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Fenstermacher SJ, Vonasek A, Gattuso H, Chaimowitz C, Dymecki SM, Jessell TM, Dasen JS. Potentiation of active locomotor state by spinal-projecting serotonergic neurons. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.09.26.615260. [PMID: 39386605 PMCID: PMC11463418 DOI: 10.1101/2024.09.26.615260] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 10/12/2024]
Abstract
Animals produce diverse motor actions that enable expression of context-appropriate behaviors. Neuromodulators facilitate behavioral flexibility by altering the temporal dynamics and output of neural circuits. Discrete populations of serotonergic (5-HT) neurons target circuits in the brainstem and spinal cord, but their role in the control of motor behavior is unclear. Here we define the pre- and post-synaptic organization of the spinal-projecting serotonergic system and define a role in locomotor control. We show that while forebrain-targeting 5-HT neurons decrease their activity during locomotion, subpopulations of spinal projecting neurons increase their activity in a context-dependent manner. Optogenetic activation of ventrally projecting 5-HT neurons does not trigger initiation of movement, but rather enhances the speed and duration of ongoing locomotion over extended time scales. These findings indicate that the descending serotonergic system potentiates locomotor output and demonstrate a role for serotonergic neurons in modulating the temporal dynamics of motor circuits.
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Gutiérrez-Ibáñez C, Wylie DR. Investigation of central pattern generators in the spinal cord of chicken embryos. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2024; 210:801-814. [PMID: 38521869 PMCID: PMC11384640 DOI: 10.1007/s00359-024-01694-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2023] [Revised: 01/29/2024] [Accepted: 02/01/2024] [Indexed: 03/25/2024]
Abstract
For most quadrupeds, locomotion involves alternating movements of the fore- and hindlimbs. In birds, however, while walking generally involves alternating movements of the legs, to generate lift and thrust, the wings are moved synchronously with each other. Neural circuits in the spinal cord, referred to as central pattern generators (CPGs), are the source of the basic locomotor rhythms and patterns. Given the differences in the patterns of movement of the wings and legs, it is likely that the neuronal components and connectivity of the CPG that coordinates wing movements differ from those that coordinate leg movements. In this study, we used in vitro preparations of embryonic chicken spinal cords (E11-E14) to compare the neural responses of spinal CPGs that control and coordinate wing flapping with those that control alternating leg movements. We found that in response to N-methyl-D-aspartate (NMDA) or a combination of NMDA and serotonin (5-HT), the intact chicken spinal cord produced rhythmic outputs that were synchronous both bilaterally and between the wing and leg segments. Despite this, we found that this rhythmic output was disrupted by an antagonist of glycine receptors in the lumbosacral (legs), but not the brachial (wing) segments. Thus, our results provide evidence of differences between CPGs that control the wings and legs in the spinal cord of birds.
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Affiliation(s)
- Cristián Gutiérrez-Ibáñez
- Department of Biological Sciences, University of Alberta, Edmonton, AB, T6G 2E0, Canada.
- Grass Laboratory, Marine Biological Laboratory, Woods Hole, MA, USA.
| | - Douglas R Wylie
- Department of Biological Sciences, University of Alberta, Edmonton, AB, T6G 2E0, Canada
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3
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Garcia-Ramirez DL, McGrath JR, Ha NT, Wheel JH, Atoche SJ, Yao L, Stachowski NJ, Giszter SF, Dougherty KJ. Covert actions of epidural stimulation on spinal locomotor circuits. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.06.18.599598. [PMID: 38948733 PMCID: PMC11213016 DOI: 10.1101/2024.06.18.599598] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/02/2024]
Abstract
Spinal circuitry produces the rhythm and patterning of locomotion. However, both descending and sensory inputs are required to initiate and adapt locomotion to the environment. Spinal cord injury (SCI) disrupts descending controls of the spinal cord, producing paralysis. Epidural stimulation (ES) is a promising clinical therapy for motor control recovery and is capable of reactivating the lumbar spinal locomotor networks, yet little is known about the effects of ES on locomotor neurons. Previously, we found that both sensory afferent pathways and serotonin exert mixed excitatory and inhibitory actions on lumbar interneurons involved in the generation of the locomotor rhythm, identified by the transcription factor Shox2. However, after chronic complete SCI, sensory afferent inputs to Shox2 interneurons become almost exclusively excitatory and Shox2 interneurons are supersensitive to serotonin. Here, we investigated the effects of ES on these SCI-induced changes. Inhibitory input from sensory pathways to Shox2 interneurons was maintained and serotonin supersensitivity was not observed in SCI mice that received daily sub-motor threshold ES. Interestingly, the effects of ES were maintained for at least three weeks after the ES was discontinued. In contrast, the effects of ES were not observed in Shox2 interneurons from mice that received ES after the establishment of the SCI-induced changes. Our results demonstrate mechanistic actions of ES at the level of identified spinal locomotor circuit neurons and the effectiveness of early treatment with ES on preservation of spinal locomotor circuitry after SCI, suggesting possible therapeutic benefits prior to the onset of motor rehabilitation.
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Cucun G, Köhler M, Pfitsch S, Rastegar S. Insights into the mechanisms of neuron generation and specification in the zebrafish ventral spinal cord. FEBS J 2024; 291:646-662. [PMID: 37498183 DOI: 10.1111/febs.16913] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2023] [Revised: 06/20/2023] [Accepted: 07/25/2023] [Indexed: 07/28/2023]
Abstract
The vertebrate nervous system is composed of a wide range of neurons and complex synaptic connections, raising the intriguing question of how neuronal diversity is generated. The spinal cord provides an excellent model for exploring the mechanisms governing neuronal diversity due to its simple neural network and the conserved molecular processes involved in neuron formation and specification during evolution. This review specifically examines two distinct progenitor domains present in the zebrafish ventral spinal cord: the lateral floor plate (LFP) and the p2 progenitor domain. The LFP is responsible for the production of GABAergic Kolmer-Agduhr neurons (KA″), glutamatergic V3 neurons, and intraspinal serotonergic neurons, while the p2 domain generates V2 precursors that subsequently differentiate into three unique subpopulations of V2 neurons, namely glutamatergic V2a, GABAergic V2b, and glycinergic V2s. Based on recent findings, we will examine the fundamental signaling pathways and transcription factors that play a key role in the specification of these diverse neurons and neuronal subtypes derived from the LFP and p2 progenitor domains.
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Affiliation(s)
- Gokhan Cucun
- Institute for Biological and Chemical Systems - Biological Information Processing (IBCS-BIP), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany
| | - Melina Köhler
- Institute for Biological and Chemical Systems - Biological Information Processing (IBCS-BIP), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany
| | - Sabrina Pfitsch
- Institute for Biological and Chemical Systems - Biological Information Processing (IBCS-BIP), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany
| | - Sepand Rastegar
- Institute for Biological and Chemical Systems - Biological Information Processing (IBCS-BIP), Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany
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Mackay K, Orssatto LBR, Polman R, Van der Pols JC, Trajano GS. Caffeine does not influence persistent inward current contribution to motoneuron firing. J Neurophysiol 2023; 130:1529-1540. [PMID: 37877186 DOI: 10.1152/jn.00350.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2023] [Revised: 10/18/2023] [Accepted: 10/19/2023] [Indexed: 10/26/2023] Open
Abstract
The purpose of this study was to investigate whether caffeine consumption would change persistent inward current (PIC) contribution to motoneuron firing at increased contraction intensities and after repetitive sustained maximal contractions. Before and after the consumption of 6 mg·kg-1 of caffeine or placebo, 16 individuals performed isometric triangular-shaped ramp dorsiflexion contractions (to 20% and 40% of peak torque), followed by four maximal contractions sustained until torque production dropped to 60% of maximum, and consecutive 20% triangular-shaped contractions. Tibialis anterior motor unit firing frequencies were analyzed from high-density surface electromyograms. PIC contribution to motor unit firing was estimated by calculating the delta frequency (ΔF) using the paired motor unit technique. Motoneuron peak firing frequencies at 20% and 40% contractions and total torque-time integral during the repetitive sustained maximal contractions were also assessed. ΔF increased 0.69 peaks per second (pps) (95% CI = -0.98, -0.405; d = -0.87) from 20% to 40% contraction intensities and reduced 0.85 pps (95% CI = 0.66, 1.05; d = 0.99) after the repetitive sustained maximal contractions, regardless of caffeine consumption. Participants produced 337 Nm·s (95% CI = 49.9, 624; d = 0.63) more torque integral during the repetitive sustained maximal contractions after caffeine consumption. A strong repeated-measures correlation (r = 0.61; 95% CI = 0.49, 0.69) was observed between reductions of ΔF and peak firing frequencies after the repetitive sustained maximal contractions. PIC contribution to motoneuron firing increases from 20% to 40% contraction intensities, with no effect of caffeine (on rested tibialis anterior). Repetitive sustained maximal contractions reduced PIC contribution to motoneuron firing, regardless of caffeine or placebo consumption, evidencing that changes in intrinsic motoneuron properties contributed to performance loss. Caffeine-attenuated reduction of torque production capacity was unlikely mediated by PICs.NEW & NOTEWORTHY Persistent inward current (PIC) contribution to motoneuron firing increases with contraction intensities and is reduced after repetitive sustained maximal contractions, regardless of caffeine consumption. Reductions of PIC contribution to motoneuron firing and peak firing frequencies were largely associated, evidencing a novel mechanism underpinning decrements in maximal torque production capacity following repetitive sustained maximal contractions. Caffeine consumption attenuated neuromuscular performance reductions-allowing higher time-torque integral production during repetitive sustained maximal contractions. This was unlikely mediated by PIC.
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Affiliation(s)
- Karen Mackay
- School of Exercise and Nutrition Sciences, Faculty of Health, Queensland University of Technology (QUT), Brisbane, Queensland, Australia
| | - Lucas B R Orssatto
- Institute for Physical Activity and Nutrition (IPAN), School of Exercise and Nutrition Sciences, Faculty of Health, Deakin University, Geelong, Victoria, Australia
| | - Remco Polman
- Institute of Health and Wellbeing, Federation University, Melbourne, Victoria, Australia
| | - Jolieke C Van der Pols
- School of Exercise and Nutrition Sciences, Faculty of Health, Queensland University of Technology (QUT), Brisbane, Queensland, Australia
| | - Gabriel S Trajano
- School of Exercise and Nutrition Sciences, Faculty of Health, Queensland University of Technology (QUT), Brisbane, Queensland, Australia
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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] [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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Khsime I, Boulain M, Fettah A, Chagraoui A, Courtand G, De Deurwaerdère P, Juvin L, Barrière G. Limiting Monoamines Degradation Increases L-DOPA Pro-Locomotor Action in Newborn Rats. Int J Mol Sci 2023; 24:14747. [PMID: 37834195 PMCID: PMC10572489 DOI: 10.3390/ijms241914747] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2023] [Revised: 09/20/2023] [Accepted: 09/25/2023] [Indexed: 10/15/2023] Open
Abstract
L-DOPA, the precursor of catecholamines, exerts a pro-locomotor action in several vertebrate species, including newborn rats. Here, we tested the hypothesis that decreasing the degradation of monoamines can promote the pro-locomotor action of a low, subthreshold dose of L-DOPA in five-day-old rats. The activity of the degrading pathways involving monoamine oxidases or catechol-O-methyltransferase was impaired by injecting nialamide or tolcapone, respectively. At this early post-natal stage, the capacity of the drugs to trigger locomotion was investigated by monitoring the air-stepping activity expressed by the animals suspended in a harness above the ground. We show that nialamide (100 mg/kg) or tolcapone (100 mg/kg), without effect on their own promotes maximal expression of air-stepping sequences in the presence of a sub-effective dose of L-DOPA (25 mg/kg). Tissue measurements of monoamines (dopamine, noradrenaline, serotonin and some of their metabolites) in the cervical and lumbar spinal cord confirmed the regional efficacy of each inhibitor toward their respective enzyme. Our experiments support the idea that the raise of monoamines boost L-DOPA's locomotor action. Considering that both inhibitors differently altered the spinal monoamines levels in response to L-DOPA, our data also suggest that maximal locomotor response can be reached with different monoamines environment.
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Affiliation(s)
- Inès Khsime
- Univ. Bordeaux, CNRS, INCIA, UMR5287, F-33000 Bordeaux, France (A.F.); (G.C.); (L.J.)
| | - Marie Boulain
- Univ. Bordeaux, CNRS, INCIA, UMR5287, F-33000 Bordeaux, France (A.F.); (G.C.); (L.J.)
| | - Abderrahman Fettah
- Univ. Bordeaux, CNRS, INCIA, UMR5287, F-33000 Bordeaux, France (A.F.); (G.C.); (L.J.)
| | - Abdeslam Chagraoui
- Laboratory of Neuronal and Neuroendocrine Differentiation and Communication, UNIROUEN, INSERM U1239, Institute for Research and Innovation in Biomedicine of Normandy (IRIB), F-76000 Rouen, France;
- Department of Medical Biochemistry, Rouen University Hospital, CHU de Rouen, F-76000 Rouen, France
| | - Gilles Courtand
- Univ. Bordeaux, CNRS, INCIA, UMR5287, F-33000 Bordeaux, France (A.F.); (G.C.); (L.J.)
| | | | - Laurent Juvin
- Univ. Bordeaux, CNRS, INCIA, UMR5287, F-33000 Bordeaux, France (A.F.); (G.C.); (L.J.)
| | - Grégory Barrière
- Univ. Bordeaux, CNRS, INCIA, UMR5287, F-33000 Bordeaux, France (A.F.); (G.C.); (L.J.)
