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Zhuang R, Yan Z, Gao Y, Nurmamat A, Zhang S, Xiu M, Zhou Y, Pang Y, Li D, Zhao L, Liu X, Han Y. Evolutionary and functional analysis of metabotropic glutamate receptors in lampreys. FISH PHYSIOLOGY AND BIOCHEMISTRY 2024; 50:1861-1877. [PMID: 38951427 DOI: 10.1007/s10695-024-01374-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2024] [Accepted: 06/22/2024] [Indexed: 07/03/2024]
Abstract
The metabotropic glutamate receptor (mGluR, GRM) family is involved in multiple signaling pathways and regulates neurotransmitter release. However, the evolutionary history, distribution, and function of the mGluRs family in lampreys have not been determined. Therefore, we identified the mGluRs gene family in the genome of Lethenteron reissneri, which has been conserved throughout vertebrate evolution. We confirmed that Lr-GRM3, Lr-GRM5, and Lr-GRM7 encode three types of mGluRs in lamprey. Additionally, we investigated the distribution of Lr-GRM3 within this species by qPCR and Western blotting. Furthermore, we conducted RNA sequencing to investigate the molecular function of Lr-GRM3 in lamprey. Our gene expression profile revealed that, similar to that in jawed vertebrates, Lr-GRM3 participates in multiple signal transduction pathways and influences synaptic excitability in lampreys. Moreover, it also affects intestinal motility and the inflammatory response in lampreys. This study not only enhances the understanding of mGluRs' gene evolution but also highlights the conservation of GRM3's role in signal transduction while expanding our knowledge of its functions specifically within lampreys. In summary, our experimental findings provide valuable insights for studying both the evolution and functionality of the mGluRs family.
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Affiliation(s)
- Ruyu Zhuang
- College of Life Sciences, Liaoning Normal University, Dalian, 116081, China
- Lamprey Research Center, College of Life Sciences, Liaoning Normal University, Dalian, 116081, China
| | - Zihao Yan
- College of Life Sciences, Liaoning Normal University, Dalian, 116081, China
- Lamprey Research Center, College of Life Sciences, Liaoning Normal University, Dalian, 116081, China
| | - Yicheng Gao
- The First Clinical College of China Medical University, Shenyang, 110001, China
| | - Ayqeqan Nurmamat
- College of Life Sciences, Liaoning Normal University, Dalian, 116081, China
- Lamprey Research Center, College of Life Sciences, Liaoning Normal University, Dalian, 116081, China
| | - Shuyuan Zhang
- College of Life Sciences, Liaoning Normal University, Dalian, 116081, China
- Lamprey Research Center, College of Life Sciences, Liaoning Normal University, Dalian, 116081, China
| | - Min Xiu
- College of Life Sciences, Liaoning Normal University, Dalian, 116081, China
- Lamprey Research Center, College of Life Sciences, Liaoning Normal University, Dalian, 116081, China
| | - Yuesi Zhou
- College of Life Sciences, Liaoning Normal University, Dalian, 116081, China
- Lamprey Research Center, College of Life Sciences, Liaoning Normal University, Dalian, 116081, China
| | - Ya Pang
- College of Life Sciences, Liaoning Normal University, Dalian, 116081, China
- Lamprey Research Center, College of Life Sciences, Liaoning Normal University, Dalian, 116081, China
| | - Ding Li
- College of Life Sciences, Liaoning Normal University, Dalian, 116081, China
- Lamprey Research Center, College of Life Sciences, Liaoning Normal University, Dalian, 116081, China
| | - Liang Zhao
- College of Life Sciences, Liaoning Normal University, Dalian, 116081, China
- Lamprey Research Center, College of Life Sciences, Liaoning Normal University, Dalian, 116081, China
| | - Xin Liu
- College of Life Sciences, Liaoning Normal University, Dalian, 116081, China
- Lamprey Research Center, College of Life Sciences, Liaoning Normal University, Dalian, 116081, China
- Collaborative Innovation Center of Seafood Deep Processing, Dalian Polytechnic University, Dalian, 116034, China
| | - Yinglun Han
- College of Life Sciences, Liaoning Normal University, Dalian, 116081, China.
- Lamprey Research Center, College of Life Sciences, Liaoning Normal University, Dalian, 116081, China.
- Collaborative Innovation Center of Seafood Deep Processing, Dalian Polytechnic University, Dalian, 116034, China.
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2
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Wang H, Peng K, Curry RJ, Li D, Wang Y, Wang X, Lu Y. Group I metabotropic glutamate receptor-triggered temporally patterned action potential-dependent spontaneous synaptic transmission in mouse MNTB neurons. Hear Res 2023; 435:108822. [PMID: 37285615 PMCID: PMC10330867 DOI: 10.1016/j.heares.2023.108822] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/02/2023] [Revised: 05/28/2023] [Accepted: 06/01/2023] [Indexed: 06/09/2023]
Abstract
Rhythmic action potentials (AP) are generated via intrinsic ionic mechanisms in pacemaking neurons, producing synaptic responses of regular inter-event intervals (IEIs) in their targets. In auditory processing, evoked temporally patterned activities are induced when neural responses timely lock to a certain phase of the sound stimuli. Spontaneous spike activity, however, is a stochastic process, rendering the prediction of the exact timing of the next event completely based on probability. Furthermore, neuromodulation mediated by metabotropic glutamate receptors (mGluRs) is not commonly associated with patterned neural activities. Here, we report an intriguing phenomenon. In a subpopulation of medial nucleus of the trapezoid body (MNTB) neurons recorded under whole-cell voltage-clamp mode in acute mouse brain slices, temporally patterned AP-dependent glycinergic sIPSCs and glutamatergic sEPSCs were elicited by activation of group I mGluRs with 3,5-DHPG (200 µM). Auto-correlation analyses revealed rhythmogenesis in these synaptic responses. Knockout of mGluR5 largely eliminated the effects of 3,5-DHPG. Cell-attached recordings showed temporally patterned spikes evoked by 3,5-DHPG in potential presynaptic VNTB cells for synaptic inhibition onto MNTB. The amplitudes of sEPSCs enhanced by 3,5-DHPG were larger than quantal size but smaller than spike-driven calyceal inputs, suggesting that non-calyceal inputs to MNTB might be responsible for the temporally patterned sEPSCs. Finally, immunocytochemical studies identified expression and localization of mGluR5 and mGluR1 in the VNTB-MNTB inhibitory pathway. Our results imply a potential central mechanism underlying the generation of patterned spontaneous spike activity in the brainstem sound localization circuit.
