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Nascimento F, Broadhead MJ, Tetringa E, Tsape E, Zagoraiou L, Miles GB. Synaptic mechanisms underlying modulation of locomotor-related motoneuron output by premotor cholinergic interneurons. eLife 2020; 9:e54170. [PMID: 32081133 PMCID: PMC7062467 DOI: 10.7554/elife.54170] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2019] [Accepted: 02/20/2020] [Indexed: 01/15/2023] Open
Abstract
Spinal motor networks are formed by diverse populations of interneurons that set the strength and rhythmicity of behaviors such as locomotion. A small cluster of cholinergic interneurons, expressing the transcription factor Pitx2, modulates the intensity of muscle activation via 'C-bouton' inputs to motoneurons. However, the synaptic mechanisms underlying this neuromodulation remain unclear. Here, we confirm in mice that Pitx2+ interneurons are active during fictive locomotion and that their chemogenetic inhibition reduces the amplitude of motor output. Furthermore, after genetic ablation of cholinergic Pitx2+ interneurons, M2 receptor-dependent regulation of the intensity of locomotor output is lost. Conversely, chemogenetic stimulation of Pitx2+ interneurons leads to activation of M2 receptors on motoneurons, regulation of Kv2.1 channels and greater motoneuron output due to an increase in the inter-spike afterhyperpolarization and a reduction in spike half-width. Our findings elucidate synaptic mechanisms by which cholinergic spinal interneurons modulate the final common pathway for motor output.
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Affiliation(s)
- Filipe Nascimento
- School of Psychology and Neuroscience, University of St AndrewsSt AndrewsUnited Kingdom
| | | | - Efstathia Tetringa
- Center of Basic Research, Biomedical Research Foundation of the Academy of AthensAthensGreece
| | - Eirini Tsape
- Center of Basic Research, Biomedical Research Foundation of the Academy of AthensAthensGreece
| | - Laskaro Zagoraiou
- Center of Basic Research, Biomedical Research Foundation of the Academy of AthensAthensGreece
| | - Gareth Brian Miles
- School of Psychology and Neuroscience, University of St AndrewsSt AndrewsUnited Kingdom
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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] [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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Więckowska A, Gajewska-Woźniak O, Głowacka A, Ji B, Grycz K, Czarkowska-Bauch J, Skup M. Spinalization and locomotor training differentially affect muscarinic acetylcholine receptor type 2 abutting on α-motoneurons innervating the ankle extensor and flexor muscles. J Neurochem 2018; 147:361-379. [DOI: 10.1111/jnc.14567] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2018] [Revised: 07/10/2018] [Accepted: 08/06/2018] [Indexed: 11/27/2022]
Affiliation(s)
| | | | - Anna Głowacka
- Nencki Institute of Experimental Biology; Warsaw Poland
| | - Benjun Ji
- Nencki Institute of Experimental Biology; Warsaw Poland
| | - Kamil Grycz
- Nencki Institute of Experimental Biology; Warsaw Poland
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Experimental Design and Data Analysis Issues Contribute to Inconsistent Results of C-Bouton Changes in Amyotrophic Lateral Sclerosis. eNeuro 2017; 4:eN-FTR-0281-16. [PMID: 28101533 PMCID: PMC5241941 DOI: 10.1523/eneuro.0281-16.2016] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2016] [Revised: 11/23/2016] [Accepted: 12/26/2016] [Indexed: 12/12/2022] Open
Abstract
The possible presence of pathological changes in cholinergic synaptic inputs [cholinergic boutons (C-boutons)] is a contentious topic within the ALS field. Conflicting data reported on this issue makes it difficult to assess the roles of these synaptic inputs in ALS. Our objective was to determine whether the reported changes are truly statistically and biologically significant and why replication is problematic. This is an urgent question, as C-boutons are an important regulator of spinal motoneuron excitability, and pathological changes in motoneuron excitability are present throughout disease progression. Using male mice of the SOD1-G93A high-expresser transgenic (G93A) mouse model of ALS, we examined C-boutons on spinal motoneurons. We performed histological analysis at high statistical power, which showed no difference in C-bouton size in G93A versus wild-type motoneurons throughout disease progression. In an attempt to examine the underlying reasons for our failure to replicate reported changes, we performed further histological analyses using several variations on experimental design and data analysis that were reported in the ALS literature. This analysis showed that factors related to experimental design, such as grouping unit, sampling strategy, and blinding status, potentially contribute to the discrepancy in published data on C-bouton size changes. Next, we systematically analyzed the impact of study design variability and potential bias on reported results from experimental and preclinical studies of ALS. Strikingly, we found that practices such as blinding and power analysis are not systematically reported in the ALS field. Protocols to standardize experimental design and minimize bias are thus critical to advancing the ALS field.