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Mohammadshirazi A, Apicella R, Zylberberg BA, Mazzone GL, Taccola G. Suprapontine Structures Modulate Brainstem and Spinal Networks. Cell Mol Neurobiol 2023:10.1007/s10571-023-01321-z. [PMID: 36732488 DOI: 10.1007/s10571-023-01321-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2022] [Accepted: 01/19/2023] [Indexed: 02/04/2023]
Abstract
Several spinal motor output and essential rhythmic behaviors are controlled by supraspinal structures, although their contribution to neuronal networks for respiration and locomotion at birth still requires better characterization. As preparations of isolated brainstem and spinal networks only focus on local circuitry, we introduced the in vitro central nervous system (CNS) from neonatal rodents to simultaneously record a stable respiratory rhythm from both cervical and lumbar ventral roots (VRs).Electrical pulses supplied to multiple sites of brainstem evoked distinct VR responses with staggered onset in the rostro-caudal direction. Stimulation of ventrolateral medulla (VLM) resulted in higher events from homolateral VRs. Stimulating a lumbar dorsal root (DR) elicited responses even from cervical VRs, albeit small and delayed, confirming functional ascending pathways. Oximetric assessments detected optimal oxygen levels on brainstem and cortical surfaces, and histological analysis of internal brain structures indicated preserved neuron viability without astrogliosis. Serial ablations showed precollicular decerebration reducing respiratory burst duration and frequency and diminishing the area of lumbar DR and VR potentials elicited by DR stimulation, while pontobulbar transection increased the frequency and duration of respiratory bursts. Keeping legs attached allows for expressing a respiratory rhythm during hindlimb stimulation. Trains of pulses evoked episodes of fictive locomotion (FL) when delivered to VLM or to a DR, the latter with a slightly better FL than in isolated cords.In summary, suprapontine centers regulate spontaneous respiratory rhythms, as well as electrically evoked reflexes and spinal network activity. The current approach contributes to clarifying modulatory brain influences on the brainstem and spinal microcircuits during development. Novel preparation of the entire isolated CNS from newborn rats unveils suprapontine modulation on brainstem and spinal networks. Preparation views (A) with and without legs attached (B). Successful fictive respiration occurs with fast dissection from P0-P2 rats (C). Decerebration speeds up respiratory rhythm (D) and reduces spinal reflexes derived from both ventral and dorsal lumbar roots (E).
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Affiliation(s)
- Atiyeh Mohammadshirazi
- Neuroscience Department, International School for Advanced Studies (SISSA), Via Bonomea 265, 34136, Trieste, Italy.,Applied Neurophysiology and Neuropharmacology Lab, Istituto di Medicina Fisica e Riabilitazione (IMFR), Via Gervasutta 48, Udine, UD, Italy
| | - Rosamaria Apicella
- Neuroscience Department, International School for Advanced Studies (SISSA), Via Bonomea 265, 34136, Trieste, Italy.,Applied Neurophysiology and Neuropharmacology Lab, Istituto di Medicina Fisica e Riabilitazione (IMFR), Via Gervasutta 48, Udine, UD, Italy
| | - Benjamín A Zylberberg
- Instituto de Investigaciones en Medicina Traslacional (IIMT)-CONICET - Universidad Austral, Av. Pte. Perón 1500, Pilar, Buenos Aires, Argentina
| | - Graciela L Mazzone
- Instituto de Investigaciones en Medicina Traslacional (IIMT)-CONICET - Universidad Austral, Av. Pte. Perón 1500, Pilar, Buenos Aires, Argentina
| | - Giuliano Taccola
- Neuroscience Department, International School for Advanced Studies (SISSA), Via Bonomea 265, 34136, Trieste, Italy. .,Applied Neurophysiology and Neuropharmacology Lab, Istituto di Medicina Fisica e Riabilitazione (IMFR), Via Gervasutta 48, Udine, UD, Italy.
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Barker CM, Miles KD, Doll CA. Fmrp regulates neuronal balance in embryonic motor circuit formation. Front Neurosci 2022; 16:962901. [PMID: 36408418 PMCID: PMC9669763 DOI: 10.3389/fnins.2022.962901] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2022] [Accepted: 10/11/2022] [Indexed: 11/05/2022] Open
Abstract
Motor behavior requires the balanced production and integration of a variety of neural cell types. Motor neurons are positioned in discrete locations in the spinal cord, targeting specific muscles to drive locomotive contractions. Specialized spinal interneurons modulate and synchronize motor neuron activity to achieve coordinated motor output. Changes in the ratios and connectivity of spinal interneurons could drastically alter motor output by tipping the balance of inhibition and excitation onto target motor neurons. Importantly, individuals with Fragile X syndrome (FXS) and associated autism spectrum disorders often have significant motor challenges, including repetitive behaviors and epilepsy. FXS stems from the transcriptional silencing of the gene Fragile X Messenger Ribonucleoprotein 1 (FMR1), which encodes an RNA binding protein that is implicated in a multitude of crucial neurodevelopmental processes, including cell specification. Our work shows that Fmrp regulates the formation of specific interneurons and motor neurons that comprise early embryonic motor circuits. We find that zebrafish fmr1 mutants generate surplus ventral lateral descending (VeLD) interneurons, an early-born cell derived from the motor neuron progenitor domain (pMN). As VeLD interneurons are hypothesized to act as central pattern generators driving the earliest spontaneous movements, this imbalance could influence the formation and long-term function of motor circuits driving locomotion. fmr1 embryos also show reduced expression of proteins associated with inhibitory synapses, including the presynaptic transporter vGAT and the postsynaptic scaffold Gephyrin. Taken together, we show changes in embryonic motor circuit formation in fmr1 mutants that could underlie persistent hyperexcitability.
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Affiliation(s)
- Chase M. Barker
- Section of Developmental Biology, Department of Pediatrics, Children’s Hospital Colorado, University of Colorado School of Medicine, Aurora, CO, United States
| | - Kaleb D. Miles
- Section of Developmental Biology, Department of Pediatrics, Children’s Hospital Colorado, University of Colorado School of Medicine, Aurora, CO, United States
- Biomedical Sciences and Biotechnology Program, Graduate School, University of Colorado, Aurora, CO, United States
| | - Caleb A. Doll
- Section of Developmental Biology, Department of Pediatrics, Children’s Hospital Colorado, University of Colorado School of Medicine, Aurora, CO, United States
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Shevtsova NA, Li EZ, Singh S, Dougherty KJ, Rybak IA. Ipsilateral and Contralateral Interactions in Spinal Locomotor Circuits Mediated by V1 Neurons: Insights from Computational Modeling. Int J Mol Sci 2022; 23:5541. [PMID: 35628347 PMCID: PMC9146873 DOI: 10.3390/ijms23105541] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2022] [Revised: 05/11/2022] [Accepted: 05/12/2022] [Indexed: 02/01/2023] Open
Abstract
We describe and analyze a computational model of neural circuits in the mammalian spinal cord responsible for generating and shaping locomotor-like oscillations. The model represents interacting populations of spinal neurons, including the neurons that were genetically identified and characterized in a series of previous experimental studies. Here, we specifically focus on the ipsilaterally projecting V1 interneurons, their possible role in the spinal locomotor circuitry, and their involvement in the generation of locomotor oscillations. The proposed connections of these neurons and their involvement in different neuronal pathways in the spinal cord allow the model to reproduce the results of optogenetic manipulations of these neurons under different experimental conditions. We suggest the existence of two distinct populations of V1 interneurons mediating different ipsilateral and contralateral interactions within the spinal cord. The model proposes explanations for multiple experimental data concerning the effects of optogenetic silencing and activation of V1 interneurons on the frequency of locomotor oscillations in the intact cord and hemicord under different experimental conditions. Our simulations provide an important insight into the organization of locomotor circuitry in the mammalian spinal cord.
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Affiliation(s)
| | | | | | | | - Ilya A. Rybak
- Department of Neurobiology and Anatomy, College of Medicine, Drexel University, Philadelphia, PA 19129, USA; (N.A.S.); (E.Z.L.); (S.S.); (K.J.D.)
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Heterozygous Dcc Mutant Mice Have a Subtle Locomotor Phenotype. eNeuro 2022; 9:ENEURO.0216-18.2021. [PMID: 35115383 PMCID: PMC8906791 DOI: 10.1523/eneuro.0216-18.2021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2018] [Revised: 12/18/2021] [Accepted: 12/20/2021] [Indexed: 11/30/2022] Open
Abstract
Axon guidance receptors such as deleted in colorectal cancer (DCC) contribute to the normal formation of neural circuits, and their mutations can be associated with neural defects. In humans, heterozygous mutations in DCC have been linked to congenital mirror movements, which are involuntary movements on one side of the body that mirror voluntary movements of the opposite side. In mice, obvious hopping phenotypes have been reported for bi-allelic Dcc mutations, while heterozygous mutants have not been closely examined. We hypothesized that a detailed characterization of Dcc heterozygous mice may reveal impaired corticospinal and spinal functions. Anterograde tracing of the Dcc+/− motor cortex revealed a normally projecting corticospinal tract, intracortical microstimulation (ICMS) evoked normal contralateral motor responses, and behavioral tests showed normal skilled forelimb coordination. Gait analyses also showed a normal locomotor pattern and rhythm in adult Dcc+/− mice during treadmill locomotion, except for a decreased occurrence of out-of-phase walk and an increased duty cycle of the stance phase at slow walking speed. Neonatal isolated Dcc+/− spinal cords had normal left-right and flexor-extensor coupling, along with normal locomotor pattern and rhythm, except for an increase in the flexor-related motoneuronal output. Although Dcc+/− mice do not exhibit any obvious bilateral impairments like those in humans, they exhibit subtle motor deficits during neonatal and adult locomotion.
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12
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Koning HK, Ahemaiti A, Boije H. A deep-dive into fictive locomotion - a strategy to probe cellular activity during speed transitions in fictively swimming zebrafish larvae. Biol Open 2022; 11:274799. [PMID: 35188534 PMCID: PMC8966775 DOI: 10.1242/bio.059167] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2021] [Accepted: 02/14/2022] [Indexed: 11/20/2022] Open
Abstract
Fictive locomotion is frequently used to study locomotor output in paralyzed animals. We have evaluated the character of swim episodes elicited by different strategies in zebrafish. Motor output was measured on both sides of a body segment using electrodes and a pipeline for synchronizing stimulation and recording, denoising data and peak-finding was developed. The optomotor response generated swims most equivalent to spontaneous activity, while electrical stimulation and NMDA application caused various artefacts. Our optimal settings, optomotor stimulation using 5-day-old larvae, were combined with calcium imaging and optogenetics to validate the setup's utility. Expression of GCaMP5G by the mnx1 promoter allowed correlation of calcium traces of dozens of motor neurons to the fictive locomotor output. Activation of motor neurons through channelrhodopsin produced aberrant locomotor episodes. This strategy can be used to investigate novel neuronal populations in a high-throughput manner to reveal their role in shaping motor output. This article has an associated First Person interview with the first author of the paper. Summary: This approach combines fictive locomotion, elicited through the optomotor response, and calcium imaging or optogenetics, to investigate the role of neuronal populations in shaping motor output.
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Affiliation(s)
- Harmen Kornelis Koning
- Department of Immunology, Genetics and Pathology, Uppsala University, S-751 08, Uppsala, Sweden
| | - Aikeremu Ahemaiti
- Department of Immunology, Genetics and Pathology, Uppsala University, S-751 08, Uppsala, Sweden
| | - Henrik Boije
- Department of Immunology, Genetics and Pathology, Uppsala University, S-751 08, Uppsala, Sweden
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Fauss GNK, Hudson KE, Grau JW. Role of Descending Serotonergic Fibers in the Development of Pathophysiology after Spinal Cord Injury (SCI): Contribution to Chronic Pain, Spasticity, and Autonomic Dysreflexia. BIOLOGY 2022; 11:234. [PMID: 35205100 PMCID: PMC8869318 DOI: 10.3390/biology11020234] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Revised: 01/27/2022] [Accepted: 01/29/2022] [Indexed: 12/12/2022]
Abstract
As the nervous system develops, nerve fibers from the brain form descending tracts that regulate the execution of motor behavior within the spinal cord, incoming sensory signals, and capacity to change (plasticity). How these fibers affect function depends upon the transmitter released, the receptor system engaged, and the pattern of neural innervation. The current review focuses upon the neurotransmitter serotonin (5-HT) and its capacity to dampen (inhibit) neural excitation. A brief review of key anatomical details, receptor types, and pharmacology is provided. The paper then considers how damage to descending serotonergic fibers contributes to pathophysiology after spinal cord injury (SCI). The loss of serotonergic fibers removes an inhibitory brake that enables plasticity and neural excitation. In this state, noxious stimulation can induce a form of over-excitation that sensitizes pain (nociceptive) circuits, a modification that can contribute to the development of chronic pain. Over time, the loss of serotonergic fibers allows prolonged motor drive (spasticity) to develop and removes a regulatory brake on autonomic function, which enables bouts of unregulated sympathetic activity (autonomic dysreflexia). Recent research has shown that the loss of descending serotonergic activity is accompanied by a shift in how the neurotransmitter GABA affects neural activity, reducing its inhibitory effect. Treatments that target the loss of inhibition could have therapeutic benefit.
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Affiliation(s)
| | | | - James W. Grau
- Department of Psychological and Brain Sciences, Texas A&M University, College Station, TX 77843, USA; (G.N.K.F.); (K.E.H.)
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Falgairolle M, O'Donovan MJ. Motoneuronal Regulation of Central Pattern Generator and Network Function. ADVANCES IN NEUROBIOLOGY 2022; 28:259-280. [PMID: 36066829 DOI: 10.1007/978-3-031-07167-6_11] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
This chapter reviews recent work showing that vertebrate motoneurons can trigger spontaneous rhythmic activity in the developing spinal cord and can modulate the function of several different central pattern generators later in development. In both the embryonic chick and the fetal mouse spinal cords, antidromic activation of motoneurons can trigger bouts of rhythmic activity. In the neonatal mouse, optogenetic manipulation of motoneuron firing can modulate the frequency of fictive locomotion activated by a drug cocktail. In adult animals, motoneurons have been shown to regulate swimming in the zebrafish, and vocalization in fish and frogs. We discuss the significance of these findings and the degree to which motoneurons may be considered a part of these central pattern generators.
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15
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Abstract
When animals walk overground, mechanical stimuli activate various receptors located in muscles, joints, and skin. Afferents from these mechanoreceptors project to neuronal networks controlling locomotion in the spinal cord and brain. The dynamic interactions between the control systems at different levels of the neuraxis ensure that locomotion adjusts to its environment and meets task demands. In this article, we describe and discuss the essential contribution of somatosensory feedback to locomotion. We start with a discussion of how biomechanical properties of the body affect somatosensory feedback. We follow with the different types of mechanoreceptors and somatosensory afferents and their activity during locomotion. We then describe central projections to locomotor networks and the modulation of somatosensory feedback during locomotion and its mechanisms. We then discuss experimental approaches and animal models used to investigate the control of locomotion by somatosensory feedback before providing an overview of the different functional roles of somatosensory feedback for locomotion. Lastly, we briefly describe the role of somatosensory feedback in the recovery of locomotion after neurological injury. We highlight the fact that somatosensory feedback is an essential component of a highly integrated system for locomotor control. © 2021 American Physiological Society. Compr Physiol 11:1-71, 2021.