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Affiliation(s)
- Huimei Wang
- Hearing Research Group, Department of Anatomy and Neurobiology, College of Medicine, Northeast Ohio Medical University, Rootstown, OH, 44272, USA
| | - Kang Peng
- Hearing Research Group, Department of Anatomy and Neurobiology, College of Medicine, Northeast Ohio Medical University, Rootstown, OH, 44272, USA
| | - Rebecca J Curry
- Hearing Research Group, Department of Anatomy and Neurobiology, College of Medicine, Northeast Ohio Medical University, Rootstown, OH, 44272, USA; School of Biomedical Sciences, Kent State University, Kent, OH, 44240, USA
| | - Dong Li
- Hearing Research Group, Department of Anatomy and Neurobiology, College of Medicine, Northeast Ohio Medical University, Rootstown, OH, 44272, USA
| | - Yuan Wang
- Department of Biomedical Science, Program in Neuroscience, Florida State University College of Medicine, Tallahassee, FL, 32306, USA
| | - Xiaoyu Wang
- Department of Biomedical Science, Program in Neuroscience, Florida State University College of Medicine, Tallahassee, FL, 32306, USA
| | - Yong Lu
- Hearing Research Group, Department of Anatomy and Neurobiology, College of Medicine, Northeast Ohio Medical University, Rootstown, OH, 44272, USA; School of Biomedical Sciences, Kent State University, Kent, OH, 44240, USA.
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3
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Albasanz JL, Santana S, Guzman-Sanchez F, León D, Burgos JS, Martín M. 2-Methyl-6-(phenylethynyl)pyridine Hydrochloride Modulates Metabotropic Glutamate 5 Receptors Endogenously Expressed in Zebrafish Brain. ACS Chem Neurosci 2016; 7:1690-1697. [PMID: 27635438 DOI: 10.1021/acschemneuro.6b00213] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Due to phylogenetic proximity to the human, zebrafish has been recognized as a reliable model to study Alzheimer's disease (AD) and other central nervous system disorders. Furthermore, metabotropic glutamate receptors have been previously reported to be impaired in brain from AD patients. Metabotropic glutamate 5 (mGlu5) receptors are G-protein coupled receptors proposed as potential targets for therapy of different neurodegenerative disorders. Thus, MPEP (2-methyl-6-(phenylethynyl)pyridine hydrochloride), a selective noncompetitive mGlu5 receptor antagonist, has been suggested for pharmacological treatment of AD. The aim of the present work was to quantify mGlu5 receptors in brain from zebrafish and to study the possible modulation of these receptors by MPEP treatment. To this end, radioligand binding assay and open field test were used. Results showed a slightly higher presence of mGlu5 receptors in brain from male than in that from female zebrafish. However, a significant increase of mGlu5 receptor in male without variation in female was observed after MPEP treatment. This gender specific response was also observed in locomotor behavior, being significantly decreased only in male zebrafish. These results confirm the presence of mGlu5 receptors in brain from zebrafish and their gender specific modulation by selective antagonist treatment and suggest a role of these receptors on locomotor activity, which is affected in many disorders. In addition, our data point to zebrafish as a useful model to study mGlu receptor function in both healthy and pathological conditions.
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Affiliation(s)
- José Luis Albasanz
- Departamento de Química Inorgánica,
Orgánica y Bioquímica, Facultad de Medicina de Ciudad
Real/Facultad de Ciencias y Tecnologías Químicas, Universidad de Castilla-La Mancha, Centro Regional de Investigaciones Biomédicas (CRIB), Avenida Camilo José Cela 10, 13071 Ciudad Real, Spain
| | | | | | - David León
- Departamento de Química Inorgánica,
Orgánica y Bioquímica, Facultad de Medicina de Ciudad
Real/Facultad de Ciencias y Tecnologías Químicas, Universidad de Castilla-La Mancha, Centro Regional de Investigaciones Biomédicas (CRIB), Avenida Camilo José Cela 10, 13071 Ciudad Real, Spain
| | | | - Mairena Martín
- Departamento de Química Inorgánica,
Orgánica y Bioquímica, Facultad de Medicina de Ciudad
Real/Facultad de Ciencias y Tecnologías Químicas, Universidad de Castilla-La Mancha, Centro Regional de Investigaciones Biomédicas (CRIB), Avenida Camilo José Cela 10, 13071 Ciudad Real, Spain
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4
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Vincen-Brown MA, Whitesitt KC, Quick FG, Pilarski JQ. Studying respiratory rhythm generation in a developing bird: Hatching a new experimental model using the classic in vitro brainstem-spinal cord preparation. Respir Physiol Neurobiol 2015; 224:62-70. [PMID: 26310580 DOI: 10.1016/j.resp.2015.08.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2015] [Revised: 08/18/2015] [Accepted: 08/19/2015] [Indexed: 01/17/2023]
Abstract
It has been more than thirty years since the in vitro brainstem-spinal cord preparation was first presented as a method to study automatic breathing behaviors in the neonatal rat. This straightforward preparation has led to an incredible burst of information about the location and coordination of several spontaneously active microcircuits that form the ventrolateral respiratory network of the brainstem. Despite these advances, our knowledge of the mechanisms that regulate central breathing behaviors is still incomplete. Investigations into the nature of spontaneous breathing rhythmicity have almost exclusively focused on mammals, and there is a need for comparative experimental models to evaluate several unresolved issues from a different perspective. With this in mind, we sought to develop a new avian in vitro model with the long term goal to better understand questions associated with the ontogeny of respiratory rhythm generation, neuroplasticity, and whether multiple, independent oscillators drive the major phases of breathing. The fact that birds develop in ovo provides unparalleled access to central neuronal networks throughout the prenatal period - from embryo to hatchling - that are free from confounding interactions with mother. Previous studies using in vitro avian models have been strictly limited to the early embryonic period. Consequently, the details and even the presence of brainstem derived breathing-related rhythmogenesis in birds have never been described. In the present study, we used the altricial zebra finch (Taeniopygia guttata) and show robust spontaneous motor outflow through cranial motor nerve IX, which is first detectable on embryonic day four and continues through prenatal and early postnatal development without interruption. We also show that brainstem oscillations change dramatically over the course of prenatal development, sometimes within hours, which suggests rapid maturational modifications in growth and connectivity. We propose that this experimental preparation will be useful for a variety of studies aimed at testing the biophysical and synaptic properties of neurons that participate in the unique spatiotemporal patterns of avian breathing behaviors, especially in the context of early development.
