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Dürst CD, Wiegert JS, Schulze C, Helassa N, Török K, Oertner TG. Vesicular release probability sets the strength of individual Schaffer collateral synapses. Nat Commun 2022; 13:6126. [PMID: 36253353 PMCID: PMC9576736 DOI: 10.1038/s41467-022-33565-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2020] [Accepted: 09/22/2022] [Indexed: 12/24/2022] Open
Abstract
Information processing in the brain is controlled by quantal release of neurotransmitters, a tightly regulated process. From ultrastructural analysis, it is known that presynaptic boutons along single axons differ in the number of vesicles docked at the active zone. It is not clear whether the probability of these vesicles to get released (pves) is homogenous or also varies between individual boutons. Here, we optically measure evoked transmitter release at individual Schaffer collateral synapses at different calcium concentrations, using the genetically encoded glutamate sensor iGluSnFR. Fitting a binomial model to measured response amplitude distributions allowed us to extract the quantal parameters N, pves, and q. We find that Schaffer collateral boutons typically release single vesicles under low pves conditions and switch to multivesicular release in high calcium saline. The potency of individual boutons is highly correlated with their vesicular release probability while the number of releasable vesicles affects synaptic output only under high pves conditions.
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Affiliation(s)
- Céline D Dürst
- Institute for Synaptic Physiology, Center for Molecular Neurobiology Hamburg (ZMNH), 20251, Hamburg, Germany
- Department of Basic Neurosciences, Center for Neurosciences (CMU), University of Geneva, 1211, Geneva, Switzerland
| | - J Simon Wiegert
- Institute for Synaptic Physiology, Center for Molecular Neurobiology Hamburg (ZMNH), 20251, Hamburg, Germany
- Research Group Synaptic Wiring and Information Processing, Center for Molecular Neurobiology Hamburg (ZMNH), 20251, Hamburg, Germany
| | - Christian Schulze
- Institute for Synaptic Physiology, Center for Molecular Neurobiology Hamburg (ZMNH), 20251, Hamburg, Germany
| | - Nordine Helassa
- Cell Biology and Genetics Research Centre, Molecular and Clinical Sciences Research Institute, St George's, University of London, London, SW17 0RE, UK
- Department of Cardiovascular and Metabolic Medicine, Institute of Life Course and Medical Sciences, University of Liverpool, Liverpool, L69 3BX, UK
| | - Katalin Török
- Cell Biology and Genetics Research Centre, Molecular and Clinical Sciences Research Institute, St George's, University of London, London, SW17 0RE, UK
| | - Thomas G Oertner
- Institute for Synaptic Physiology, Center for Molecular Neurobiology Hamburg (ZMNH), 20251, Hamburg, Germany.
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2
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Sun W, Tang D, Yang Y, Wu Z, Li X, An L. Melamine impairs working memory and reduces prefrontal activity associated with inhibition of AMPA receptor GluR2/3 subunit expression. Toxicol Lett 2021; 350:171-184. [PMID: 34280503 DOI: 10.1016/j.toxlet.2021.07.009] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Revised: 06/11/2021] [Accepted: 07/15/2021] [Indexed: 11/29/2022]
Abstract
Recent studies have reported that melamine can accumulate in several regions of the brain including the medial prefrontal cortex (mPFC). Although melamine accumulation in the hippocampus has been verified to induce cognitive impairments, whether it can cause mPFC-dependent working memory deficits is still unknown. After chronic treatment with melamine (150 (Mel(150)) or 300 (Mel(300)) mg/kg), rats were tested during both delay nonmatching-to-sample spatial and odor discrimination tasks. Levels of AMPA receptor subunits in the mPFC were detected using western blotting. To further explore the mechanism at the cellular level, prefrontal activity was recorded during the odor discrimination. The working memory of Mel(150) rats was found to be significantly impaired in a 3-minute delay odor discrimination task (control: n = 6, Mel(150): n = 6; P < 0.05). Compared with the control group (n = 6), rats in the 300 mg/kg Mel(300)-treated group (n = 8) displayed working memory deficits in 60-second delay Y-maze task (P < 0.05), 1-minute and 3-minute delay odor discrimination tasks (both P < 0.05). The levels of AMPA receptor mGluR2/3 subunit were significantly decreased in rats of the Mel(150) (n = 7) and Mel(300) (n = 7) groups (both P < 0.05). Exposure to 150 (n = 7) or 300 mg/kg (n = 7) melamine resulted in significant inhibition of the regular-spiking neuron activity during the delay period of the memory test (both P < 0.05). Intraperitoneal (n = 7) and intra-mPFC (n = 6) infusions of GluR2/3 agonists, effectively enhanced the neural correlate (both P < 0.05) while rescuing cognitive deficits in Mel(300)-treated rats (both P < 0.05). Collectively, these findings suggested that melamine could induce prefrontal dysfunction and cause cognitive impairments.