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Affiliation(s)
- Alain Frigon
- Department of Pharmacology-Physiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Quebec, Canada
| | - Turgay Akay
- Department of Medical Neuroscience, Atlantic Mobility Action Project, Brain Repair Center, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Boris I Prilutsky
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
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16
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Quilgars C, Cazalets JR, Bertrand SS. Developmentally Regulated Modulation of Lumbar Motoneurons by Metabotropic Glutamate Receptors: A Cellular and Behavioral Analysis in Newborn Mice. Front Cell Neurosci 2021; 15:770250. [PMID: 34955751 PMCID: PMC8699010 DOI: 10.3389/fncel.2021.770250] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2021] [Accepted: 11/19/2021] [Indexed: 11/18/2022] Open
Abstract
The present study explores the impact of metabotropic glutamate receptor (mGluR) activation on activity-dependent synaptic plasticity (ADSP) and the intrinsic membrane properties of lumbar motoneurons (MNs) using a combination of biochemical, pharmacological, electrophysiological and behavioral techniques. Using spinal cord slices from C57BL/6JRJ mice at two developmental stages, 1-3 and 8-12 postnatal days (P1-P3; P8-P12, respectively), we found that ADSP expressed at glutamatergic synapses between axons conveyed in the ventrolateral funiculus (VLF) and MNs, involved mGluR activation. Using specific agonists of the three groups of mGluRs, we observed that mGluR stimulation causes subtype-specific and developmentally regulated modulation of the ADSP and synaptic transmission at VLF-MN synapses as well as the intrinsic membrane properties of MNs. RT-qPCR analysis revealed a downregulation of mGluR gene expression with age in the ventral part of the lumbar spinal cord. Interestingly, the selective harvest by laser microdissection of MNs innervating the Gastrocnemius and Tibialis anterior muscles unraveled that the level of Grm2 expression is higher in Tibialis MNs compared to Gastrocnemius MNs suggesting a specific mGluR gene expression profile in these two MN pools. Finally, we assessed the functional impact of mGluR modulation on electrically induced bouts of fictive locomotion in the isolated spinal cord preparation of P1-P3 mice, and in vivo during spontaneous episodes of swimming activity in both P1-P3 and P8-P12 mouse pups. We observed that the mGluR agonists induced distinct and specific effects on the motor burst amplitudes and period of the locomotor rhythms tested and that their actions are function of the developmental stage of the animals. Altogether our data show that the metabotropic glutamatergic system exerts a complex neuromodulation in the developing spinal lumbar motor networks and provide new insights into the expression and modulation of ADSP in MNs.
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Affiliation(s)
- Camille Quilgars
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine (INCIA), CNRS UMR 5287, Université de Bordeaux, Bordeaux, France.,Ecole Pratique des Hautes Etudes (EPHE), Paris Sciences et Lettres University, Paris, France
| | - Jean-René Cazalets
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine (INCIA), CNRS UMR 5287, Université de Bordeaux, Bordeaux, France.,Ecole Pratique des Hautes Etudes (EPHE), Paris Sciences et Lettres University, Paris, France
| | - Sandrine S Bertrand
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine (INCIA), CNRS UMR 5287, Université de Bordeaux, Bordeaux, France.,Ecole Pratique des Hautes Etudes (EPHE), Paris Sciences et Lettres University, Paris, France
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17
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Moriya R, Kanamaru M, Okuma N, Yoshikawa A, Tanaka KF, Hokari S, Ohshima Y, Yamanaka A, Honma M, Onimaru H, Kikuchi T, Izumizaki M. Optogenetic activation of DRN 5-HT neurons induced active wakefulness, not quiet wakefulness. Brain Res Bull 2021; 177:129-142. [PMID: 34563634 DOI: 10.1016/j.brainresbull.2021.09.019] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Revised: 09/18/2021] [Accepted: 09/21/2021] [Indexed: 11/16/2022]
Abstract
There has been a long-standing controversy regarding the physiological role of serotonin (5-HT) neurons in the dorsal raphe nucleus (DRN) in sleep/wake architecture. Some studies have reported that 5-HT acts as a sleep-promoting agent, but several studies have suggested that DRN 5-HT neurons function predominantly to promote wakefulness and inhibit rapid eye movement (REM) sleep. Furthermore, recent studies have reported that there is a clear neurobiological difference between a waking state that includes alertness and active exploration (i.e., active wakefulness) and a waking state that is devoid of locomotion (i.e., quiet wakefulness). These states have also been shown to differ clinically in terms of memory consolidation. However, the effects of 5-HT neurons on the regulation of these two different waking states have not been fully elucidated. In the present study, we attempted to examine the physiological role of DRN 5-HT neurons in various sleep/wake states using optogenetic methods that allowed manipulation of cell-type specific neuronal activation with high temporal and anatomical precision. We crossed TPH2-tTA and TetO-ChR2(C128S) mice to obtain mice with channelrhodopsin-2 (ChR2) [C128S]-expressing central 5-HT neurons, and we activated DRN-5HT neurons or medullary 5-HT neurons. Optogenetic activation of DRN 5-HT neurons caused rapid transition from non-REM sleep to active wakefulness, not quiet wakefulness, whereas activation of medullary 5-HT neurons did not appear to affect sleep/wake states or locomotor activity. Our results may shed light on the physiological role of DRN 5-HT neurons in sleep/wake architecture and encourage further investigations of the cortical functional connectivity involved in sleep/wake state regulation.
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Affiliation(s)
- Rika Moriya
- Department of Physiology, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan; Department of Respiratory Medicine and Infectious Diseases, Niigata University Graduate School of Medical and Dental Sciences, 757-1 Asahimachi-dori, Chuo-ku, Niigata, Niigata 951-8520, Japan
| | - Mitsuko Kanamaru
- Department of Physiology, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan
| | - Naoki Okuma
- Department of Physiology, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan
| | - Akira Yoshikawa
- Department of Physiology, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan
| | - Kenji F Tanaka
- Department of Neuropsychiatry, Keio University School of Medicine, 35 Shinanomachi, Shinjyuku-ku, Tokyo 160-8582, Japan
| | - Satoshi Hokari
- Department of Respiratory Medicine and Infectious Diseases, Niigata University Graduate School of Medical and Dental Sciences, 757-1 Asahimachi-dori, Chuo-ku, Niigata, Niigata 951-8520, Japan
| | - Yasuyoshi Ohshima
- Department of Respiratory Medicine and Infectious Diseases, Niigata University Graduate School of Medical and Dental Sciences, 757-1 Asahimachi-dori, Chuo-ku, Niigata, Niigata 951-8520, Japan
| | - Akihiro Yamanaka
- Department of Neuroscience II, Research Institute of Environmental Medicine, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
| | - Motoyasu Honma
- Department of Physiology, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan
| | - Hiroshi Onimaru
- Department of Physiology, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan
| | - Toshiaki Kikuchi
- Department of Respiratory Medicine and Infectious Diseases, Niigata University Graduate School of Medical and Dental Sciences, 757-1 Asahimachi-dori, Chuo-ku, Niigata, Niigata 951-8520, Japan
| | - Masahiko Izumizaki
- Department of Physiology, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8555, Japan.
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18
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Kaur J, Mazzone GL, Aquino JB, Nistri A. Nicotine Neurotoxicity Involves Low Wnt1 Signaling in Spinal Locomotor Networks of the Postnatal Rodent Spinal Cord. Int J Mol Sci 2021; 22:ijms22179572. [PMID: 34502498 PMCID: PMC8431663 DOI: 10.3390/ijms22179572] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2021] [Revised: 08/29/2021] [Accepted: 08/31/2021] [Indexed: 12/29/2022] Open
Abstract
The postnatal rodent spinal cord in-vitro is a useful model to investigate early pathophysiological changes after injury. While low dose nicotine (1 µM) induces neuroprotection, how higher doses affect spinal networks is unknown. Using spinal preparations of postnatal wild-type Wistar rat and Wnt1Cre2:Rosa26Tom double-transgenic mouse, we studied the effect of nicotine (0.5–10 µM) on locomotor networks in-vitro. Nicotine 10 µM induced motoneuron depolarization, suppressed monosynaptic reflexes, and decreased fictive locomotion in rat spinal cord. Delayed fall in neuronal numbers (including motoneurons) of central and ventral regions emerged without loss of dorsal neurons. Conversely, nicotine (0.5–1 µM) preserved neurons throughout the spinal cord and strongly activated the Wnt1 signaling pathway. High-dose nicotine enhanced expression of S100 and GFAP in astrocytes indicating a stress response. Excitotoxicity induced by kainate was contrasted by nicotine (10 µM) in the dorsal area and persisted in central and ventral regions with no change in basal Wnt signaling. When combining nicotine with kainate, the activation of Wnt1 was reduced compared to kainate/sham. The present results suggest that high dose nicotine was neurotoxic to central and ventral spinal neurons as the neuroprotective role of Wnt signaling became attenuated. This also corroborates the risk of cigarette smoking for the foetus/newborn since tobacco contains nicotine.
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Affiliation(s)
- Jaspreet Kaur
- Department of Neuroscience, University of Copenhagen, 2200 Copenhagen N, Denmark
- Department of Neuroscience, International School for Advanced Studies (SISSA), 34136 Trieste, Italy;
- Correspondence: (J.K.); (G.L.M.); Tel.: +45-5260-1502 (J.K.); +54-23-0438-7425 (G.L.M.)
| | - Graciela L. Mazzone
- Department of Neuroscience, International School for Advanced Studies (SISSA), 34136 Trieste, Italy;
- Instituto de Investigaciones en Medicina Traslacional (IIMT), CONICET-Universidad Austral, Av. Pte. Perón 1500, Pilar B1629AHJ, Buenos Aires, Argentina;
- Correspondence: (J.K.); (G.L.M.); Tel.: +45-5260-1502 (J.K.); +54-23-0438-7425 (G.L.M.)
| | - Jorge B. Aquino
- Instituto de Investigaciones en Medicina Traslacional (IIMT), CONICET-Universidad Austral, Av. Pte. Perón 1500, Pilar B1629AHJ, Buenos Aires, Argentina;
| | - Andrea Nistri
- Department of Neuroscience, International School for Advanced Studies (SISSA), 34136 Trieste, Italy;
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Boulain M, Yuan W, Oueghlani Z, Khsime I, Salvi V, Courtand G, Halgand C, Morin D, de Deurwaerdere P, Barrière G, Juvin L. L-DOPA and 5-HTP modulation of air-stepping in newborn rats. J Physiol 2021; 599:4455-4476. [PMID: 34411301 DOI: 10.1113/jp281983] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2021] [Accepted: 08/03/2021] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS In newborn rats, L-DOPA increases the occurrence of air-stepping activity without affecting movement characteristics. L-DOPA administration increases the spinal content of dopamine in a dose-dependent manner. Injection of 5-HTP increases the spinal serotonin content but does not trigger air-stepping. 5-HTP counteracts the pro-locomotor action of L-DOPA. Less dopamine and serotonin are synthesized when L-DOPA and 5-HTP are administered as a cocktail. ABSTRACT The catecholamine precursor, L-3,4-dihydroxyphenylalanine (L-DOPA), is a well-established pharmacological agent for promoting locomotor action in vertebrates, including triggering air-stepping activities in the neonatal rat. Serotonin is also a well-known neuromodulator of the rodent spinal locomotor networks. Here, using kinematic analysis, we compared locomotor-related activities expressed by newborn rats in response to varying doses of L-DOPA and the serotonin precursor 5-hydroxytryptophan (5-HTP) administered separately or in combination. L-DOPA alone triggered episodes of air-stepping in a dose-dependent manner (25-100 mg/kg), notably determining the duration of locomotor episodes, but without affecting step cycle frequency or amplitude. In contrast, 5-HTP (25-150 mg/kg) was ineffective in instigating air-stepping, but altered episode durations of L-DOPA-induced air-stepping, and decreased locomotor cycle frequency. High performance liquid chromatography revealed that L-DOPA, which was undetectable in control conditions, accumulated in a dose-dependent manner in the lumbar spinal cord 30 min after its administration. This was paralleled by an increase in dopamine levels, whereas the spinal content of noradrenaline and serotonin remained unaffected. In the same way, the spinal levels of serotonin increased in parallel with the dose of 5-HTP without affecting the levels of dopamine and noradrenaline. When both precursors are administrated, they counteract each other for the production of serotonin and dopamine. Our data thus indicate for the first time that both L-DOPA and 5-HTP exert opposing neuromodulatory actions on air-stepping behaviour in the developing rat, and we speculate that competition for the production of dopamine and serotonin occurs when they are administered as a cocktail.
