1
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Zych SM, Ford CP. Divergent properties and independent regulation of striatal dopamine and GABA co-transmission. Cell Rep 2022; 39:110823. [PMID: 35584679 PMCID: PMC9134867 DOI: 10.1016/j.celrep.2022.110823] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2021] [Revised: 03/03/2022] [Accepted: 04/24/2022] [Indexed: 01/11/2023] Open
Abstract
Substantia nigra pars compacta (SNc) dopamine neurons play a key role in regulating the activity of striatal circuits within the basal ganglia. In addition to dopamine, these neurons release several other transmitters, including the major inhibitory neurotransmitter γ-aminobutyric acid (GABA). Both dopamine and GABA are loaded into SNc synaptic vesicles by the vesicular monoamine transporter 2 (VMAT2), and co-release of GABA provides strong inhibition to the striatum by directly inhibiting striatal medium spiny projection neurons (MSNs) through activation of GABAA receptors. Here, we found that despite both dopamine and GABA being co-packaged by VMAT2, the properties of transmission, including Ca2+ sensitivity, release probability, and requirement of active zone scaffolding proteins, differ between the two transmitters. Moreover, the extent by which presynaptic neuromodulators inhibit co-transmission also varied. Differences in modulation and the mechanisms controlling release allow for independent regulation of dopamine and GABA signals despite both being loaded via similar mechanisms.
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Affiliation(s)
- Sarah M Zych
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, 12800 E 19th Ave, Aurora, CO 80045, USA
| | - Christopher P Ford
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, 12800 E 19th Ave, Aurora, CO 80045, USA.
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2
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Alten B, Guzikowski NJ, Zurawski Z, Hamm HE, Kavalali ET. Presynaptic mechanisms underlying GABA B-receptor-mediated inhibition of spontaneous neurotransmitter release. Cell Rep 2022; 38:110255. [PMID: 35045279 PMCID: PMC8793855 DOI: 10.1016/j.celrep.2021.110255] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Revised: 06/15/2021] [Accepted: 12/21/2021] [Indexed: 01/08/2023] Open
Abstract
Inhibition of neurotransmitter release by neurotransmitter substances constitutes a fundamental means of neuromodulation. In contrast to well-delineated mechanisms that underlie inhibition of evoked release via suppression of voltage-gated Ca2+ channels, processes that underlie neuromodulatory inhibition of spontaneous release remain unclear. Here, we interrogated inhibition of spontaneous glutamate and GABA release by presynaptic metabotropic GABAB receptors. Our findings show that this inhibition relies on Gβγ subunit action at the membrane, and it is largely independent of presynaptic Ca2+ signaling for both forms of release. In the case of spontaneous glutamate release, inhibition requires Gβγ interaction with the C terminus of the key fusion machinery component SNAP25, and it is modulated by synaptotagmin-1. Inhibition of spontaneous GABA release, on the other hand, is independent of these pathways and likely requires alternative Gβγ targets at the presynaptic terminal.
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Affiliation(s)
- Baris Alten
- Department of Pharmacology, Vanderbilt University, 7130A MRB III 465 21st Avenue South, Nashville, TN 37240-7933, USA,Vanderbilt Brain Institute, Vanderbilt University, Nashville, TN 37240-7933, USA
| | - Natalie J. Guzikowski
- Department of Pharmacology, Vanderbilt University, 7130A MRB III 465 21st Avenue South, Nashville, TN 37240-7933, USA,Vanderbilt Brain Institute, Vanderbilt University, Nashville, TN 37240-7933, USA
| | - Zack Zurawski
- Department of Pharmacology, Vanderbilt University, 7130A MRB III 465 21st Avenue South, Nashville, TN 37240-7933, USA
| | - Heidi E. Hamm
- Department of Pharmacology, Vanderbilt University, 7130A MRB III 465 21st Avenue South, Nashville, TN 37240-7933, USA
| | - Ege T. Kavalali
- Department of Pharmacology, Vanderbilt University, 7130A MRB III 465 21st Avenue South, Nashville, TN 37240-7933, USA,Vanderbilt Brain Institute, Vanderbilt University, Nashville, TN 37240-7933, USA,Lead contact,Correspondence:
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3
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Gong S, Fayette N, Heinsbroek JA, Ford CP. Cocaine shifts dopamine D2 receptor sensitivity to gate conditioned behaviors. Neuron 2021; 109:3421-3435.e5. [PMID: 34506723 PMCID: PMC8571051 DOI: 10.1016/j.neuron.2021.08.012] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2021] [Revised: 07/16/2021] [Accepted: 08/11/2021] [Indexed: 12/21/2022]
Abstract
Cocaine addiction is a chronic, relapsing disorder characterized by maladaptation in the brain mesolimbic and nigrostriatal dopamine system. Although changes in the properties of D2-receptor-expressing medium spiny neurons (D2-MSNs) and connected striatal circuits following cocaine treatment are known, the contributions of altered D2-receptor (D2R) function in mediating the rewarding properties of cocaine remain unclear. Here, we describe how a 7-day exposure to cocaine alters dopamine signaling by selectively reducing the sensitivity, but not the expression, of nucleus accumbens D2-MSN D2Rs via an alteration in the relative expression and coupling of G protein subunits. This cocaine-induced reduction of D2R sensitivity facilitated the development of the rewarding effects of cocaine as blocking the reduction in G protein expression was sufficient to prevent cocaine-induced behavioral adaptations. These findings identify an initial maladaptive change in sensitivity by which mesolimbic dopamine signals are encoded by D2Rs following cocaine exposure.
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Affiliation(s)
- Sheng Gong
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, Aurora, CO 80045, USA; Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Nicholas Fayette
- Department of Anesthesiology, University of Colorado School of Medicine, Anschutz Medical Campus, Aurora, CO 80045, USA
| | - Jasper A Heinsbroek
- Department of Anesthesiology, University of Colorado School of Medicine, Anschutz Medical Campus, Aurora, CO 80045, USA
| | - Christopher P Ford
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, Aurora, CO 80045, USA.
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4
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Abstract
Circadian clocks are biochemical time-keeping machines that synchronize animal behavior and physiology with planetary rhythms. In Drosophila, the core components of the clock comprise a transcription/translation feedback loop and are expressed in seven neuronal clusters in the brain. Although it is increasingly evident that the clocks in each of the neuronal clusters are regulated differently, how these clocks communicate with each other across the circadian neuronal network is less clear. Here, we review the latest evidence that describes the physical connectivity of the circadian neuronal network . Using small ventral lateral neurons as a starting point, we summarize how one clock may communicate with another, highlighting the signaling pathways that are both upstream and downstream of these clocks. We propose that additional efforts are required to understand how temporal information generated in each circadian neuron is integrated across a neuronal circuit to regulate rhythmic behavior.
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Affiliation(s)
- Myra Ahmad
- Department of Pediatrics, Division of Medical Genetics, Dalhousie University, Halifax, NS, Canada
- Department of Pharmacology, Dalhousie University, Halifax, NS, Canada
| | - Wanhe Li
- Laboratory of Genetics, The Rockefeller University, New York, NY, USA
| | - Deniz Top
- Department of Pediatrics, Division of Medical Genetics, Dalhousie University, Halifax, NS, Canada
- Department of Pharmacology, Dalhousie University, Halifax, NS, Canada
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5
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Gaidhani N, Tucci FC, Kem WR, Beaton G, Uteshev VV. Therapeutic efficacy of α7 ligands after acute ischaemic stroke is linked to conductive states of α7 nicotinic ACh receptors. Br J Pharmacol 2021; 178:1684-1704. [PMID: 33496352 DOI: 10.1111/bph.15392] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2020] [Revised: 12/22/2020] [Accepted: 01/21/2021] [Indexed: 12/19/2022] Open
Abstract
BACKGROUND AND PURPOSE Targeting α7 nicotinic ACh receptors (nAChRs) in neuroinflammatory disorders including acute ischaemic stroke holds significant therapeutic promise. However, therapeutically relevant signalling mechanisms remain unidentified. Activation of neuronal α7 nAChRs triggers ionotropic signalling, but there is limited evidence for it in immunoglial tissues. The α7 ligands which are effective in reducing acute ischaemic stroke damage promote α7 ionotropic activity, suggesting a link between their therapeutic effects for treating acute ischaemic stroke and activation of α7 conductive states. EXPERIMENTAL APPROACH This hypothesis was tested using a transient middle cerebral artery occlusion (MCAO) model of acute ischaemic stroke, NS6740, a known selective non-ionotropic agonist of α7 nAChRs and 4OH-GTS-21, a partial α7 agonist. NS6740-like ligands exhibiting low efficacy/potency for ionotropic activity will be referred to as non-ionotropic agonists or "metagonists". KEY RESULTS 4OH-GTS-21, used as a positive control, significantly reduced neurological deficits and brain injury after MCAO as compared to vehicle and NS6740. By contrast, NS6740 was ineffective in identical assays and reversed the effects of 4OH-GTS-21 when these compounds were co-applied. Electrophysiological recordings from acute hippocampal slices obtained from NS6740-injected animals demonstrated its remarkable brain availability and protracted effects on α7 nAChRs as evidenced by sustained (>8 h) alterations in α7 ionotropic responsiveness. CONCLUSION AND IMPLICATIONS These results suggest that α7 ionotropic activity may be obligatory for therapeutic efficacy of α7 ligands after acute ischaemic stroke yet, highlight the potential for selective application of α7 ligands to disease states based on their mode of receptor activation.
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Affiliation(s)
- Nikhil Gaidhani
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, Texas, USA
| | - Fabio C Tucci
- Epigen Biosciences, Inc., San Diego, California, USA
| | - William R Kem
- Department of Pharmacology and Therapeutics, University of Florida College of Medicine, Gainesville, Florida, USA
| | - Graham Beaton
- Epigen Biosciences, Inc., San Diego, California, USA
| | - Victor V Uteshev
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, Texas, USA
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6
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Cai Y, Nielsen BE, Boxer EE, Aoto J, Ford CP. Loss of nigral excitation of cholinergic interneurons contributes to parkinsonian motor impairments. Neuron 2021; 109:1137-1149.e5. [PMID: 33600762 DOI: 10.1016/j.neuron.2021.01.028] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Revised: 01/22/2021] [Accepted: 01/28/2021] [Indexed: 12/18/2022]
Abstract
Progressive loss of dopamine inputs in Parkinson's disease leads to imbalances in coordinated signaling of dopamine and acetylcholine (ACh) in the striatum, which is thought to contribute to parkinsonian motor symptoms. As reciprocal interactions between dopamine inputs and cholinergic interneurons (ChIs) control striatal dopamine and ACh transmission, we examined how partial dopamine depletion in an early-stage mouse model for Parkinson's disease alters nigral regulation of cholinergic activity. We found region-specific alterations in how remaining dopamine inputs regulate cholinergic excitability that differ between the dorsomedial (DMS) and dorsolateral (DLS) striatum. Specifically, we found that dopamine depletion downregulates metabotropic glutamate receptors (mGluR1) on DLS ChIs at synapses where dopamine inputs co-release glutamate, abolishing the ability of dopamine inputs to drive burst firing. This loss underlies parkinsonian motor impairments, as viral rescue of mGluR1 signaling in DLS ChIs was sufficient to restore circuit function and attenuate motor deficits in early-stage parkinsonian mice.
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7
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Abstract
Excitotoxicity is classically attributed to Ca2+ influx through NMDA receptors (NMDAr), leading to production of nitric oxide by neuronal nitric oxide synthase and superoxide by mitochondria, which react to form highly cytotoxic peroxynitrite. More recent observations warrant revision of the classic view and help to explain some otherwise puzzling aspects of excitotoxic cell injury. Studies using pharmacological and genetic approaches show that superoxide produced by NMDAr activation originates primarily from NADPH oxidase rather than from mitochondria. As NADPH oxidase is localized to the plasma membrane, this also provides an explanation for the extracellular release of superoxide and cell-to-cell “spread” of excitotoxic injury observed in vitro and in vivo. The signaling pathway linking NMDAr to NADPH oxidase involves Ca2+ influx, phosphoinositol-3-kinase, and protein kinase Cζ, and interventions at any of these steps can prevent superoxide production and excitotoxic injury. Ca2+ influx specifically through NMDAr is normally required to induce excitotoxicity, through a mechanism presumed to involve privileged Ca2+ access to local signaling domains. However, experiments using selective blockade of the NMDAr ion channel and artificial reconstitution of Ca2+ by other routes indicate that the special effects of NMDAr activation are attributable instead to concurrent non-ionotropic NMDAr signaling by agonist binding to NMDAr. The non-ionotropic signaling driving NADPH oxidase activation is mediated in part by phosphoinositol-3-kinase binding to the C-terminal domain of GluN2B receptor subunits. These more recently identified aspects of excitotoxicity expand our appreciation of the complexity of excitotoxic processes and suggest novel approaches for limiting neuronal injury.