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Affiliation(s)
| | - Kaitlyn C Whitesitt
- Department of Biological Sciences, Idaho State University, Pocatello, ID, 83 209, USA
| | - Forrest G Quick
- Department of Biological Sciences, Idaho State University, Pocatello, ID, 83 209, USA
| | - Jason Q Pilarski
- Department of Biological Sciences, Idaho State University, Pocatello, ID, 83 209, USA; Department of Dental Sciences, Idaho State University, Pocatello, ID, 83 209 USA.
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5
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Gating the polarity of endocannabinoid-mediated synaptic plasticity by nitric oxide in the spinal locomotor network. J Neurosci 2012; 32:5097-105. [PMID: 22496555 DOI: 10.1523/jneurosci.5850-11.2012] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The final motor output underlying behavior arises from an appropriate balance between excitation and inhibition within neural networks. Retrograde signaling by endocannabinoids adapts synaptic strengths and the global activity of neural networks. In the spinal cord, endocannabinoids are mobilized postsynaptically from network neurons and act retrogradely on presynaptic cannabinoid receptors to potentiate the locomotor frequency. However, it is still unclear whether mechanisms exist within the locomotor networks that determine the sign of the modulation by cannabinoid receptors to differentially regulate excitation and inhibition. In this study, using the lamprey spinal cord in vitro, we first report that 2-AG (2-arachidonyl glycerol) is mobilized by network neurons and underlies a form of modulation that is embedded within the locomotor networks. We then show that the polarity of the endocannabinoid modulation is gated by nitric oxide to enable simultaneously potentiation of excitation and depression of inhibition within the spinal locomotor networks. Our results suggest that endocannabinoid and nitric oxide systems interact to mediate inversion of the polarity of synaptic plasticity within the locomotor networks. Thus, endocannabinoid and nitric oxide shift in the excitation-inhibition balance to set the excitability of the spinal locomotor network.
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6
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Miles GB, Sillar KT. Neuromodulation of Vertebrate Locomotor Control Networks. Physiology (Bethesda) 2011; 26:393-411. [DOI: 10.1152/physiol.00013.2011] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Vertebrate locomotion must be adaptable in light of changing environmental, organismal, and developmental demands. Much of the underlying flexibility in the output of central pattern generating (CPG) networks of the spinal cord and brain stem is endowed by neuromodulation. This review provides a synthesis of current knowledge on the way that various neuromodulators modify the properties of and connections between CPG neurons to sculpt CPG network output during locomotion.
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Affiliation(s)
- Gareth B. Miles
- School of Biology, University of St. Andrews, St. Andrews, Scotland, United Kingdom
| | - Keith T. Sillar
- School of Biology, University of St. Andrews, St. Andrews, Scotland, United Kingdom
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7
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Beyond connectivity of locomotor circuitry-ionic and modulatory mechanisms. PROGRESS IN BRAIN RESEARCH 2011; 187:99-110. [PMID: 21111203 DOI: 10.1016/b978-0-444-53613-6.00007-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/24/2023]
Abstract
Discrete neural networks in the central nervous system generate the repertoire of motor behavior necessary for animal survival. The final motor output of these networks is the result of the anatomical connectivity between the individual neurons and also their biophysical properties as well as the dynamics of their synaptic transmission. To illustrate how this processing takes place to produce coordinated motor activity, we have summarized some of the results available from the lamprey spinal locomotor network. The detailed knowledge available in this model system on the organization of the network together with the properties of the constituent neurons and the modulatory systems allows us to determine how the impact of specific ion channels and receptors is translated to the global activity of the locomotor circuitry. Understanding the logic of the neuronal and synaptic processing within the locomotor network will provide information about not only their normal operation but also how they react to disruption such as injuries or trauma.
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8
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Iwagaki N, Miles GB. Activation of group I metabotropic glutamate receptors modulates locomotor-related motoneuron output in mice. J Neurophysiol 2011; 105:2108-20. [PMID: 21346211 DOI: 10.1152/jn.01037.2010] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Fast glutamatergic transmission via ionotropic receptors is critical for the generation of locomotion by spinal motor networks. In addition, glutamate can act via metabotropic glutamate receptors (mGluRs) to modulate the timing of ongoing locomotor activity. In the present study, we investigated whether mGluRs also modulate the intensity of motor output generated by spinal motor networks. Application of the group I mGluR agonist (S)-3,5-dihydroxyphenylglycine (DHPG) reduced the amplitude and increased the frequency of locomotor-related motoneuron output recorded from the lumbar ventral roots of isolated mouse spinal cord preparations. Whole cell patch-clamp recordings of spinal motoneurons revealed multiple mechanisms by which group I mGluRs modulate motoneuron output. Although DHPG depolarized the resting membrane potential and reduced the voltage threshold for action potential generation, the activation of group I mGluRs had a net inhibitory effect on motoneuron output that appeared to reflect the modulation of fast, inactivating Na(+) currents and action potential parameters. In addition, group I mGluR activation decreased the amplitude of locomotor-related excitatory input to motoneurons. Analyses of miniature excitatory postsynaptic currents indicated that mGluRs modulate synaptic drive to motoneurons via both pre- and postsynaptic mechanisms. These data highlight group I mGluRs as a potentially important source of neuromodulation within the spinal cord that, in addition to modulating components of the central pattern generator for locomotion, can modulate the intensity of motoneuron output during motor behavior. Given that group I mGluR activation reduces motoneuron excitability, mGluRs may provide negative feedback control of motoneuron output, particularly during high levels of glutamatergic stimulation.