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Affiliation(s)
- Wei Sun
- Behavioural Neuroscience Lab, The First Affiliated Hospital, Guizhou University of Traditional Chinese Medicine, Guiyang, Guizhou 550001, China; Department of Pediatric, The First Affiliated Hospital, Guizhou University of Traditional Chinese Medicine, Guiyang, Guizhou 550001, China
| | - Dongxin Tang
- Behavioural Neuroscience Lab, The First Affiliated Hospital, Guizhou University of Traditional Chinese Medicine, Guiyang, Guizhou 550001, China
| | - Yang Yang
- Department of Pediatric, The First Affiliated Hospital, Guizhou University of Traditional Chinese Medicine, Guiyang, Guizhou 550001, China
| | - Zexiang Wu
- Department of Pediatric, The First Affiliated Hospital, Guizhou University of Traditional Chinese Medicine, Guiyang, Guizhou 550001, China
| | - Xiaoliang Li
- Department of Neurology, Jinan Geriatric/Rehabilitation Hospital, Jinan 250013, China
| | - Lei An
- Behavioural Neuroscience Lab, The First Affiliated Hospital, Guizhou University of Traditional Chinese Medicine, Guiyang, Guizhou 550001, China; Department of Pediatric, The First Affiliated Hospital, Guizhou University of Traditional Chinese Medicine, Guiyang, Guizhou 550001, China; Department of Neurology, The First Affiliated Hospital, Guizhou University of Traditional Chinese Medicine, Guiyang, Guizhou 550001, China.
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3
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von Engelhardt J. Role of AMPA receptor desensitization in short term depression - lessons from retinogeniculate synapses. J Physiol 2021; 600:201-215. [PMID: 34197645 DOI: 10.1113/jp280878] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2021] [Accepted: 06/28/2021] [Indexed: 12/22/2022] Open
Abstract
Repetitive synapse activity induces various forms of short-term plasticity. The role of presynaptic mechanisms such as residual Ca2+ and vesicle depletion in short-term facilitation and short-term depression is well established. On the other hand, the contribution of postsynaptic mechanisms such as receptor desensitization and saturation to short-term plasticity is less well known and often ignored. In this review, I will describe short-term plasticity in retinogeniculate synapses of relay neurons of the dorsal lateral geniculate nucleus (dLGN) to exemplify the synaptic properties that facilitate the contribution of AMPA receptor desensitization to short-term plasticity. These include high vesicle release probability, glutamate spillover and, importantly, slow recovery from desensitization of AMPA receptors. The latter is strongly regulated by the interaction of AMPA receptors with auxiliary proteins such as CKAMP44. Finally, I discuss the relevance of short-term plasticity in retinogeniculate synapses for the processing of visual information by LGN relay neurons.
