: 01/06/2005] [Indexed: 10/25/2022]
Abstract
We have used calcium imaging to visualize the spatiotemporal organization of activity generated by in vitro spinal cord preparations of the developing chick embryo and the neonatal mouse. During each episode of spontaneous activity, we found that chick spinal neurons were activated rhythmically and synchronously throughout the transverse extent of the spinal cord. At the onset of a spontaneous episode, optical activity originated in the ventrolateral part of the cord. Back-labeling of spinal interneurons with calcium dyes suggested that this ventrolateral initiation was mediated by activation of a class of interneurons, located dorsomedial to the motor nucleus, that receive direct monosynaptic input from motoneurons. Studies of locomotor-like activity in the anterior lumbar segments of the neonatal mouse cord revealed the existence of a rostrocaudal wave in the oscillatory component of each cycle of rhythmic motoneuron activity. This finding raises the possibility that the activation of mammalian motoneurons during locomotion may share some of the same rostrocaudally organized mechanisms that evolved to control swimming in fishes.
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Affiliation(s)
- Michael J O'Donovan
- Laboratory of Neural Control, Section on Developmental Neurobiology, NINDS, NIH, Bethesda, MD 20892, USA.
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41
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Abstract
Calcium imaging of neural network function has been limited by the extent of tissue labeled or the time taken for labeling. We now describe the use of electroporation-an established technique for transfecting cells with genes-to load neurons with calcium-sensitive dyes in the isolated spinal cord of the neonatal mouse in vitro. The dyes were injected subdurally, intravascularly, or into the central canal. This technique results in rapid and extensive labeling of neurons and their processes at all depths of the spinal cord, over a rostrocaudal extent determined by the position and size of the electrodes. Our results suggest that vascular distribution of the dye is involved in all three types of injections. Electroporation disrupts local reflex and network function only transiently (approximately 1 h), after which time they recover. We describe applications of the method to image activity of neuronal populations and individual neurons during antidromic, reflex, and locomotor-like behaviors. We show that these different motor behaviors are characterized by distinct patterns of activation among the labeled populations of cells.
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Affiliation(s)
- Agnès Bonnot
- Laboratory of Neural Control, Section on Developmental Neurobiology, NINDS, National Institutes of Health, 35 Convent Dr., Rm. 3C1010, Bethesda, MD 20892, USA.
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42
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Abstract
We examined the expression of the three Trk receptors for neurotrophins (TrkA, TrkB, and TrkC) in the extraocular motor nuclei of the adult cat by using antibodies directed against the full-Trk proteins in combination with horseradish peroxidase retrograde tracing. The three receptors were present in all neuronal populations investigated, including abducens motoneurons and internuclear neurons, medial rectus motoneurons of the oculomotor nucleus, and trochlear motoneurons. They were also present in the vestibular and prepositus hypoglossi nuclei. TrkA, TrkB, and TrkC immunopositive cells were found in similar percentages in the oculomotor and in the trochlear nuclei. In the abducens nucleus, however, a significantly higher percentage of cells expressed TrkB than the other two receptors, among both motoneurons (81.8%) and internuclear neurons (88.4%). The percentages obtained for the three Trk receptors in identified neuronal populations pointed to the colocalization of two or three receptors in a large number of cells. We used confocal microscopy to elucidate the subcellular location of Trk receptors. In this case, abducens motoneurons and internuclear neurons were identified with antibodies against choline acetyltransferase and calretinin, respectively. We found a different pattern of staining for each neurotrophin receptor, suggesting the possibility that each receptor and its cognate ligand may use a different route for cellular signaling. Therefore, the expression of Trk receptors in oculomotor, trochlear, and abducens motoneurons, as well as abducens internuclear neurons, suggests that their associated neurotrophins may exert an influence on the normal operation of the oculomotor circuitry. The presence of multiple Trk receptors on individual cells indicates that they likely act in concert with each other to regulate distinct functions.