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Affiliation(s)
- Jiejie Wang
- Department of Neurology, University of California, San Francisco, and San Francisco Veterans Affairs Health Care System, San Francisco, CA, United States
| | - Raymond A Swanson
- Department of Neurology, University of California, San Francisco, and San Francisco Veterans Affairs Health Care System, San Francisco, CA, United States
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8
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Pressey JC, Woodin MA. Kainate receptor regulation of synaptic inhibition in the hippocampus. J Physiol 2020; 599:485-492. [PMID: 32162694 DOI: 10.1113/jp279645] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2020] [Accepted: 03/02/2020] [Indexed: 12/13/2022] Open
Abstract
Kainate receptors (KARs) are glutamate-type receptors that mediate both canonical ionotropic currents and non-canonical metabotropic signalling. While KARs are expressed widely throughout the brain, synaptic KAR currents have only been recorded at a limited set of synapses, and the KAR currents that have been recorded are relatively small and slow, which has led to the question, what is the functional significance of KARs? While the KAR current itself is relatively modest, its impact on inhibition in the hippocampus can be profound. In the CA1 region of the hippocampus, presynaptic KAR activation bidirectionally regulates γ-aminobutyric acid (GABA) release in a manner that depends on the glutamate concentration; lower levels of glutamate facilitate GABA release via an ionotropic pathway, while higher levels of glutamate depress GABA release via a metabotropic pathway. Postsynaptic interneuron KAR activation increases spike frequency through an ionotropic current, which in turn can strengthen inhibition. In the CA3 region, postsynaptic KAR activation in pyramidal neurons also strengthens inhibition, but in this case through a metabotropic pathway which regulates the neuronal chloride gradient and hyperpolarizes the reversal potential for GABA (EGABA ). Taken together, the evidence for KAR-mediated regulation of the strength of inhibition via pre- and postsynaptic mechanisms provides compelling evidence that KARs are ideally positioned to regulate excitation-inhibition balance - through sensing the excitatory tone and concomitantly tuning the strength of inhibition.
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Affiliation(s)
- Jessica C Pressey
- Department of Cell and Systems Biology, University of Toronto, Toronto, Ontario, Canada
| | - Melanie A Woodin
- Department of Cell and Systems Biology, University of Toronto, Toronto, Ontario, Canada
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9
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Sanchez-Vives MV, Barbero-Castillo A, Perez-Zabalza M, Reig R. GABA B receptors: modulation of thalamocortical dynamics and synaptic plasticity. Neuroscience 2021; 456:131-42. [PMID: 32194227 DOI: 10.1016/j.neuroscience.2020.03.011] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2019] [Revised: 03/05/2020] [Accepted: 03/06/2020] [Indexed: 01/03/2023]
Abstract
GABAB-receptors (GABAB-Rs) are metabotropic, G protein-coupled receptors for the neurotransmitter GABA. Their activation induces slow inhibitory control of the neuronal excitability mediated by pre- and postsynaptic inhibition. Presynaptically GABAB-Rs reduce GABA and glutamate release inhibiting presynaptic Ca2+ channels in both inhibitory and excitatory synapses while postsynaptic GABAB-Rs induce robust slow hyperpolarization by the activation of K+ channels. GABAB-Rs are activated by non-synaptic or volume transmission, which requires high levels of GABA release, either by the simultaneous discharge of GABAergic interneurons or very intense discharges in the thalamus or by means of the activation of a neurogliaform interneurons in the cortex. The main receptor subunits GABAB1a, GABAB1b and GABAB2 are strongly expressed in neurons and glial cells throughout the central nervous system and GABAB-R activation is related to many neuronal processes such as the modulation of rhythmic activity in several brain regions. In the thalamus, GABAB-Rs modulate the generation of the main thalamic rhythm, spindle waves. In the cerebral cortex, GABAB-Rs also modulate the most prominent emergent oscillatory activity-slow oscillations-as well as faster oscillations like gamma frequency. Further, recent studies evaluating the complexity expressed by the cortical network, a parameter associated with consciousness levels, have found that GABAB-Rs enhance this complexity, while their blockade decreases it. This review summarizes the current results on how the activation of GABAB-Rs affects the interchange of information between brain areas by controlling rhythmicity as well as synaptic plasticity.
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10
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Bowers MS, Cacheaux LP, Sahu SU, Schmidt ME, Sennello JA, Leaderbrand K, Khan MA, Kroes RA, Moskal JR. NYX-2925 induces metabotropic N-methyl-d-aspartate receptor (NMDAR) signaling that enhances synaptic NMDAR and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor. J Neurochem 2020; 152:523-541. [PMID: 31376158 PMCID: PMC7065110 DOI: 10.1111/jnc.14845] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2018] [Revised: 07/05/2019] [Accepted: 07/08/2019] [Indexed: 12/18/2022]
Abstract
N-methyl-d-aspartate receptors (NMDARs) mediate both physiological and pathophysiological processes, although selective ligands lack broad clinical utility. NMDARs are composed of multiple subunits, but N-methyl-d-aspartate receptor subunit 2 (GluN2) is predominately responsible for functional heterogeneity. Specifically, the GluN2A- and GluN2B-containing subtypes are enriched in adult hippocampus and cortex and impact neuronal communication via dynamic trafficking into and out of the synapse. We sought to understand if ((2S, 3R)-3-hydroxy-2-((R)-5-isobutyryl-1-oxo-2,5-diazaspiro[3,4]octan-2-yl) butanamide (NYX-2925), a novel NMDAR modulator, alters synaptic levels of GluN2A- or GluN2B-containing NMDARs. Low-picomolar NYX-2925 increased GluN2B colocalization with the excitatory post-synaptic marker post-synaptic density protein 95 (PSD-95) in rat primary hippocampal neurons within 30 min. Twenty-four hours following oral administration, 1 mg/kg NYX-2925 increased GluN2B in PSD-95-associated complexes ex vivo, and low-picomolar NYX-2925 regulated numerous trafficking pathways in vitro. Because the NYX-2925 concentration that increases synaptic GluN2B was markedly below that which enhances long-term potentiation (mid-nanomolar), we sought to elucidate the basis of this effect. Although NMDAR-dependent, NYX-2925-mediated colocalization of GluN2B with PSD-95 occurred independent of ion flux, as colocalization increased in the presence of either the NMDAR channel blocker (5R,10S)-(-)-5-Methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate or glycine site antagonist 7-chlorokynurenic acid. Moreover, while mid-nanomolar NYX-2925 concentrations, which do not increase synaptic GluN2B, enhanced calcium transients, functional plasticity was only enhanced by picomolar NYX-2925. Thus, NYX-2925 concentrations that increase synaptic GluN2B facilitated the chemical long-term potentiation induced insertion of synaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor GluA1 subunit levels. Basal (unstimulated by chemical long-term potentiation) levels of synaptic GluA1 were only increased by mid-nanomolar NYX-2925. These data suggest that NYX-2925 facilitates homeostatic plasticity by initially increasing synaptic GluN2B via metabotropic-like NMDAR signaling. Cover Image for this issue: doi: 10.1111/jnc.14735.
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Affiliation(s)
- M. Scott Bowers
- Falk Center for Molecular Therapeutics, Biomedical EngineeringNorthwestern UniversityEvanstonIllinoisUSA
- Aptinyx, Inc.EvanstonIllinoisUSA
| | | | - Srishti U. Sahu
- Falk Center for Molecular Therapeutics, Biomedical EngineeringNorthwestern UniversityEvanstonIllinoisUSA
| | | | | | | | | | - Roger A. Kroes
- Falk Center for Molecular Therapeutics, Biomedical EngineeringNorthwestern UniversityEvanstonIllinoisUSA
- Aptinyx, Inc.EvanstonIllinoisUSA
| | - Joseph R. Moskal
- Falk Center for Molecular Therapeutics, Biomedical EngineeringNorthwestern UniversityEvanstonIllinoisUSA
- Aptinyx, Inc.EvanstonIllinoisUSA
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11
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Cid JM, Lavreysen H, Tresadern G, Pérez-Benito L, Tovar F, Fontana A, Trabanco AA. Computationally Guided Identification of Allosteric Agonists of the Metabotropic Glutamate 7 Receptor. ACS Chem Neurosci 2019; 10:1043-1054. [PMID: 30216043 DOI: 10.1021/acschemneuro.8b00331] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
The metabotropic glutamate 7 (mGlu7) receptor belongs to the group III of mGlu receptors. Since the mGlu7 receptor can control excitatory neurotransmission in the hippocampus and cortex, modulation of the receptor may have therapeutic benefit in several CNS diseases. However, mGlu7 remains relatively unexplored among the eight known mGlu receptors partly because of the limited availability of tool compounds to interrogate its potential therapeutic utility. Here we report the discovery of a new class of mGlu7 allosteric agonists. Hits originating from virtual screening were followed up with further analogue searching and screening, leading to a novel series of mGlu7 allosteric agonists. Guided by docking into a structural model of the mGlu7 receptor the initial hit 5 was successfully optimized to analogues with comparable potencies and more attractive drug-like attributes than AMN082.
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Affiliation(s)
- Jose María Cid
- Janssen Research and Development, Calle Jarama 75A, Toledo 45007, Spain
| | - Hilde Lavreysen
- Janssen Research and Development, Turnhoutseweg 30, 2440 Beerse, Belgium
| | - Gary Tresadern
- Janssen Research and Development, Turnhoutseweg 30, 2440 Beerse, Belgium
| | - Laura Pérez-Benito
- Laboratori de Medicina Computacional Unitat de Bioestadistica, Facultat de Medicina, Universitat Autonoma de Barcelona, Bellaterra 08193, Spain
| | - Fulgencio Tovar
- Villapharma Research
S.L., Parque Tecnológico de Fuente Álamo. Ctra. El Estrecho-Lobosillo, Km. 2.5- Av. Azul, 30320 Fuente Álamo de Murcia, Murcia, Spain
| | - Alberto Fontana
- Janssen Research and Development, Calle Jarama 75A, Toledo 45007, Spain
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12
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Garand D, Mahadevan V, Woodin MA. Ionotropic and metabotropic kainate receptor signalling regulates Cl - homeostasis and GABAergic inhibition. J Physiol 2019; 597:1677-1690. [PMID: 30570751 PMCID: PMC6418771 DOI: 10.1113/jp276901] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Accepted: 12/19/2018] [Indexed: 12/28/2022] Open
Abstract
KEY POINTS Potassium-chloride co-transporter 2 (KCC2) plays a critical role in regulating chloride homeostasis, which is essential for hyperpolarizing inhibition in the mature nervous system. KCC2 interacts with many proteins involved in excitatory neurotransmission, including the GluK2 subunit of the kainate receptor (KAR). We show that activation of KARs hyperpolarizes the reversal potential for GABA (EGABA ) via both ionotropic and metabotropic signalling mechanisms. KCC2 is required for the metabotropic KAR-mediated regulation of EGABA , although ionotropic KAR signalling can hyperpolarize EGABA independent of KCC2 transporter function. The KAR-mediated hyperpolarization of EGABA is absent in the GluK1/2-/- mouse and is independent of zinc release from mossy fibre terminals. The ability of KARs to regulate KCC2 function may have implications in diseases with disrupted excitation: inhibition balance, such as epilepsy, neuropathic pain, autism spectrum disorders and Down's syndrome. ABSTRACT Potassium-chloride co-transporter 2 (KCC2) plays a critical role in the regulation of chloride (Cl- ) homeostasis within mature neurons. KCC2 is a secondarily active transporter that extrudes Cl- from the neuron, which maintains a low intracellular Cl- concentration [Cl- ]. This results in a hyperpolarized reversal potential of GABA (EGABA ), which is required for fast synaptic inhibition in the mature central nervous system. KCC2 also plays a structural role in dendritic spines and at excitatory synapses, and interacts with 'excitatory' proteins, including the GluK2 subunit of kainate receptors (KARs). KARs are glutamate receptors that display both ionotropic and metabotropic signalling. We show that activating KARs in the hippocampus hyperpolarizes EGABA , thus strengthening inhibition. This hyperpolarization occurs via both ionotropic and metabotropic KAR signalling in the CA3 region, whereas it is absent in the GluK1/2-/- mouse, and is independent of zinc release from mossy fibre terminals. The metabotropic signalling mechanism is dependent on KCC2, although the ionotropic signalling mechanism produces a hyperpolarization of EGABA even in the absence of KCC2 transporter function. These results demonstrate a novel functional interaction between a glutamate receptor and KCC2, a transporter critical for maintaining inhibition, suggesting that the KAR:KCC2 complex may play an important role in excitatory:inhibitory balance in the hippocampus. Additionally, the ability of KARs to regulate chloride homeostasis independently of KCC2 suggests that KAR signalling can regulate inhibition via multiple mechanisms. Activation of kainate-type glutamate receptors could serve as an important mechanism for increasing the strength of inhibition during periods of strong glutamatergic activity.
