401
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Greger IH, Esteban JA. AMPA receptor biogenesis and trafficking. Curr Opin Neurobiol 2007; 17:289-97. [PMID: 17475474 DOI: 10.1016/j.conb.2007.04.007] [Citation(s) in RCA: 118] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2007] [Accepted: 04/18/2007] [Indexed: 12/25/2022]
Abstract
AMPA-type glutamate receptors mediate the majority of fast excitatory transmission in the central nervous system. The trafficking of AMPA receptors to and from synapses alters synaptic strength and has been recognized as a central mechanism underlying various forms of synaptic plasticity. Both secretory and endocytic trafficking events seem to be driven by the subunit composition of AMPA receptor tetramers. Moreover, recent work suggests that synapses employ different tetramer combinations in response to altered synaptic input, suggesting the existence of signalling pathways that mediate remodelling of AMPA receptors. These latest developments and recent progress in elucidating the mechanisms that underlie channel assembly and trafficking are the subject of this review.
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Affiliation(s)
- Ingo H Greger
- Neurobiology Division, MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK.
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402
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Sossa KG, Beattie JB, Carroll RC. AMPAR exocytosis through NO modulation of PICK1. Neuropharmacology 2007; 53:92-100. [PMID: 17555774 PMCID: PMC2040303 DOI: 10.1016/j.neuropharm.2007.04.005] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2007] [Revised: 04/13/2007] [Accepted: 04/16/2007] [Indexed: 11/28/2022]
Abstract
The activation of NMDA receptors (NMDARs) triggers long-term changes in AMPA receptor-mediated synaptic transmission in the CNS. These long-lasting changes occur via the addition or removal of AMPA receptors (AMPARs) at the synaptic membrane and are mediated by a number of regulatory proteins including the GluR2 AMPAR-interacting proteins n-ethylmaleimide sensitive factor (NSF) and Protein Interacting with C Kinase (PICK1). We have shown that the potent activation of NMDARs drives unclustering of PICK1 and PICK1-GluR2 dissociation in dendrites resulting in increased surface delivery of AMPARs. Here we show that the dispersal of PICK1 is mediated by the actions of NSF. We find that elevated NMDAR signaling leads to the S-nitrosylation of NSF and increased NSF-GluR2 association. Both NMDAR-dependent unclustering of PICK1 and the delivery of surface AMPARs are dependent on release of nitric oxide (NO). Our data suggest that NMDAR activation can drive the surface delivery of AMPARs from a pool of intracellular AMPARs retained by PICK1 through the NO-dependent modification of NSF.
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Affiliation(s)
- Kenneth G Sossa
- Albert Einstein College of Medicine of Yeshiva University, Dominick P. Purpura Department of Neuroscience, Rose F. Kennedy Center for Mental Retardation, 1410 Pelham Parkway South, Bronx, NY 10461, USA
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403
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Bloodgood BL, Sabatini BL. Ca(2+) signaling in dendritic spines. Curr Opin Neurobiol 2007; 17:345-51. [PMID: 17451936 DOI: 10.1016/j.conb.2007.04.003] [Citation(s) in RCA: 112] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2007] [Accepted: 04/11/2007] [Indexed: 11/16/2022]
Abstract
Recent studies have revealed that Ca(2+) signals evoked by action potentials or by synaptic activity within individual dendritic spines are regulated at multiple levels. Ca(2+) influx through glutamate receptors and voltage-sensitive Ca(2+) channels located on spines depends on the channel subunit composition, the activity of kinases and phosphatases, the local membrane potential and past patterns of activity. Furthermore, sources of spine Ca(2+) interact nonlinearly such that activation of one Ca(2+) channel can enhance or depress the activity of others. These studies have revealed that each spine is a complex and partitioned Ca(2+) signaling domain capable of autonomously regulating the electrical and biochemical consequences of synaptic activity.