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Affiliation(s)
- Marie Boulain
- CNRS, EPHE, INCIA, University of Bordeaux, UMR5287 F-33000, Bordeaux, France
| | - Wei Yuan
- Department of Orthopedics, The First Hospital of China Medical University, Shenyang, China
| | - Zied Oueghlani
- CNRS, EPHE, INCIA, University of Bordeaux, UMR5287 F-33000, Bordeaux, France
| | - Inès Khsime
- CNRS, EPHE, INCIA, University of Bordeaux, UMR5287 F-33000, Bordeaux, France
| | - Vianney Salvi
- CNRS, EPHE, INCIA, University of Bordeaux, UMR5287 F-33000, Bordeaux, France
| | - Gilles Courtand
- CNRS, EPHE, INCIA, University of Bordeaux, UMR5287 F-33000, Bordeaux, France
| | - Christophe Halgand
- CNRS, EPHE, INCIA, University of Bordeaux, UMR5287 F-33000, Bordeaux, France
| | - Didier Morin
- CNRS, EPHE, INCIA, University of Bordeaux, UMR5287 F-33000, Bordeaux, France
| | | | - Grégory Barrière
- CNRS, EPHE, INCIA, University of Bordeaux, UMR5287 F-33000, Bordeaux, France
| | - Laurent Juvin
- CNRS, EPHE, INCIA, University of Bordeaux, UMR5287 F-33000, Bordeaux, France
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Boulain M, Khsime I, Sourioux M, Thoby-Brisson M, Barrière G, Simmers J, Morin D, Juvin L. Synergistic interaction between sensory inputs and propriospinal signalling underlying quadrupedal locomotion. J Physiol 2021; 599:4477-4496. [PMID: 34412148 DOI: 10.1113/jp281861] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Accepted: 08/05/2021] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Stimulation of hindlimb afferent fibres can both stabilize and increase the activity of fore- and hindlimb motoneurons during fictive locomotion. The increase in motoneuron activity is at least partially due to the production of doublets of action potentials in a subpopulation of motoneurons. These results were obtained using an in vitro brainstem/spinal cord preparation of neonatal rat. ABSTRACT Quadrupedal locomotion relies on a dynamic coordination between central pattern generators (CPGs) located in the cervical and lumbar spinal cord, and controlling the fore- and hindlimbs, respectively. It is assumed that this CPG interaction is achieved through separate closed-loop processes involving propriospinal and sensory pathways. However, the functional consequences of a concomitant involvement of these different influences on the degree of coordination between the fore- and hindlimb CPGs is still largely unknown. Using an in vitro brainstem/spinal cord preparation of neonatal rat, we found that rhythmic, bilaterally alternating stimulation of hindlimb sensory input pathways elicited coordinated hindlimb and forelimb CPG activity. During pharmacologically induced fictive locomotion, lumbar dorsal root (DR) stimulation entrained and stabilized an ongoing cervico-lumbar locomotor-like rhythm and increased the amplitude of both lumbar and cervical ventral root bursting. The increase in cervical burst amplitudes was correlated with the occurrence of doublet action potential firing in a subpopulation of motoneurons, enabling the latter to transition between low and high frequency discharge according to the intensity of DR stimulation. Moreover, our data revealed that propriospinal and sensory pathways act synergistically to strengthen cervico-lumbar interactions. Indeed, split-bath experiments showed that fully coordinated cervico-lumbar fictive locomotion was induced by combining pharmacological stimulation of either the lumbar or cervical CPGs with lumbar DR stimulation. This study thus highlights the powerful interactions between sensory and propriospinal pathways which serve to ensure the coupling of the fore- and hindlimb CPGs for effective quadrupedal locomotion.
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Affiliation(s)
- Marie Boulain
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, Unité Mixte de Recherche 5287, CNRS, Université de Bordeaux, CNRS, EPHE, INCIA, UMR5287 F-33000, Bordeaux, France
| | - Inès Khsime
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, Unité Mixte de Recherche 5287, CNRS, Université de Bordeaux, CNRS, EPHE, INCIA, UMR5287 F-33000, Bordeaux, France
| | - Mélissa Sourioux
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, Unité Mixte de Recherche 5287, CNRS, Université de Bordeaux, CNRS, EPHE, INCIA, UMR5287 F-33000, Bordeaux, France
| | - Muriel Thoby-Brisson
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, Unité Mixte de Recherche 5287, CNRS, Université de Bordeaux, CNRS, EPHE, INCIA, UMR5287 F-33000, Bordeaux, France
| | - Grégory Barrière
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, Unité Mixte de Recherche 5287, CNRS, Université de Bordeaux, CNRS, EPHE, INCIA, UMR5287 F-33000, Bordeaux, France
| | - John Simmers
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, Unité Mixte de Recherche 5287, CNRS, Université de Bordeaux, CNRS, EPHE, INCIA, UMR5287 F-33000, Bordeaux, France
| | - Didier Morin
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, Unité Mixte de Recherche 5287, CNRS, Université de Bordeaux, CNRS, EPHE, INCIA, UMR5287 F-33000, Bordeaux, France
| | - Laurent Juvin
- Institut de Neurosciences Cognitives et Intégratives d'Aquitaine, Unité Mixte de Recherche 5287, CNRS, Université de Bordeaux, CNRS, EPHE, INCIA, UMR5287 F-33000, Bordeaux, France
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21
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Expiratory abdominal muscle nerve is active at flexor phase, while inspiratory phrenic nerve is not active during locomotion evoked by 5-HT and NMDA in the neonatal rat. Neurosci Res 2021; 174:9-18. [PMID: 34324893 DOI: 10.1016/j.neures.2021.07.004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2021] [Revised: 07/15/2021] [Accepted: 07/21/2021] [Indexed: 11/21/2022]
Abstract
Abdominal muscles are involved in respiration and locomotion. In the isolated pons-spinal cord-rib attached preparation from neonatal rat, the phrenic nerve and abdominal muscles show inspiratory and expiratory activity, respectively. Using this preparation, we investigated whether the bath application of NMDA and 5-HT could evoke locomotor activities in the fourth cervical ventral root (C4VR), phrenic nerve, and abdominal muscle nerve (ilioinguinal nerve, IIG-n). We also observed rib and abdominal muscle movements visually. The phrenic nerve and C4VR showed inspiratory activity consistently under the control conditions, whereas IIG-n showed expiratory activity only at the beginning of the experiment. During the chemically-induced locomotion, both C4VR and IIG-n showed locomotor activity, and IIG-n in particular showed flexor activity. During the flexor activity, lateral bending of the rib cage to the recording site was observed. The phrenic nerve showed weak or no apparent locomotor activity. We concluded that the central pattern generator (CPG) for locomotion provides stronger excitatory synaptic inputs to C4 motoneurons innervating neck and shoulder muscles than the inputs to the phrenic motoneurons. Thus, the locomotor CPG provides a suitable amount of inputs to the functionally proper motoneurons. This preparation will be useful to explore how the respiratory and locomotor CPGs select proper motoneurons to give synaptic inputs and are coordinated with each other.
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Garcia-Ramirez DL, Ha NT, Bibu S, Stachowski NJ, Dougherty KJ. Spinal Cord Injury Alters Spinal Shox2 Interneurons by Enhancing Excitatory Synaptic Input and Serotonergic Modulation While Maintaining Intrinsic Properties in Mouse. J Neurosci 2021; 41:5833-5848. [PMID: 34006587 PMCID: PMC8265802 DOI: 10.1523/jneurosci.1576-20.2021] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2020] [Revised: 05/03/2021] [Accepted: 05/05/2021] [Indexed: 12/11/2022] Open
Abstract
Neural circuitry generating locomotor rhythm and pattern is located in the spinal cord. Most spinal cord injuries (SCIs) occur above the level of spinal locomotor neurons; therefore, these circuits are a target for improving motor function after SCI. Despite being relatively intact below the injury, locomotor circuitry undergoes substantial plasticity with the loss of descending control. Information regarding cell type-specific plasticity within locomotor circuits is limited. Shox2 interneurons (INs) have been linked to locomotor rhythm generation and patterning, making them a potential therapeutic target for the restoration of locomotion after SCI. The goal of the present study was to identify SCI-induced plasticity at the level of Shox2 INs in a complete thoracic transection model in adult male and female mice. Whole-cell patch-clamp recordings of Shox2 INs revealed minimal changes in intrinsic excitability properties after SCI. However, afferent stimulation resulted in mixed excitatory and inhibitory input to Shox2 INs in uninjured mice which became predominantly excitatory after SCI. Shox2 INs were differentially modulated by serotonin (5-HT) in a concentration-dependent manner in uninjured conditions but following SCI, 5-HT predominantly depolarized Shox2 INs. 5-HT7 receptors mediated excitatory effects on Shox2 INs from both uninjured and SCI mice, but activation of 5-HT2B/2C receptors enhanced excitability of Shox2 INs only after SCI. Overall, SCI alters sensory afferent input pathways to Shox2 INs and 5-HT modulation of Shox2 INs to enhance excitatory responses. Our findings provide relevant information regarding the locomotor circuitry response to SCI that could benefit strategies to improve locomotion after SCI.SIGNIFICANCE STATEMENT Current therapies to gain locomotor control after spinal cord injury (SCI) target spinal locomotor circuitry. Improvements in therapeutic strategies will require a better understanding of the SCI-induced plasticity within specific locomotor elements and their controllers, including sensory afferents and serotonergic modulation. Here, we demonstrate that excitability and intrinsic properties of Shox2 interneurons, which contribute to the generation of the locomotor rhythm and pattering, remain intact after SCI. However, SCI induces plasticity in both sensory afferent pathways and serotonergic modulation, enhancing the activation and excitation of Shox2 interneurons. Our findings will impact future strategies looking to harness these changes with the ultimate goal of restoring functional locomotion after SCI.
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Affiliation(s)
- D Leonardo Garcia-Ramirez
- Marion Murray Spinal Cord Research Center, Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129
| | - Ngoc T Ha
- Marion Murray Spinal Cord Research Center, Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129
| | - Steve Bibu
- Marion Murray Spinal Cord Research Center, Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129
| | - Nicholas J Stachowski
- Marion Murray Spinal Cord Research Center, Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129
| | - Kimberly J Dougherty
- Marion Murray Spinal Cord Research Center, Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129
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Unusual Quadrupedal Locomotion in Rat during Recovery from Lumbar Spinal Blockade of 5-HT 7 Receptors. Int J Mol Sci 2021; 22:ijms22116007. [PMID: 34199392 PMCID: PMC8199611 DOI: 10.3390/ijms22116007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2021] [Revised: 05/27/2021] [Accepted: 05/28/2021] [Indexed: 01/18/2023] Open
Abstract
Coordination of four-limb movements during quadrupedal locomotion is controlled by supraspinal monoaminergic descending pathways, among which serotoninergic ones play a crucial role. Here we investigated the locomotor pattern during recovery from blockade of 5-HT7 or 5-HT2A receptors after intrathecal application of SB269970 or cyproheptadine in adult rats with chronic intrathecal cannula implanted in the lumbar spinal cord. The interlimb coordination was investigated based on electromyographic activity recorded from selected fore- and hindlimb muscles during rat locomotion on a treadmill. In the time of recovery after hindlimb transient paralysis, we noticed a presence of an unusual pattern of quadrupedal locomotion characterized by a doubling of forelimb stepping in relation to unaffected hindlimb stepping (2FL-1HL) after blockade of 5-HT7 receptors but not after blockade of 5-HT2A receptors. The 2FL-1HL pattern, although transient, was observed as a stable form of fore-hindlimb coupling during quadrupedal locomotion. We suggest that modulation of the 5-HT7 receptors on interneurons located in lamina VII with ascending projections to the forelimb spinal network can be responsible for the 2FL-1HL locomotor pattern. In support, our immunohistochemical analysis of the lumbar spinal cord demonstrated the presence of the 5-HT7 immunoreactive cells in the lamina VII, which were rarely 5-HT2A immunoreactive.
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GABAergic Mechanisms Can Redress the Tilted Balance between Excitation and Inhibition in Damaged Spinal Networks. Mol Neurobiol 2021; 58:3769-3786. [PMID: 33826070 PMCID: PMC8279998 DOI: 10.1007/s12035-021-02370-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2020] [Accepted: 03/22/2021] [Indexed: 12/19/2022]
Abstract
Correct operation of neuronal networks depends on the interplay between synaptic excitation and inhibition processes leading to a dynamic state termed balanced network. In the spinal cord, balanced network activity is fundamental for the expression of locomotor patterns necessary for rhythmic activation of limb extensor and flexor muscles. After spinal cord lesion, paralysis ensues often followed by spasticity. These conditions imply that, below the damaged site, the state of balanced networks has been disrupted and that restoration might be attempted by modulating the excitability of sublesional spinal neurons. Because of the widespread expression of inhibitory GABAergic neurons in the spinal cord, their role in the early and late phases of spinal cord injury deserves full attention. Thus, an early surge in extracellular GABA might be involved in the onset of spinal shock while a relative deficit of GABAergic mechanisms may be a contributor to spasticity. We discuss the role of GABA A receptors at synaptic and extrasynaptic level to modulate network excitability and to offer a pharmacological target for symptom control. In particular, it is proposed that activation of GABA A receptors with synthetic GABA agonists may downregulate motoneuron hyperexcitability (due to enhanced persistent ionic currents) and, therefore, diminish spasticity. This approach might constitute a complementary strategy to regulate network excitability after injury so that reconstruction of damaged spinal networks with new materials or cell transplants might proceed more successfully.
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Orssatto LBR, Mackay K, Shield AJ, Sakugawa RL, Blazevich AJ, Trajano GS. Estimates of persistent inward currents increase with the level of voluntary drive in low-threshold motor units of plantar flexor muscles. J Neurophysiol 2021; 125:1746-1754. [PMID: 33788617 DOI: 10.1152/jn.00697.2020] [Citation(s) in RCA: 33] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
This study tested whether estimates of persistent inward currents (PICs) in the human plantar flexors would increase with the level of voluntary drive. High-density surface electromyograms were collected from soleus and gastrocnemius medialis of 21 participants (29.2 ± 2.6 yr) during ramp-shaped isometric contractions to 10%, 20%, and 30% (torque rise and decline of 2%/s and 30-s duration) of each participant's maximal torque. Motor units identified in all the contraction intensities were included in the paired-motor unit analysis to calculate delta frequency (ΔF) and estimate the PICs. ΔF is the difference in discharge rate of the control unit at the time of recruitment and derecruitment of the test unit. Increases in PICs were observed from 10% to 20% [Δ = 0.6 pulse per second (pps); P < 0.001] and from 20% to 30% (Δ = 0.5 pps; P < 0.001) in soleus and from 10% to 20% (Δ = 1.2 pps; P < 0.001) but not from 20% to 30% (Δ = 0.09 pps; P = 0.724) in gastrocnemius medialis. Maximal discharge rate increased for soleus and gastrocnemius medialis from 10% to 20% [Δ = 1.75 pps (P < 0.001) and Δ = 2.43 pps (P < 0.001), respectively] and from 20% to 30% [Δ = 0.80 pps (P < 0.017) and Δ = 0.92 pps (P = 0.002), respectively]. The repeated-measures correlation identified associations between ΔF and increases in maximal discharge rate for soleus (r = 0.64; P < 0.001) and gastrocnemius medialis (r = 0.77; P < 0.001). An increase in voluntary drive tends to increase PIC strength, which has key implications for the control of force but also for comparisons between muscles or studies when relative force levels might be different. Increases in voluntary descending drive amplify PICs in humans and provide an important spinal mechanism for motor unit discharging, and thus force output modulation.NEW & NOTEWORTHY Animal experiments and computational models have shown that motor neurons can amplify the synaptic input they receive via persistent inward currents. Here we show in humans that this amplification varies proportionally to the magnitude of the voluntary drive to the muscle.