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MESH Headings
- Animals
- CA1 Region, Hippocampal/cytology
- CA1 Region, Hippocampal/metabolism
- CA1 Region, Hippocampal/physiology
- CA3 Region, Hippocampal/cytology
- CA3 Region, Hippocampal/metabolism
- CA3 Region, Hippocampal/physiology
- Cells, Cultured
- Chlorides/metabolism
- Female
- Homeostasis
- Inhibitory Postsynaptic Potentials
- Male
- Mice
- Mice, Inbred C57BL
- Mossy Fibers, Hippocampal/metabolism
- Mossy Fibers, Hippocampal/physiology
- Pyramidal Cells/metabolism
- Pyramidal Cells/physiology
- Receptors, GABA/metabolism
- Receptors, Kainic Acid/metabolism
- Symporters/metabolism
- K Cl- Cotransporters
- GluK2 Kainate Receptor
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Affiliation(s)
- Danielle Garand
- Department of Cell and Systems BiologyUniversity of TorontoTorontoONCanada
| | - Vivek Mahadevan
- Department of Cell and Systems BiologyUniversity of TorontoTorontoONCanada
| | - Melanie A. Woodin
- Department of Cell and Systems BiologyUniversity of TorontoTorontoONCanada
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13
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Sanderson TM, Bradley CA, Georgiou J, Hong YH, Ng AN, Lee Y, Kim HD, Kim D, Amici M, Son GH, Zhuo M, Kim K, Kaang BK, Kim SJ, Collingridge GL. The Probability of Neurotransmitter Release Governs AMPA Receptor Trafficking via Activity-Dependent Regulation of mGluR1 Surface Expression. Cell Rep 2018; 25:3631-3646.e3. [PMID: 30590038 PMCID: PMC6315206 DOI: 10.1016/j.celrep.2018.12.010] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Revised: 09/28/2018] [Accepted: 12/03/2018] [Indexed: 12/14/2022] Open
Abstract
A major mechanism contributing to synaptic plasticity involves alterations in the number of AMPA receptors (AMPARs) expressed at synapses. Hippocampal CA1 synapses, where this process has been most extensively studied, are highly heterogeneous with respect to their probability of neurotransmitter release, P(r). It is unknown whether there is any relationship between the extent of plasticity-related AMPAR trafficking and the initial P(r) of a synapse. To address this question, we induced metabotropic glutamate receptor (mGluR) dependent long-term depression (mGluR-LTD) and assessed AMPAR trafficking and P(r) at individual synapses, using SEP-GluA2 and FM4-64, respectively. We found that either pharmacological or synaptic activation of mGluR1 reduced synaptic SEP-GluA2 in a manner that depends upon P(r); this process involved an activity-dependent reduction in surface mGluR1 that selectively protects high-P(r) synapses from synaptic weakening. Consequently, the extent of postsynaptic plasticity can be pre-tuned by presynaptic activity.
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Affiliation(s)
- Thomas M Sanderson
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul 151-746, Korea; Neuroscience Research Institute, Seoul National University College of Medicine, 28 Yeongeon-dong, Jongno-gu, Seoul 110-799, Korea; School of Physiology, Pharmacology & Neuroscience, University of Bristol, Dorothy Hodgkin Building, Whitson Street, Bristol BS1 3NY, UK; Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, ON M5G 1X5, Canada
| | - Clarrisa A Bradley
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul 151-746, Korea; Neuroscience & Mental Health Program, The Hospital for Sick Children, Toronto, ON, Canada
| | - John Georgiou
- Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, ON M5G 1X5, Canada
| | - Yun Hwa Hong
- Neuroscience Research Institute, Seoul National University College of Medicine, 28 Yeongeon-dong, Jongno-gu, Seoul 110-799, Korea; Department of Physiology, Seoul National University College of Medicine, 28, Yeongeon-dong, Jongno-gu, Seoul 110-799, Korea
| | - Ai Na Ng
- School of Physiology, Pharmacology & Neuroscience, University of Bristol, Dorothy Hodgkin Building, Whitson Street, Bristol BS1 3NY, UK
| | - Yeseul Lee
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul 151-746, Korea; School of Physiology, Pharmacology & Neuroscience, University of Bristol, Dorothy Hodgkin Building, Whitson Street, Bristol BS1 3NY, UK
| | - Hee-Dae Kim
- Department of Brain and Cognitive Sciences, DGIST, and Korea Brain Institute (KBRI), Daegu, 41068, Korea
| | - Doyeon Kim
- Department of Brain and Cognitive Sciences, DGIST, and Korea Brain Institute (KBRI), Daegu, 41068, Korea
| | - Mascia Amici
- School of Physiology, Pharmacology & Neuroscience, University of Bristol, Dorothy Hodgkin Building, Whitson Street, Bristol BS1 3NY, UK
| | - Gi Hoon Son
- Department of Biomedical Sciences, Korea University College of Medicine, Seoul 136-705, Seoul, Korea
| | - Min Zhuo
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul 151-746, Korea; Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada; Department of Biological Sciences, College of Natural Sciences, Seoul National University, Building 504, Room 202, 599 Gwanangno, Gwanak-gu 151-747, Seoul, Korea; Center for Neuron and Disease, Frontier Institutes of Science and Technology, Xi'an Jiaotong University, Xi'an, 710049, China
| | - Kyungjin Kim
- Department of Brain and Cognitive Sciences, DGIST, and Korea Brain Institute (KBRI), Daegu, 41068, Korea
| | - Bong-Kiun Kaang
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul 151-746, Korea; Department of Biological Sciences, College of Natural Sciences, Seoul National University, Building 504, Room 202, 599 Gwanangno, Gwanak-gu 151-747, Seoul, Korea; Center for Neuron and Disease, Frontier Institutes of Science and Technology, Xi'an Jiaotong University, Xi'an, 710049, China
| | - Sang Jeong Kim
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul 151-746, Korea; Neuroscience Research Institute, Seoul National University College of Medicine, 28 Yeongeon-dong, Jongno-gu, Seoul 110-799, Korea; Department of Physiology, Seoul National University College of Medicine, 28, Yeongeon-dong, Jongno-gu, Seoul 110-799, Korea.
| | - Graham L Collingridge
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul 151-746, Korea; School of Physiology, Pharmacology & Neuroscience, University of Bristol, Dorothy Hodgkin Building, Whitson Street, Bristol BS1 3NY, UK; Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, ON M5G 1X5, Canada; Department of Physiology, Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada.
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14
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Brewer CL, Baccei ML. Enhanced Postsynaptic GABA B Receptor Signaling in Adult Spinal Projection Neurons after Neonatal Injury. Neuroscience 2018; 384:329-339. [PMID: 29885525 PMCID: PMC6053268 DOI: 10.1016/j.neuroscience.2018.05.046] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Revised: 04/28/2018] [Accepted: 05/30/2018] [Indexed: 12/19/2022]
Abstract
Clinical and basic science research have revealed persistent effects of early-life injury on nociceptive processing and resulting pain sensitivity. While recent work has identified clear deficits in fast GABAA- and glycine receptor-mediated inhibition in the adult spinal dorsal horn after neonatal tissue damage, the effects of early injury on slow, metabotropic inhibition within spinal pain circuits are poorly understood. Here we provide evidence that neonatal surgical incision significantly enhances postsynaptic GABAB receptor signaling within the mature superficial dorsal horn (SDH) in a cell type-dependent manner. In vitro patch-clamp recordings were obtained from identified lamina I projection neurons and GABAergic interneurons in the SDH of adult female mice following hindpaw incision at postnatal day (P)3. Early tissue damage increased the density of the outward current evoked by baclofen, a selective GABAB receptor agonist, in projection neurons but not inhibitory interneurons. This could reflect enhanced postsynaptic expression of downstream G protein-coupled inward-rectifying potassium channels (GIRKs), as the response to the GIRK agonist ML297 was greater in projection neurons from neonatally incised mice compared to naive littermate controls. Meanwhile, presynaptic GABAB receptor-mediated reduction of spontaneous neurotransmitter release onto both neuronal populations was unaffected by early-life injury. Collectively, our findings suggest that ascending nociceptive transmission to the adult brain is under stronger control by spinal metabotropic inhibition in the aftermath of neonatal tissue damage.
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Affiliation(s)
- Chelsie L Brewer
- Neuroscience Graduate Program, University of Cincinnati College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267, USA; Pain Research Center, Department of Anesthesiology, University of Cincinnati Medical Center, 231 Albert Sabin Way, Cincinnati, OH 45267, USA
| | - Mark L Baccei
- Neuroscience Graduate Program, University of Cincinnati College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267, USA; Pain Research Center, Department of Anesthesiology, University of Cincinnati Medical Center, 231 Albert Sabin Way, Cincinnati, OH 45267, USA.
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15
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Marcott PF, Gong S, Donthamsetti P, Grinnell SG, Nelson MN, Newman AH, Birnbaumer L, Martemyanov KA, Javitch JA, Ford CP. Regional Heterogeneity of D2-Receptor Signaling in the Dorsal Striatum and Nucleus Accumbens. Neuron 2018; 98:575-587.e4. [PMID: 29656874 PMCID: PMC6048973 DOI: 10.1016/j.neuron.2018.03.038] [Citation(s) in RCA: 45] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2017] [Revised: 02/20/2018] [Accepted: 03/21/2018] [Indexed: 12/24/2022]
Abstract
Dopamine input to the dorsal and ventral striatum originates from separate populations of midbrain neurons. Despite differences in afferent inputs and behavioral output, little is known about how dopamine release is encoded by dopamine receptors on medium spiny neurons (MSNs) across striatal subregions. Here we examined the activation of D2 receptors following the synaptic release of dopamine in the dorsal striatum (DStr) and nucleus accumbens (NAc) shell. We found that D2 receptor-mediated synaptic currents were slower in the NAc and this difference occurred at the level of D2-receptor signaling. As a result of preferential coupling to Gαo, we also found that D2 receptors in MSNs demonstrated higher sensitivity for dopamine in the NAc. The higher sensitivity in the NAc was eliminated following cocaine exposure. These results identify differences in the sensitivity and timing of D2-receptor signaling across the striatum that influence how nigrostriatal and mesolimbic signals are encoded across these circuits.
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Affiliation(s)
- Pamela F Marcott
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, Aurora, CO 80045, USA; Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
| | - Sheng Gong
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, Aurora, CO 80045, USA; Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
| | | | - Steven G Grinnell
- Department of Psychiatry, Columbia University, New York, NY 10032, USA; Division of Molecular Therapeutics, New York State Psychiatric Institute, New York, NY 10032, USA
| | - Melissa N Nelson
- Department of Psychiatry, Columbia University, New York, NY 10032, USA; Division of Molecular Therapeutics, New York State Psychiatric Institute, New York, NY 10032, USA
| | - Amy H Newman
- National Institute of Drug Abuse - Intramural Research Program, NIH, Baltimore, MD 21224, USA
| | - Lutz Birnbaumer
- Neurobiology Laboratory, National Institute of Environmental Health Sciences, Durham, NC 27709, USA; Institute of Biomedical Research (BIOMED), Catholic University of Argentina, Buenos Aires C1107AAZ, Argentina
| | - Kirill A Martemyanov
- Department of Neuroscience, The Scripps Research Institute, Jupiter, FL 33458, USA
| | - Jonathan A Javitch
- Department of Pharmacology, Columbia University, New York, NY 10032, USA; Department of Psychiatry, Columbia University, New York, NY 10032, USA; Division of Molecular Therapeutics, New York State Psychiatric Institute, New York, NY 10032, USA
| | - Christopher P Ford
- Department of Pharmacology, University of Colorado School of Medicine, Anschutz Medical Campus, Aurora, CO 80045, USA; Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.
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16
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Negrete-Díaz JV, Sihra TS, Flores G, Rodríguez-Moreno A. Non-canonical Mechanisms of Presynaptic Kainate Receptors Controlling Glutamate Release. Front Mol Neurosci 2018; 11:128. [PMID: 29731708 PMCID: PMC5920280 DOI: 10.3389/fnmol.2018.00128] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2018] [Accepted: 03/29/2018] [Indexed: 01/09/2023] Open
Abstract
A metabotropic modus operandi for kainate receptors (KARs) was first discovered in 1998 modulating GABA release. These receptors have been also found to modulate glutamate release at different synapses in several brain regions. Mechanistically, a general biphasic mechanism for modulating glutamate release by presynaptic KARs with metabotropic actions has emerged, with low KA concentrations invoking an increase in glutamate release, whereas higher concentrations of KA mediate a decrease in the release of this neurotransmitter. The molecular mechanisms underpinning the opposite modulation of glutamate release are distinct, with a G-protein-independent, adenylate cyclase (AC)- and protein kinase A (PKA)-dependent mechanism mediating the facilitation of glutamate release, while a G-protein dependent mechanism (with or without protein kinase recruitment) is involved in the decrease of neurotransmitter release. In the present review, we revisit the mechanisms underlying the non-canonical modus operandi of KARs effecting the bimodal control of glutamatergic transmission in different brain regions, and address the possible functions that this modulation may support.
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Affiliation(s)
- José V Negrete-Díaz
- Laboratory of Cellular Neuroscience and Plasticity, Department of Physiology, Anatomy and Cell Biology, University Pablo de Olavide, Seville, Spain.,División de Ciencias de la Salud e Ingenierías, Universidad de Guanajuato, Guanajuato, Mexico
| | - Talvinder S Sihra
- Department of Neuroscience, Physiology and Pharmacology, University College London, London, United Kingdom
| | - Gonzalo Flores
- Laboratorio de Neuropsiquiatría, Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, Puebla, Mexico
| | - Antonio Rodríguez-Moreno
- Laboratory of Cellular Neuroscience and Plasticity, Department of Physiology, Anatomy and Cell Biology, University Pablo de Olavide, Seville, Spain
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17
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Wong JM, Gray JA. Long-Term Depression Is Independent of GluN2 Subunit Composition. J Neurosci 2018; 38:4462-70. [PMID: 29593052 DOI: 10.1523/JNEUROSCI.0394-18.2018] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2018] [Revised: 03/16/2018] [Accepted: 03/20/2018] [Indexed: 11/21/2022] Open
Abstract
NMDA receptors (NMDARs) mediate both long-term potentiation and long-term depression (LTD) and understanding how a single receptor can initiate both phenomena remains a major question in neuroscience. A prominent hypothesis implicates the NMDAR subunit composition, specifically GluN2A and GluN2B, in dictating the rules of synaptic plasticity. However, studies testing this hypothesis have yielded inconsistent and often contradictory results, especially for LTD. These inconsistent results may be due to challenges in the interpretation of subunit-selective pharmacology and in dissecting out the contributions of differential channel properties versus the interacting proteins unique to GluN2A or GluN2B. In this study, we address the pharmacological and biochemical challenges by using a single-neuron genetic approach to delete NMDAR subunits in conditional knock-out mice. In addition, the recently discovered non-ionotropic nature of NMDAR-dependent LTD allowed the rigorous assessment of unique subunit contributions to NMDAR-dependent LTD while eliminating the variable of differential charge transfer. Here we find that neither the GluN2A nor the GluN2B subunit is strictly necessary for either non-ionotropic or ionotropic LTD.SIGNIFICANCE STATEMENT NMDA receptors are key regulators of bidirectional synaptic plasticity. Understanding the mechanisms regulating bidirectional plasticity will guide development of therapeutic strategies to treat the dysfunctional synaptic plasticity in multiple neuropsychiatric disorders. Because of the unique properties of the NMDA receptor GluN2 subunits, they have been postulated to differentially affect synaptic plasticity. However, there has been significant controversy regarding the roles of the GluN2 subunits in synaptic long term depression (LTD). Using single-neuron knock-out of the GluN2 subunits, we show that LTD requires neither GluN2A nor GluN2B.