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Affiliation(s)
- Noboru Iwagaki
- School of Biology, University of St. Andrews, St. Andrews, Fife, United Kingdom
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Specific brainstem neurons switch each other into pacemaker mode to drive movement by activating NMDA receptors. J Neurosci 2011; 30:16609-20. [PMID: 21148000 DOI: 10.1523/jneurosci.3695-10.2010] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Rhythmic activity is central to brain function. In the vertebrate CNS, the neuronal circuits for breathing and locomotion involve inhibition and also neurons acting as pacemakers, but identifying the neurons responsible has proven difficult. By studying simple hatchling Xenopus laevis tadpoles, we have already identified a population of electrically coupled hindbrain neurons (dINs) that drive swimming. During rhythm generation, dINs release glutamate to excite each other and activate NMDA receptors (NMDARs). The resulting depolarization enables a network mechanism for swimming rhythm generation that depends on reciprocal inhibition between antagonistic right and left sides. Surprisingly, a surgically isolated hemi-CNS without inhibition can still generate swimming-like rhythms. We have now discovered that activation of NMDARs transforms dINs, which normally fire singly to current injection, into pacemakers firing within the normal swimming frequency range (10-25 Hz). When dIN firing is blocked pharmacologically, this NMDAR activation produces 10 Hz membrane potential oscillations that persist when electrical coupling is blocked but not when the voltage-dependent gating of NMDARs by Mg²+ is removed. The NMDA-induced oscillations and pacemaker firing at swimming frequency are unique to the dIN population and do not occur in other spinal neurons. We conclude that NMDAR-mediated self-resetting switches critical neurons that drive swimming into pacemaker mode only during locomotion where it provides an additional, parallel mechanism for rhythm generation. This allows rhythm generation in a half-CNS and raises the possibility that such concealed pacemaker properties may be present underlying rhythm generation in other vertebrate brain networks.
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Brocard F, Tazerart S, Vinay L. Do pacemakers drive the central pattern generator for locomotion in mammals? Neuroscientist 2010; 16:139-55. [PMID: 20400712 DOI: 10.1177/1073858409346339] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Locomotor disorders profoundly impact quality of life of patients with spinal cord injury. Understanding the neuronal networks responsible for locomotion remains a major challenge for neuroscientists and a fundamental prerequisite to overcome motor deficits. Although neuronal circuitry governing swimming activities in lower vertebrates has been studied in great details, determinants of walking activities in mammals remain elusive. The manuscript reviews some of the principles relevant to the functional organization of the mammalian locomotor network and mainly focuses on mechanisms involved in rhythmogenesis. Based on recent publications supplemented with new experimental data, the authors will specifically discuss a new working hypothesis in which pacemakers, cells characterized by inherent oscillatory properties, might be functionally integrated in the locomotor network in mammals.
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Affiliation(s)
- Frédéric Brocard
- Lab Plasticité et Physio-Pathologie de la Motricité, Centre National De La Recherche Scientifique, Université Aix-Marseille, Marseille, France.
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11
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El Manira A, Kyriakatos A. The role of endocannabinoid signaling in motor control. Physiology (Bethesda) 2010; 25:230-8. [PMID: 20699469 DOI: 10.1152/physiol.00007.2010] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cannabinoid receptors and endocannabinoid signaling are distributed throughout the rostrocaudal neuraxis. Retrograde signaling via endocannabinoid mediates synaptic plasticity in many regions in the central nervous system. Here, we review the role of endocannabinoid signaling in different parts of the vertebrate motor system from networks responsible for the execution of movement to planning centers in the basal ganglia and cortex. The ubiquity of endocannabinoid-mediated plasticity suggests that it plays an important role in producing motion from defined circuitries and also for reconfiguring networks to learn new motor skills. The long-term plasticity induced by endocannabinoids may provide a long-term buffer that stabilizes the organization of motor circuits and their activity.
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Affiliation(s)
- A El Manira
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden.
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12
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Nanou E, El Manira A. Mechanisms of modulation of AMPA-induced Na+-activated K+ current by mGluR1. J Neurophysiol 2009; 103:441-5. [PMID: 19889851 DOI: 10.1152/jn.00584.2009] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Na(+)-activated K(+) (K(Na)) channels can be activated by Na(+) influx via ionotropic receptors and play a role in shaping synaptic transmission. In expression systems, K(Na) channels are modulated by G protein-coupled receptors, but such a modulation has not been shown for the native channels. In this study, we examined whether K(Na) channels coupled to AMPA receptors are modulated by metabotropic glutamate receptors (mGluRs) in lamprey spinal cord neurons. Activation of mGluR1 strongly inhibited the AMPA-induced K(Na) current. However, when intracellular Ca(2+) was chelated with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), the K(Na) current was enhanced by mGluR1. Activation of protein kinase C (PKC) mimicked the inhibitory effect of mGluR1 on the K(Na) current. Blockade of PKC prevented the mGluR1-induced inhibition of the K(Na) current, but did not affect the enhancement of the current seen in BAPTA. Together these results suggest that mGluR1 can differentially modulate AMPA-induced K(Na) current in a Ca(2+)- and PKC-dependent manner.