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Affiliation(s)
- Brenda L Bloodgood
- Department of Neurobiology, Harvard Medical School, 220 Longwood Avenue, Boston, MA 02115, USA
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404
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Osswald IK, Galan A, Bowie D. Light triggers expression of philanthotoxin-insensitive Ca2+-permeable AMPA receptors in the developing rat retina. J Physiol 2007; 582:95-111. [PMID: 17430992 PMCID: PMC2075288 DOI: 10.1113/jphysiol.2007.127894] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Ca2+-permeable AMPA receptors (AMPARs) are expressed throughout the adult CNS but yet their role in development is poorly understood. In the developing retina, most investigations have focused on Ca2+ influx through NMDARs in promoting synapse maturation and not on AMPARs. However, NMDARs are absent from many retinal cells suggesting that other Ca2+-permeable glutamate receptors may be important to consider. Here we show that inhibitory horizontal and AII amacrine cells lack NMDARs but express Ca2+-permeable AMPARs. Before eye-opening, AMPARs were fully blocked by philanthotoxin (PhTX), a selective antagonist of Ca2+-permeable AMPARs. After eye-opening, however, a subpopulation of Ca2+-permeable AMPARs were unexpectedly PhTX resistant. Furthermore, Joro spider toxin (JSTX) and IEM-1460 also failed to antagonize, demonstrating that this novel pharmacology is shared by several AMPAR channel blockers. Interestingly, PhTX-insensitive AMPARs failed to express in retinae from dark-reared animals demonstrating that light entering the eye triggers their expression. Eye-opening coincides with the consolidation of inhibitory cell connections suggesting that the developmental switch to a Ca2+-permeable AMPAR with novel pharmacology may be critical to synapse maturation in the mammalian retina.
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Affiliation(s)
- Ingrid K Osswald
- Department of Pharmacology & Therapeutics, McIntyre Medical Sciences Building, Room 1317, McGill University, Montreal, Québec, Canada H3A 1Y6
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405
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Rao VR, Finkbeiner S. NMDA and AMPA receptors: old channels, new tricks. Trends Neurosci 2007; 30:284-91. [PMID: 17418904 DOI: 10.1016/j.tins.2007.03.012] [Citation(s) in RCA: 172] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2007] [Revised: 03/14/2007] [Accepted: 03/30/2007] [Indexed: 12/21/2022]
Abstract
Learning and memory depend on persistent changes in synaptic strength that require neuronal gene expression. An unresolved question concerns the mechanisms by which activity at synapses is transduced into a nuclear transcriptional response. In the prevailing view, N-methyl-D-aspartate (NMDA)- and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors have distinct roles in controlling synaptic strength: AMPA receptors effect short-term changes in synaptic strength, whereas NMDA receptors regulate genes that are required for the long-term maintenance of these changes. Here, we review recent data on the roles of these two types of receptor in activity-dependent gene expression. We discuss evidence that signals from NMDA receptors and AMPA receptors are integrated to specify transcriptional responses for particular plasticity related genes.
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Affiliation(s)
- Vikram R Rao
- Gladstone Institute of Neurological Disease, 1650 Owens Street, San Francisco, CA 94158, USA
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406
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Derkach VA, Oh MC, Guire ES, Soderling TR. Regulatory mechanisms of AMPA receptors in synaptic plasticity. Nat Rev Neurosci 2007; 8:101-13. [PMID: 17237803 DOI: 10.1038/nrn2055] [Citation(s) in RCA: 539] [Impact Index Per Article: 31.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Activity-dependent changes in the strength of excitatory synapses are a cellular mechanism for the plasticity of neuronal networks that is widely recognized to underlie cognitive functions such as learning and memory. AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid)-type glutamate receptors (AMPARs) are the main transducers of rapid excitatory transmission in the mammalian CNS, and recent discoveries indicate that the mechanisms which regulate AMPARs are more complex than previously thought. This review focuses on recent evidence that alterations to AMPAR functional properties are coupled to their trafficking, cytoskeletal dynamics and local protein synthesis. These relationships offer new insights into the regulation of AMPARs and synaptic strength by cellular signalling.
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Affiliation(s)
- Victor A Derkach
- Vollum Institute, Oregon Health and Sciences University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, USA.