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18
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Sheahan TD, Valtcheva MV, McIlvried LA, Pullen MY, Baranger DA, Gereau RW. Metabotropic Glutamate Receptor 2/3 (mGluR2/3) Activation Suppresses TRPV1 Sensitization in Mouse, But Not Human, Sensory Neurons. eNeuro 2018; 5:ENEURO.0412-17.2018. [PMID: 29662945 PMCID: PMC5898698 DOI: 10.1523/eneuro.0412-17.2018] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2017] [Revised: 02/06/2018] [Accepted: 02/07/2018] [Indexed: 01/08/2023] Open
Abstract
The use of human tissue to validate putative analgesic targets identified in rodents is a promising strategy for improving the historically poor translational record of preclinical pain research. We recently demonstrated that in mouse and human sensory neurons, agonists for metabotropic glutamate receptors 2 and 3 (mGluR2/3) reduce membrane hyperexcitability produced by the inflammatory mediator prostaglandin E2 (PGE2). Previous rodent studies indicate that mGluR2/3 can also reduce peripheral sensitization by suppressing inflammation-induced sensitization of TRPV1. Whether this observation similarly translates to human sensory neurons has not yet been tested. We found that activation of mGluR2/3 with the agonist APDC suppressed PGE2-induced sensitization of TRPV1 in mouse, but not human, sensory neurons. We also evaluated sensory neuron expression of the gene transcripts for mGluR2 (Grm2), mGluR3 (Grm3), and TRPV1 (Trpv1). The majority of Trpv1+ mouse and human sensory neurons expressed Grm2 and/or Grm3, and in both mice and humans, Grm2 was expressed in a greater percentage of sensory neurons than Grm3. Although we demonstrated a functional difference in the modulation of TRPV1 sensitization by mGluR2/3 activation between mouse and human, there were no species differences in the gene transcript colocalization of mGluR2 or mGluR3 with TRPV1 that might explain this functional difference. Taken together with our previous work, these results suggest that mGluR2/3 activation suppresses only some aspects of human sensory neuron sensitization caused by PGE2. These differences have implications for potential healthy human voluntary studies or clinical trials evaluating the analgesic efficacy of mGluR2/3 agonists or positive allosteric modulators.
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Affiliation(s)
- Tayler D. Sheahan
- Washington University Pain Center and Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110
- Washington University Program in Neuroscience, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Manouela V. Valtcheva
- Washington University Pain Center and Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110
- Washington University Program in Neuroscience, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Lisa A. McIlvried
- Washington University Pain Center and Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Melanie Y. Pullen
- Washington University Pain Center and Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110
| | - David A.A. Baranger
- Washington University Program in Neuroscience, Washington University School of Medicine, St. Louis, Missouri 63110
- BRAIN Laboratory, Department of Psychological and Brain Sciences, Washington University in St. Louis, St. Louis, Missouri 63130
| | - Robert W. Gereau
- Washington University Pain Center and Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110
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19
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Tidball P, Burn HV, Teh KL, Volianskis A, Collingridge GL, Fitzjohn SM. Differential ability of the dorsal and ventral rat hippocampus to exhibit group I metabotropic glutamate receptor-dependent synaptic and intrinsic plasticity. Brain Neurosci Adv 2017; 1. [PMID: 28413831 PMCID: PMC5390859 DOI: 10.1177/2398212816689792] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Background: The hippocampus is critically involved in learning and memory processes. Although once considered a relatively homogenous structure, it is now clear that the hippocampus can be divided along its longitudinal axis into functionally distinct domains, responsible for the encoding of different types of memory or behaviour. Although differences in extrinsic connectivity are likely to contribute to this functional differentiation, emerging evidence now suggests that cellular and molecular differences at the level of local hippocampal circuits may also play a role. Methods: In this study, we have used extracellular field potential recordings to compare basal input/output function and group I metabotropic glutamate receptor-dependent forms of synaptic and intrinsic plasticity in area CA1 of slices taken from the dorsal and ventral sectors of the adult rat hippocampus. Results: Using two extracellular electrodes to simultaneously record field EPSPs and population spikes, we show that dorsal and ventral hippocampal slices differ in their basal levels of excitatory synaptic transmission, paired-pulse facilitation, and EPSP-to-Spike coupling. Furthermore, we show that slices taken from the ventral hippocampus have a greater ability than their dorsal counterparts to exhibit long-term depression of synaptic transmission and EPSP-to-Spike potentiation induced by transient application of the group I mGluR agonist (RS)-3,5-dihydroxyphenylglycine. Conclusions: Together, our results provide further evidence that the information processing properties of local hippocampal circuits differ in the dorsal and ventral hippocampal sectors, and that these differences may in turn contribute to the functional differentiation that exists along the hippocampal longitudinal axis.
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Affiliation(s)
- Patrick Tidball
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
| | - Hannah V Burn
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
| | - Kai Lun Teh
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
| | - Arturas Volianskis
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
| | - Graham L Collingridge
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK.,Department of Physiology, University of Toronto, Toronto, Ontario, Canada.,Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada
| | - Stephen M Fitzjohn
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
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20
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Jaso BA, Niciu MJ, Iadarola ND, Lally N, Richards EM, Park M, Ballard ED, Nugent AC, Machado-Vieira R, Zarate CA. Therapeutic Modulation of Glutamate Receptors in Major Depressive Disorder. Curr Neuropharmacol 2017; 15:57-70. [PMID: 26997505 PMCID: PMC5327449 DOI: 10.2174/1570159x14666160321123221] [Citation(s) in RCA: 66] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2015] [Revised: 11/09/2015] [Accepted: 01/30/2016] [Indexed: 12/12/2022] Open
Abstract
Current pharmacotherapies for major depressive disorder (MDD) have a distinct lag of onset that can prolong distress and impairment for patients, and realworld effectiveness trials further suggest that antidepressant efficacy is limited in many patients. All currently approved antidepressant medications for MDD act primarily through monoaminergic mechanisms, e.g., receptor/reuptake agonists or antagonists with varying affinities for serotonin, norepinephrine, or dopamine. Glutamate is the major excitatory neurotransmitter in the central nervous system, and glutamate and its cognate receptors are implicated in the pathophysiology of MDD, as well as in the development of novel therapeutics for this disorder. Since the rapid and robust antidepressant effects of the N-methyl-D-aspartate (NMDA) antagonist ketamine were first observed in 2000, other NMDA receptor antagonists have been studied in MDD. These have been associated with relatively modest antidepressant effects compared to ketamine, but some have shown more favorable characteristics with increased potential in clinical practice (for instance, oral administration, decreased dissociative and/or psychotomimetic effects, and reduced abuse/diversion liability). This article reviews the clinical evidence supporting the use of glutamate receptor modulators with direct affinity for cognate receptors: 1) non-competitive NMDA receptor antagonists (ketamine, memantine, dextromethorphan, AZD6765); 2) subunit (NR2B)-specific NMDA receptor antagonists (CP- 101,606/traxoprodil, MK-0657); 3) NMDA receptor glycine-site partial agonists (D-cycloserine, GLYX- 13); and 4) metabotropic glutamate receptor (mGluR) modulators (AZD2066, RO4917523/basimglurant). Several other theoretical glutamate receptor targets with preclinical antidepressant-like efficacy, but that have yet to be studied clinically, are also briefly discussed; these include α-amino-3-hydroxyl-5-methyl-4- isoxazoleproprionic acid (AMPA) agonists, mGluR2/3 negative allosteric modulators, and mGluR7 agonists.
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Affiliation(s)
- Brittany A. Jaso
- Experimental Therapeutics and Pathophysiology Branch, National Institute of Mental Health, National Institutes of Health, 10 Center Dr., Building 10/CRC, Room 7-5545, Bethesda, MD 20892, USA
| | - Mark J. Niciu
- Experimental Therapeutics and Pathophysiology Branch, National Institute of Mental Health, National Institutes of Health, 10 Center Dr., Building 10/CRC, Room 7-5545, Bethesda, MD 20892, USA
| | - Nicolas D. Iadarola
- Experimental Therapeutics and Pathophysiology Branch, National Institute of Mental Health, National Institutes of Health, 10 Center Dr., Building 10/CRC, Room 7-5545, Bethesda, MD 20892, USA
| | - Níall Lally
- Experimental Therapeutics and Pathophysiology Branch, National Institute of Mental Health, National Institutes of Health, 10 Center Dr., Building 10/CRC, Room 7-5545, Bethesda, MD 20892, USA
| | - Erica M. Richards
- Experimental Therapeutics and Pathophysiology Branch, National Institute of Mental Health, National Institutes of Health, 10 Center Dr., Building 10/CRC, Room 7-5545, Bethesda, MD 20892, USA
| | - Minkyung Park
- Experimental Therapeutics and Pathophysiology Branch, National Institute of Mental Health, National Institutes of Health, 10 Center Dr., Building 10/CRC, Room 7-5545, Bethesda, MD 20892, USA
| | - Elizabeth D. Ballard
- Experimental Therapeutics and Pathophysiology Branch, National Institute of Mental Health, National Institutes of Health, 10 Center Dr., Building 10/CRC, Room 7-5545, Bethesda, MD 20892, USA
| | - Allison C. Nugent
- Experimental Therapeutics and Pathophysiology Branch, National Institute of Mental Health, National Institutes of Health, 10 Center Dr., Building 10/CRC, Room 7-5545, Bethesda, MD 20892, USA
| | - Rodrigo Machado-Vieira
- Experimental Therapeutics and Pathophysiology Branch, National Institute of Mental Health, National Institutes of Health, 10 Center Dr., Building 10/CRC, Room 7-5545, Bethesda, MD 20892, USA
| | - Carlos A. Zarate
- Experimental Therapeutics and Pathophysiology Branch, National Institute of Mental Health, National Institutes of Health, 10 Center Dr., Building 10/CRC, Room 7-5545, Bethesda, MD 20892, USA
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21
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Molliver DC, Rau KK, Jankowski MP, Soneji DJ, Baumbauer KM, Koerber HR. Deletion of the murine ATP/UTP receptor P2Y2 alters mechanical and thermal response properties in polymodal cutaneous afferents. Neuroscience 2016; 332:223-30. [PMID: 27393251 DOI: 10.1016/j.neuroscience.2016.06.054] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2015] [Revised: 06/27/2016] [Accepted: 06/29/2016] [Indexed: 12/18/2022]
Abstract
P2Y2 is a member of the P2Y family of G protein-coupled nucleotide receptors that is widely co-expressed with TRPV1 in peripheral sensory neurons of the dorsal root ganglia. To characterize P2Y2 function in cutaneous afferents, intracellular recordings from mouse sensory neurons were made using an ex vivo preparation in which hindlimb skin, saphenous nerve, dorsal root ganglia and spinal cord are dissected intact. The peripheral response properties of individual cutaneous C-fibers were analyzed using digitally controlled mechanical and thermal stimuli in male P2Y2(+/+) and P2Y2(-/-) mice. Selected sensory neurons were labeled with Neurobiotin and further characterized by immunohistochemistry. In wildtype preparations, C-fibers responding to both mechanical and thermal stimuli (CMH or CMHC) preferentially bound the lectin marker IB4 and were always immunonegative for TRPV1. Conversely, cells that fired robustly to noxious heat, but were insensitive to mechanical stimuli, were TRPV1-positive and IB4-negative. P2Y2 gene deletion resulted in reduced firing by TRPV1-negative CMH fibers to a range of heat stimuli. However, we also identified an atypical population of IB4-negative, TRPV1-positive CMH fibers. Compared to wildtype CMH fibers, these TRPV1-positive neurons exhibited lower firing rates in response to mechanical stimulation, but had increased firing to noxious heat (43-51°C). Collectively, these results demonstrate that P2Y2 contributes to response properties of cutaneous afferents, as P2Y2 deletion reduces responsiveness of conventional unmyelinated polymodal afferents to heat and appears to result in the acquisition of mechanical responsiveness in a subset of TRPV1-expressing afferents.