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Affiliation(s)
- Evanthia Nanou
- Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden
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13
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Kyriakatos A, Molinari M, Mahmood R, Grillner S, Sillar KT, El Manira A. Nitric oxide potentiation of locomotor activity in the spinal cord of the lamprey. J Neurosci 2009; 29:13283-91. [PMID: 19846716 PMCID: PMC6665181 DOI: 10.1523/jneurosci.3069-09.2009] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2009] [Revised: 08/21/2009] [Accepted: 09/02/2009] [Indexed: 11/21/2022] Open
Abstract
To understand the intrinsic operation of spinal networks generating locomotion, we need to not only characterize the constituent neurons and their connectivity, but also determine the role of intrinsic modulation in shaping the final motor output. We have focused on the effects of nitric oxide (NO) on the locomotor frequency and the underlying synaptic mechanisms in the lamprey spinal cord. To identify the source of NO, we used NADPH-diaphorase histochemistry and nNOS immunocytochemistry. Gray matter and sensory neurons were positively labeled using both methods. Preparations preincubated with NO synthase inhibitors displayed slower locomotor frequency that increased upon washout of the inhibitors, suggesting that NO is an endogenous neuromodulator in the spinal cord. Application of NO donors increased the locomotor frequency that was blocked by an NO scavenger and partially reduced by an inhibitor of sGC. To analyze the synaptic modulation underlying the NO-induced increase of the locomotor frequency we performed intracellular recordings from motoneurons and interneurons. The NO-induced increase in locomotor frequency was associated with a decrease in the midcycle inhibition and an increase in on-cycle excitation. To determine the site of action of NO, we examined the effect of NO donors on miniature PSCs. NO increased both the frequency and amplitude of mEPSCs while it only decreased the frequency of mIPSCs, suggesting the increased excitation is mediated by both presynaptic and postsynaptic mechanisms, while the decrease in inhibition involves only presynaptic mechanisms. Our results demonstrate a significant role of NO in adult vertebrate motor control which, via modulation of both excitatory and inhibitory transmission, increases the locomotor burst frequency.
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Affiliation(s)
| | - Micol Molinari
- School of Biology, University of St Andrews, St Andrews, Fife KY16 9TS, United Kingdom
| | - Riyadh Mahmood
- Department of Neuroscience, Karolinska Institutet, SE-171 77 Stockholm, Sweden, and
| | - Sten Grillner
- Department of Neuroscience, Karolinska Institutet, SE-171 77 Stockholm, Sweden, and
| | - Keith T. Sillar
- School of Biology, University of St Andrews, St Andrews, Fife KY16 9TS, United Kingdom
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14
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Nanou E, Kyriakatos A, Kettunen P, El Manira A. Separate signalling mechanisms underlie mGluR1 modulation of leak channels and NMDA receptors in the network underlying locomotion. J Physiol 2009; 587:3001-8. [PMID: 19403613 DOI: 10.1113/jphysiol.2009.172452] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Metabotropic glutamate receptor subtype 1 (mGluR1) contributes importantly to the activity of the spinal locomotor network. For example, it potentiates NMDA current and inhibits leak conductance in lamprey spinal cord neurons. In this study we examined the signalling pathways underlying the mGluR1 modulation of NMDA receptors and leak channels, respectively. Our results show that mGluR1-induced potentiation of NMDA current required activation of phospholipase C (PLC) and was independent of the increase in the intracellular Ca2+ concentration because it was unaffected by the Ca2+ chelator BAPTA and by depletion of the internal Ca2+ stores with thapsigargin. We also show that the mGluR1-mediated inhibition of leak channels is mediated by activation of G-proteins. Finally, we show that blockade of protein kinase C (PKC) abolished the mGluR1-induced inhibition of leak current without affecting the potentiation of NMDA receptors. The contribution of mGluR1-mediated modulation of leak channels to the potentiation of the locomotor cycle frequency was assessed during fictive locomotion. Blockade of PKC significantly decreased the short-term potentiation of locomotor cycle frequency by mGluR1. These results show that the effects of mGluR1 activation on the two cellular targets, the NMDA receptor and leak channels, are mediated through separate signalling pathways.
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Affiliation(s)
- Evanthia Nanou
- Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden
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Group I metabotropic glutamate receptors control metaplasticity of spinal cord learning through a protein kinase C-dependent mechanism. J Neurosci 2009; 28:11939-49. [PMID: 19005059 DOI: 10.1523/jneurosci.3098-08.2008] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Neurons within the spinal cord can support several forms of plasticity, including response-outcome (instrumental) learning. After a complete spinal transection, experimental subjects are capable of learning to hold the hindlimb in a flexed position (response) if shock (outcome) is delivered to the tibialis anterior muscle when the limb is extended. This response-contingent shock produces a robust learning that is mediated by ionotropic glutamate receptors (iGluRs). Exposure to nociceptive stimuli that are independent of limb position (e.g., uncontrollable shock; peripheral inflammation) produces a long-term (>24 h) inhibition of spinal learning. This inhibition of plasticity in spinal learning is itself a form of plasticity that requires iGluR activation and protein synthesis. Plasticity of plasticity (metaplasticity) in the CNS has been linked to group I metabotropic glutamate receptors (subtypes mGluR1 and mGluR5) and activation of protein kinase C (PKC). The present study explores the role of mGluRs and PKC in the metaplastic inhibition of spinal cord learning using a combination of behavioral, pharmacological, and biochemical techniques. Activation of group I mGluRs was found to be both necessary and sufficient for metaplastic inhibition of spinal learning. PKC was activated by stimuli that inhibit spinal learning, and inhibiting PKC activity restored the capacity for spinal learning. Finally, a PKC inhibitor blocked the metaplastic inhibition of spinal learning produced by a group I mGluR agonist. The data strongly suggest that group I mGluRs control metaplasticity of spinal learning through a PKC-dependent mechanism, providing a potential therapeutic target for promoting use-dependent plasticity after spinal cord injury.
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16
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Long-term plasticity of the spinal locomotor circuitry mediated by endocannabinoid and nitric oxide signaling. J Neurosci 2007; 27:12664-74. [PMID: 18003846 DOI: 10.1523/jneurosci.3174-07.2007] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Retrograde signaling by endocannabinoids is known to induce short- and long-term synaptic plasticity, but the significance of this modulation for the activity of neural networks underlying motor behavior is largely unclear. Here, we used the isolated lamprey spinal cord to show that endocannabinoids released by activation of metabotropic glutamate receptor 1 (mGluR1) induce long-term synaptic plasticity during an ongoing locomotor rhythm and how this is translated onto the integrated activity of the spinal circuitry. A brief activation of mGluR1 induces a long-term increase in the locomotor frequency that is mediated by a concomitant long-term depression of midcycle reciprocal inhibition and long-term potentiation of ipsilateral synaptic excitation arising from locomotor circuit interneurons. Blockade of cannabinoid receptors with AM251 prevented the mGluR1-mediated long-term plasticity of both inhibitory and excitatory synaptic transmission, as well as that of the locomotor activity. Similarly, inhibition of nitric oxide signaling blocked the mGluR1-mediated long-term plasticity. These results show that the locomotor circuitry is endowed with a "memory" capacity mediated by a long-term shift in the balance between synaptic inhibition and excitation. This is triggered by activation of mGluR1 and requires subsequent endocannabinoid and nitric oxide signaling.