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407
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Deng YP, Xie JP, Wang HB, Lei WL, Chen Q, Reiner A. Differential localization of the GluR1 and GluR2 subunits of the AMPA-type glutamate receptor among striatal neuron types in rats. J Chem Neuroanat 2007; 33:167-92. [PMID: 17446041 PMCID: PMC1993922 DOI: 10.1016/j.jchemneu.2007.02.008] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2006] [Revised: 02/26/2007] [Accepted: 02/27/2007] [Indexed: 01/05/2023]
Abstract
Differences among the various striatal projection neuron and interneuron types in cortical input, function, and vulnerability to degenerative insults may be related to differences among them in AMPA-type glutamate receptor abundance and subunit configuration. We therefore used immunolabeling to assess the frequency and abundance of GluR1 and GluR2, the most common AMPA subunits in striatum, in the main striatal neuron types. All neurons projecting to the external pallidum (GPe), internal pallidum (GPi) or substantia nigra, as identified by retrograde labeling, possessed perikaryal GluR2, while GluR1 was more common in striato-GPe than striato-GPi perikarya. The frequency and intensity of immunostaining indicated the rank order of their perikaryal GluR1:GluR2 ratio to be striato-GPe>striatonigral>striato-GPi. Ultrastructural studies suggested a differential localization of GluR1 and GluR2 to striatal projection neuron dendritic spines as well, with GluR1 seemingly more common in striato-GPe spines and GluR2 more common in striato-GPi and/or striatonigral spines. Comparisons among projection neurons and interneurons revealed GluR1 to be most common and abundant in parvalbuminergic interneurons, and GluR2 most common and abundant in projection neurons, with the rank order for the GluR1:GluR2 ratio being parvalbuminergic interneurons>calretinergic interneurons>cholinergic interneurons>projection neurons>somatostatinergic interneurons. Striosomal projection neurons had a higher GluR1:GluR2 ratio than did matrix projection neurons. The abundance of both GluR1 and GluR2 in striatal parvalbuminergic interneurons and projection neurons is consistent with their prominent cortical input and susceptibility to excitotoxic insult, while differences in GluR1:GluR2 ratio among projection neurons are likely to yield differences in Ca(2+) permeability, desensitization, and single channel current, which may contribute to differences among them in plasticity, synaptic integration, and excitotoxic vulnerability. The apparent association of the GluR1 subunit with synaptic plasticity, in particular, suggests striato-GPe neuron spines as a particular site of corticostriatal synaptic plasticity, presumably associated with motor learning.
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Affiliation(s)
- Y P Deng
- Department of Anatomy and Neurobiology, University of Tennessee Health Science Center, Memphis, TN 38163, USA
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408
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Lamsa KP, Heeroma JH, Somogyi P, Rusakov DA, Kullmann DM. Anti-Hebbian long-term potentiation in the hippocampal feedback inhibitory circuit. Science 2007; 315:1262-6. [PMID: 17332410 PMCID: PMC3369266 DOI: 10.1126/science.1137450] [Citation(s) in RCA: 193] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Long-term potentiation (LTP), which approximates Hebb's postulate of associative learning, typically requires depolarization-dependent glutamate receptors of the NMDA (N-methyl-D-aspartate) subtype. However, in some neurons, LTP depends instead on calcium-permeable AMPA-type receptors. This is paradoxical because intracellular polyamines block such receptors during depolarization. We report that LTP at synapses on hippocampal interneurons mediating feedback inhibition is "anti-Hebbian":Itis induced by presynaptic activity but prevented by postsynaptic depolarization. Anti-Hebbian LTP may occur in interneurons that are silent during periods of intense pyramidal cell firing, such as sharp waves, and lead to their altered activation during theta activity.
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Affiliation(s)
- Karri P. Lamsa
- Institute of Neurology, University College London, Queen Square, London WC1N 3BG, UK
| | - Joost H. Heeroma
- Institute of Neurology, University College London, Queen Square, London WC1N 3BG, UK
| | - Peter Somogyi
- Anatomical Neuropharmacology Unit, Medical Research Council, Oxford University, Mansfield Road, Oxford OXI 3HT, UK
| | - Dmitri A. Rusakov
- Institute of Neurology, University College London, Queen Square, London WC1N 3BG, UK
| | - Dimitri M. Kullmann
- Institute of Neurology, University College London, Queen Square, London WC1N 3BG, UK
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409
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Reymann KG, Frey JU. The late maintenance of hippocampal LTP: Requirements, phases, ‘synaptic tagging’, ‘late-associativity’ and implications. Neuropharmacology 2007; 52:24-40. [PMID: 16919684 DOI: 10.1016/j.neuropharm.2006.07.026] [Citation(s) in RCA: 230] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2006] [Revised: 07/14/2006] [Accepted: 07/17/2006] [Indexed: 11/28/2022]
Abstract
Our review focuses on the mechanisms which enable the late maintenance of hippocampal long-term potentiation (LTP; >3h), a phenomenon which is thought to underlie prolonged memory. About 20 years ago we showed for the first time that the maintenance of LTP - like memory storage--depends on intact protein synthesis and thus, consists of at least two temporal phases. Here we concentrate on mechanisms required for the induction of the transient early-LTP and of the protein synthesis-dependent late-LTP. Our group has shown that the induction of late-LTP requires the associative activation of heterosynaptic inputs, i.e. the synergistic activation of glutamatergic and modulatory, reinforcing inputs within specific, effective time windows. The induction of late-LTP is characterized by novel, late-associative properties such as 'synaptic tagging' and 'late-associative reinforcement'. Both phenomena require the associative setting of synaptic tags as well as the availability of plasticity-related proteins (PRPs) and they are restricted to functional dendritic compartments, in general. 'Synaptic tagging' guarantees input specificity and thus the specific processing of afferent signals for the establishment of late-LTP. 'Late-associative reinforcement' describes a process where early-LTP by the co-activation of modulatory inputs can be transformed into late-LTP in activated synapses where a tag is set. Recent evidence from behavioral experiments, which studied processes of emotional and cognitive reinforcement of LTP, point to the physiological relevance of the above mechanisms during cellular and system's memory formation.