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43
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Pastor AM, Mentis GZ, De La Cruz RR, Díaz E, Navarrete R. Increased electrotonic coupling in spinal motoneurons after transient botulinum neurotoxin paralysis in the neonatal rat. J Neurophysiol 2003; 89:793-805. [PMID: 12574457 DOI: 10.1152/jn.00498.2002] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The effect of early postnatal blockade of neuromuscular transmission using botulinum neurotoxin (BoNT) type A on motoneuron gap junctional coupling was studied by means of intracellular recordings and biocytin labeling using the in vitro hemisected spinal cord preparation of neonatal rats. The somata of tibialis anterior (TA) motoneurons were retrogradely labeled at birth (P0) by intramuscular injection of fluorescent tracers. Two days later, BoNT was injected unilaterally into the TA muscle. The toxin blocked neuromuscular transmission for the period studied (P4-P7) as shown by tension recordings of the TA muscle. Retrograde horseradish peroxidase tracing in animals reared to adulthood demonstrated no significant cell death or changes in the soma size of BoNT-treated TA motoneurons. Intracellular recordings were carried out in prelabeled control and BoNT-treated TA motoneurons from P4 to P7. Graded stimulation of the ventral root at subthreshold intensities elicited short-latency depolarizing (SLD) potentials that consisted of several discrete components reflecting electrotonic coupling between two or more motoneurons. BoNT treatment produced a significant increase (67%) in the maximum amplitude of the SLD and in the number of SLD components as compared with control (3.1 +/- 1.7 vs. 1.4 +/- 0.7; means +/- SD). The morphological correlates of electrotonic coupling were investigated at the light microscope level by studying the transfer of biocytin to other motoneurons and the putative sites of gap junctional interaction. The dye-coupled neurons clustered around the injected cell with close somato-somatic, dendro-somatic and -dendritic appositions that might represent the sites of electrotonic coupling. The size of the motoneuron cluster was, on average, 2.2 times larger after BoNT treatment. Our findings demonstrate that a short-lasting functional disconnection of motoneurons from their target muscle delays motoneuron maturation by halting the elimination of gap junctional coupling that normally occurs during early postnatal development.
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Affiliation(s)
- Angel M Pastor
- Departamento de Fisiología y Zoología, Facultad de Biología, 41012-Sevilla, Spain.
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44
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Mentis GZ, Díaz E, Moran LB, Navarrete R. Increased incidence of gap junctional coupling between spinal motoneurones following transient blockade of NMDA receptors in neonatal rats. J Physiol 2002; 544:757-64. [PMID: 12411521 PMCID: PMC2290633 DOI: 10.1113/jphysiol.2002.028159] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Neonatal rat motoneurones are electrically coupled via gap junctions and the incidence of this coupling declines during postnatal development. The mechanisms involved in this developmental regulation of gap junctional communication are largely unknown. Here we have studied the role of NMDA receptor-mediated glutamatergic synaptic activity in the regulation of motoneurone coupling. Gap junctional coupling was demonstrated by the presence of graded, short latency depolarising potentials following ventral root stimulation, and by the transfer of the low molecular weight tracer Neurobiotin to neighbouring motoneurones. Sites of close apposition between the somata and/or dendrites of the dye-coupled motoneurones were identified as potential sites of gap junctional coupling. Early postnatal blockade of the NMDA subtype of glutamate receptors using the non-competitive antagonist dizocilpine maleate (MK801) arrested the developmental decrease in electrotonic and dye coupling during the first postnatal week. These results suggest that the postnatal increase in glutamatergic synaptic activity associated with the onset of locomotion promote the loss of gap junctional connections between developing motoneurones.
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Affiliation(s)
- George Z Mentis
- Division of Neuroscience and Psychological Medicine, Department of Neuromuscular Diseases, Imperial College London, Fulham Palace Road, UK
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45
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Abstract
This report describes locomotor-like activity generated by the neonatal mouse spinal cord in vitro. We demonstrate that locomotor-like activity can be produced either spontaneously or by a train of stimuli applied to the dorsal roots or in the presence of bath-applied drugs. Calcium imaging of the motoneuron activity generated by a train of dorsal root stimuli revealed a rostrocaudally propagating component of the optical signal in the anterior lumbar (L1-L3) and in the caudal segments (S1-S4). We hypothesize that this spatio-temporal pattern arises from a rostrocaudal gradient of excitability in the relevant segments. Our experiments suggest that left/right reciprocal inhibition and NMDA-mediated oscillations are not essential mechanisms underlying rhythmogenesis in the neonatal mouse cord. Finally, our data are discussed in the context of other models of locomotion in lower and higher vertebrates.
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Affiliation(s)
- Agnès Bonnot
- Laboratory of Neural Control, Section on Developmental Neurobiology, NINDS, NIH, Bethesda, MD 20892, USA.