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17
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Abstract
We have explored the potential involvement of the three main classes of metabotropic glutamate receptor in the modulation of a spinal locomotor network using tadpoles of the anuran amphibian Xenopus laevis. Selective activation of group I receptors in Xenopus embryos and young larvae using the general group I agonist DHPG [(S)-3,5-dihyroxyphenylglycine] significantly increased the frequency of swimming and the number of spontaneously occurring swimming episodes, as monitored by extracellular recordings from ventral roots. Group I receptor activation was without significant effect on the duration or amplitude of motor bursts, the duration of swimming episodes, or the head-to-tail delay in the propagation of swimming activity. Activation of either group II or group III receptors, however, following bath applications of the specific agonists APDC [(2R,4R)-aminopyrrolidine-2,4-dicarboxylic acid] and L-AP4 (L-2-amino-4-phosphonobutanoate), respectively, produced a net inhibitory effect on many of the parameters of fictive swimming at both developmental stages, including a reduction in swimming frequency and episode duration, along with a significant reduction in motor burst amplitude and duration in larval animals only. Applications of selective antagonists provide evidence for activation of all three groups during swimming. The group II and III antagonists EGLU (1-ethyl-2-benzimidazolinone) and MAP4 [(S)-2-amino-2-methyl-4-phosphonobutanoate], respectively, increased, while group I antagonists, CPCCOEt and MPEP, decreased swim frequency. Our findings thus provide evidence for the presence and endogenous activation of three classes of metabotropic glutamate receptor which may function as an intrinsic modulatory control system during fictive swimming in Xenopus tadpoles.
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Affiliation(s)
- Rebecca J Chapman
- School of Biology, Bute Medical Buildings, University of St. Andrews, St. Andrews, Fife KY16 9TS, UK
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18
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El Manira A, Kyriakatos A, Nanou E, Mahmood R. Endocannabinoid signaling in the spinal locomotor circuitry. ACTA ACUST UNITED AC 2007; 57:29-36. [PMID: 17719648 DOI: 10.1016/j.brainresrev.2007.06.020] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2007] [Accepted: 06/26/2007] [Indexed: 11/25/2022]
Abstract
To understand how the spinal central pattern generators produce locomotor movements, it is necessary to characterize the network's connectivity, the intrinsic properties of the constituent neurons and the modulatory mechanisms. Modulation operating within spinal locomotor networks is required for the generation of the final motor output. In this review, we have summarized how endocannabinoids released by locomotor network neurons contribute to setting the baseline locomotor frequency. They are synthesized on demand as a result of activation of mGluR1 and act as retrograde messengers to depress inhibitory synaptic transmission. We also discuss how endogenous activation of mGluR1 contributes to the normal operation of the spinal locomotor network and the underlying cellular and synaptic mechanisms.
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Affiliation(s)
- Abdeljabbar El Manira
- Nobel Institute for Neurophysiology, Department of Neuroscience, Karolinska Institutet, SE-171 77 Stockholm, Sweden.
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19
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Abstract
In 1900, Ramón y Cajal advanced the neuron doctrine, defining the neuron as the fundamental signaling unit of the nervous system. Over a century later, neurobiologists address the circuit doctrine: the logic of the core units of neuronal circuitry that control animal behavior. These are circuits that can be called into action for perceptual, conceptual, and motor tasks, and we now need to understand whether there are coherent and overriding principles that govern the design and function of these modules. The discovery of central motor programs has provided crucial insight into the logic of one prototypic set of neural circuits: those that generate motor patterns. In this review, I discuss the mode of operation of these pattern generator networks and consider the neural mechanisms through which they are selected and activated. In addition, I will outline the utility of computational models in analysis of the dynamic actions of these motor networks.
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Affiliation(s)
- Sten Grillner
- Nobel Institute for Neurophysiology, Department of Neuroscience, Karolinska Institute, SE 171 77 Stockholm, Sweden.
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20
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Levi R, Selverston AI. Mechanisms underlying type I mGluR-induced activation of lobster gastric mill neurons. J Neurophysiol 2006; 96:3378-88. [PMID: 16943312 DOI: 10.1152/jn.00591.2005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In addition to ionotropic effects, glutamate and acetylcholine have metabotropic modulatory effects on many neurons. Here we show that in the stomatogastric ganglion of the lobster, glutamate, one of the main ionotropic neurotransmitters, modulates the excitability of gastric mill neurons. The neurons in this well-studied system produce rhythmic output to a subset of lobster foregut muscles. Recently, metabotropic glutamate receptor (mGluR) agonists were suggested as modulators of the rhythmic output, in addition to the previously described muscarinic modulation by acetylcholine. However, the cellular mechanisms responsible for these effects on the pattern are not known. Using intracellular recording methods and calcium imaging, we show that glutamate has an excitatory effect on specific neurons in the stomatogastric ganglion, which is mediated by mGluRs. Responses to the application of mGluR type I agonists are transient oscillations in the system, probably arising from network interactions. We show that the excitatory effect is sensitive to phospholipase-C and IP(3) and is G-protein dependent. The G-protein dependency was demonstrated by GDPbetaS and GTPgammaS injection into identified neurons. The depolarizations and oscillations were accompanied by an increase of intracellular Ca(2+) levels and correlated Ca(2+) oscillations. By using cyclopiazonic acid, an endoreticular Ca(2+) uptake inhibitor, we show that some internal calcium release may augment the response, but is not crucial for its production. Interestingly, although Ca(2+) concentration increase is typically associated with the phosphoinositide pathway, in the lobster, the Ca(2+) concentration increase-either voltage dependent or independent-cannot account for the observed depolarization.