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22
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Dore K, Aow J, Malinow R. Agonist binding to the NMDA receptor drives movement of its cytoplasmic domain without ion flow. Proc Natl Acad Sci U S A 2015; 112:14705-10. [PMID: 26553997 DOI: 10.1073/pnas.1520023112] [Citation(s) in RCA: 74] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The NMDA receptor (R) plays important roles in brain physiology and pathology as an ion channel. Here we examine the ion flow-independent coupling of agonist to the NMDAR cytoplasmic domain (cd). We measure FRET between fluorescently tagged cytoplasmic domains of GluN1 subunits of NMDARs expressed in neurons. Different neuronal compartments display varying levels of FRET, consistent with different NMDARcd conformations. Agonist binding drives a rapid and transient ion flow-independent reduction in FRET between GluN1 subunits within individual NMDARs. Intracellular infusion of an antibody targeting the GluN1 cytoplasmic domain blocks agonist-driven FRET changes in the absence of ion flow, supporting agonist-driven movement of the NMDARcd. These studies indicate that extracellular ligand binding to the NMDAR can transmit conformational information into the cell in the absence of ion flow.
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Rutkowska-Wlodarczyk I, Aller MI, Valbuena S, Bologna JC, Prézeau L, Lerma J. A proteomic analysis reveals the interaction of GluK1 ionotropic kainate receptor subunits with Go proteins. J Neurosci 2015; 35:5171-9. [PMID: 25834043 DOI: 10.1523/JNEUROSCI.5059-14.2015] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Kainate receptors (KARs) are found ubiquitously in the CNS and are present presynaptically and postsynaptically regulating synaptic transmission and excitability. Functional studies have proven that KARs act as ion channels as well as potentially activating G-proteins, thus indicating the existance of a dual signaling system for KARs. Nevertheless, it is not clear how these ion channels activate G-proteins and which of the KAR subunits is involved. Here we performed a proteomic analysis to define proteins that interact with the C-terminal domain of GluK1 and we identified a variety of proteins with many different functions, including a Go α subunit. These interactions were verified through distinct in vitro and in vivo assays, and the activation of the Go protein by GluK1 was validated in bioluminescence resonance energy transfer experiments, while the specificity of this association was confirmed in GluK1-deficient mice. These data reveal components of the KAR interactome, and they show that GluK1 and Go proteins are natural partners, accounting for the metabotropic effects of KARs.
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Wyeth MS, Pelkey KA, Petralia RS, Salter MW, McInnes RR, McBain CJ. Neto auxiliary protein interactions regulate kainate and NMDA receptor subunit localization at mossy fiber-CA3 pyramidal cell synapses. J Neurosci 2014; 34:622-8. [PMID: 24403160 DOI: 10.1523/JNEUROSCI.3098-13.2014] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Neto1 and Neto2 auxiliary subunits coassemble with NMDA receptors (NMDARs) and kainate receptors (KARs) to modulate their function. In the hippocampus, Neto1 enhances the amplitude and prolongs the kinetics of KAR-mediated currents at mossy fiber (MF)-CA3 pyramidal cell synapses. However, whether Neto1 trafficks KARs to synapses or simply alters channel properties is unresolved. Therefore, postembedding electron microscopy was performed to investigate the localization of GluK2/3 subunits at MF-CA3 synapses in Neto-null mice. Postsynaptic GluK2/3 Immunogold labeling was substantially reduced in Neto-null mice compared with wild types. Moreover, spontaneous KAR-mediated synaptic currents and metabotropic KAR signaling were absent in CA3 pyramidal cells of Neto-null mice. A similar loss of ionotropic and metabotropic KAR function was observed in Neto1, but not Neto2, single knock-out mice, specifically implicating Neto1 in regulating CA3 pyramidal cell KAR localization and function. Additional controversy pertains to the role of Neto proteins in modulating synaptic NMDARs. While Immunogold labeling for GluN2A at MF-CA3 synapses was comparable between wild-type and Neto-null mice, labeling for postsynaptic GluN2B was robustly increased in Neto-null mice. Accordingly, NMDAR-mediated currents at MF-CA3 synapses exhibited increased sensitivity to a GluN2B-selective antagonist in Neto1 knockouts relative to wild types. Thus, despite preservation of the overall MF-CA3 synaptic NMDAR-mediated current, loss of Neto1 alters NMDAR subunit composition. These results confirm that Neto protein interactions regulate synaptic localization of KAR and NMDAR subunits at MF-CA3 synapses, with implications for both ionotropic and metabotropic glutamatergic recruitment of the CA3 network.
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Botta P, Zucca A, Valenzuela CF. Acute ethanol exposure inhibits silencing of cerebellar Golgi cell firing induced by granule cell axon input. Front Integr Neurosci 2014; 8:10. [PMID: 24567705 PMCID: PMC3915290 DOI: 10.3389/fnint.2014.00010] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2013] [Accepted: 01/16/2014] [Indexed: 11/13/2022] Open
Abstract
Golgi cells (GoCs) are specialized interneurons that provide inhibitory input to granule cells in the cerebellar cortex. GoCs are pacemaker neurons that spontaneously fire action potentials, triggering spontaneous inhibitory postsynaptic currents in granule cells and also contributing to the generation tonic GABAA receptor-mediated currents in granule cells. In turn, granule cell axons provide feedback glutamatergic input to GoCs. It has been shown that high frequency stimulation of granule cell axons induces a transient pause in GoC firing in a type 2-metabotropic glutamate receptor (mGluR2)-dependent manner. Here, we investigated the effect ethanol on the pause of GoC firing induced by high frequency stimulation of granule cell axons. GoC electrophysiological recordings were performed in parasagittal cerebellar vermis slices from postnatal day 23 to 26 rats. Loose-patch cell-attached recordings revealed that ethanol (40 mM) reversibly decreases the pause duration. An antagonist of mGluR2 reduced the pause duration but did not affect the effect of ethanol. Whole-cell voltage-clamp recordings showed that currents evoked by an mGluR2 agonist were not significantly affected by ethanol. Perforated-patch experiments in which hyperpolarizing and depolarizing currents were injected into GoCs demonstrated that there is an inverse relationship between spontaneous firing and pause duration. Slight inhibition of the Na+/K+ pump mimicked the effect of ethanol on pause duration. In conclusion, ethanol reduces the granule cell axon-mediated feedback mechanism by reducing the input responsiveness of GoCs. This would result in a transient increase of GABAA receptor-mediated inhibition of granule cells, limiting information flow at the input stage of the cerebellar cortex.
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Affiliation(s)
- Paolo Botta
- Department of Neurosciences, University of New Mexico Health Sciences Center Albuquerque, NM, USA
| | - Aya Zucca
- Department of Neurosciences, University of New Mexico Health Sciences Center Albuquerque, NM, USA
| | - C Fernando Valenzuela
- Department of Neurosciences, University of New Mexico Health Sciences Center Albuquerque, NM, USA
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Chung C. NMDA receptor as a newly identified member of the metabotropic glutamate receptor family: clinical implications for neurodegenerative diseases. Mol Cells 2013; 36:99-104. [PMID: 23740429 PMCID: PMC3887951 DOI: 10.1007/s10059-013-0113-y] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2013] [Revised: 05/08/2013] [Accepted: 05/09/2013] [Indexed: 12/17/2022] Open
Abstract
Recent reports have proposed a novel function for the N-methyl-D-aspartate (NMDA) receptor (NMDAR), a well-known excitatory, ionotropic receptor. A series of observations employing pharmacological techniques has proposed that upon ligand binding, this ionotropic receptor can actually function via signaling cascades independent of traditional ionotropic action. Moreover, the "metabotropic" action of NMDARs is suggested to mediate a form of synaptic plasticity, namely long-term synaptic depression (LTD), which shares cellular mechanisms with the synaptic deficits observed in Alzheimer's disease. Given that a growing body of clinical and preclinical evidence strongly recommends NMDAR antagonists for their therapeutic potentials and advantages in a variety of diseases, further investigation into their molecular and cellular mechanisms is required to better understand the "metabotropic" action of NMDARs.
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Affiliation(s)
- ChiHye Chung
- Department of Biological Sciences, Konkuk University, Seoul 143-701, Korea.
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Abstract
At present, all medications for schizophrenia function primarily by blocking dopamine D2 receptors. Over 50 years ago, the first observations were made that subsequently led to development of alternative, glutamatergic conceptualizations. This special issue traces the historic development of the phencyclidine (PCP) model of schizophrenia from the initial description of the psychotomimetic effects of PCP in the early 1960s, through discovery of the link to N-methyl-D-aspartate-type glutamate receptors (NMDAR) in the 1980s, and finally to the development of NMDA-based treatment strategies starting in the 1990s. NMDAR antagonists uniquely reproduce both positive and negative symptoms of schizophrenia, and induce schizophrenia-like cognitive deficits and neurophysiological dysfunction. At present, there remain several hypotheses concerning mechanisms by which NMDAR dysfunction leads to symptoms/deficits, and several theories regarding ideal NMDAR-based treatment approaches as outlined in the issue. Several classes of agent, including metabotropic glutamate agonists, glycine transport inhibitors, and D-serine-based compounds are currently in late-stage clinical development and may provide long-sought treatments for persistent positive and negative symptoms and cognitive dysfunction in schizophrenia.
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Affiliation(s)
- Daniel C. Javitt
- To whom correspondence should be addressed; tel: 845-398-6534, fax: 845-398-6546, e-mail:
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Vinson PN, Conn PJ. Metabotropic glutamate receptors as therapeutic targets for schizophrenia. Neuropharmacology 2012; 62:1461-72. [PMID: 21620876 PMCID: PMC3189289 DOI: 10.1016/j.neuropharm.2011.05.005] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2010] [Revised: 05/02/2011] [Accepted: 05/08/2011] [Indexed: 01/13/2023]
Abstract
Treatment options for schizophrenia that address all symptom categories (positive, negative, and cognitive) are lacking in current therapies for this disorder. Compounds targeting the metabotropic glutamate (mGlu) receptors hold promise as a more comprehensive therapeutic alternative to typical and atypical antipsychotics and may avoid the occurrence of extrapyramidal side effects that accompany these treatments. Activation of the group II mGlu receptors (mGlu(2) and mGlu(3)) and the group I mGlu(5) are hypothesized to normalize the disruption of thalamocortical glutamatergic circuitry that results in abnormal glutamaterigic signaling in the prefrontal cortex (PFC). Agonists of mGlu(2) and mGlu(3) have demonstrated efficacy for the positive symptom group in both animal models and clinical trials with mGlu(2) being the subtype most likely responsible for the therapeutic effect. Limitations in the chemical space tolerated by the orthosteric site of the mGlu receptors has led to the pursuit of compounds that potentiate the receptor's response to glutamate by acting at less highly conserved allosteric sites. Several series of selective positive allosteric modulators (PAMs) for mGlu(2) and mGlu(5) have demonstrated efficacy in animal models used for the evaluation of antipsychotic agents. In addition, evidence from animal studies indicates that mGlu(5) PAMs hold promise for the treatment of cognitive deficits that occur in schizophrenia. Hopefully, further optimization of allosteric modulators of mGlu receptors will yield clinical candidates that will allow full evaluation of the potential efficacy of these compounds in the treatment of multiple symptom domains in schizophrenia patients in the near future.
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Affiliation(s)
- Paige N. Vinson
- Vanderbilt University Medical Center, Department of Pharmacology and Vanderbilt Center for Neuroscience Drug Discovery, Nashville, TN 37202
| | - P. Jeffrey Conn
- Vanderbilt University Medical Center, Department of Pharmacology and Vanderbilt Center for Neuroscience Drug Discovery, Nashville, TN 37202
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Lyon L, Burnet PW, Kew JN, Corti C, Rawlins JN, Lane T, De Filippis B, Harrison PJ, Bannerman DM. Fractionation of spatial memory in GRM2/3 (mGlu2/mGlu3) double knockout mice reveals a role for group II metabotropic glutamate receptors at the interface between arousal and cognition. Neuropsychopharmacology 2011; 36:2616-28. [PMID: 21832989 DOI: 10.1038/npp.2011.145] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Group II metabotropic glutamate receptors (mGluR2 and mGluR3, encoded by GRM2 and GRM3) are implicated in hippocampal function and cognition, and in the pathophysiology and treatment of schizophrenia and other psychiatric disorders. However, pharmacological and behavioral studies with group II mGluR agonists and antagonists have produced complex results. Here, we studied hippocampus-dependent memory in GRM2/3 double knockout (GRM2/3(-/-)) mice in an iterative sequence of experiments. We found that they were impaired on appetitively motivated spatial reference and working memory tasks, and on a spatial novelty preference task that relies on animals' exploratory drive, but were unimpaired on aversively motivated spatial memory paradigms. GRM2/3(-/-) mice also performed normally on an appetitively motivated, non-spatial, visual discrimination task. These results likely reflect an interaction between GRM2/3 genotype and the arousal-inducing properties of the experimental paradigm. The deficit seen on appetitive and exploratory spatial memory tasks may be absent in aversive tasks because the latter induce higher levels of arousal, which rescue spatial learning. Consistent with an altered arousal-cognition relationship in GRM2/3(-/-) mice, injection stress worsened appetitively motivated, spatial working memory in wild-types, but enhanced performance in GRM2/3(-/-) mice. GRM2/3(-/-) mice were also hypoactive in response to amphetamine. This fractionation of hippocampus-dependent memory depending on the appetitive-aversive context is to our knowledge unique, and suggests a role for group II mGluRs at the interface of arousal and cognition. These arousal-dependent effects may explain apparently conflicting data from previous studies, and have translational relevance for the involvement of these receptors in schizophrenia and other disorders.