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Affiliation(s)
- Lucas B R Orssatto
- School of Exercise and Nutrition Sciences, Faculty of Health, Queensland University of Technology (QUT), Brisbane, Queensland, Australia
| | - Karen Mackay
- School of Exercise and Nutrition Sciences, Faculty of Health, Queensland University of Technology (QUT), Brisbane, Queensland, Australia
| | - Anthony J Shield
- School of Exercise and Nutrition Sciences, Faculty of Health, Queensland University of Technology (QUT), Brisbane, Queensland, Australia
| | - Raphael L Sakugawa
- Biomechanics Laboratory, Department of Physical Education, Federal University of Santa Catarina, Florianopolis, Brazil
| | - Anthony J Blazevich
- Centre for Exercise and Sports Science Research (CESSR), School of Medical and Health Sciences, Edith Cowan University, Joondalup, Western Australia, Australia
| | - Gabriel S Trajano
- School of Exercise and Nutrition Sciences, Faculty of Health, Queensland University of Technology (QUT), Brisbane, Queensland, Australia
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Montgomery JE, Wahlstrom‐Helgren S, Vanpelt KT, Masino MA. Repetitive optogenetic stimulation of glutamatergic neurons: An alternative to NMDA treatment for generating locomotor activity in spinalized zebrafish larvae. Physiol Rep 2021; 9:e14774. [PMID: 33769694 PMCID: PMC7995545 DOI: 10.14814/phy2.14774] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2020] [Revised: 01/29/2021] [Accepted: 02/01/2021] [Indexed: 11/29/2022] Open
Abstract
N-methyl-d-aspartate (NMDA) application has conventionally been used to activate spinal networks to induce locomotion in spinalized animals. We recently described an alternative approach in which application of continuous blue light activates channelrhodopsin-2 in vesicular glutamate transporter 2a (vglut2a)-expressing spinal neurons to produce organized, rhythmic locomotor activity in spinally-transected larval zebrafish. This technique arguably enhances research validity, because endogenous glutamate is released into existing synapses instead of activating only a subset of glutamatergic (NMDA) receptors with an exogenous compound. Here, we explored the viability of this approach in the context of using it for longer-term experiments. Fictive swimming was induced through repetitive application of 10-s blue light stimuli to spinalized preparations for up to 60 min at intervals of 1, 3, or 15 min. Locomotor activity was maintained throughout the experimental timecourse, demonstrating the robustness of the system. Although locomotor bursts remained organized into episodes of activity, the number of bursts elicited during each successive stimulus decreased. This was in contrast to NMDA bath application, in which bursts became less episodically organized while the overall number of bursts remained unchanged. The efficacy of the repetitive optogenetic stimulation paradigm was demonstrated through application of exogenous dopamine, which reversibly decreased the number of bursts produced per stimulus compared with untreated preparations. Finally, increasing the stimulus interval to 15 min lessened, but did not eliminate locomotor fatigue from repetitive activation. Altogether, we established repetitive optogenetic stimulation of vglut2a-expressing neurons as a viable alternative to NMDA application for activation of the zebrafish spinal locomotor network.
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Affiliation(s)
| | | | - Kayce T. Vanpelt
- Department of NeuroscienceUniversity of MinnesotaMinneapolisMNUSA
| | - Mark A. Masino
- Department of NeuroscienceUniversity of MinnesotaMinneapolisMNUSA
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27
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Mille T, Quilgars C, Cazalets J, Bertrand SS. Acetylcholine and spinal locomotor networks: The insider. Physiol Rep 2021; 9:e14736. [PMID: 33527727 PMCID: PMC7851432 DOI: 10.14814/phy2.14736] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2020] [Revised: 01/05/2021] [Accepted: 01/07/2021] [Indexed: 01/07/2023] Open
Abstract
This article aims to review studies that have investigated the role of neurons that use the transmitter acetylcholine (ACh) in controlling the operation of locomotor neural networks within the spinal cord. This cholinergic system has the particularity of being completely intraspinal. We describe the different effects exerted by spinal cholinergic neurons on locomotor circuitry by the pharmacological activation or blockade of this propriospinal system, as well as describing its different cellular and subcellular targets. Through the activation of one ionotropic receptor, the nicotinic receptor, and five metabotropic receptors, the M1 to M5 muscarinic receptors, the cholinergic system exerts a powerful control both on synaptic transmission and locomotor network neuron excitability. Although tremendous advances have been made in our understanding of the spinal cholinergic system's involvement in the physiology and pathophysiology of locomotor networks, gaps still remain, including the precise role of the different subtypes of cholinergic neurons as well as their pre- and postsynaptic partners. Improving our knowledge of the propriospinal cholinergic system is of major relevance to finding new cellular targets and therapeutics in countering the debilitating effects of neurodegenerative diseases and restoring motor functions after spinal cord injury.
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Affiliation(s)
- Théo Mille
- Université de BordeauxCNRS UMR 5287INCIABordeauxFrance
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28
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Buspirone for functional improvement after acute traumatic spinal cord injury: a propensity score-matched cohort study. Spinal Cord 2021; 59:563-570. [PMID: 33495579 DOI: 10.1038/s41393-020-00606-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2020] [Revised: 11/22/2020] [Accepted: 12/02/2020] [Indexed: 11/08/2022]
Abstract
STUDY DESIGN Retrospective analysis of treated inpatients compared to expected neurorecovery from a propensity score-matched national database cohort. OBJECTIVE Evaluate the effectiveness of buspirone on clinical neurorecovery following traumatic SCI when started during acute inpatient rehabilitation. SETTING University-based hospital in Boston, USA. METHODS Chart review yielded thirty-one individuals with acute, traumatic SCI treated with buspirone during inpatient rehabilitation from 2011-2017. Propensity score matching to a cohort of individuals from the spinal cord injury model systems (SCIMS) national database was completed. Changes in upper extremity motor score (UEMS), lower extremity motor score (LEMS), American Spinal Injury Association Impairment Scale (AIS), neurological level of injury (NLI), and functional impairment measure (FIM) from admission to discharge and discharge to 1 year were computed and compared between matched pairs (buspirone and mean national SCIMs cohort). A local control cohort not treated with buspirone was similarly compared to a matched mean national SCIMs group to identify location-specific effects. RESULTS From admission to discharge from inpatient rehabilitation, 95% confidence intervals of changes in UEMS (-2.43 to +2.78), LEMS (-1.02 to +6.02), AIS (-0.04 to +0.35), NLI (-0.42 to +1.08), and FIM (-4.42 to +6.40) were not significantly different between those individuals who received buspirone and their propensity-matched SCIMS cohort. Similarly, changes in these metrics were not significantly different at 1-year follow up. Buspirone group individuals with initial clinically complete SCI demonstrated a higher 1-year conversion rate to incomplete injury (6 out of 14; 42.9%) compared to the matched national SCIMS cohort (14 out of 70; 21.2%, p = 0.047) though this was not significantly different from non-buspirone local controls (p = 0.25). CONCLUSIONS Retrospective analysis shows no statistically significant difference in gross markers of neurorecovery following acute traumatic SCI when buspirone is initiated indiscriminately during acute inpatient rehabilitation. In individuals with clinically complete SCI, findings suggest possible increased rates of 1-year conversion to incomplete injury.
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29
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Guillaud E, Seyres P, Barrière G, Jecko V, Bertrand SS, Cazalets JR. Locomotion and dynamic posture: neuro-evolutionary basis of bipedal gait. Neurophysiol Clin 2020; 50:467-477. [PMID: 33176989 DOI: 10.1016/j.neucli.2020.10.012] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2020] [Revised: 10/23/2020] [Accepted: 10/23/2020] [Indexed: 12/24/2022] Open
Abstract
Body displacement during locomotion is a major challenge for motor control, requiring complex synergistic postural regulation and the integrated functioning of all body musculature, including that of the four limbs, trunk and neck. Despite the obvious pivotal role played by the trunk during locomotion, most studies devoted to understanding the neural basis of locomotor control have only addressed the operation of the neural circuits driving leg movements, and relatively little is known of the networks that control trunk muscles in limbed vertebrates. This review addresses this issue, both in animals and humans. We first review studies addressing the central role played by central pattern generator (CPG) circuit interactions within the spinal cord in coordinating trunk and hind limb muscle activities in a variety of vertebrates, and present evidence that vestibulo-spinal reflexes are differentially involved in trunk and hind limb control. We finally highlight the role of the various components that participate in maintaining dynamic equilibrium during stepping, including connective tissues. We propose that many aspects of the organization of the motor systems involved in trunk-hind limb movement control in vertebrates have been highly conserved throughout evolution.
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Affiliation(s)
- Etienne Guillaud
- Université de Bordeaux, CNRS UMR 5287, INCIA, Zone nord, Bat 2, 2e étage, 146 rue Léo Saignat, 33076 Bordeaux cedex, France
| | - Philippe Seyres
- Université de Bordeaux, CNRS UMR 5287, INCIA, Zone nord, Bat 2, 2e étage, 146 rue Léo Saignat, 33076 Bordeaux cedex, France
| | - Gregory Barrière
- Université de Bordeaux, CNRS UMR 5287, INCIA, Zone nord, Bat 2, 2e étage, 146 rue Léo Saignat, 33076 Bordeaux cedex, France
| | - Vincent Jecko
- Université de Bordeaux, CNRS UMR 5287, INCIA, Zone nord, Bat 2, 2e étage, 146 rue Léo Saignat, 33076 Bordeaux cedex, France
| | - Sandrine S Bertrand
- Université de Bordeaux, CNRS UMR 5287, INCIA, Zone nord, Bat 2, 2e étage, 146 rue Léo Saignat, 33076 Bordeaux cedex, France
| | - Jean-René Cazalets
- Université de Bordeaux, CNRS UMR 5287, INCIA, Zone nord, Bat 2, 2e étage, 146 rue Léo Saignat, 33076 Bordeaux cedex, France.
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30
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Flaive A, Fougère M, van der Zouwen CI, Ryczko D. Serotonergic Modulation of Locomotor Activity From Basal Vertebrates to Mammals. Front Neural Circuits 2020; 14:590299. [PMID: 33224027 PMCID: PMC7674590 DOI: 10.3389/fncir.2020.590299] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Accepted: 09/28/2020] [Indexed: 12/14/2022] Open
Abstract
During the last 50 years, the serotonergic (5-HT) system was reported to exert a complex modulation of locomotor activity. Here, we focus on two key factors that likely contribute to such complexity. First, locomotion is modulated directly and indirectly by 5-HT neurons. The locomotor circuitry is directly innervated by 5-HT neurons in the caudal brainstem and spinal cord. Also, indirect control of locomotor activity results from ascending projections of 5-HT cells in the rostral brainstem that innervate multiple brain centers involved in motor action planning. Second, each approach used to manipulate the 5-HT system likely engages different 5-HT-dependent mechanisms. This includes the recruitment of different 5-HT receptors, which can have excitatory or inhibitory effects on cell activity. These receptors can be located far or close to the 5-HT release sites, making their activation dependent on the level of 5-HT released. Here we review the activity of different 5-HT nuclei during locomotor activity, and the locomotor effects of 5-HT precursors, exogenous 5-HT, selective 5-HT reuptake inhibitors (SSRI), electrical or chemical stimulation of 5-HT neurons, genetic deletions, optogenetic and chemogenetic manipulations. We highlight both the coherent and controversial aspects of 5-HT modulation of locomotor activity from basal vertebrates to mammals. This mini review may hopefully inspire future studies aiming at dissecting the complex effects of 5-HT on locomotor function.
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Affiliation(s)
- Aurélie Flaive
- Département de Pharmacologie-Physiologie, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, Sherbrooke, QC, Canada
| | - Maxime Fougère
- Département de Pharmacologie-Physiologie, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, Sherbrooke, QC, Canada
| | - Cornelis Immanuel van der Zouwen
- Département de Pharmacologie-Physiologie, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, Sherbrooke, QC, Canada
| | - Dimitri Ryczko
- Département de Pharmacologie-Physiologie, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, Sherbrooke, QC, Canada.,Centre de Recherche du Centre Hospitalier Universitaire de Sherbrooke, Sherbrooke, QC, Canada.,Institut de Pharmacologie de Sherbrooke, Sherbrooke, QC, Canada.,Centre des Neurosciences de Sherbrooke, Sherbrooke, QC, Canada
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31
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Zhang Q, Dai Y. A modeling study of spinal motoneuron recruitment regulated by ionic channels during fictive locomotion. J Comput Neurosci 2020; 48:409-428. [PMID: 32895895 DOI: 10.1007/s10827-020-00763-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Revised: 07/31/2020] [Accepted: 08/06/2020] [Indexed: 11/24/2022]
Abstract
During fictive locomotion cat lumbar motoneurons exhibit changes in membrane proprieties including a decrease in voltage threshold (Vth), afterhyperpolarization (AHP) and input resistance (Rin) and an increase in non-linear membrane property. The impact of these changes on the motoneuron recruitment remains unknown. Using modeling approach we investigated the channel mechanism regulating the motoneuron recruitment. Three types of motoneuron pools including slow (S), fatigue-resistant (FR) and fast-fatigable (FF) motoneurons were constructed based on the membrane proprieties of cat lumbar motoneurons. The transient sodium (NaT), persistent sodium (NaP), delayed-rectifier potassium [K(DR)], Ca2+-dependent K+ [K(AHP)] and L-type calcium (CaL) channels were included in the models. Simulation results showed that (1) Strengthening synaptic inputs increased the number of recruitments in all three types of motoneurons following the size principle. (2) Increasing NaT or NaP or decreasing K(DR) or K(AHP) lowered rheobase of spike generation thus increased recruitment of motoneuron pools. (3) Decreasing Rin reduced recruitment in all three types of motoneurons. (4) The FF-type motoneuron pool, followed by FR- and S-type, were the most sensitive to increase of synaptic inputs, reduction of Rin, upregulation of NaT and NaP, and downregulation of K(DR) and K(AHP). (5) Increasing CaL enhanced overall discharge rate of motoneuron pools with little effect on the recruitment. Simulation results suggested that modulation of ionic channels altered the output of motoneuron pools with either modulating the number of recruited motoneurons or regulating the overall discharge rate of motoneuron pools. Multiple channels contributed to the recruitment of motoneurons with interaction of excitatory and inhibitory synaptic inputs during walking.