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46
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Tapia JC, Mentis GZ, Navarrete R, Nualart F, Figueroa E, Sánchez A, Aguayo LG. Early expression of glycine and GABA(A) receptors in developing spinal cord neurons. Effects on neurite outgrowth. Neuroscience 2002; 108:493-506. [PMID: 11738262 DOI: 10.1016/s0306-4522(01)00348-7] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Using fluorometric and immunocytochemical techniques, we found that high glycine concentrations or blockade of glycine receptors increases neurite outgrowth in developing mouse spinal cord neurons. Glycine- and GABA(A)-activated currents were demonstrated during applications of glycine and GABA (50-100 microM) in 5 days in vitro (DIV) neurons. Long application (> or =10 min) of 100 microM glycine desensitized the membrane response by more than 95%. Application of glutamate in the absence of external Mg(2+), at several membrane potentials, did not produce any detectable membrane response in these cells. Immunocytochemical studies with NR1 and GluR1 antibodies showed a delayed appearance of N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors respectively. Spontaneous synaptic activity was readily observed in 5 DIV neurons. The use of various receptor antagonists (strychnine, bicuculline, DL-2-amino-5-phosphonovalerate [APV], 6-cyano-7-nitroquinoxaline-2,3-dione [CNQX]) revealed that this activity was predominantly glycinergic, and to a smaller extent, GABAergic. In the presence of bicuculline, APV and CNQX, we detected abundant spontaneous depolarizing potentials which often reached the action potential threshold. Further evidence for functional synaptic activity was provided by the detection of co-localization of gephyrin and synaptophysin at 5 DIV using confocal microscopy. Fluorometric studies with Fluo-3, a Ca(2+) indicator, in 5 DIV cultures showed the presence of spontaneous fluctuations associated with tetrodotoxin-sensitive synaptic events. The number of neurons displaying these fluctuations was significantly increased (>100%) when the cells were bathed in a strychnine-containing solution. On the other hand, these synaptically mediated Ca(2+) events were blocked by the co-application of strychnine and bicuculline. This suggests that glycine and GABA(A) receptors provide a fundamental regulation of both neuronal excitability and intracellular Ca(2+) at this early time of development.The neurotrophic effects of agonists and antagonists for glycine, GABA(A) and glutamate receptors were examined in neurons cultured for 2 or 5 DIV. From all the agonists used, only high concentrations of glycine increased neurite outgrowth in 5 DIV neurons. We found that strychnine also increased neurite outgrowth, whereas tetrodotoxin (1 microM), nimodipine (4 microM) and bicuculline (20 microM) completely blocked it. On the other hand, APV (50 microM) and CNQX (20 microM) were unable to affect neurite outgrowth. These data suggest that spinal glycine receptors depress neurite outgrowth by shunting neuronal excitability. Outgrowth induction possibly results from the enhanced activity found after the inhibition of glycinergic activity. We postulate that this resets the intracellular calcium at a concentration that favors neurite outgrowth.
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Affiliation(s)
- J C Tapia
- Laboratory of Neurophysiology, Department of Physiology, University of Concepción, Chile
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47
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Bonnot A, Whelan PJ, Mentis GZ, O'Donovan MJ. Spatiotemporal pattern of motoneuron activation in the rostral lumbar and the sacral segments during locomotor-like activity in the neonatal mouse spinal cord. J Neurosci 2002; 22:RC203. [PMID: 11826149 PMCID: PMC6758517] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/23/2023] Open
Abstract
We used calcium imaging to visualize the spatiotemporal pattern of motoneuron activity during dorsal root-evoked locomotor-like bursting in the lumbosacral spinal cord of the neonatal mouse. Dorsal root stimuli elicited a tonic discharge in motoneurons on which alternating left-right rhythmic discharges were superimposed. Both the tonic and the rhythmic components could be recorded optically from populations of motoneurons labeled with calcium-green dextran. Optical and electrical recordings revealed that rhythmic signals from different parts of the lumbar (L1, L2) and sacral (S1-S3) segments rose, peaked, and decayed in a rostrocaudal sequence. This pattern gave rise to a rostrocaudal "wave" in the activation of motoneurons during each cycle of locomotor-like activity. A similar rostrocaudal delay was observed during episodes of alternation that occurred in the absence of stimulation, suggesting that this delay was not caused by the train of dorsal root stimuli. It is hypothesized that this behavior may simplify the appropriate sequencing of motoneurons during locomotion.
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Affiliation(s)
- Agnès Bonnot
- Laboratory of Neural Control, Section on Developmental Neurobiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892, USA.
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48
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Tapia JC, Cárdenas AM, Nualart F, Mentis GZ, Navarrete R, Aguayo LG. Neurite outgrowth in developing mouse spinal cord neurons is modulated by glycine receptors. Neuroreport 2000; 11:3007-10. [PMID: 11006984 DOI: 10.1097/00001756-200009110-00036] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The effect of glycine receptor activation on neurite outgrowth and survival was studied in 5 DIV (days in vitro) spinal neurons. These neurons were depolarized by spontaneous synaptic activity and by glycine, but not by glutamate. These responses were accompanied by increases in intracellular calcium concentration measured with Indo-1 and Fluo-3. Glycine (100 microM, 48 h) increased (46 +/- 6%) the number of primary neurites and total neuritic length. This effect was mediated by synaptic activity and calcium influx because TTX (1 microM) and nimodipine (4 microM) blocked the stimulatory effect of glycine. Neuronal survival, on the other hand, was not affected. This study shows for the first time the modulatory effect of glycine receptors on spinal neuron development.