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D'Souza MS, Liechti ME, Ramirez-Niño AM, Kuczenski R, Markou A. The metabotropic glutamate 2/3 receptor agonist LY379268 blocked nicotine-induced increases in nucleus accumbens shell dopamine only in the presence of a nicotine-associated context in rats. Neuropsychopharmacology 2011; 36:2111-24. [PMID: 21654734 DOI: 10.1038/npp.2011.103] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The metabotropic glutamate 2/3 (mGlu2/3) receptor agonist LY379268 ([-]-2-oxa-4-aminobicyclo [3.1.0] hexane-4,6-dicarboxylate) attenuates both nicotine self-administration and cue-induced nicotine seeking in rats. In this study, the effects of LY379268 (1 mg/kg) or saline pretreatment on nicotine-induced increases in nucleus accumbens (NAcc) shell dopamine were evaluated using in vivo microdialysis under different experimental conditions: (i) nicotine (0.4 mg/kg, base) was experimenter-administered subcutaneously to nicotine-naïve rats; (ii) nicotine was experimenter-administered either subcutaneously (0.4 mg/kg) or by a single experimenter-administered infusion (0.06 mg/kg, base) in rats with a history of nicotine self-administration (nicotine experienced) in the absence of a nicotine-associated context (ie, context and cues associated with nicotine self-administration); (iii) nicotine (0.06 mg/kg) was self-administered or experimenter-administered in nicotine-experienced rats in the presence of a nicotine-associated context. In saline-pretreated nicotine-naïve and nicotine-experienced rats, nicotine increased NAcc shell dopamine regardless of the context used for testing. Interestingly, LY379268 pretreatment blocked nicotine-induced increases in NAcc shell dopamine in nicotine-experienced rats only when tested in the presence of a nicotine-associated context. LY379268 did not block nicotine-induced increases in NAcc shell dopamine in nicotine-naïve or -experienced rats tested in the absence of a nicotine-associated context. These intriguing findings suggest that activation of mGlu2/3 receptors negatively modulates the combined effects of nicotine and nicotine-associated contexts/cues on NAcc dopamine. Thus, these data highlight a critical role for mGlu2/3 receptors in context/cue-induced drug-seeking behavior and suggest a neurochemical mechanism by which mGlu2/3 receptor agonists may promote smoking cessation by preventing relapse induced by the combination of nicotine and nicotine-associated contexts and cues.
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Reichel CM, Schwendt M, McGinty JF, Olive MF, See RE. Loss of object recognition memory produced by extended access to methamphetamine self-administration is reversed by positive allosteric modulation of metabotropic glutamate receptor 5. Neuropsychopharmacology 2011; 36:782-92. [PMID: 21150906 PMCID: PMC3052905 DOI: 10.1038/npp.2010.212] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/07/2010] [Revised: 11/06/2010] [Accepted: 11/08/2010] [Indexed: 11/09/2022]
Abstract
Chronic methamphetamine (meth) abuse can lead to persisting cognitive deficits. Here, we utilized a long-access meth self-administration (SA) protocol to assess recognition memory and metabotropic glutamate receptor (mGluR) expression, and the possible reversal of cognitive impairments with the mGluR5 allosteric modulator, 3-cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl) benzamide (CDPPB). Male, Long-Evans rats self-administered i.v. meth (0.02 mg/infusion) on an FR1 schedule of reinforcement or received yoked-saline infusions. After seven daily 1-h sessions, rats were switched to 6-h daily sessions for 14 days, and then underwent drug abstinence. Rats were tested for object recognition memory at 1 week after meth SA at 90 min and 24 h retention intervals. In a separate experiment, rats underwent the same protocol, but received either vehicle or CDPPB (30 mg/kg) after familiarization. Rats were killed on day 8 or 14 post-SA and brain tissue was obtained. Meth intake escalated over the extended access period. Additionally, meth-experienced rats showed deficits in both short- and long-term recognition memory, demonstrated by a lack of novel object exploration. The deficit at 90 min was reversed by CDPPB treatment. On day 8, meth intake during SA negatively correlated with mGluR expression in the perirhinal and prefrontal cortex, and mGluR5 receptor expression was decreased 14 days after discontinuation of meth. This effect was specific to mGluR5 levels in the perirhinal cortex, as no differences were identified in the hippocampus or in mGluR2/3 receptors. These results from a clinically-relevant animal model of addiction suggest that mGluR5 receptor modulation may be a potential treatment of cognitive dysfunction in meth addiction.
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Affiliation(s)
- Carmela M Reichel
- Department of Neurosciences, Medical University of South Carolina, Charleston, SC, USA
| | - Marek Schwendt
- Department of Neurosciences, Medical University of South Carolina, Charleston, SC, USA
| | - Jacqueline F McGinty
- Department of Neurosciences, Medical University of South Carolina, Charleston, SC, USA
| | - M Foster Olive
- Department of Neurosciences, Medical University of South Carolina, Charleston, SC, USA
| | - Ronald E See
- Department of Neurosciences, Medical University of South Carolina, Charleston, SC, USA
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Abstract
For a number of disease entities, oxidative stress becomes a significant factor in the etiology and progression of cell dysfunction and injury. Therapeutic strategies that can identify novel signal transduction pathways to ameliorate the toxic effects of oxidative stress may lead to new avenues of treatment for a spectrum of disorders that include diabetes, Alzheimer's disease, Parkinson's disease and immune system dysfunction. In this respect, metabotropic glutamate receptors (mGluRs) may offer exciting prospects for several disorders since these receptors can limit or prevent apoptotic cell injury as well as impact upon cellular development and function. Yet the role of mGluRs is complex in nature and may require specific mGluR modulation for a particular disease entity to maximize clinical efficacy and limit potential disability. Here we discuss the potential clinical translation of mGluRs and highlight the role of novel signal transduction pathways in the metabotropic glutamate system that may be vital for the clinical utility of mGluRs.
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Affiliation(s)
- Kenneth Maiese
- Division of Cellular and Molecular Cerebral Ischemia, Wayne State University School of Medicine, Detroit, Michigan 48201, USA.
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Bishop JR, Miller DD, Ellingrod VL, Holman T. Association between type-three metabotropic glutamate receptor gene (GRM3) variants and symptom presentation in treatment refractory schizophrenia. Hum Psychopharmacol 2011; 26:28-34. [PMID: 21344500 PMCID: PMC3199025 DOI: 10.1002/hup.1163] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
OBJECTIVE Positive associations between polymorphisms in the type-three metabotropic glutamate receptor gene (GRM3) and the pathogenesis of schizophrenia as well as response to antipsychotic treatment have been reported. The objective of this study was to determine whether refractory psychiatric symptoms in antipsychotic non-responders are related to polymorphisms in GRM3. METHODS Ninety-five treatment refractory schizophrenia participants were enrolled. Prior to a medication switch, global psychopathology and negative symptoms were rated. These participants were genotyped for seven markers in GRM3. Genotype associations with symptoms were assessed. RESULTS Two markers in GRM3 (rs1989796 and rs1476455), were associated with the presence of refractory global symptoms as measured by the Brief Psychiatric Rating Scale (BPRS) Total scores. Participants with an rs1476455_CC genotype had significantly higher BPRS scores than A-carriers (55.1±10.4 vs. 48.3±9.2; F=7.6, p=0.0071). Additionally, participants with the rs1989796_CC genotype had significantly higher BPRS scores than T-carriers (50.1±5.7 vs. 55.8±10.5, F=7.1, p=0.0091). No evidence for significant associations with negative symptoms was observed. CONCLUSIONS Polymorphisms in the GRM3 gene may be associated with refractory global psychosis symptoms but not negative symptoms in persons with schizophrenia.
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Affiliation(s)
- Jeffrey R. Bishop
- University of Illinois at Chicago Colleges of Pharmacy and Medicine, Department of Pharmacy Practice and Department of Psychiatry, Center for Cognitive Medicine
| | - Del D. Miller
- University of Iowa Carver College of Medicine Department of Psychiatry
| | - Vicki L. Ellingrod
- University of Michigan College of Pharmacy and College of Medicine, Department of Psychiatry
| | - Timothy Holman
- University of Iowa Carver College of Medicine Department of Psychiatry
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Cid JM, Duvey G, Cluzeau P, Nhem V, Macary K, Raux A, Poirier N, Muller J, Boléa C, Finn T, Poli S, Epping-Jordan M, Chamelot E, Derouet F, Girard F, Macdonald GJ, Vega JA, de Lucas AI, Matesanz E, Lavreysen H, Linares ML, Oehlrich D, Oyarzábal J, Tresadern G, Trabanco AA, Andrés JI, Le Poul E, Imogai H, Lutjens R, Rocher JP. Discovery of 1,5-disubstituted pyridones: a new class of positive allosteric modulators of the metabotropic glutamate 2 receptor. ACS Chem Neurosci 2010; 1:788-95. [PMID: 22778815 DOI: 10.1021/cn1000638] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2010] [Accepted: 07/20/2010] [Indexed: 11/28/2022] Open
Abstract
A series of 1,5-disubstituted pyridones was identified as positive allosteric modulators (PAMs) of the metabotropic glutamate receptor 2 (mGluR2) via high throughput screening (HTS). Subsequent SAR exploration led to the identification of several compounds with improved in vitro activity. Lead compound 8 was further profiled and found to attenuate the increase in PCP induced locomotor activity in mice.
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Affiliation(s)
- Jose María Cid
- Neuroscience Medicinal Chemistry, Johnson & Johnson Pharmaceutical Research & Development, Janssen-Cilag S.A., Calle Jarama 75, Polígono Industrial, Toledo 45007, Spain
| | - Guillaume Duvey
- Addex Pharmaceuticals, 12 chemin des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland
| | - Philippe Cluzeau
- Addex Pharmaceuticals, 12 chemin des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland
| | - Vanthea Nhem
- Addex Pharmaceuticals, 12 chemin des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland
| | - Karim Macary
- Addex Pharmaceuticals, 12 chemin des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland
| | - Alexandre Raux
- Addex Pharmaceuticals, 12 chemin des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland
| | - Nicolas Poirier
- Addex Pharmaceuticals, 12 chemin des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland
| | - Jessica Muller
- Addex Pharmaceuticals, 12 chemin des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland
| | - Christelle Boléa
- Addex Pharmaceuticals, 12 chemin des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland
| | - Terry Finn
- Addex Pharmaceuticals, 12 chemin des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland
| | - Sonia Poli
- Addex Pharmaceuticals, 12 chemin des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland
| | - Mark Epping-Jordan
- Addex Pharmaceuticals, 12 chemin des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland
| | - Emilie Chamelot
- Addex Pharmaceuticals, 12 chemin des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland
| | - Francis Derouet
- Addex Pharmaceuticals, 12 chemin des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland
| | - Francoise Girard
- Addex Pharmaceuticals, 12 chemin des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland
| | - Gregor J. Macdonald
- Neuroscience Medicinal Chemistry, Johnson & Johnson Pharmaceutical Research & Development, Janssen Pharmaceutica N.V., Turnhoutseweg 30, B-2340, Beerse, Belgium
| | - Juan Antonio Vega
- Neuroscience Medicinal Chemistry, Johnson & Johnson Pharmaceutical Research & Development, Janssen-Cilag S.A., Calle Jarama 75, Polígono Industrial, Toledo 45007, Spain
| | - Ana Isabel de Lucas
- Neuroscience Medicinal Chemistry, Johnson & Johnson Pharmaceutical Research & Development, Janssen-Cilag S.A., Calle Jarama 75, Polígono Industrial, Toledo 45007, Spain
| | - Encarnación Matesanz
- Neuroscience Medicinal Chemistry, Johnson & Johnson Pharmaceutical Research & Development, Janssen-Cilag S.A., Calle Jarama 75, Polígono Industrial, Toledo 45007, Spain
| | - Hilde Lavreysen
- Neuroscience, Johnson & Johnson Pharmaceutical Research & Development, Janssen Pharmaceutica N.V., Turnhoutseweg 30 B-2340, Beerse, Belgium
| | - María Lourdes Linares
- Neuroscience Medicinal Chemistry, Johnson & Johnson Pharmaceutical Research & Development, Janssen-Cilag S.A., Calle Jarama 75, Polígono Industrial, Toledo 45007, Spain
| | - Daniel Oehlrich
- Neuroscience Medicinal Chemistry, Johnson & Johnson Pharmaceutical Research & Development, Janssen-Cilag S.A., Calle Jarama 75, Polígono Industrial, Toledo 45007, Spain
| | - Julen Oyarzábal
- Research Informatics, Johnson & Johnson Pharmaceutical Research & Development, Janssen-Cilag S.A., Calle Jarama 75, Polígono Industrial, Toledo 45007, Spain
| | - Gary Tresadern
- Research Informatics, Johnson & Johnson Pharmaceutical Research & Development, Janssen-Cilag S.A., Calle Jarama 75, Polígono Industrial, Toledo 45007, Spain
| | - Andrés A. Trabanco
- Neuroscience Medicinal Chemistry, Johnson & Johnson Pharmaceutical Research & Development, Janssen-Cilag S.A., Calle Jarama 75, Polígono Industrial, Toledo 45007, Spain
| | - Jose Ignacio Andrés
- Neuroscience Medicinal Chemistry, Johnson & Johnson Pharmaceutical Research & Development, Janssen-Cilag S.A., Calle Jarama 75, Polígono Industrial, Toledo 45007, Spain
| | - Emmanuel Le Poul
- Addex Pharmaceuticals, 12 chemin des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland
| | - Hassan Imogai
- Addex Pharmaceuticals, 12 chemin des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland
| | - Robert Lutjens
- Addex Pharmaceuticals, 12 chemin des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland
| | - Jean-Philippe Rocher
- Addex Pharmaceuticals, 12 chemin des Aulx, 1228 Plan-les-Ouates, Geneva, Switzerland
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Goulton CS, Patten AR, Kerr JR, Kerr DS. Pharmacological Preconditioning with GYKI 52466: A Prophylactic Approach to Neuroprotection. Front Neurosci 2010; 4. [PMID: 20953290 PMCID: PMC2955399 DOI: 10.3389/fnins.2010.00054] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2010] [Accepted: 07/02/2010] [Indexed: 11/13/2022] Open
Abstract
Some toxins and drugs can trigger lasting neuroprotective mechanisms that enable neurons to resist a subsequent severe insult. This “pharmacological preconditioning” has far-reaching implications for conditions in which blood flow to the brain is interrupted. We have previously shown that in vitro preconditioning with the AMPA receptor antagonist GYKI 52466 induces tolerance to kainic acid (KA) toxicity in hippocampus. This effect persists well after washout of the drug and may be mediated via inverse agonism of G-protein coupled receptors (GPCRs). Given the amplifying nature of metabotropic modulation, we hypothesized that GYKI 52466 may be effective in reducing seizure severity at doses well below those normally associated with adverse side effects. Here we report that pharmacological preconditioning with low-dose GYKI imparts a significant protection against KA-induced seizures in vivo. GYKI (3 mg/kg, s.c.), 90–180 min prior to high-dose KA, markedly reduced seizure scores, virtually abolished all level 3 and level 4 seizures, and completely suppressed KA-induced hippocampal c-FOS expression. In addition, preconditioned animals exhibited significant reductions in high frequency/high amplitude spiking and ECoG power in the delta, theta, alpha, and beta bands during KA. Adverse behaviors often associated with higher doses of GYKI were not evident during preconditioning. The fact that GYKI is effective at doses well-below, and at pre-administration intervals well-beyond previous studies, suggests that a classical blockade of ionotropic AMPA receptors does not underlie anticonvulsant effects. Low-dose GYKI preconditioning may represent a novel, prophylactic strategy for neuroprotection in a field almost completely devoid of effective pharmaceuticals.