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Affiliation(s)
- Rafael Levi
- Institute for Nonlinear Science, University of California-San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0402, USA.
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21
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Lieske SP, Ramirez JM. Pattern-specific synaptic mechanisms in a multifunctional network. II. Intrinsic modulation by metabotropic glutamate receptors. J Neurophysiol 2006; 95:1334-44. [PMID: 16492945 DOI: 10.1152/jn.00506.2004] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The in vitro respiratory network contained in the transverse brain stem slice of mice simultaneously generates fast (approximately 15 min(-1)) and slow ( approximately 0.5 min(-1)) rhythmic activities corresponding to fictive eupnea ("normal" breathing) and fictive sighs. We show that these two activity patterns are differentially controlled through the modulatory actions of metabotropic glutamate receptors (mGluRs). Sighs were selectively inhibited by agonists of the group III mGluRs according to a pharmacological profile most consistent with activation of mGluR8. Sighs were also blocked by the supposedly inactive L-isomer of the widely used N-methyl-D-aspartate (NMDA) receptor antagonist 2-amino-5-phosphonopentanoic acid (L-AP5, 5 microM), an effect that was abolished in the presence of group III mGluR antagonists. Excitatory postsynaptic potentials (EPSPs) were recorded in pre-Bötzinger Complex neurons after stimulation of the contralateral ventral respiratory group (VRG); evoked EPSP amplitude was variably reduced after bath application of the group III agonist L-serine-O-phosphate (L-SOP), with an average reduction of 15%. Therefore although group III mGluRs do play a role in regulating synapse strength, this seems to be only a minor factor in the regulation of synapses made by midline-crossing axons. Intrinsic modulation of the respiratory central pattern generator by mGluRs appears to be an essential component of the multifunctionality that characterizes this network.
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Affiliation(s)
- Steven P Lieske
- Committee on Neurobiology, The University of Chicago, 1027 E. 57th St., Chicago, IL 60637-1508, USA
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22
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Nistri A, Ostroumov K, Sharifullina E, Taccola G. Tuning and playing a motor rhythm: how metabotropic glutamate receptors orchestrate generation of motor patterns in the mammalian central nervous system. J Physiol 2006; 572:323-34. [PMID: 16469790 PMCID: PMC1779665 DOI: 10.1113/jphysiol.2005.100610] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Repeated motor activities like locomotion, mastication and respiration need rhythmic discharges of functionally connected neurons termed central pattern generators (CPGs) that cyclically activate motoneurons even in the absence of descending commands from higher centres. For motor pattern generation, CPGs require integration of multiple processes including activation of ion channels and transmitter receptors at strategic locations within motor networks. One emerging mechanism is activation of glutamate metabotropic receptors (mGluRs) belonging to group I, while group II and III mGluRs appear to play an inhibitory function on sensory inputs. Group I mGluRs generate neuronal membrane depolarization with input resistance increase and rapid fluctuations in intracellular Ca(2+), leading to enhanced excitability and rhythmicity. While synchronicity is probably due to modulation of inhibitory synaptic transmission, these oscillations occurring in coincidence with strong afferent stimuli or application of excitatory agents can trigger locomotor-like patterns. Hence, mGluR-sensitive spinal oscillators play a role in accessory networks for locomotor CPG activation. In brainstem networks supplying tongue muscle motoneurons, group I receptors facilitate excitatory synaptic inputs and evoke synchronous oscillations which stabilize motoneuron firing at regular, low frequency necessary for rhythmic tongue contractions. In this case, synchronicity depends on the strong electrical coupling amongst motoneurons rather than inhibitory transmission, while cyclic activation of K(ATP) conductances sets its periodicity. Activation of mGluRs is therefore a powerful strategy to trigger and recruit patterned discharges of motoneurons.
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Affiliation(s)
- Andrea Nistri
- Neurobiology Sector, CNR-INFM DEMOCRITOS National Simulation Center, International School for Advanced Studies (SISSA), Trieste, Italy.
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23
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Kettunen P, Kyriakatos A, Hallén K, El Manira A. Neuromodulation via conditional release of endocannabinoids in the spinal locomotor network. Neuron 2005; 45:95-104. [PMID: 15629705 DOI: 10.1016/j.neuron.2004.12.022] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2004] [Revised: 06/24/2004] [Accepted: 11/15/2004] [Indexed: 10/26/2022]
Abstract
Endocannabinoids act as retrograde signals to modulate synaptic transmission. Little is known, however, about their significance in integrated network activity underlying motor behavior. We have examined the physiological effects of endocannabinoids in a neuronal network underlying locomotor behavior using the isolated lamprey spinal cord. Our results show that endocannabinoids are released during locomotor activity and participate in setting the baseline burst rate. They are released in response to mGluR1 activation and act as retrograde messengers. This conditional release of endocannabinoids can transform motoneurons and crossing interneurons into modulatory neurons by enabling them to regulate their inhibitory synaptic inputs and thus contribute to the modulation of the locomotor burst frequency. These results provide evidence that endocannabinoid retrograde signaling occurs within the locomotor network and contributes to motor pattern generation and regulation in the spinal cord.