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Affiliation(s)
- Jakob von Engelhardt
- Institute of Pathophysiology, Focus Program Translational Neuroscience (FTN), University Medical Center of the Johannes Gutenberg University Mainz, Mainz, Germany
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4
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Jacobi E, Engelhardt J. Modulation of information processing by AMPA receptor auxiliary subunits. J Physiol 2020; 599:471-483. [DOI: 10.1113/jp276698] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2020] [Accepted: 06/25/2020] [Indexed: 12/13/2022] Open
Affiliation(s)
- Eric Jacobi
- Institute of Pathophysiology University Medical Center of the Johannes Gutenberg University Mainz Mainz Germany
- Focus Program Translational Neurosciences (FTN) University Medical Center of the Johannes Gutenberg‐University Mainz Mainz Germany
| | - Jakob Engelhardt
- Institute of Pathophysiology University Medical Center of the Johannes Gutenberg University Mainz Mainz Germany
- Focus Program Translational Neurosciences (FTN) University Medical Center of the Johannes Gutenberg‐University Mainz Mainz Germany
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5
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Kiyonaka S, Sakamoto S, Wakayama S, Morikawa Y, Tsujikawa M, Hamachi I. Ligand-Directed Chemistry of AMPA Receptors Confers Live-Cell Fluorescent Biosensors. ACS Chem Biol 2018; 13:1880-1889. [PMID: 29437380 DOI: 10.1021/acschembio.7b01042] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
AMPA-type glutamate receptors (AMPARs) mediate fast excitatory synaptic transmission in the central nervous system. Dysregulation of AMPAR function is associated with many kinds of neurological, neurodegenerative, and psychiatric disorders. As a result, molecules capable of controlling AMPAR functions are potential therapeutic agents. Fluorescent semisynthetic biosensors have attracted considerable interest for the discovery of ligands selectively acting on target proteins. Given the large protein complex formation of AMPARs in live cells, biosensors using full-length AMPARs retaining original functionality are ideal for drug screening. Here, we demonstrate that fluorophore-labeled AMPARs prepared by ligand-directed acyl imidazole chemistry can act as turn-on fluorescent biosensors for AMPAR ligands in living cells. These biosensors selectively detect orthosteric ligands of AMPARs among the glutamate receptor family. Notably, the dissociation constants of agonists and antagonists for AMPARs were determined in live cells, which revealed that the ligand-binding properties of AMPARs to agonists are largely different in living cells, compared with noncellular conditions. We also show that these sensors can be applied to detecting allosteric modulators or subunit-selective ligands of AMPARs. Thus, our protein-based biosensors can be useful for discovering pharmaceutical agents to treat AMPAR-related neurological disorders.
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Affiliation(s)
- Shigeki Kiyonaka
- Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan
| | - Seiji Sakamoto
- Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan
| | - Sho Wakayama
- Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan
| | - Yuma Morikawa
- Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan
| | - Muneo Tsujikawa
- Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan
| | - Itaru Hamachi
- Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan
- CREST(Core Research for Evolutional Science and Technology, JST), Chiyodaku, Tokyo, 102-0075, Japan
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6
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Cabrera-Pastor A, Taoro-González L, López-Merino E, Celma F, Llansola M, Felipo V. Chronic hyperammonemia alters in opposite ways membrane expression of GluA1 and GluA2 AMPA receptor subunits in cerebellum. Molecular mechanisms involved. Biochim Biophys Acta Mol Basis Dis 2017; 1864:286-295. [PMID: 29107806 DOI: 10.1016/j.bbadis.2017.10.031] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2017] [Revised: 10/14/2017] [Accepted: 10/26/2017] [Indexed: 02/07/2023]
Abstract
Hyperammonemia contributes to altered neurotransmission and cognition in patients with hepatic encephalopathy. Hyperammonemia in rats affects differently high- and low-affinity AMPA receptors (AMPARs) in cerebellum. We hypothesized that hyperammonemia would alter differently membrane expression of AMPARs GluA1 and GluA2 subunits by altering its phosphorylation. This work aims were: 1) assess if hyperammonemia alters GluA1 and GluA2 subunits membrane expression in cerebellum and 2) analyze the underlying mechanisms. Hyperammonemia reduces membrane expression of GluA2 and enhances membrane expression of GluA1 in vivo. We show that changes in GluA2 and GluA1 membrane expression in hyperammonemia would be due to enhanced NMDA receptors activation which reduces cGMP levels and phosphodiesterase 2 (PDE2) activity, resulting in increased cAMP levels. This leads to increased protein kinase A (PKA) activity which activates phospholipase C (PLC) and protein kinase C (PKC) thus increasing phosphorylation of GluA2 in Ser880, which reduces GluA2 membrane expression, and phosphorylation of GluA1 in Ser831, which increases GluA1 membrane expression. Blocking NMDA receptors or inhibiting PKA, PLC or PKC normalizes GluA2 and GluA1 phosphorylation and membrane expression in hyperammonemic rats. Altered GluA2 and GluA1 membrane expression would alter signal transduction which may contribute to cognitive and motor alterations in hyperammonemia and hepatic encephalopathy.