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Affiliation(s)
- J C Tapia
- Laboratory of Neurophysiology, University of Concepción, Chile
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49
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Virgo L, Dekkers J, Mentis GZ, Navarrete R, de Belleroche J. Changes in expression of NMDA receptor subunits in the rat lumbar spinal cord following neonatal nerve injury. Neuropathol Appl Neurobiol 2000; 26:258-72. [PMID: 10886684 DOI: 10.1046/j.1365-2990.2000.00244.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The vulnerability of motoneurones to glutamate has been implicated in neurological disorders such as amyotrophic lateral sclerosis but it is not known whether specific receptor subtypes mediate this effect. In order to investigate this further, the expression of N-methyl-D-aspartate (NMDA) receptor subunits was studied during the first three post-natal weeks when motoneurones are differentially vulnerable to injury following neonatal nerve crush compared to the adult. Unilateral nerve crush was carried out at day 2 after birth (P2) which causes a decrease of 66% in motoneurone number by 14 days (P14). To study receptor expression in identified motoneurones, serial section analysis was carried out on retrogradely labelled common peroneal (CP) motoneurones by combined immunocytochemistry and in situ hybridization (ISH). mRNA levels were also quantified in homogenates from lumbar spinal cords in which the side ipsilateral to the crush was separated from the contralateral side. The NR1 subunit of the NMDA receptor was widely distributed in the spinal cord being expressed most strongly in motoneurone somata particularly during the neonatal period (P3-P7). The NR2 subunits were also expressed at higher levels in the somata and dendrites of neonatal motoneurones compared to older animals. NR2B mRNA was expressed at low to moderate levels throughout the studied period whereas NR2A mRNA levels were low until P21. Following unilateral nerve crush, an initial decrease in NR1 mRNA occurred at one day after nerve crush (P3) in labelled CP motoneurones ipsilateral to the crush which was followed by a significant increase in NR1 subunit expression at 5 days post-injury. This increase was bilateral although reaching greater significance ipsilateral to the crush compared with sham-operated animals. A significant increase in NR1 and NR2B mRNA post injury was also detected in spinal cord homogenates. In addition, the changes in levels of NR1 and NR2B mRNA were reflected by comparable bilateral changes at P7 in receptor protein determined by quantitative immunocytochemical analysis of NR1 and NR2 subunit expression in identified CP motoneurones indicating a co-ordinated regulation of receptor subunits in response to injury.
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Affiliation(s)
- L Virgo
- Division of Neuroscience & Psychological Medicine, Department of Neuromuscular Diseases, Imperial College School of Medicine, Charing Cross Hospital, London, UK
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50
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Greensmith L, Sanusi J, Mentis GZ, Vrbová G. Transient muscle paralysis in neonatal rats renders motoneurons susceptible to N-methyl-D-aspartate-induced neurotoxicity. Neuroscience 1995; 64:109-15. [PMID: 7708198 DOI: 10.1016/0306-4522(94)00387-k] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Paralysis of the soleus muscle in newborn rats causes a large proportion of motoneurons to die by 10 weeks of age. However, all of these neurons are still present at three to four weeks of age. We have previously shown that although nerve injury at five days does not result in any motoneuron death, it does render these neurons susceptible to the toxic effects of the glutamate agonist N-methyl-D-aspartate. Using retrograde labelling of soleus motoneurons, in this study we show that an increased susceptibility to glutamate also plays a role in the eventual death of those motoneurons which survive for three weeks after interruption of neuromuscular transmission at birth but die by 10 weeks. Treatment with dizocilpine maleate an antagonist of the N-methyl-D-aspartate receptor increased the survival of motoneurons to alpha-bungarotoxin-treated soleus muscles. By 10 weeks of age the size of motoneurons to alpha-bungarotoxin-treated soleus muscles is smaller than that of controls, but after treatment with dizocilpine maleate the sizes of motoneurons to control and treated muscles are similar. Moreover, only 55 +/- 2.7% of motoneurons to the soleus muscle paralysed at birth with alpha-bungarotoxin survive for three weeks after a single injection of N-methyl-D-aspartate at 12 days of age. This motoneuron death is due to the application of N-methyl-D-aspartate since treatment with alpha-bungarotoxin alone causes no loss of neurons at this age.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- L Greensmith
- Department of Anatomy and Developmental Biology, University College, London, U.K
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