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Casanovas A, Salvany S, Lahoz V, Tarabal O, Piedrafita L, Sabater R, Hernández S, Calderó J, Esquerda JE. Neuregulin 1-ErbB module in C-bouton synapses on somatic motor neurons: molecular compartmentation and response to peripheral nerve injury. Sci Rep 2017; 7:40155. [PMID: 28065942 PMCID: PMC5220293 DOI: 10.1038/srep40155] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2016] [Accepted: 12/02/2016] [Indexed: 12/30/2022] Open
Abstract
The electric activity of lower motor neurons (MNs) appears to play a role in determining cell-vulnerability in MN diseases. MN excitability is modulated by cholinergic inputs through C-type synaptic boutons, which display an endoplasmic reticulum-related subsurface cistern (SSC) adjacent to the postsynaptic membrane. Besides cholinergic molecules, a constellation of proteins involved in different signal-transduction pathways are clustered at C-type synaptic sites (M2 muscarinic receptors, Kv2.1 potassium channels, Ca2+ activated K+ [SK] channels, and sigma-1 receptors [S1R]), but their collective functional significance so far remains unknown. We have previously suggested that neuregulin-1 (NRG1)/ErbBs-based retrograde signalling occurs at this synapse. To better understand signalling through C-boutons, we performed an analysis of the distribution of C-bouton-associated signalling proteins. We show that within SSC, S1R, Kv2.1 and NRG1 are clustered in highly specific, non-overlapping, microdomains, whereas ErbB2 and ErbB4 are present in the adjacent presynaptic compartment. This organization may define highly ordered and spatially restricted sites for different signal-transduction pathways. SSC associated proteins are disrupted in axotomised MNs together with the activation of microglia, which display a positive chemotactism to C-bouton sites. This indicates that C-bouton associated molecules are also involved in neuroinflammatory signalling in diseased MNs, emerging as new potential therapeutic targets.
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Affiliation(s)
- Anna Casanovas
- Departament de Medicina Experimental, Patologia Neuromuscular Experimental, Facultat de Medicina, Universitat de Lleida/IRBLLEIDA, Av. Rovira Roure 80, 25198 Lleida, Catalonia, Spain
| | - Sara Salvany
- Departament de Medicina Experimental, Patologia Neuromuscular Experimental, Facultat de Medicina, Universitat de Lleida/IRBLLEIDA, Av. Rovira Roure 80, 25198 Lleida, Catalonia, Spain
| | - Víctor Lahoz
- Departament de Medicina Experimental, Patologia Neuromuscular Experimental, Facultat de Medicina, Universitat de Lleida/IRBLLEIDA, Av. Rovira Roure 80, 25198 Lleida, Catalonia, Spain
| | - Olga Tarabal
- Departament de Medicina Experimental, Patologia Neuromuscular Experimental, Facultat de Medicina, Universitat de Lleida/IRBLLEIDA, Av. Rovira Roure 80, 25198 Lleida, Catalonia, Spain
| | - Lídia Piedrafita
- Departament de Medicina Experimental, Patologia Neuromuscular Experimental, Facultat de Medicina, Universitat de Lleida/IRBLLEIDA, Av. Rovira Roure 80, 25198 Lleida, Catalonia, Spain
| | - Raimundo Sabater
- Departament de Medicina Experimental, Patologia Neuromuscular Experimental, Facultat de Medicina, Universitat de Lleida/IRBLLEIDA, Av. Rovira Roure 80, 25198 Lleida, Catalonia, Spain
| | - Sara Hernández
- Departament de Medicina Experimental, Patologia Neuromuscular Experimental, Facultat de Medicina, Universitat de Lleida/IRBLLEIDA, Av. Rovira Roure 80, 25198 Lleida, Catalonia, Spain
| | - Jordi Calderó
- Departament de Medicina Experimental, Patologia Neuromuscular Experimental, Facultat de Medicina, Universitat de Lleida/IRBLLEIDA, Av. Rovira Roure 80, 25198 Lleida, Catalonia, Spain
| | - Josep E. Esquerda
- Departament de Medicina Experimental, Patologia Neuromuscular Experimental, Facultat de Medicina, Universitat de Lleida/IRBLLEIDA, Av. Rovira Roure 80, 25198 Lleida, Catalonia, Spain
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6