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Affiliation(s)
- Andrea Cabrera-Pastor
- Laboratory of Neurobiology, Centro de Investigacion Príncipe Felipe, 46012, Valencia, Spain
| | - Lucas Taoro-González
- Laboratory of Neurobiology, Centro de Investigacion Príncipe Felipe, 46012, Valencia, Spain
| | - Esperanza López-Merino
- Laboratory of Neurobiology, Centro de Investigacion Príncipe Felipe, 46012, Valencia, Spain
| | - Ferran Celma
- Laboratory of Neurobiology, Centro de Investigacion Príncipe Felipe, 46012, Valencia, Spain
| | - Marta Llansola
- Laboratory of Neurobiology, Centro de Investigacion Príncipe Felipe, 46012, Valencia, Spain
| | - Vicente Felipo
- Laboratory of Neurobiology, Centro de Investigacion Príncipe Felipe, 46012, Valencia, Spain.
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7
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Diversity in AMPA receptor complexes in the brain. Curr Opin Neurobiol 2017; 45:32-38. [DOI: 10.1016/j.conb.2017.03.001] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2016] [Revised: 02/28/2017] [Accepted: 03/03/2017] [Indexed: 11/23/2022]
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Cabrera-Pastor A, Taoro L, Llansola M, Felipo V. Roles of the NMDA Receptor and EAAC1 Transporter in the Modulation of Extracellular Glutamate by Low and High Affinity AMPA Receptors in the Cerebellum in Vivo: Differential Alteration in Chronic Hyperammonemia. ACS Chem Neurosci 2015; 6:1913-21. [PMID: 26428532 DOI: 10.1021/acschemneuro.5b00212] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The roles of high- and low-affinity AMPA receptors in modulating extracellular glutamate in the cerebellum remain unclear. Altered glutamatergic neurotransmission is involved in neurological alterations in hyperammonemia, which differently affects high- and low-affinity AMPA receptors. The aims were to assess by in vivo microdialysis (a) the effects of high- and low-affinity AMPA receptor activation on extracellular glutamate in the cerebellum; (b) whether chronic hyperammonemia alters extracellular glutamate modulation by high- and/or low-affinity AMPA receptors; and (c) the contribution of NMDA receptors and EAAC1 transporter to AMPA-induced changes in extracellular glutamate. In control rats, high affinity receptor activation does not affect extracellular glutamate but increases glutamate if NMDA receptors are blocked. Low affinity AMPA receptor activation increases transiently extracellular glutamate followed by reduction below basal levels and return to basal values. The reduction is associated with transient increased membrane expression of EAAC1 and is prevented by blocking NMDA receptors. Blocking NMDA receptors with MK-801 induces a transient increase in extracellular glutamate which is associated with reduced membrane expression of EAAC1 followed by increased membrane expression of the glutamate transporter GLT-1. Chronic hyperammonemia does not affect responses to activation of low affinity AMPA receptors. Activation of high affinity AMPA receptors increases extracellular glutamate in hyperammonemic rats by an NMDA receptor-dependent mechanism. In conclusion, these results show that there is a tightly controlled interplay between AMPA and NMDA receptors and an EAAC1 transporter in controlling extracellular glutamate. Hyperammonemia alters high- but not low-affinity AMPA receptors.
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Affiliation(s)
- Andrea Cabrera-Pastor
- Laboratory of Neurobiology, Centro de Investigación Príncipe Felipe, Calle Eduardo Primo Yufera, 3, 46012 Valencia, Spain
| | - Lucas Taoro
- Laboratory of Neurobiology, Centro de Investigación Príncipe Felipe, Calle Eduardo Primo Yufera, 3, 46012 Valencia, Spain
| | - Marta Llansola
- Laboratory of Neurobiology, Centro de Investigación Príncipe Felipe, Calle Eduardo Primo Yufera, 3, 46012 Valencia, Spain
| | - Vicente Felipo
- Laboratory of Neurobiology, Centro de Investigación Príncipe Felipe, Calle Eduardo Primo Yufera, 3, 46012 Valencia, Spain
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9
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Abstract
We delineate perspectives for the design and discovery of antiepileptic drugs (AEDs) with fewer side effects by focusing on astroglial modulation of spatiotemporal seizure dynamics. It is now recognized that the major inhibitory neurotransmitter of the brain, γ-aminobutyric acid (GABA), can be released through the reversal of astroglial GABA transporters. Synaptic spillover and subsequent glutamate (Glu) uptake in neighboring astrocytes evoke replacement of extracellular Glu for GABA, driving neurons away from the seizure threshold. Attenuation of synaptic signaling by this negative feedback through the interplay of Glu and GABA transporters of adjacent astroglia can result in shortened seizures. By contrast, long-range activation of astroglia through gap junctions may promote recurrent seizures on the model of pharmacoresistant temporal lobe epilepsy. From their first detection to our current understanding, we identify various targets that shape both short- and long-range neuro-astroglia coupling, as these are manifest in epilepsy phenomena and in the associated research promotions of AED.