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Affiliation(s)
- Chelsea S Goulton
- Department of Pharmacology and Toxicology, School of Medical Sciences, University of Otago Dunedin, New Zealand
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Abstract
Autism is an umbrella diagnosis with several different etiologies. Fragile X syndrome (FXS), one of the first identified and leading causes of autism, has been modeled in mice using molecular genetic manipulation. These Fmr1 knockout mice have recently been used to identify a new putative therapeutic target, the metabotropic glutamate receptor 5 (mGluR5), for the treatment of FXS. Moreover, mGluR5 signaling cascades interact with a number of synaptic proteins, many of which have been implicated in autism, raising the possibility that therapeutic targets identified for FXS may have efficacy in treating multiple other causes of autism.
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Affiliation(s)
- Gül Dölen
- Department of Brain and Cognitive Sciences, Howard Hughes Medical Institute, The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, MA, USA,
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Guetg N, Seddik R, Vigot R, Turecek R, Gassmann M, Vogt KE, Bräuner-Osborne H, Shigemoto R, Kretz O, Frotscher M, Kulik Á, Bettler B. The GABAB1a isoform mediates heterosynaptic depression at hippocampal mossy fiber synapses. J Neurosci 2009; 29:1414-23. [PMID: 19193888 PMCID: PMC6666076 DOI: 10.1523/jneurosci.3697-08.2009] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2008] [Revised: 12/02/2008] [Accepted: 12/31/2008] [Indexed: 12/22/2022] Open
Abstract
GABA(B) receptor subtypes are based on the subunit isoforms GABA(B1a) and GABA(B1b), which associate with GABA(B2) subunits to form pharmacologically indistinguishable GABA(B(1a,2)) and GABA(B(1b,2)) receptors. Studies with mice selectively expressing GABA(B1a) or GABA(B1b) subunits revealed that GABA(B(1a,2)) receptors are more abundant than GABA(B(1b,2)) receptors at glutamatergic terminals. Accordingly, it was found that GABA(B(1a,2)) receptors are more efficient than GABA(B(1b,2)) receptors in inhibiting glutamate release when maximally activated by exogenous application of the agonist baclofen. Here, we used a combination of genetic, ultrastructural and electrophysiological approaches to analyze to what extent GABA(B(1a,2)) and GABA(B(1b,2)) receptors inhibit glutamate release in response to physiological activation. We first show that at hippocampal mossy fiber (MF)-CA3 pyramidal neuron synapses more GABA(B1a) than GABA(B1b) protein is present at presynaptic sites, consistent with the findings at other glutamatergic synapses. In the presence of baclofen at concentrations >or=1 microm, both GABA(B(1a,2)) and GABA(B(1b,2)) receptors contribute to presynaptic inhibition of glutamate release. However, at lower concentrations of baclofen, selectively GABA(B(1a,2)) receptors contribute to presynaptic inhibition. Remarkably, exclusively GABA(B(1a,2)) receptors inhibit glutamate release in response to synaptically released GABA. Specifically, we demonstrate that selectively GABA(B(1a,2)) receptors mediate heterosynaptic depression of MF transmission, a physiological phenomenon involving transsynaptic inhibition of glutamate release via presynaptic GABA(B) receptors. Our data demonstrate that the difference in GABA(B1a) and GABA(B1b) protein levels at MF terminals is sufficient to produce a strictly GABA(B1a)-specific effect under physiological conditions. This consolidates that the differential subcellular localization of the GABA(B1a) and GABA(B1b) proteins is of regulatory relevance.
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Affiliation(s)
- Nicole Guetg
- Department of Biomedicine, Institute of Physiology, Pharmazentrum, and
- Institute of Anatomy and Cell Biology, Department of Neuroanatomy, University of Freiburg, 79104 Freiburg, Germany
| | - Riad Seddik
- Department of Biomedicine, Institute of Physiology, Pharmazentrum, and
| | - Réjan Vigot
- Department of Biomedicine, Institute of Physiology, Pharmazentrum, and
| | - Rostislav Turecek
- Department of Biomedicine, Institute of Physiology, Pharmazentrum, and
| | - Martin Gassmann
- Department of Biomedicine, Institute of Physiology, Pharmazentrum, and
| | - Kaspar E. Vogt
- Division of Pharmacology and Neurobiology, Biozentrum, University of Basel, 4056 Basel, Switzerland
| | - Hans Bräuner-Osborne
- Department of Biomedicine, Institute of Physiology, Pharmazentrum, and
- Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Ryuichi Shigemoto
- Division of Cerebral Structure, National Institute for Physiological Sciences, and
- Department of Physiological Sciences, The Graduate University of Advanced Studies (Sokendai), Myodaiji, Okazaki 444-8787, Japan, and
- Solution Oriented Research for Science and Technology, Japan Science and Technology Corporation, Kawaguchi 332-0012, Japan
| | - Oliver Kretz
- Institute of Anatomy and Cell Biology, Department of Neuroanatomy, University of Freiburg, 79104 Freiburg, Germany
| | - Michael Frotscher
- Institute of Anatomy and Cell Biology, Department of Neuroanatomy, University of Freiburg, 79104 Freiburg, Germany
| | - Ákos Kulik
- Institute of Anatomy and Cell Biology, Department of Neuroanatomy, University of Freiburg, 79104 Freiburg, Germany
| | - Bernhard Bettler
- Department of Biomedicine, Institute of Physiology, Pharmazentrum, and
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Palmatier MI, Liu X, Donny EC, Caggiula AR, Sved AF. Metabotropic glutamate 5 receptor (mGluR5) antagonists decrease nicotine seeking, but do not affect the reinforcement enhancing effects of nicotine. Neuropsychopharmacology 2008; 33:2139-47. [PMID: 18046312 DOI: 10.1038/sj.npp.1301623] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Nicotine self-administration models typically evaluate the effects of smoking cessation aides on 'primary reinforcement' engendered by nicotine. However, the more recently described reinforcement enhancing effects of the drug are not always included in experimental analyses of potential therapeutics. We evaluated the effects of pretreatment with noncompetitive antagonists of the metabotropic glutamate 5 receptor (mGluR5) on each reinforcement-related effect of nicotine using a model in which a reinforcing visual stimulus (VS) and nicotine infusions were concurrently available. Five groups (2-lever, VS-only, NIC+VS, NIC-only, or SAL-only) were instrumented for self-administration. The 2-lever group could earn a nicotine infusion (0.06 mg/kg per infusion free base) for meeting the schedule on one lever (eg right), or VS for meeting the schedule on the other lever (eg left). The VS-only group could earn VS or saline under similar contingencies. Remaining rats could press one lever to earn both reinforcers (NIC+VS), nicotine infusions (NIC-only), or saline infusions (SAL-only); the other lever was 'inactive'. Responding on the VS lever in the 2-lever group was greater than that of the VS-only group, reflecting the reinforcement-enhancing effect of nicotine. Pretreatment with 2-methyl-6-(phenylethynyl)-pyridine (MPEP) or 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP) decreased nicotine intake as well as the enhanced responding for the concurrently available VS. In follow-up studies, replacing nicotine via experimenter-administered infusions sustained the drugs reinforcement enhancing effect; neither MPEP nor MTEP decreased the enhancing effects of nicotine. These findings are consistent with other studies suggesting that mGlu5 receptors mediate nicotine seeking, but do not alter the reinforcement enhancing effects of nicotine.
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Frerking M, Schmitz D, Zhou Q, Johansen J, Nicoll RA. Kainate receptors depress excitatory synaptic transmission at CA3-->CA1 synapses in the hippocampus via a direct presynaptic action. J Neurosci 2001; 21:2958-66. [PMID: 11312279 PMCID: PMC6762553] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/19/2023] Open
Abstract
Kainate receptor activation depresses synaptic release of neurotransmitter at a number of synapses in the CNS. The mechanism underlying this depression is controversial, and both ionotropic and metabotropic mechanisms have been suggested. We report here that the AMPA/kainate receptor agonists domoate (DA) and kainate (KA) cause a presynaptic depression of glutamatergic transmission at CA3-->CA1 synapses in the hippocampus, which is not blocked by the AMPA receptor antagonist GYKI 53655 but is blocked by the AMPA/KA receptor antagonist CNQX. Neither a blockade of interneuronal discharge nor antagonists of several neuromodulators affect the depression, suggesting that it is not the result of indirect excitation and subsequent release of a neuromodulator. Presynaptic depolarization, achieved via increasing extracellular K(+), caused a depression of the presynaptic fiber volley and an increase in the frequency of miniature EPSCs. Neither effect was observed with DA, suggesting that DA does not depress transmission via a presynaptic depolarization. However, the effects of DA were abolished by the G-protein inhibitors N-ethylmaleimide and pertussis toxin. These results suggest that KA receptor activation depresses synaptic transmission at this synapse via a direct, presynaptic, metabotropic action.
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Affiliation(s)
- M Frerking
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, California 94143-0450, USA
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Hubert GW, Paquet M, Smith Y. Differential subcellular localization of mGluR1a and mGluR5 in the rat and monkey Substantia nigra. J Neurosci 2001; 21:1838-47. [PMID: 11245668 PMCID: PMC6762609] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2000] [Revised: 12/08/2000] [Accepted: 12/22/2000] [Indexed: 02/19/2023] Open
Abstract
Neurons in the rat substantia nigra (SN) are enriched in group I metabotropic glutamate receptor (mGluR) subtypes and respond to group I mGluR activation. To better understand the mechanisms by which mGluR1 and mGluR5 mediate these effects, the goal of this study was to elucidate the subsynaptic localization of these two receptor subtypes in the rat and monkey substantia nigra. At the light microscope level, neurons of the SN pars reticulata (SNr) displayed moderate to strong immunoreactivity for both mGluR1a and mGluR5 in rats and monkeys. However, mGluR1a labeling was much stronger in monkey than in rat SN pars compacta (SNc) neurons, whereas a moderate level of mGluR5 immunoreactivity was found in both species. At the electron microscope level, the immunoreactivity for both group I mGluR subtypes was primarily expressed postsynaptically, although light mGluR1a labeling was occasionally seen in axon terminals in the rat SNr. Immunogold studies revealed a striking difference in the subcellular distribution of mGluR1a and mGluR5 immunoreactivity in SNr and SNc neurons. Although the bulk of mGluR1a was attached to the plasma membrane, >80% of mGluR5 immunoreactivity was intracellular. Plasma membrane-bound immunoreactivity for group I mGluRs in both SNc and SNr neurons was mostly extrasynaptic or in the main body of symmetric, putative GABAergic synapses. On the other hand, asymmetric synapses either were nonimmunoreactive or displayed perisynaptic labeling. These data raise important questions about the trafficking, internalization, and potential functions of group I mGluRs at extrasynaptic sites or symmetric synapses in the substantia nigra.