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Affiliation(s)
- Petronella Kettunen
- Nobel Institute for Neurophysiology, Department of Neuroscience, Karolinska Institutet, 171 77 Stockholm, Sweden
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24
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Taccola G, Marchetti C, Nistri A. Modulation of rhythmic patterns and cumulative depolarization by group I metabotropic glutamate receptors in the neonatal rat spinal cord in vitro. Eur J Neurosci 2004; 19:533-41. [PMID: 14984404 DOI: 10.1111/j.0953-816x.2003.03148.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The role of group I metabotropic glutamate receptors (mGluRs), and their subtypes 1 or 5, in rhythmic patterns generated by the neonatal rat spinal cord was investigated. Fictive locomotor patterns induced by N-methyl-d-aspartate + serotonin were slowed down by the subtype 1 antagonists (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA) or 7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxylate ethyl ester (CPCCOEt) and unaffected by the subtype 5 antagonist 2-methyl-6-(phenylethynyl)pyridine hydrochloride (MPEP). The group I agonist (RS)-3,5-dihydroxyphenylglycine (DHPG) depolarized ventral roots and disrupted fictive locomotion, an effect blocked by AIDA (or CPCCOEt) and reversed by increasing the N-methyl-d-aspartate concentration. Cumulative depolarization induced by low frequency trains of dorsal root stimuli was attenuated by DHPG and unchanged by AIDA or MPEP while rhythmic patterns or motoneuron spike wind-up persisted. Disinhibited bursting induced by strychnine + bicuculline was accelerated by DHPG, slowed down by AIDA (which prevented the action of DHPG), unaffected by MPEP and counteracted by the selective group II agonist (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine. The DHPG transformed regular bursting into arrhythmic bursting, a phenomenon also produced by the group II mGluR antagonist (2S)-alpha-ethylglutamic acid. These results indicate that, during fictive locomotion or disinhibited bursting, endogenous glutamate could activate discrete clusters of subtype 1 mGluRs to facilitate discharges. Diffuse activation by the exogenous agonist DHPG of group I mGluRs throughout spinal networks had an excitatory effect overshadowed by its much stronger depressant action due to concomitant facilitation of glycinergic transmission. Irregular disinhibited bursting caused by activation of subtype 1 receptors or block of group II receptors suggests that mGluRs could control not only the frequency but also the periodicity of bursting patterns, outlining novel mechanisms contributing to burst duration.
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Affiliation(s)
- Giuliano Taccola
- Neurobiology Sector and Istituto Nazionale di Fisica della Materia Unit, International School for Advanced Studies (SISSA), Via Beirut 4, 34014 Trieste, Italy
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25
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Taccola G, Marchetti C, Nistri A. Role of group II and III metabotropic glutamate receptors in rhythmic patterns of the neonatal rat spinal cord in vitro. Exp Brain Res 2004; 156:495-504. [PMID: 15007577 DOI: 10.1007/s00221-003-1798-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2003] [Accepted: 11/28/2003] [Indexed: 10/26/2022]
Abstract
Electrophysiological recordings were used to explore the role of group II and III metabotropic glutamate receptors (mGluRs) in oscillatory patterns generated by the neonatal rat spinal cord in vitro. Neither the group II agonist DCG-IV (and the selective antagonist EGLU), nor the group III agonist L-AP4 (and its selective antagonist CPPG) had any effect on lumbar motoneuron membrane potential or input resistance. This observation suggests that motoneurons expressed no functional group II and III mGluRs and received no network-based, tonic influence mediated by them. DCG-IV or L-AP4 strongly depressed synaptic responses evoked by single dorsal root (DR) stimuli, an effect counteracted by their respective antagonist. EGLU or CPPG per se had no effect on synaptic responses, indicating no mGluR autoreceptor-dependent control of transmitter release. L-AP4 largely depressed cumulative depolarization, windup and associated oscillations, whereas synaptic depression induced by DCG-IV waned with repeated stimuli. L-AP4 slowed down fictive locomotor patterns and arrested disinhibited bursting, which could, however, be promptly restored by DR electrical stimulation. DCG-IV had no significant effect on fictive locomotion, but it blocked disinhibited bursting. EGLU facilitated bursting, suggesting that burst termination was partly controlled by group II mGluRs. All these effects were reversible on washout. It is concluded that activation of group II and III mGluRs differentially modulated rhythmic patterns recorded from motoneurons via network-dependent actions, which probably included decrease in the release of neurotransmitters at key circuit points.
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Affiliation(s)
- Giuliano Taccola
- Neurobiology Sector and INFM Unit, International School for Advanced Studies (SISSA), Via Beirut 4, 34014 Trieste, Italy
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26
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Kettunen P, Hess D, El Manira A. mGluR1, but not mGluR5, mediates depolarization of spinal cord neurons by blocking a leak current. J Neurophysiol 2003; 90:2341-8. [PMID: 12815014 DOI: 10.1152/jn.01132.2002] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The modulation of neuronal excitability by group I metabotropic glutamate receptors (mGluRs) was studied in isolated lamprey spinal cord. At resting potential, application of the group I mGluR agonist (R,S)-3,5-dihydroxyphenylglycine (DHPG) slightly depolarized the cells. However, at depolarized membrane potentials, this agonist induced repetitive firing. When Na+ channels were blocked by TTX, DHPG induced a slight depolarization at rest that increased in amplitude as the neurons were held at more depolarized membrane potentials. In voltage-clamp conditions, DHPG application induced an inward current associated with a decrease in membrane conductance when cells were held at -40 mV. At resting membrane potential, no significant change in the current was induced by DHPG, although a decrease in membrane conductance was seen. The conductance blocked by DHPG corresponded to a leak current, since DHPG had no effect on the voltage-gated current elicited by a voltage step from -60 to -40 mV, when leak currents were subtracted. The leak current blocked by DHPG is mediated by fluxes of both K+ and Na+. The subtype of group I mGluR mediating the block of the leak current was characterized using specific antagonists for mGluR1 and mGluR5. The inhibition of the leak current was blocked by the mGluR1 antagonist LY 367385 but not by the mGluR5 antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP). The DHPG-induced blockage of the leak current required phospholipase C (PLC)-activation and release of Ca2+ from internal stores as the effect of DHPG was suppressed by the PLC-blocker U-73122 and after depletion of intracellular Ca2+ pools by thapsigargin. Our results thus show that mGluR1 activation depolarizes spinal neurons by inhibiting a leak current. This will boost membrane depolarization and result in an increase in the excitability of spinal cord neurons, which could contribute to the modulation of the activity of the spinal locomotor network.
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Affiliation(s)
- Petronella Kettunen
- Nobel Institute for Neurophysiology, Department of Neuroscience, Karolinska Institutet, SE-171 77 Stockholm, Sweden.
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