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Affiliation(s)
- Julianna Kardos
- Functional Pharmacology Research Group, Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, 1117 Budapest, Hungary
| | - Zsolt Szabó
- Functional Pharmacology Research Group, Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, 1117 Budapest, Hungary
| | - László Héja
- Functional Pharmacology Research Group, Institute of Organic Chemistry, Research Centre for Natural Sciences, Hungarian Academy of Sciences, 1117 Budapest, Hungary
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10
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Cabrera-Pastor A, Llansola M, Reznikov V, Boix J, Felipo V. Differential effects of chronic hyperammonemia on modulation of the glutamate-nitric oxide-cGMP pathway by metabotropic glutamate receptor 5 and low and high affinity AMPA receptors in cerebellum in vivo. Neurochem Int 2012; 61:63-71. [PMID: 22521775 DOI: 10.1016/j.neuint.2012.04.006] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2012] [Revised: 03/27/2012] [Accepted: 04/05/2012] [Indexed: 01/06/2023]
Abstract
Previous studies show that chronic hyperammonemia impairs learning ability of rats by impairing the glutamate-nitric oxide (NO)-cyclic guanosine mono-phosphate (cGMP) pathway in cerebellum. Three types of glutamate receptors cooperate in modulating the NO-cGMP pathway: metabotropic glutamate receptor 5 (mGluR5), (RS)-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-d-aspartic acid (NMDA) receptors. The aim of this work was to assess whether hyperammonemia alters the modulation of this pathway by mGluR5 and AMPA receptors in cerebellum in vivo. The results support that in control rats: (1) low AMPA concentrations (0.1mM) activate nearly completely Ca(2+)-permeable (glutamate receptor subunit 2 (GluR2)-lacking) AMPA receptors and the NO-cGMP pathway; (2) higher AMPA concentrations (0.3 mM) also activate Ca(2+)-impermeable (GluR2-containing) AMPA receptors, leading to activation of NMDA receptors and of NO-cGMP pathway. Moreover, the data support that chronic hyperammonemia: (1) reduces glutamate release and activation of the glutamate-NO-cGMP pathway by activation of mGluR5; (2) strongly reduces the direct activation by AMPA receptors of the NO-cGMP pathway, likely due to reduced entry of Ca(2+) through GluR2-lacking, high affinity AMPA receptors; (3) strongly increases the indirect activation of the NO-cGMP pathway by high affinity AMPA receptors, likely due to increased entry of Na(+) through GluR2-lacking AMPA receptors and NMDA receptors activation; (4) reduces the indirect activation of the NO-cGMP pathway by low affinity AMPA receptors, likely due to reduced activation of NMDA receptors.
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Affiliation(s)
- Andrea Cabrera-Pastor
- Laboratory of Neurobiology, Centro de Investigación Príncipe Felipe, Av. Autopista del Saler, 16, 46012 Valencia, Spain.
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11
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Sawant PM, Tyndall JDA, Holland PT, Peake BM, Mountfort DO, Kerr DS. In vivo seizure induction and affinity studies of domoic acid and isodomoic acids-D, -E and -F. Neuropharmacology 2010; 59:129-38. [PMID: 20416329 DOI: 10.1016/j.neuropharm.2010.03.019] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2009] [Revised: 03/15/2010] [Accepted: 03/31/2010] [Indexed: 11/20/2022]
Abstract
Domoic acid and its isomers are produced via algal blooms and are found in high concentrations in shellfish. Here, we assessed the acute seizurogenic potencies of isomers-D, -E and -F and their binding affinities at heterogeneous populations of KA receptors from rat cerebrum. In addition, binding affinities of all six isomers (Iso-A through -F) were assessed at AMPA receptors. Radioligand displacement studies indicated that the seizurogenic potency of Iso-F (E-configuration) closely correlates with its affinities at both KA and AMPA receptors, whereas isomers-D (Z) and -E (E), which exhibit distinctly lower seizurogenic potencies, are quite weak displacers. Previously observed functional potencies for isomers-A, -B and -C (Sawant et al., 2008) correlated with AMPA receptor affinities observed here. Taken together, these findings call into question previous structure-activity rules. Significantly, in our hands, Iso-D was ten-fold less potent than Iso-F. To further explain observed links between structural conformation and functional potency, molecular modeling was employed. Modeling results closely matched the rank order of potency and binding data observed. We further assessed the efficacy of isomers-D, -E and -F as pharmacological preconditioning agents. Acute preconditioning with low-dose Iso-D, -E or -F, before high-dose DA failed to impart behavioural tolerance. This study has shed new light on structural conformations affecting non-NMDA ionotropic glutamate receptor binding and functional potency, and provides a foundation for future work in areas of AMPA and KA receptor modeling.