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Affiliation(s)
- Qiang Zhang
- Shanghai Key Laboratory of Multidimensional Information Processing, School of Communication and Electronic Engineering, East China Normal University, Shanghai, 200241, China
| | - Yue Dai
- Shanghai Key Laboratory of Multidimensional Information Processing, School of Communication and Electronic Engineering, East China Normal University, Shanghai, 200241, China. .,Key Laboratory of Adolescent Health Assessment and Exercise Intervention of Ministry of Education, School of Physical Education and Health Care, East China Normal University, Shanghai, 200241, China.
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Citalopram Administration Does Not Promote Function or Histological Recovery after Spinal Cord Injury. Int J Mol Sci 2020; 21:ijms21145062. [PMID: 32709070 PMCID: PMC7404289 DOI: 10.3390/ijms21145062] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Revised: 07/07/2020] [Accepted: 07/08/2020] [Indexed: 12/25/2022] Open
Abstract
Citalopram is a selective serotonin reuptake inhibitor, and although widely used as an antidepressant, this drug has also demonstrated interesting repairing properties leading to motor recovery and pathology amelioration in animal models of stroke and degeneration. Here, we tested the efficacy of both 7-day and 8-week citalopram treatment in a contusive spinal cord injury (SCI) rat model. A combination of behavioral tests, histological and serum cytokine analysis was used to assess overall recovery. Despite promoting a mild reduction of inflammatory cells as well as an early, but transient increase of specific serum cytokines, citalopram administration showed no overall beneficial effects on motor performance or lesion extension. Our results do not support citalopram treatment as a therapeutic strategy for SCI.
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33
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Flaive A, Cabelguen JM, Ryczko D. The serotonin reuptake blocker citalopram destabilizes fictive locomotor activity in salamander axial circuits through 5-HT 1A receptors. J Neurophysiol 2020; 123:2326-2342. [PMID: 32401145 DOI: 10.1152/jn.00179.2020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Serotoninergic (5-HT) neurons are powerful modulators of spinal locomotor circuits. Most studies on 5-HT modulation focused on the effect of exogenous 5-HT and these studies provided key information about the cellular mechanisms involved. Less is known about the effects of increased release of endogenous 5-HT with selective serotonin reuptake inhibitors. In mammals, such molecules were shown to destabilize the fictive locomotor output of spinal limb networks through 5-HT1A receptors. However, in tetrapods little is known about the effects of increased 5-HT release on the locomotor output of axial networks, which are coordinated with limb circuits during locomotion from basal vertebrates to mammals. Here, we examined the effect of citalopram on fictive locomotion generated in axial segments of isolated spinal cords in salamanders, a tetrapod where raphe 5-HT reticulospinal neurons and intraspinal 5-HT neurons are present as in other vertebrates. Using electrophysiological recordings of ventral roots, we show that fictive locomotion generated by bath-applied glutamatergic agonists is destabilized by citalopram. Citalopram-induced destabilization was prevented by a 5-HT1A receptor antagonist, whereas a 5-HT1A receptor agonist destabilized fictive locomotion. Using immunofluorescence experiments, we found 5-HT-positive fibers and varicosities in proximity with motoneurons and glutamatergic interneurons that are likely involved in rhythmogenesis. Our results show that increasing 5-HT release has a deleterious effect on axial locomotor activity through 5-HT1A receptors. This is consistent with studies in limb networks of turtle and mouse, suggesting that this part of the complex 5-HT modulation of spinal locomotor circuits is common to limb and axial networks in limbed vertebrates.NEW & NOTEWORTHY Little is known about the modulation exerted by endogenous serotonin on axial locomotor circuits in tetrapods. Using axial ventral root recordings in salamanders, we found that a serotonin reuptake blocker destabilized fictive locomotor activity through 5-HT1A receptors. Our anatomical results suggest that serotonin is released on motoneurons and glutamatergic interneurons possibly involved in rhythmogenesis. Our study suggests that common serotoninergic mechanisms modulate axial motor circuits in amphibians and limb motor circuits in reptiles and mammals.
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Affiliation(s)
- Aurélie Flaive
- Département de Pharmacologie-Physiologie, Faculté de médecine et des sciences de la santé, Université de Sherbrooke, Sherbrooke, Quebec, Canada
| | - Jean-Marie Cabelguen
- Neurocentre Magendie, INSERM U 862, Université de Bordeaux, Bordeaux Cedex, France
| | - Dimitri Ryczko
- Département de Pharmacologie-Physiologie, Faculté de médecine et des sciences de la santé, Université de Sherbrooke, Sherbrooke, Quebec, Canada.,Centre de recherche du Centre Hospitalier Universitaire de Sherbrooke, Sherbrooke, Quebec, Canada.,Institut de Pharmacologie de Sherbrooke, Sherbrooke, Quebec, Canada.,Centre des neurosciences de Sherbrooke, Sherbrooke, Quebec, Canada
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Majczyński H, Cabaj AM, Jordan LM, Sławińska U. Contribution of 5-HT 2 Receptors to the Control of the Spinal Locomotor System in Intact Rats. Front Neural Circuits 2020; 14:14. [PMID: 32425760 PMCID: PMC7212388 DOI: 10.3389/fncir.2020.00014] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2019] [Accepted: 03/24/2020] [Indexed: 11/13/2022] Open
Abstract
Applying serotonergic (5-HT) agonists or grafting of fetal serotonergic cells into the spinal cord improves locomotion after spinal cord injury. Little is known about the role of 5-HT receptors in the control of voluntary locomotion, so we administered inverse agonists of 5-HT2 (Cyproheptadine; Cypr), 5-HT2A neutral antagonist (Volinanserin; Volin), 5-HT2C neutral antagonist (SB 242084), and 5-HT2B/2C inverse agonist (SB 206553) receptors intrathecally in intact rats and monitored their effects on unrestrained locomotion. An intrathecal cannula was introduced at the low thoracic level and pushed caudally until the tip reached the L2/L3 or L5/L6 spinal segments. Locomotor performance was evaluated using EMG activity of hindlimb muscles during locomotion on a 2 m long runway. Motoneuron excitability was estimated using EMG recordings during dorsi- and plantar flexion at the ankle. Locomotion was dramatically impaired after the blockage of 5-HT2A receptors. The effect of Cypr was more pronounced than that of Volin since in the L5/L6 rats Cypr (but not Volin) induced significant alteration of the strength of interlimb coordination followed by total paralysis. These agents significantly decreased locomotor EMG amplitude and abolished or substantially decreased stretch reflexes. Blocking 5-HT2B/2C receptors had no effect either on locomotion or reflexes. We suggest that in intact rats serotonin controls timing and amplitude of muscle activity by acting on 5-HT2A receptors on both CPG interneurons and motoneurons, while 5-HT2B/2C receptors are not involved in control of the locomotor pattern in lumbar spinal cord.
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Affiliation(s)
- Henryk Majczyński
- Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland
| | - Anna M Cabaj
- Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland
| | - Larry M Jordan
- Department of Physiology and Pathophysiology, University of Manitoba, Winnipeg, MB, Canada
| | - Urszula Sławińska
- Nencki Institute of Experimental Biology, Polish Academy of Sciences, Warsaw, Poland
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Bacqué-Cazenave J, Bharatiya R, Barrière G, Delbecque JP, Bouguiyoud N, Di Giovanni G, Cattaert D, De Deurwaerdère P. Serotonin in Animal Cognition and Behavior. Int J Mol Sci 2020; 21:ijms21051649. [PMID: 32121267 PMCID: PMC7084567 DOI: 10.3390/ijms21051649] [Citation(s) in RCA: 160] [Impact Index Per Article: 40.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2020] [Revised: 02/25/2020] [Accepted: 02/25/2020] [Indexed: 12/20/2022] Open
Abstract
Serotonin (5-hydroxytryptamine, 5-HT) is acknowledged as a major neuromodulator of nervous systems in both invertebrates and vertebrates. It has been proposed for several decades that it impacts animal cognition and behavior. In spite of a completely distinct organization of the 5-HT systems across the animal kingdom, several lines of evidence suggest that the influences of 5-HT on behavior and cognition are evolutionary conserved. In this review, we have selected some behaviors classically evoked when addressing the roles of 5-HT on nervous system functions. In particular, we focus on the motor activity, arousal, sleep and circadian rhythm, feeding, social interactions and aggressiveness, anxiety, mood, learning and memory, or impulsive/compulsive dimension and behavioral flexibility. The roles of 5-HT, illustrated in both invertebrates and vertebrates, show that it is more able to potentiate or mitigate the neuronal responses necessary for the fine-tuning of most behaviors, rather than to trigger or halt a specific behavior. 5-HT is, therefore, the prototypical neuromodulator fundamentally involved in the adaptation of all organisms across the animal kingdom.
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Affiliation(s)
- Julien Bacqué-Cazenave
- INCIA, UMR5287, Centre National de la Recherche Scientifique, 33076 Bordeaux, France; (J.B.-C.); (R.B.); (G.B.); (J.-P.D.); (N.B.)
| | - Rahul Bharatiya
- INCIA, UMR5287, Centre National de la Recherche Scientifique, 33076 Bordeaux, France; (J.B.-C.); (R.B.); (G.B.); (J.-P.D.); (N.B.)
- Department of Biomedical Sciences, Section of Neuroscience and Clinical Pharmacology, University of Cagliari, 09100 Cagliari, Italy
| | - Grégory Barrière
- INCIA, UMR5287, Centre National de la Recherche Scientifique, 33076 Bordeaux, France; (J.B.-C.); (R.B.); (G.B.); (J.-P.D.); (N.B.)
| | - Jean-Paul Delbecque
- INCIA, UMR5287, Centre National de la Recherche Scientifique, 33076 Bordeaux, France; (J.B.-C.); (R.B.); (G.B.); (J.-P.D.); (N.B.)
| | - Nouhaila Bouguiyoud
- INCIA, UMR5287, Centre National de la Recherche Scientifique, 33076 Bordeaux, France; (J.B.-C.); (R.B.); (G.B.); (J.-P.D.); (N.B.)
| | - Giuseppe Di Giovanni
- Laboratory of Neurophysiology, Department of Physiology and Biochemistry, Faculty of Medicine and Surgery, University of Malta, MSD 2080 Msida, Malta;
- School of Biosciences, Neuroscience Division, Cardiff University, Cardiff CF24 4HQ, UK
| | - Daniel Cattaert
- INCIA, UMR5287, Centre National de la Recherche Scientifique, 33076 Bordeaux, France; (J.B.-C.); (R.B.); (G.B.); (J.-P.D.); (N.B.)
- Correspondence: (D.C.); (P.D.D.)
| | - Philippe De Deurwaerdère
- INCIA, UMR5287, Centre National de la Recherche Scientifique, 33076 Bordeaux, France; (J.B.-C.); (R.B.); (G.B.); (J.-P.D.); (N.B.)
- Correspondence: (D.C.); (P.D.D.)
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Opris I, Dai X, Johnson DMG, Sanchez FJ, Villamil LM, Xie S, Lee-Hauser CR, Chang S, Jordan LM, Noga BR. Activation of Brainstem Neurons During Mesencephalic Locomotor Region-Evoked Locomotion in the Cat. Front Syst Neurosci 2019; 13:69. [PMID: 31798423 PMCID: PMC6868058 DOI: 10.3389/fnsys.2019.00069] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Accepted: 10/31/2019] [Indexed: 12/26/2022] Open
Abstract
The distribution of locomotor-activated neurons in the brainstem of the cat was studied by c-Fos immunohistochemistry in combination with antibody-based cellular phenotyping following electrical stimulation of the mesencephalic locomotor region (MLR) – the anatomical constituents of which remain debated today, primarily between the cuneiform (CnF) and the pedunculopontine tegmental nuclei (PPT). Effective MLR sites were co-extensive with the CnF nucleus. Animals subject to the locomotor task showed abundant Fos labeling in the CnF, parabrachial nuclei of the subcuneiform region, periaqueductal gray, locus ceruleus (LC)/subceruleus (SubC), Kölliker–Fuse, magnocellular and lateral tegmental fields, raphe, and the parapyramidal region. Labeled neurons were more abundant on the side of stimulation. In some animals, Fos-labeled cells were also observed in the ventral tegmental area, medial and intermediate vestibular nuclei, dorsal motor nucleus of the vagus, n. tractus solitarii, and retrofacial nucleus in the ventrolateral medulla. Many neurons in the reticular formation were innervated by serotonergic fibers. Numerous locomotor-activated neurons in the parabrachial nuclei and LC/SubC/Kölliker–Fuse were noradrenergic. Few cholinergic neurons within the PPT stained for Fos. In the medulla, serotonergic neurons within the parapyramidal region and the nucleus raphe magnus were positive for Fos. Control animals, not subject to locomotion, showed few Fos-labeled neurons in these areas. The current study provides positive evidence for a role for the CnF in the initiation of locomotion while providing little evidence for the participation of the PPT. The results also show that MLR-evoked locomotion involves the parallel activation of reticular and monoaminergic neurons in the pons/medulla, and provides the anatomical and functional basis for spinal monoamine release during evoked locomotion. Lastly, the results indicate that vestibular, cardiovascular, and respiratory centers are centrally activated during MLR-evoked locomotion. Altogether, the results show a complex pattern of neuromodulatory influences of brainstem neurons by electrical activation of the MLR.