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Affiliation(s)
- G W Hubert
- Yerkes Regional Primate Research Center, Division of Neuroscience and Department of Neurology, Emory University, Atlanta, Georgia 30322, USA
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Pagano A, Rovelli G, Mosbacher J, Lohmann T, Duthey B, Stauffer D, Ristig D, Schuler V, Meigel I, Lampert C, Stein T, Prezeau L, Blahos J, Pin J, Froestl W, Kuhn R, Heid J, Kaupmann K, Bettler B. C-terminal interaction is essential for surface trafficking but not for heteromeric assembly of GABA(b) receptors. J Neurosci 2001; 21:1189-202. [PMID: 11160389 PMCID: PMC6762227] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/18/2023] Open
Abstract
Assembly of fully functional GABA(B) receptors requires heteromerization of the GABA(B(1)) and GABA(B(2)) subunits. It is thought that GABA(B(1)) and GABA(B(2)) undergo coiled-coil dimerization in their cytoplasmic C termini and that assembly is necessary to overcome GABA(B(1)) retention in the endoplasmatic reticulum (ER). We investigated the mechanism underlying GABA(B(1)) trafficking to the cell surface. We identified a signal, RSRR, proximal to the coiled-coil domain of GABA(B(1)) that when deleted or mutagenized allows for surface delivery in the absence of GABA(B(2)). A similar motif, RXR, was recently shown to function as an ER retention/retrieval (ERR/R) signal in K(ATP) channels, demonstrating that G-protein-coupled receptors (GPCRs) and ion channels use common mechanisms to control surface trafficking. A C-terminal fragment of GABA(B(2)) is able to mask the RSRR signal and to direct the GABA(B(1)) monomer to the cell surface, where it is functionally inert. This indicates that in the heteromer, GABA(B(2)) participates in coupling to the G-protein. Mutagenesis of the C-terminal coiled-coil domains in GABA(B(1)) and GABA(B(2)) supports the possibility that their interaction is involved in shielding the ERR/R signal. However, assembly of heteromeric GABA(B) receptors is possible in the absence of the C-terminal domains, indicating that coiled-coil interaction is not necessary for function. Rather than guaranteeing heterodimerization, as previously assumed, the coiled-coil structure appears to be important for export of the receptor complex from the secretory apparatus.
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Affiliation(s)
- A Pagano
- Novartis Pharma AG, Therapeutic Area Nervous System, CH-4002 Basle, Switzerland
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Schaffhauser H, Cai Z, Hubalek F, Macek TA, Pohl J, Murphy TJ, Conn PJ. cAMP-dependent protein kinase inhibits mGluR2 coupling to G-proteins by direct receptor phosphorylation. J Neurosci 2000; 20:5663-70. [PMID: 10908604 PMCID: PMC6772548] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2023] Open
Abstract
One of the primary physiological roles of group II and group III metabotropic glutamate receptors (mGluRs) is to presynaptically reduce synaptic transmission at glutamatergic synapses. Interestingly, previous studies suggest that presynaptic mGluRs are tightly regulated by protein kinases. cAMP analogs and the adenylyl cyclase activator forskolin inhibit the function of presynaptic group II mGluRs in area CA3 of the hippocampus. We now report that forskolin has a similar inhibitory effect on putative mGluR2-mediated responses at the medial perforant path synapse and that this effect of forskolin is blocked by a selective inhibitor of cAMP-dependent protein kinase (PKA). A series of biochemical and molecular studies was used to determine the precise mechanism by which PKA inhibits mGluR2 function. Our studies reveal that PKA directly phosphorylates mGluR2 at a single serine residue (Ser(843)) on the C-terminal tail region of the receptor. Site-directed mutagenesis combined with biochemical measures of mGluR2 function reveal that phosphorylation of this site inhibits coupling of mGluR2 from GTP-binding proteins
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Affiliation(s)
- H Schaffhauser
- Department of Pharmacology, Program in Molecular Therapeutics and Toxicology, Winship Cancer Institute, Emory University School of Medicine, Atlanta, GA 30322-3090, USA
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Nawy S. Regulation of the on bipolar cell mGluR6 pathway by Ca2+. J Neurosci 2000; 20:4471-9. [PMID: 10844016 PMCID: PMC6772459] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/16/2023] Open
Abstract
Glutamate produces a hyperpolarizing synaptic potential in On bipolar cells by binding to the metabotropic glutamate receptor mGluR6, leading to closure of a cation channel. Here it is demonstrated that this cation channel is regulated by intracellular Ca(2+). Glutamate-evoked currents were recorded from On bipolar cells in light-adapted salamander retinal slices in the presence of 2 mm external Ca(2+). When glutamate was applied almost continuously, interrupted only briefly to measure the size of the response, the glutamate response remained robust. However, currents elicited by intermittent and brief applications of glutamate exhibited time-dependent run down. Run down of the glutamate response was also voltage dependent, because it was accelerated by membrane hyperpolarization. Run down was triggered, at least in part, by a rise in intracellular Ca(2+); measured as a function of time or voltage, it was attenuated by intracellular buffering of Ca(2+) with BAPTA or by omitting Ca(2+) from the bathing solution. Current-voltage measurements demonstrated that Ca(2+) induced run down of the glutamate response by downregulating cation channel function, rather than by preventing closure of the channel by glutamate and mGluR6. A major source of the Ca(2+) that mediated this inhibition is the cation channel itself, which was found to be permeable to Ca(2+), accounting for the use dependence of the run down. These results suggest that Ca(2+) influx through the cation channel during background illumination could provide a signal to close the cation channel and repolarize the membrane toward its dark potential, an adaptive mechanism for coping with changes in ambient light.
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Affiliation(s)
- S Nawy
- Department of Ophthalmology, Visual Science and of Neuroscience, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
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Gomperts SN, Carroll R, Malenka RC, Nicoll RA. Distinct roles for ionotropic and metabotropic glutamate receptors in the maturation of excitatory synapses. J Neurosci 2000; 20:2229-37. [PMID: 10704498 PMCID: PMC6772494] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/1999] [Revised: 12/23/1999] [Accepted: 01/05/2000] [Indexed: 02/15/2023] Open
Abstract
We used the single-cell culture preparation to study the role of activity in the development of glutamatergic synapses in vitro. Rat hippocampal cells grown in isolation on glial islands formed functional autaptic connections and continued to elaborate new synapses throughout the 2 week investigation, resulting in increases in both the evoked AMPA receptor (AMPAR) and NMDA receptor (NMDAR) components of the EPSC. Synaptogenesis was not prevented by chronic blockade of sodium channels or all of the known glutamate receptors. Analysis of miniature EPSCs revealed that AMPAR quantal size doubled over time in vitro whereas NMDAR quantal size remained constant. However, the proportion of synaptic responses mediated only by NMDARs increased over time in vitro. The increase in AMPAR quantal size was prevented by TTX and ionotropic glutamate receptor antagonists, whereas the increase in the proportion of NMDAR-only synapses was prevented by metabotropic glutamate receptor antagonists. Notably, chronic NMDAR blockade incubation did not block the formation of the AMPAR EPSC, indicating that NMDAR-dependent plasticity is not necessary for the onset of AMPAR synaptic transmission in this system. We conclude that action potentials and ionotropic glutamate receptor activation are necessary for the developmental increase in AMPAR quantal size and that metabotropic glutamate receptor activation is required for the production of NMDAR-only synapses, but none of these is essential for synapse formation.
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Affiliation(s)
- S N Gomperts
- Department of Cellular Pharmacology, University of California, San Francisco, San Francisco, California 94143, USA
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45
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Curti S, Falconi A, Morales FR, Borde M. Mauthner cell-initiated electromotor behavior is mediated via NMDA and metabotropic glutamatergic receptors on medullary pacemaker neurons in a gymnotid fish. J Neurosci 1999; 19:9133-40. [PMID: 10516331 PMCID: PMC6782784] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/14/2023] Open
Abstract
Weakly electric fish generate meaningful electromotor behaviors by specific modulations of the discharge of their medullary pacemaker nucleus from which the rhythmic command for each electric organ discharge (EOD) arises. Certain electromotor behaviors seem to involve the activation of specific neurotransmitter receptors on particular target cells within the nucleus, i.e., on pacemaker or on relay cells. This paper deals with the neural basis of the electromotor behavior elicited by activation of Mauthner cells in Gymnotus carapo. This behavior consists of an abrupt and prolonged increase in the rate of the EOD. The effects of specific glutamate agonists and antagonists on basal EOD frequency and on EOD accelerations induced by Mauthner cell activation were assessed. Injections of both ionotropic (AMPA, kainate, and NMDA) and metabotropic (trans-(+/-)-1-amino-1,3-cyclopentanedicarboxylic acid) glutamate agonists induced increases in EOD rate that were maximal when performed close to the soma of pacemaker cells. In contrast, injections in the proximity of relay cells were ineffective. Therefore, pacemaker neurons are probably endowed with diverse glutamate receptor subtypes, whereas relay cells are probably not. The Mauthner cell-evoked electromotor behavior was suppressed by injections of AP-5 and (+/-)-amino-4-carboxy-methyl-phenylacetic acid, NMDA receptor and metabotropic glutamate receptor antagonists, respectively. Thus, this electromotor behavior relies on the activation of the NMDA and metabotropic glutamate receptor subtypes of pacemaker cells. Our study gives evidence for the synergistic effects of NMDA and metabotropic receptor activation and shows how a simple circuit can produce specific electromotor outputs.
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Affiliation(s)
- S Curti
- Departamento de Fisiología, Laboratorio de Neurofisiología Celular, Facultad de Medicina and Facultad de Ciencias, Montevideo, Uruguay
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Kawai F, Sterling P. AMPA receptor activates a G-protein that suppresses a cGMP-gated current. J Neurosci 1999; 19:2954-9. [PMID: 10191313 PMCID: PMC6782299] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/11/2023] Open
Abstract
The AMPA receptor, ubiquitous in brain, is termed "ionotropic" because it gates an ion channel directly. We found that an AMPA receptor can also modulate a G-protein to gate an ion channel indirectly. Glutamate applied to a retinal ganglion cell briefly suppresses the inward current through a cGMP-gated channel. AMPA and kainate also suppress the current, an effect that is blocked both by their general antagonist CNQX and also by the relatively specific AMPA receptor antagonist GYKI-52466. Neither NMDA nor agonists of metabotropic glutamate receptors are effective. The AMPA-induced suppression of the cGMP-gated current is blocked when the patch pipette includes GDP-beta-S, whereas the suppression is irreversible when the pipette contains GTP-gamma-S. This suggests a G-protein mediator, and, consistent with this, pertussis toxin blocks the current suppression. Nitric oxide (NO) donors induce the current suppressed by AMPA, and phosphodiesterase inhibitors prevent the suppression. Apparently, the AMPA receptor can exhibit a "metabotropic" activity that allows it to antagonize excitation evoked by NO.
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Affiliation(s)
- F Kawai
- Department of Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6058, USA
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Grabb MC, Choi DW. Ischemic tolerance in murine cortical cell culture: critical role for NMDA receptors. J Neurosci 1999; 19:1657-62. [PMID: 10024352 PMCID: PMC6782179] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/1998] [Revised: 12/10/1998] [Accepted: 12/18/1998] [Indexed: 02/10/2023] Open
Abstract
Murine cortical cultures containing both neurons and glia (days in vitro 13-15) were exposed to periods of oxygen-glucose deprivation (5-30 min) too brief to induce neuronal death. Cultures "preconditioned" by sublethal oxygen-glucose deprivation exhibited 30-50% less neuronal death than controls when exposed to a 45-55 min period of oxygen-glucose deprivation 24 hr later. This preconditioning-induced neuroprotection was specific in that neuronal death induced by exposure to excitotoxins or to staurosporine was not attenuated. Neuroprotection was lost if the time between the preconditioning and severe insult were decreased to 7 hr or increased to 72 hr and was blocked if the NMDA antagonist 100 microM 3-((D)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid was applied during the preconditioning insult. This was true even if the duration of preconditioning was increased as far as possible (while still remaining sublethal). A similar preconditioning effect was also produced by sublethal exposure to high K+, glutamate, or NMDA but not to kainate or trans-1-aminocyclopentane-1, 3-dicarboxylic acid.
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Affiliation(s)
- M C Grabb
- Center for the Study of Nervous System Injury and Department of Neurology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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48
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Dixon DB, Copenhagen DR. Metabotropic glutamate receptor-mediated suppression of an inward rectifier current is linked via a cGMP cascade. J Neurosci 1997; 17:8945-54. [PMID: 9364042 PMCID: PMC6573620] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Glutamate, the neurotransmitter released by photoreceptors, excites horizontal cells and OFF-type bipolar cells by activating ionotropic receptors. This study investigated an additional action of glutamate in which it modulates a voltage-gated ion channel in horizontal cells. We find that glutamate and APB (2-amino-4-phosphonobutyrate) produce a delayed and moderately prolonged suppression of an inward rectifier current (IRK+). This effect is proposed to occur via an APB-sensitive metabotropic glutamate receptor (mGluR) because common agonists for the ionotropic or APB-insensitive mGluRs are ineffective and the APB-insensitive receptor antagonist alpha-methyl-4-carboxyphenylglycine (MCPG) does not block the actions of glutamate or APB. 8-Br-cGMP, 1-methyl-3-isobutylxanthine (IBMX), and atrial natriuretic peptide (ANP) but not 8-Br-cAMP mimic the suppression of IRK+. The effects of glutamate and APB are blocked by protein kinase inhibitors including Rp-8-pCPT-cGMPS, H-8, and H-7 as well as by ATPgammaS. We hypothesize that the APB receptor suppresses IRK+ via upregulation of cGMP and subsequent activation of a cGMP-dependent protein kinase. This pathway is likely regulated by an ATP-dependent phosphorylation. This is a novel signaling pathway for mGluRs and indicates that at least two distinct APB-activated pathways exist in the retina. Functionally, this APB receptor-mediated action found in horizontal cells would provide a means by which spatially restricted changes of glutamate, produced by local illumination of photoreceptors, could regulate IRK+ and consequently the response properties of these neurons. This would serve to adapt selectively retinal regions stimulated by small regions of the visual world.
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Affiliation(s)
- D B Dixon
- Department of Ophthalmology, University of California, San Francisco, California 94143, USA
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