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Milan L, Courtand G, Cardoit L, Masmejean F, Barrière G, Cazalets JR, Garret M, Bertrand SS. Age-Related Changes in Pre- and Postsynaptic Partners of the Cholinergic C-Boutons in Wild-Type and SOD1G93A Lumbar Motoneurons. PLoS One 2015; 10:e0135525. [PMID: 26305672 PMCID: PMC4549056 DOI: 10.1371/journal.pone.0135525] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2015] [Accepted: 07/22/2015] [Indexed: 11/19/2022] Open
Abstract
Large cholinergic synaptic terminals known as C-boutons densely innervate the soma and proximal dendrites of motoneurons that are prone to neurodegeneration in amyotrophic lateral sclerosis (ALS). Studies using the Cu/Zn-superoxide dismutase (SOD1) mouse model of ALS have generated conflicting data regarding C-bouton alterations exhibited during ALS pathogenesis. In the present work, a longitudinal study combining immunohistochemistry, biochemical approaches and extra- and intra-cellular electrophysiological recordings revealed that the whole spinal cholinergic system is modified in the SOD1 mouse model of ALS compared to wild type (WT) mice as early as the second postnatal week. In WT motoneurons, both C-bouton terminals and associated M2 postsynaptic receptors presented a complex age-related dynamic that appeared completely disrupted in SOD1 motoneurons. Indeed, parallel to C-bouton morphological alterations, analysis of confocal images revealed a clustering process of M2 receptors during WT motoneuron development and maturation that was absent in SOD1 motoneurons. Our data demonstrated for the first time that the lamina X cholinergic interneurons, the neuronal source of C-boutons, are over-abundant in high lumbar segments in SOD1 mice and are subject to neurodegeneration in the SOD1 animal model. Finally, we showed that early C-bouton system alterations have no physiological impact on the cholinergic neuromodulation of newborn motoneurons. Altogether, these data suggest a complete reconfiguration of the spinal cholinergic system in SOD1 spinal networks that could be part of the compensatory mechanisms established during spinal development.
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Affiliation(s)
- Léa Milan
- INCIA, Université de Bordeaux, CNRS UMR5287, Bordeaux, France
| | - Gilles Courtand
- INCIA, Université de Bordeaux, CNRS UMR5287, Bordeaux, France
| | - Laura Cardoit
- INCIA, Université de Bordeaux, CNRS UMR5287, Bordeaux, France
| | | | | | | | - Maurice Garret
- INCIA, Université de Bordeaux, CNRS UMR5287, Bordeaux, France
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Deardorff AS, Romer SH, Sonner PM, Fyffe REW. Swimming against the tide: investigations of the C-bouton synapse. Front Neural Circuits 2014; 8:106. [PMID: 25278842 PMCID: PMC4167003 DOI: 10.3389/fncir.2014.00106] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2014] [Accepted: 08/17/2014] [Indexed: 11/19/2022] Open
Abstract
C-boutons are important cholinergic modulatory loci for state-dependent alterations in motoneuron firing rate. m2 receptors are concentrated postsynaptic to C-boutons, and m2 receptor activation increases motoneuron excitability by reducing the action potential afterhyperpolarization. Here, using an intensive review of the current literature as well as data from our laboratory, we illustrate that C-bouton postsynaptic sites comprise a unique structural/functional domain containing appropriate cellular machinery (a “signaling ensemble”) for cholinergic regulation of outward K+ currents. Moreover, synaptic reorganization at these critical sites has been observed in a variety of pathologic states. Yet despite recent advances, there are still great challenges for understanding the role of C-bouton regulation and dysregulation in human health and disease. The development of new therapeutic interventions for devastating neurological conditions will rely on a complete understanding of the molecular mechanisms that underlie these complex synapses. Therefore, to close this review, we propose a comprehensive hypothetical mechanism for the cholinergic modification of α-MN excitability at C-bouton synapses, based on findings in several well-characterized neuronal systems.