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Affiliation(s)
- Ioan Opris
- The Miami Project to Cure Paralysis, Department of Neurological Surgery, University of Miami Miller School of Medicine, Miami, FL, United States
| | - Xiaohong Dai
- Department of Physiology, Spinal Cord Research Centre, University of Manitoba, Winnipeg, MB, Canada
| | - Dawn M G Johnson
- The Miami Project to Cure Paralysis, Department of Neurological Surgery, University of Miami Miller School of Medicine, Miami, FL, United States
| | - Francisco J Sanchez
- The Miami Project to Cure Paralysis, Department of Neurological Surgery, University of Miami Miller School of Medicine, Miami, FL, United States
| | - Luz M Villamil
- The Miami Project to Cure Paralysis, Department of Neurological Surgery, University of Miami Miller School of Medicine, Miami, FL, United States
| | - Songtao Xie
- The Miami Project to Cure Paralysis, Department of Neurological Surgery, University of Miami Miller School of Medicine, Miami, FL, United States
| | - Cecelia R Lee-Hauser
- The Miami Project to Cure Paralysis, Department of Neurological Surgery, University of Miami Miller School of Medicine, Miami, FL, United States
| | - Stephano Chang
- The Miami Project to Cure Paralysis, Department of Neurological Surgery, University of Miami Miller School of Medicine, Miami, FL, United States
| | - Larry M Jordan
- Department of Physiology, Spinal Cord Research Centre, University of Manitoba, Winnipeg, MB, Canada
| | - Brian R Noga
- The Miami Project to Cure Paralysis, Department of Neurological Surgery, University of Miami Miller School of Medicine, Miami, FL, United States
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Bacqué-Cazenave J, Fossat P, Issa FA, Edwards DH, Delbecque JP, Cattaert D. Duality of 5-HT Effects on Crayfish Motoneurons. Front Physiol 2019; 10:1280. [PMID: 31695619 PMCID: PMC6817598 DOI: 10.3389/fphys.2019.01280] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2019] [Accepted: 09/24/2019] [Indexed: 11/13/2022] Open
Abstract
Serotonin (5-HT) is a major neuromodulator acting on the nervous system. Its various effects have been studied in vertebrates, as well as in arthropods, from the cellular and subcellular compartments up to the behavioral level, which includes the control of mood, aggression, locomotion, and anxiety. The diversity of responses of neurons to 5-HT has been related to its mode of application, the diversity of 5-HT-receptors, and the animals’ social status history. In the locomotor network of socially isolated crayfish, the duality of 5-HT-evoked responses (excitatory/inhibitory) on motoneurons (MNs), sensorimotor pathways, and their consequences on motor network activity has largely been studied. The aim of the present report is to examine if this duality of exogenous 5-HT-evoked responses in the crayfish locomotor network can be reproduced by direct activation of 5-HT neurons in the case of socially isolated animals. Our previous studies have focused on the mechanisms supporting these opposite effects on MNs, pointing out spatial segregation of 5-HT receptors responsible either for positive or negative responses. Here, we report new findings indicating that excitatory and inhibitory effects can be achieved simultaneously in different leg MNs by the activation of a single 5-HT cell in the first abdominal ganglion.
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Affiliation(s)
- Julien Bacqué-Cazenave
- University of Bordeaux, CNRS, Institut de Neurosciences Cognitives et Intégratives d'Aquitaine (INCIA) UMR5287, Bordeaux, France
| | - Pascal Fossat
- University of Bordeaux, CNRS, Institut de Neurosciences Cognitives et Intégratives d'Aquitaine (INCIA) UMR5287, Bordeaux, France
| | - Fadi A Issa
- Neuroscience Institute, College of Arts and Sciences, Georgia State University, Atlanta, GA, United States
| | - Donald H Edwards
- Neuroscience Institute, College of Arts and Sciences, Georgia State University, Atlanta, GA, United States
| | - Jean Paul Delbecque
- University of Bordeaux, CNRS, Institut de Neurosciences Cognitives et Intégratives d'Aquitaine (INCIA) UMR5287, Bordeaux, France
| | - Daniel Cattaert
- University of Bordeaux, CNRS, Institut de Neurosciences Cognitives et Intégratives d'Aquitaine (INCIA) UMR5287, Bordeaux, France
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Serotonergic modulation of sacral dorsal root stimulation-induced locomotor output in newborn rat. Neuropharmacology 2019; 170:107815. [PMID: 31634501 DOI: 10.1016/j.neuropharm.2019.107815] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2019] [Revised: 10/14/2019] [Accepted: 10/15/2019] [Indexed: 12/22/2022]
Abstract
Descending neuromodulators from the brainstem play a major role in the development and regulation of spinal sensorimotor functions. Here, the contribution of serotonergic signaling in the lumbar spinal cord was investigated in the context of the generation of locomotor activity. Experiments were performed on in vitro spinal cord preparations from newborn rats (0-5 days). Rhythmic locomotor episodes (fictive locomotion) triggered by tonic electrical stimulations (2Hz, 30s) of a single sacral dorsal root were recorded from bilateral flexor-dominated (L2) and extensor-dominated (L5) ventral roots. We found that the activity pattern induced by sacral stimulation evolves over the 5 post-natal (P) day period. Although alternating rhythmic flexor-like motor bursts were expressed at all ages, the locomotor pattern of extensor-like bursting was progressively lost from P1 to P5. At later stages, serotonin (5-HT) and quipazine (5-HT2A receptor agonist) at concentrations sub-threshold for direct locomotor network activation promoted sacral stimulation-induced fictive locomotion. The 5-HT2A receptor antagonist ketanserin could reverse the agonist's action but was ineffective when fictive locomotion was already expressed in the absence of 5-HT (mainly before P2). Although inhibiting 5-HT7 receptors with SB266990 did not affect locomotor pattern organization, activating 5-HT1A receptors with 8-OH-DPAT specifically deteriorated extensor phase motor burst activity. We conclude that during the first 5 post-natal days in rat, serotonergic signaling in the lumbar cord becomes increasingly critical for the expression of fictive locomotion. Our findings therefore further underline the importance of both descending serotonergic and sensory afferent pathways in shaping locomotor activity during postnatal development. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.
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Balanced cholinergic modulation of spinal locomotor circuits via M2 and M3 muscarinic receptors. Sci Rep 2019; 9:14051. [PMID: 31575899 PMCID: PMC6773880 DOI: 10.1038/s41598-019-50452-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2019] [Accepted: 09/12/2019] [Indexed: 01/05/2023] Open
Abstract
Neuromodulation ensures that neural circuits produce output that is flexible whilst remaining within an optimal operational range. The neuromodulator acetylcholine is released during locomotion to regulate spinal motor circuits. However, the range of receptors and downstream mechanisms by which acetylcholine acts have yet to be fully elucidated. We therefore investigated metabotropic acetylcholine receptor-mediated modulation by using isolated spinal cord preparations from neonatal mice in which locomotor-related output can be induced pharmacologically. We report that M2 receptor blockade decreases the frequency and amplitude of locomotor-related activity, whilst reducing its variability. In contrast, M3 receptor blockade destabilizes locomotor-related bursting. Motoneuron recordings from spinal cord slices revealed that activation of M2 receptors induces an outward current, decreases rheobase, reduces the medium afterhyperpolarization, shortens spike duration and decreases synaptic inputs. In contrast, M3 receptor activation elicits an inward current, increases rheobase, extends action potential duration and increases synaptic inputs. Analysis of miniature postsynaptic currents support that M2 and M3 receptors modulate synaptic transmission via different mechanisms. In summary, we demonstrate that M2 and M3 receptors have opposing modulatory actions on locomotor circuit output, likely reflecting contrasting cellular mechanisms of action. Thus, intraspinal cholinergic systems mediate balanced, multimodal control of spinal motor output.
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Three-week treadmill training changes the electrophysiological properties of spinal interneurons in the mice. Exp Brain Res 2019; 237:2925-2938. [PMID: 31494682 DOI: 10.1007/s00221-019-05647-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2019] [Accepted: 09/03/2019] [Indexed: 12/20/2022]
Abstract
It was shown in previous studies that endurance training enhanced excitability of rat spinal motoneurons. However, the influence of the training on the spinal interneurons remains unclear. In this study, we investigated the training effects on spinal interneurons in dorsal and ventromedial area in mice (P42-P50). The electrophysiological properties of the interneurons were recorded from spinal cord slices (T13-L6) by whole-cell patch-clamp recording. The interneurons could be classified into three types based on their response to step currents: single spike (type 1), phasic firing (type 2), and tonic firing (type 3) in both control and trained mice. Interneurons collected from control mice possessed rheobase of 11.3 ± 6.0 pA and voltage threshold (Vth) of - 37.3 ± 4.7 mV. Treadmill training reduced the rheobase by 4.8 ± 1.5 pA and Vth by 3.1 ± 1.2 mV (P < 0.05). Furthermore, the training effects were dependent on the distribution and types of the interneurons. Treadmill training hyperpolarized Vth and decreased rheobase in ventromedial interneurons, while the significant change was observed only in the action potation height of the interneurons in dorsal horn. Treadmill training also hyperpolarized Vth and increased input resistance in type 3 interneurons, but none of these changes was shown in type 1 and 2 interneurons. Bath application of 5-HT (10-20 μM) increased the neuronal excitability in both control and trained mice. Serotonin had similar effect on membrane properties of the interneurons collected from both groups. This study suggested that treadmill training increased excitability of spinal interneurons of the mice and thus would make the spinal motor system easier to generate locomotion.
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Steuer I, Guertin PA. Central pattern generators in the brainstem and spinal cord: an overview of basic principles, similarities and differences. Rev Neurosci 2019; 30:107-164. [PMID: 30543520 DOI: 10.1515/revneuro-2017-0102] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2017] [Accepted: 03/30/2018] [Indexed: 12/11/2022]
Abstract
Central pattern generators (CPGs) are generally defined as networks of neurons capable of enabling the production of central commands, specifically controlling stereotyped, rhythmic motor behaviors. Several CPGs localized in brainstem and spinal cord areas have been shown to underlie the expression of complex behaviors such as deglutition, mastication, respiration, defecation, micturition, ejaculation, and locomotion. Their pivotal roles have clearly been demonstrated although their organization and cellular properties remain incompletely characterized. In recent years, insightful findings about CPGs have been made mainly because (1) several complementary animal models were developed; (2) these models enabled a wide variety of techniques to be used and, hence, a plethora of characteristics to be discovered; and (3) organizations, functions, and cell properties across all models and species studied thus far were generally found to be well-preserved phylogenetically. This article aims at providing an overview for non-experts of the most important findings made on CPGs in in vivo animal models, in vitro preparations from invertebrate and vertebrate species as well as in primates. Data about CPG functions, adaptation, organization, and cellular properties will be summarized with a special attention paid to the network for locomotion given its advanced level of characterization compared with some of the other CPGs. Similarities and differences between these networks will also be highlighted.
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Affiliation(s)
- Inge Steuer
- Neuroscience Unit, Laval University Medical Center (CHUL - CHU de Québec), 2705 Laurier Blvd, Quebec City, Quebec G1V 4G2, Canada
| | - Pierre A Guertin
- Neuroscience Unit, Laval University Medical Center (CHUL - CHU de Québec), 2705 Laurier Blvd, Quebec City, Quebec G1V 4G2, Canada
- Faculty of Medicine, Department of Psychiatry and Neurosciences, Laval University, Quebec City, Quebec G1V 0A6, Canada
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Rancic V, Haque F, Ballanyi K, Gosgnach S. Using an upright preparation to identify and characterize locomotor related neurons across the transverse plane of the neonatal mouse spinal cord. J Neurosci Methods 2019; 323:90-97. [PMID: 31132372 DOI: 10.1016/j.jneumeth.2019.05.010] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Revised: 05/20/2019] [Accepted: 05/22/2019] [Indexed: 11/19/2022]
Abstract
BACKGROUND The basic rhythmicity underlying stepping in mammals is generated by a neural network, situated in the spinal cord, known as the locomotor central pattern generator (CPG). While a molecular approach has provided information regarding neuronal populations that participate in locomotor activity and their specific function, the distributed nature of the locomotor CPG has made it difficult to identify and characterize the specific neurons belonging to each population that are rhythmically-active during stepping. NEW METHOD We describe a preparation in which we isolate the spinal cord from a neonatal mouse, section it at a lumbar segment, situate it in an upright orientation under the objective lens of a 2- photon microscope, and evoke fictive locomotion. RESULTS This preparation allows us to image rhythmic Ca2+ oscillations in spinal neurons, and visually identify those that are involved in fictive locomotor activity. We can then characterize unique features of these neurons. COMPARISON WITH EXISTING METHODS This builds on existing fictive locomotor preparations and is the first which allows for the visual identification of locomotor related neurons spanning the transverse plane of the spinal cord, facilitating their electrophysiological and anatomical characterization CONCLUSIONS: This approach promises to provide new information regarding the distribution of the locomotor CPG in the transverse plane, the characteristics of its component interneurons, as well as the cellular mechanisms and network properties which underlie rhythm generation. By altering the location of Ca2+ indicator application it can also be used to identify and characterize neurons involved in other facets of sensorimotor processing.
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Affiliation(s)
- Vladimir Rancic
- Department of Physiology, University of Alberta, 3-020D Katz Building, Edmonton, Alberta, T6G 2E1, Canada
| | - Farhia Haque
- Neuroscience and Mental Health Institute, University of Alberta, 3-020D Katz Building, Edmonton, Alberta, T6G 2E1, Canada
| | - Klaus Ballanyi
- Department of Physiology, University of Alberta, 3-020D Katz Building, Edmonton, Alberta, T6G 2E1, Canada; Neuroscience and Mental Health Institute, University of Alberta, 3-020D Katz Building, Edmonton, Alberta, T6G 2E1, Canada
| | - Simon Gosgnach
- Department of Physiology, University of Alberta, 3-020D Katz Building, Edmonton, Alberta, T6G 2E1, Canada; Neuroscience and Mental Health Institute, University of Alberta, 3-020D Katz Building, Edmonton, Alberta, T6G 2E1, Canada.
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Perrin FE, Noristani HN. Serotonergic mechanisms in spinal cord injury. Exp Neurol 2019; 318:174-191. [PMID: 31085200 DOI: 10.1016/j.expneurol.2019.05.007] [Citation(s) in RCA: 47] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2019] [Revised: 05/07/2019] [Accepted: 05/08/2019] [Indexed: 12/12/2022]
Abstract
Spinal cord injury (SCI) is a tragic event causing irreversible losses of sensory, motor, and autonomic functions, that may also be associated with chronic neuropathic pain. Serotonin (5-HT) neurotransmission in the spinal cord is critical for modulating sensory, motor, and autonomic functions. Following SCI, 5-HT axons caudal to the lesion site degenerate, and the degree of axonal degeneration positively correlates with lesion severity. Rostral to the lesion, 5-HT axons sprout, irrespective of the severity of the injury. Unlike callosal fibers and cholinergic projections, 5-HT axons are more resistant to an inhibitory milieu and undergo active sprouting and regeneration after central nervous system (CNS) traumatism. Numerous studies suggest that a chronic increase in serotonergic neurotransmission promotes 5-HT axon sprouting in the intact CNS. Moreover, recent studies in invertebrates suggest that 5-HT has a pro-regenerative role in injured axons. Here we present a brief description of 5-HT discovery, 5-HT innervation of the CNS, and physiological functions of 5-HT in the spinal cord, including its role in controlling bladder function. We then present a comprehensive overview of changes in serotonergic axons after CNS damage, and discuss their plasticity upon altered 5-HT neurotransmitter levels. Subsequently, we provide an in-depth review of therapeutic approaches targeting 5-HT neurotransmission, as well as other pre-clinical strategies to promote an increase in re-growth of 5-HT axons, and their functional consequences in SCI animal models. Finally, we highlight recent findings signifying the direct role of 5-HT in axon regeneration and suggest strategies to further promote robust long-distance re-growth of 5-HT axons across the lesion site and eventually achieve functional recovery following SCI.