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Affiliation(s)
- P M Sawant
- Department of Pharmacology and Toxicology, University of Otago School of Medical Sciences, Dunedin, New Zealand.
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12
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Fenwick MK, Oswald RE. On the mechanisms of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor binding to glutamate and kainate. J Biol Chem 2010; 285:12334-43. [PMID: 20110361 DOI: 10.1074/jbc.m109.086371] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) subtype of ionotropic glutamate receptors mediates much of the fast excitatory neurotransmission in the central nervous system. The ability of these receptors to shape such responses appears to be due in part to dynamic processes induced by agonists in the ligand-binding domain. Previous studies employing fluorescence spectroscopy and whole cell recording suggest that agonist binding is followed by sequential transitions to one or more distinct conformational states. Here, we used hydrogen-deuterium exchange to determine the mechanisms of binding of glutamate and kainate (full and partial agonists, respectively) to a soluble ligand-binding domain of GluR2. Our results provide a structural basis for sequential state models of agonist binding and the free energy changes of the associated state-to-state transitions. For glutamate, a multi-equilibrium binding reaction was discerned involving distinct ligand docking, domain isomerization, and lobe-locking steps. In contrast, kainate binding involves a simpler dock-isomerization process in which the isomerization equilibrium is shifted dramatically toward open domain conformations. In light of increasing evidence that the stability, in addition to the extent, of domain closure is a critical component of the channel activation mechanism, the differences in domain opening and closing equilibria detected for glutamate and kainate should be useful structural measures for interpreting the markedly different current responses evoked by these agonists.
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Affiliation(s)
- Michael K Fenwick
- Department of Molecular Medicine, Cornell University, Ithaca, New York 14853, USA
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13
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Montgomery KE, Kessler M, Arai AC. Modulation of agonist binding to AMPA receptors by 1-(1,4-benzodioxan-6-ylcarbonyl)piperidine (CX546): differential effects across brain regions and GluA1-4/transmembrane AMPA receptor regulatory protein combinations. J Pharmacol Exp Ther 2009; 331:965-74. [PMID: 19717789 DOI: 10.1124/jpet.109.158014] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Ampakines are cognitive enhancers that potentiate alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor currents and synaptic responses by slowing receptor deactivation. Their efficacy varies greatly between classes of neurons and brain regions, but the factor responsible for this effect remains unclear. Ampakines also increase agonist affinity in binding tests in ways that are related to their physiological action. We therefore examined 1) whether ampakine effects on agonist binding vary across brain regions and 2) whether they differ across receptor subunits expressed alone and together with transmembrane AMPA receptor regulatory proteins (TARPs), which associate with AMPA receptors in the brain. We found that the maximal increase in agonist binding (E(max)) caused by the prototypical ampakine 1-(1,4-benzodioxan-6-ylcarbonyl)piperidine (CX546) differs significantly between brain regions, with effects in hippocampus and cerebellum being nearly three times larger than that in thalamus, brainstem, and striatum, and cortex being intermediate. These differences can be explained at least in part by regional variations in receptor subunit and TARP expression because combinations prevalent in hippocampus (GluA2 with TARPs gamma3 and gamma8) exhibited E(max) values nearly twice those of combinations abundant in thalamus (GluA4 with gamma2 or gamma4). TARPs seem to be critical because GluA2 and GluA4 alone had comparable E(max) and also because hippocampal and thalamic receptors had similar E(max) after solubilization with Triton X-100, which probably removes associated proteins. Taken together, our data suggest that variations in physiological drug efficacy, such as the 3-fold difference previously seen in recordings from hippocampus versus thalamus, may be explained by region-specific expression of GluA1-4 as well as TARPs.
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Affiliation(s)
- Kyle E Montgomery
- Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, Illinois 62794-9629, USA.
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