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Affiliation(s)
- Adam S Deardorff
- Boonshoft School of Medicine, Department of Neuroscience, Cell Biology and Physiology, Wright State University Dayton, OH, USA
| | - Shannon H Romer
- Boonshoft School of Medicine, Department of Neuroscience, Cell Biology and Physiology, Wright State University Dayton, OH, USA
| | - Patrick M Sonner
- Boonshoft School of Medicine, Department of Neuroscience, Cell Biology and Physiology, Wright State University Dayton, OH, USA
| | - Robert E W Fyffe
- Boonshoft School of Medicine, Department of Neuroscience, Cell Biology and Physiology, Wright State University Dayton, OH, USA
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8
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Skup M, Gajewska-Wozniak O, Grygielewicz P, Mankovskaya T, Czarkowska-Bauch J. Different effects of spinalization and locomotor training of spinal animals on cholinergic innervation of the soleus and tibialis anterior motoneurons. Eur J Neurosci 2012; 36:2679-88. [PMID: 22708650 DOI: 10.1111/j.1460-9568.2012.08182.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Cholinergic input modulates excitability of motoneurons and plays an important role in the control of locomotion in both intact and spinalized animals. However, spinal cord transection in adult rats affects cholinergic innervation of only some hindlimb motoneurons, suggesting that specificity of this response is related to functional differences between motoneurons. Our aim was therefore to compare cholinergic input to motoneurons innervating the soleus (Sol) and tibialis anterior (TA) motoneurons following spinal cord transection at a low-thoracic level. The second aim was to investigate whether deficits in cholinergic input to these motoneurons could be modified by locomotor training. The Sol and TA motoneurons were identified by retrograde labelling with fluorescent dyes injected intramuscularly. Cholinergic terminals were detected using anti-vesicular acetylcholine transporter (VAChT) antibody. Overall innervation of motoneurons was evaluated with anti-synaptophysin antibody. After spinalization we found a decrease in the number of VAChT-positive boutons apposing perikarya of the Sol (to 49%) but not TA motoneurons. Locomotor training, resulting in moderate functional improvement, partly reduced the deficit in cholinergic innervation of Sol motoneurons by increasing the number of VAChT-positive boutons. However, the optical density of VAChT-positive boutons terminating on various motoneurons, which decreased after spinalization, continued to decrease despite the training, suggesting an impairment of acetylcholine availability in the terminals. Different effects of spinal cord transection on cholinergic innervation of motoneurons controlling the ankle extensor and flexor muscles point to different functional states of these muscles in paraplegia as a possible source of activity-dependent signaling regulating cholinergic input to the motoneurons.
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Affiliation(s)
- Malgorzata Skup
- Department of Neurophysiology, Nencki Institute of Experimental Biology, Warsaw, Poland.
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9
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Mavlyutov TA, Epstein ML, Liu P, Verbny YI, Ziskind-Conhaim L, Ruoho AE. Development of the sigma-1 receptor in C-terminals of motoneurons and colocalization with the N,N'-dimethyltryptamine forming enzyme, indole-N-methyl transferase. Neuroscience 2012; 206:60-8. [PMID: 22265729 PMCID: PMC3321351 DOI: 10.1016/j.neuroscience.2011.12.040] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2011] [Revised: 12/22/2011] [Accepted: 12/22/2011] [Indexed: 11/17/2022]
Abstract
The function of the sigma-1 receptor (S1R) has been linked to modulating the activities of ion channels and G-protein-coupled receptors (GPCR). In the CNS, the S1R is expressed ubiquitously but is enriched in mouse motoneurons (MN), where it is localized to subsurface cisternae of cholinergic postsynaptic densities, also known as C-terminals. We found that S1R is enriched in mouse spinal MN at late stages of embryonic development when it is first visualized in the endoplasmic reticulum. S1Rs appear to concentrate at C-terminals of mouse MN only on the second week of postnatal development. We found that indole-N-methyl transferase (INMT), an enzyme that converts tryptamine into the sigma-1 ligand dimethyltryptamine (DMT), is also localized to postsynaptic sites of C-terminals in close proximity to the S1R. This close association of INMT and S1Rs suggest that DMT is synthesized locally to effectively activate S1R in MN.
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Affiliation(s)
- T A Mavlyutov
- Department of Neuroscience, University of Wisconsin, School of Medicine and Public Health, 1300 University Ave, Madison, WI 53706, USA.