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Affiliation(s)
- Florence Evelyne Perrin
- University of Montpellier, Montpellier, F-34095 France; INSERM, U1198, Montpellier, F-34095 France; EPHE, Paris, F-75014 France
| | - Harun Najib Noristani
- Shriners Hospitals Pediatric Research Center, Center for Neural Repair, Lewis Katz School of Medicine, Temple University, Philadelphia, PA 19140, USA; Department of Anatomy and Cell Biology, Lewis Katz School of Medicine, Temple University, Philadelphia, PA 19140, USA.
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Kondratskaya E, Ievglevskyi O, Züchner M, Samara A, Glover JC, Boulland JL. Locomotor central pattern generator excitability states and serotonin sensitivity after spontaneous recovery from a neonatal lumbar spinal cord injury. Brain Res 2019; 1708:10-19. [PMID: 30521786 DOI: 10.1016/j.brainres.2018.12.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2018] [Revised: 10/24/2018] [Accepted: 12/03/2018] [Indexed: 11/30/2022]
Abstract
The spinal locomotor central pattern generator (CPG) in neonatal mice exhibits diverse output patterns, ranging from sub-rhythmic to multi-rhythmic to fictive locomotion, depending on its general level of excitation and neuromodulatory status. We have recently reported that the locomotor CPG in neonatal mice rapidly recovers the ability to produce neurochemically induced fictive locomotion following an upper lumbar spinal cord compression injury. Here we address the question of recovery of multi-rhythmic activity and the serotonin-sensitivity of the CPG. In isolated spinal cords from control and 3 days post-injury mice, application of dopamine and NMDA elicited multi-rhythmic activity with slow and fast components. The slow component comprised 10-20 s episodes of activity that were synchronous in ipsilateral or all lumbar ventral roots, and the fast components involved bursts within these episodes that displayed coordinated patterns of alternation between ipsilateral roots. Rhythm strength was the same in control and injured spinal cords. However, power spectral analysis of signal within episodes showed a reduced peak frequency after recovery. In control spinal cords, serotonin triggered fictive locomotion only when applied at high concentration (30 µM, constant NMDA). By contrast, in about 50% of injured preparations fictive locomotion was evoked by 2-3 times lower serotonin concentrations (10-15 µM). This increased serotonin sensitivity was correlated with post-injury changes in the expression of specific serotonin receptor transcripts, but not of dopamine receptor transcripts.
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Affiliation(s)
- Elena Kondratskaya
- Norwegian Center for Stem Cell Research, Oslo University Hospital, Norway; Laboratory of Neural Development and Optical Recording (NDEVOR), Division of Physiology, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Norway
| | - Oleksandr Ievglevskyi
- Laboratory of Neural Development and Optical Recording (NDEVOR), Division of Physiology, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Norway
| | - Mark Züchner
- Norwegian Center for Stem Cell Research, Oslo University Hospital, Norway; Department of Neurosurgery, Oslo University Hospital, Norway; Laboratory of Neural Development and Optical Recording (NDEVOR), Division of Physiology, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Norway
| | - Athina Samara
- Norwegian Center for Stem Cell Research, Oslo University Hospital, Norway; Laboratory of Neural Development and Optical Recording (NDEVOR), Division of Physiology, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Norway
| | - Joel C Glover
- Norwegian Center for Stem Cell Research, Oslo University Hospital, Norway; Laboratory of Neural Development and Optical Recording (NDEVOR), Division of Physiology, Department of Molecular Medicine, Institute of Basic Medical Sciences, University of Oslo, Norway
| | - Jean-Luc Boulland
- Norwegian Center for Stem Cell Research, Oslo University Hospital, Norway.
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Petrović A, Kaur J, Tomljanović I, Nistri A, Mladinic M. Pharmacological induction of Heat Shock Protein 70 by celastrol protects motoneurons from excitotoxicity in rat spinal cord in vitro. Eur J Neurosci 2018; 49:215-231. [PMID: 30362615 DOI: 10.1111/ejn.14218] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2018] [Revised: 09/14/2018] [Accepted: 10/15/2018] [Indexed: 12/29/2022]
Abstract
The secondary phase of spinal cord injury arising after the primary lesion largely extends the damage severity with delayed negative consequences for sensory-motor pathways. It is, therefore, important to find out if enhancing intrinsic mechanisms of neuroprotection can spare motoneurons that are very vulnerable cells. This issue was investigated with an in vitro model of rat spinal cord excitotoxicity monitored for up to 24 hr after the primary injury evoked by kainate. This study sought to pharmacologically boost the expression of heat shock proteins (HSP) to protect spinal motoneurons using celastrol to investigate if the rat spinal cord can upregulate HSP as neuroprotective mechanism. Despite its narrow range of drug safety in vitro, celastrol was not toxic to the rat spinal cord at 0.75 μM concentration and enhanced the expression of HSP70 by motoneurons. When celastrol was applied either before or after kainate, the number of dead motoneurons was significantly decreased and the nuclear localization of the cell death biomarker AIF strongly inhibited. Nevertheless, electrophysiological recording showed that protection of lumbar motor networks by celastrol was rather limited as reflex activity was impaired and fictive locomotion largely depressed, suggesting that functional deficit persisted, though the networks could express slow rhythmic oscillations. While our data do not exclude further recovery at later times beyond the experimental observations, the present results indicate that the upregulated expression of HSP in the aftermath of acute injury may be an interesting avenue for early protection of spinal motoneurons.
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Affiliation(s)
- Antonela Petrović
- Department of Biotechnology, University of Rijeka, Rijeka, Croatia.,Neuroscience Department, International School for Advanced Studies (SISSA), Trieste, Italy
| | - Jaspreet Kaur
- Neuroscience Department, International School for Advanced Studies (SISSA), Trieste, Italy
| | | | - Andrea Nistri
- Neuroscience Department, International School for Advanced Studies (SISSA), Trieste, Italy
| | - Miranda Mladinic
- Department of Biotechnology, University of Rijeka, Rijeka, Croatia
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V2a interneuron diversity tailors spinal circuit organization to control the vigor of locomotor movements. Nat Commun 2018; 9:3370. [PMID: 30135498 PMCID: PMC6105610 DOI: 10.1038/s41467-018-05827-9] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2018] [Accepted: 07/31/2018] [Indexed: 01/12/2023] Open
Abstract
Locomotion is a complex motor task generated by spinal circuits driving motoneurons in a precise sequence to control the timing and vigor of movements, but the underlying circuit logic remains to be understood. Here we reveal, in adult zebrafish, how the diversity and selective distribution of two V2a interneuron types within the locomotor network transform commands into an appropriate, task-dependent circuit organization. Bursting-type V2a interneurons with unidirectional axons predominantly target distal dendrites of slow motoneurons to provide potent, non-linear excitation involving NMDA-dependent potentiation. A second type, non-bursting V2a interneurons with bidirectional axons, predominantly target somata of fast motoneurons, providing weaker, non-potentiating excitation. Together, this ensures the rapid, first-order recruitment of the slow circuit, while reserving the fast circuit for highly salient stimuli involving synchronous inputs. Our results thus identify how interneuron diversity is captured and transformed into a parsimonious task-specific circuit design controlling the vigor of locomotion.
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48
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Chen B, Li Y, Yu B, Zhang Z, Brommer B, Williams PR, Liu Y, Hegarty SV, Zhou S, Zhu J, Guo H, Lu Y, Zhang Y, Gu X, He Z. Reactivation of Dormant Relay Pathways in Injured Spinal Cord by KCC2 Manipulations. Cell 2018; 174:521-535.e13. [PMID: 30033363 PMCID: PMC6063786 DOI: 10.1016/j.cell.2018.06.005] [Citation(s) in RCA: 106] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2017] [Revised: 03/24/2018] [Accepted: 05/31/2018] [Indexed: 12/22/2022]
Abstract
Many human spinal cord injuries are anatomically incomplete but exhibit complete paralysis. It is unknown why spared axons fail to mediate functional recovery in these cases. To investigate this, we undertook a small-molecule screen in mice with staggered bilateral hemisections in which the lumbar spinal cord is deprived of all direct brain-derived innervation, but dormant relay circuits remain. We discovered that a KCC2 agonist restored stepping ability, which could be mimicked by selective expression of KCC2, or hyperpolarizing DREADDs, in the inhibitory interneurons between and around the staggered spinal lesions. Mechanistically, these treatments transformed this injury-induced dysfunctional spinal circuit to a functional state, facilitating the relay of brain-derived commands toward the lumbar spinal cord. Thus, our results identify spinal inhibitory interneurons as a roadblock limiting the integration of descending inputs into relay circuits after injury and suggest KCC2 agonists as promising treatments for promoting functional recovery after spinal cord injury.
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Affiliation(s)
- Bo Chen
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, and Department of Neurology, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
| | - Yi Li
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, and Department of Neurology, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
| | - Bin Yu
- Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, Co-innovation Center of Neuroregeneration, Nantong University, Nantong, 226001 Jiangsu, China
| | - Zicong Zhang
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, and Department of Neurology, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
| | - Benedikt Brommer
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, and Department of Neurology, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
| | - Philip Raymond Williams
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, and Department of Neurology, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
| | - Yuanyuan Liu
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, and Department of Neurology, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
| | - Shane Vincent Hegarty
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, and Department of Neurology, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
| | - Songlin Zhou
- Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, Co-innovation Center of Neuroregeneration, Nantong University, Nantong, 226001 Jiangsu, China
| | - Junjie Zhu
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, and Department of Neurology, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
| | - Hong Guo
- Department of Neurosurgery, Brigham and Women's Hospital, 60 Fenwood Road., BTM 4th Floor, Boston, MA 02115, USA
| | - Yi Lu
- Department of Neurosurgery, Brigham and Women's Hospital, 60 Fenwood Road., BTM 4th Floor, Boston, MA 02115, USA
| | - Yiming Zhang
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, and Department of Neurology, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA
| | - Xiaosong Gu
- Key Laboratory of Neuroregeneration of Jiangsu and Ministry of Education, Co-innovation Center of Neuroregeneration, Nantong University, Nantong, 226001 Jiangsu, China.
| | - Zhigang He
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, and Department of Neurology, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115, USA.
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49
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Brainstem Steering of Locomotor Activity in the Newborn Rat. J Neurosci 2018; 38:7725-7740. [PMID: 30037828 DOI: 10.1523/jneurosci.1074-18.2018] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2018] [Revised: 07/17/2018] [Accepted: 07/18/2018] [Indexed: 11/21/2022] Open
Abstract
Control of locomotion relies on motor loops conveying modulatory signals between brainstem and spinal motor circuits. We investigated the steering control of the brainstem reticular formation over the spinal locomotor networks using isolated brainstem-spinal cord preparations of male and female neonatal rats. First, we performed patch-clamp recordings of identified reticulospinal cells during episodes of fictive locomotion. This revealed that a spinal ascending phasic modulation of reticulospinal cell activity is already present at birth. Half of the cells exhibited tonic firing during locomotion, while the other half emitted phasic discharges of action potentials phase locked to ongoing activity. We next showed that mimicking the phasic activity of reticulospinal neurons by applying patterned electrical stimulation bilaterally at the ventral caudal medulla level triggered fictive locomotion efficiently. Moreover, the brainstem stimuli-induced locomotor rhythm was entrained in a one-to-one coupling over a range of cycle periods (2-6 s). Additionally, we induced turning like motor outputs by either increasing or decreasing the relative duration of the stimulation trains on one side of the brainstem compared to the other. The ability of the patterned descending command to control the locomotor output depended on the functional integrity of ventral reticulospinal pathways and the involvement of local spinal central pattern generator circuitry. Altogether, this study provides a mechanism by which brainstem reticulospinal neurons relay steering and speed commands to the spinal locomotor networks.SIGNIFICANCE STATEMENT Locomotor function allows the survival of most animal species while sustaining the expression of fundamental behaviors. Locomotor activities adapt from moment to moment to behavioral and environmental changes. We show that the brainstem can control the spinal locomotor network outputs through phasic descending commands that alternate bilaterally. Manipulating the periodicity and/or the relative durations of the left and right descending commands at the brainstem level is efficient to set the locomotor speed and sustain directional changes.
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Sourioux M, Bertrand SS, Cazalets JR. Cholinergic-mediated coordination of rhythmic sympathetic and motor activities in the newborn rat spinal cord. PLoS Biol 2018; 16:e2005460. [PMID: 29985914 PMCID: PMC6053244 DOI: 10.1371/journal.pbio.2005460] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2018] [Revised: 07/19/2018] [Accepted: 06/22/2018] [Indexed: 02/07/2023] Open
Abstract
Here, we investigated intrinsic spinal cord mechanisms underlying the physiological requirement for autonomic and somatic motor system coupling. Using an in vitro spinal cord preparation from newborn rat, we demonstrate that the specific activation of muscarinic cholinergic receptors (mAchRs) (with oxotremorine) triggers a slow burst rhythm in thoracic spinal segments, thereby revealing a rhythmogenic capability in this cord region. Whereas axial motoneurons (MNs) were rhythmically activated during both locomotor activity and oxotremorine-induced bursting, intermediolateral sympathetic preganglionic neurons (IML SPNs) exhibited rhythmicity solely in the presence of oxotremorine. This somato-sympathetic synaptic drive shared by MNs and IML SPNs could both merge with and modulate the locomotor synaptic drive produced by the lumbar motor networks. This study thus sheds new light on the coupling between somatic and sympathetic systems and suggests that an intraspinal network that may be conditionally activated under propriospinal cholinergic control constitutes at least part of the synchronizing mechanism.
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Affiliation(s)
| | | | - Jean-René Cazalets
- Université de Bordeaux, CNRS UMR 5287, Bordeaux, France
- * E-mail: (JRC); (SSB)
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