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Mir M, Asensio VJ, Tolosa L, Gou-Fabregas M, Soler RM, Lladó J, Olmos G. Tumor necrosis factor alpha and interferon gamma cooperatively induce oxidative stress and motoneuron death in rat spinal cord embryonic explants. Neuroscience 2009; 162:959-71. [PMID: 19477238 DOI: 10.1016/j.neuroscience.2009.05.049] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2009] [Revised: 05/15/2009] [Accepted: 05/21/2009] [Indexed: 12/13/2022]
Abstract
The accumulation of reactive microglia in the degenerating areas of amyotrophic lateral sclerosis (ALS) tissue is a key cellular event creating a chronic inflammatory environment that results in motoneuron death. We have developed a new culture system that consists in rat spinal cord embryonic explants in which motoneurons migrate outside the explant, growing as a monolayer in the presence of glial cells. The proinflammatory cytokines tumor necrosis factor alpha (TNF-alpha) and interferon gamma (IFN-gamma) have been proposed to be involved in ALS-linked microglial activation. In our explants, the combined exposure to these cytokines resulted in an increased expression of the pro-oxidative enzymes inducible nitric oxide synthase (iNOS), the catalytic subunit of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, gp91(phox) and cyclooxygenase-2 (COX-2), as compared to each cytokine alone. This effect was related to their cooperation in the activation of the transcription factor nuclear factor kappa B (NF-kappaB). TNF-alpha and IFN-gamma also cooperated to promote protein oxidation and nitration, thus increasing the percentage of motoneurons immunoreactive for nitrotyrosine. Apoptotic motoneuron death, measured through annexin V-Cy3 and active caspase-3 immunoreactivities, was also found cooperatively induced by TNF-alpha and IFN-gamma. Interestingly, these cytokines did not affect the viability of purified spinal cord motoneurons in the absence of glial cells. It is proposed that the proinflammatory cytokines TNF-alpha and IFN-gamma have cooperative/complementary roles in inflammation-induced motoneuron death.
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Affiliation(s)
- M Mir
- Grup de Neurobiologia Cel.lular, Institut Universitari d'Investigacions en Ciències de la Salut/Departament de Biologia, Universitat de les Illes Balears, Cra. de Valldemossa, km 7.5, E-07122 Palma de Mallorca, Illes Balears, Spain
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11
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Ranson RN, Dowling P, Santer RM, Watson AHD. The effects of ageing on the distribution of vesicular acetylcholine transporter immunoreactive inputs to pelvic motoneurons of male Wistar rats. Neuroscience 2006; 144:636-44. [PMID: 17074444 DOI: 10.1016/j.neuroscience.2006.09.036] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2006] [Revised: 09/19/2006] [Accepted: 09/20/2006] [Indexed: 11/27/2022]
Abstract
Age-related changes in the number and size of large cholinergic terminals immunoreactive for vesicular acetylcholine transporter (VAChT), were documented for the dorsolateral nucleus (DLN), retrodorsolateral nucleus (RDLN) and spinal nucleus of the bulbospongiosus (SNB) of the lumbosacral spinal cord of male rats. The most significant changes were a large increase in the number and size of cholinergic terminals within the DLN of aged animals, together with a small decrease in terminal number within the RDLN. No significant age-associated differences in VAChT labeling were seen within the SNB. In both age groups, SNB motoneurons projecting to the levator ani muscle received about 9 to 10 contacts from large cholinergic terminals. Ultrastructural examination of the terminals revealed structures likely to be postsynaptic subsurface cisterns that are characteristic of type C terminal boutons. Since both the DLN and SNB contain motoneurons innervating pelvic muscles and sphincters, these findings provide further evidence for a central cholinergic influence on micturition and sexual reflexes and suggest that this may remain robust in the face of ageing.
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Affiliation(s)
- R N Ranson
- Cardiff School of Biosciences, Biomedical Sciences Buildings, Cardiff University, Museum Avenue, Cardiff, UK.
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12
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Wilson JM, Rempel J, Brownstone RM. Postnatal development of cholinergic synapses on mouse spinal motoneurons. J Comp Neurol 2004; 474:13-23. [PMID: 15156576 DOI: 10.1002/cne.20089] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Following birth, when mammals are relatively immobile, significant development of the motor system facilitates weight bearing and locomotion. Prominent cholinergic C-terminals develop on somata and proximal dendrites of spinal motoneurons during this time period. It is hypothesized that these terminals are essential in regulating motoneuron excitability and thus their development contributes to motor system maturation. Therefore, the development of pre- and postsynaptic components of the C-terminal synapse on motoneurons in mice during the early postnatal period was investigated. Fluorescence immunohistochemical studies revealed that developmental increases in punctate labeling of presynaptic cholinergic terminals, as visualized by vesicular acetylcholine transporter immunoreactivity (VAChT-IR) corresponded to the progressive expression and spatial restriction of immunoreactivity for the calcium channel subunit alpha(1)2.2 (N-type) located presynaptically and the muscarinic type 2 acetylcholine receptor situated postsynaptically. In addition, clustering of immunoreactivity for the potassium channel subunit K(V)2.1 occurred within the early postnatal period in concert and colocalized with the maturation of the C-terminals. The time course of development of these components of the C-terminal synapse corresponds to the maturation of the motor system that enables the animal to locomote in an adult-like fashion.
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Affiliation(s)
- Jennifer M Wilson
- Department of Anatomy and Neurobiology, Dalhousie University, Halifax, Nova Scotia B3H 4H7, Canada
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Muennich EAL, Fyffe REW. Focal aggregation of voltage-gated, Kv2.1 subunit-containing, potassium channels at synaptic sites in rat spinal motoneurones. J Physiol 2003; 554:673-85. [PMID: 14608003 PMCID: PMC1664801 DOI: 10.1113/jphysiol.2003.056192] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Delayed rectifier K+ currents are involved in the control of alpha-motoneurone excitability, but the precise spatial distribution and organization of the membrane ion channels that contribute to these currents have not been defined. Voltage-activated Kv2.1 channels have properties commensurate with a contribution to delayed rectifier currents and are expressed in neurones throughout the mammalian central nervous system. A specific antibody against Kv2.1 channel subunits was used to determine the surface distribution and clustering of Kv2.1 subunit-containing channels in the cell membrane of alpha-motoneurones and other spinal cord neurones. In alpha-motoneurones, Kv2.1 immunoreactivity (-IR) was abundant in the surface membrane of the soma and large proximal dendrites, and was present also in smaller diameter distal dendrites. Plasma membrane-associated Kv2.1-IR in alpha-motoneurones was distributed in a mosaic of small irregularly shaped, and large disc-like, clusters. However, only small to medium clusters of Kv2.1-IR were observed in spinal interneurones and projection neurones, and some interneurones, including Renshaw cells, lacked demonstrable Kv2.1-IR. In alpha-motoneurones, dual immunostaining procedures revealed that the prominent disc-like domains of Kv2.1-IR are invariably apposed to presynaptic cholinergic C-terminals. Further, Kv2.1-IR colocalizes with immunoreactivity against postsynaptic muscarinic (m2) receptors at these locations. Ultrastructural examination confirmed the postsynaptic localization of Kv2.1-IR at C-terminal synapses, and revealed clusters of Kv2.1-IR at a majority of S-type, presumed excitatory, synapses. Kv2.1-IR in alpha-motoneurones is not directly associated with presumed inhibitory (F-type) synapses, nor is it present in presynaptic structures apposed to the motoneurone. Occasionally, small patches of extrasynaptic Kv2.1-IR labelling were observed in surface membrane apposed by glial processes. Voltage-gated potassium channels responsible for the delayed rectifier current, including Kv2.1, are usually assigned roles in the repolarization of the action potential. However, the strategic localization of Kv2.1 subunit-containing channels at specific postsynaptic sites suggests that this family of voltage-activated K+ channels may have additional roles and/or regulatory components.
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Characterization of the circuits that generate spontaneous episodes of activity in the early embryonic mouse spinal cord. J Neurosci 2003. [PMID: 12533619 DOI: 10.1523/jneurosci.23-02-00587.2003] [Citation(s) in RCA: 183] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
In the developing nervous system, patterned spontaneous activity affects a variety of developmental processes. Thus, it is important to identify the earliest time that such activity occurs and to characterize the underlying circuitry. In isolated mouse spinal cord-limb preparations, highly rhythmic spontaneous activity occurred as early as embryonic day 11 (E11)-E12, when many lumbosacral motoneurons were still migrating and extending their peripheral projections. This activity required both electrical and chemical transmission, and acetylcholine, rather than glutamate, provided the main excitatory drive. Our data are consistent with motoneurons themselves playing a critical role in generating such activity by making excitatory connections on each other and on GABAergic interneurons via dihydro-beta-erythroidine hydrobromide (DHbetaE)-insensitive nicotinic receptors. This resulted in the generation of local bursts. Consistent with these observations, E12-E12.5 mouse motoneurons retrogradely labeled by HRP were observed to have extensive axon collaterals that projected locally within the lateral motor column and to interneuron-containing regions dorsal and medial of the lateral motor column. Cholinergic axons, presumably from motoneurons, were also observed in the ventral and lateral funiculi. However, for local bursts to propagate throughout the cord, a second DHbetaE-sensitive cholinergic pathway that also involved glycinergic interneurons was required. This circuit characterization should facilitate the use of genetic mutations that alter specific subpopulations of interneurons or cholinergic transmission to determine how modifying different aspects of this early activity affects subsequent development of the spinal motor circuit.
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