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Affiliation(s)
- Klaus G Reymann
- Department for Neurophysiology, Leibniz Institute for Neurobiology, Brenneckestrasse 6, D-39118 Magdeburg, Germany
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410
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Thiagarajan TC, Lindskog M, Malgaroli A, Tsien RW. LTP and adaptation to inactivity: Overlapping mechanisms and implications for metaplasticity. Neuropharmacology 2007; 52:156-75. [PMID: 16949624 DOI: 10.1016/j.neuropharm.2006.07.030] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2006] [Revised: 07/20/2006] [Accepted: 07/21/2006] [Indexed: 11/16/2022]
Abstract
LTP and other rapidly induced forms of synaptic modification tune individual synaptic weights, whereas slower forms of plasticity such as adaptation to inactivity are thought to keep neurons within their firing limits and preserve their capability for information processing. Here we describe progress in understanding the relationship between LTP and adaptation to inactivity. A prevailing view is that adaptation to inactivity is purely postsynaptic, scales synaptic strength uniformly across all synapses, and thus preserves relative synaptic weights without interfering with signatures of prior LTP or the relative capacity for future LTP. However, recent evidence in hippocampal neurons indicates that, like LTP, adaptation to AMPA receptor blockade can draw upon a repertoire of synaptic expression mechanisms including enhancement of presynaptic vesicular turnover and increased quantal amplitude mediated by recruitment of homomeric GluR1 AMPA receptors. These pre- and postsynaptic changes appeared coordinated and preferentially expressed at subset of synapses, thereby increasing the variability of miniature EPSCs. In contrast to the NMDA receptor-, Ca2+ entry-dependent induction of LTP, adaptation to inactivity may be mediated by attenuation of voltage-sensitive L-type Ca2+ channel function. The associated intracellular signaling involves elevation of betaCaMKII, which in turn downregulates alphaCaMKII, a key player in LTP. Thus, adaptation to inactivity and LTP are not strictly independent with regard to mechanisms of signaling and expression. Indeed, we and others have found that responses to LTP-inducing stimuli can be sharply altered by prior inactivity, suggesting that the slow adaptation changes the rules of plasticity-an interesting example of "metaplasticity".
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Affiliation(s)
- Tara C Thiagarajan
- Department of Molecular & Cellular Physiology, Stanford University School of Medicine, B105 Beckman Center, Stanford, CA 94305, USA
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411
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Lai C, Xie C, McCormack SG, Chiang HC, Michalak MK, Lin X, Chandran J, Shim H, Shimoji M, Cookson MR, Huganir RL, Rothstein JD, Price DL, Wong PC, Martin LJ, Zhu JJ, Cai H. Amyotrophic lateral sclerosis 2-deficiency leads to neuronal degeneration in amyotrophic lateral sclerosis through altered AMPA receptor trafficking. J Neurosci 2006; 26:11798-806. [PMID: 17093100 PMCID: PMC2556290 DOI: 10.1523/jneurosci.2084-06.2006] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Amyotrophic lateral sclerosis (ALS), the most common adult-onset motor neuron disease is caused by a selective loss of motor neurons. One form of juvenile onset autosomal recessive ALS (ALS2) has been linked to the loss of function of the ALS2 gene. The pathogenic mechanism of ALS2-deficiency, however, remains unclear. To further understand the function of alsin that is encoded by the full-length ALS2 gene, we screened proteins interacting with alsin. Here, we report that alsin interacted with glutamate receptor interacting protein 1 (GRIP1) both in vitro and in vivo, and colocalized with GRIP1 in neurons. In support of the physiological interaction between alsin and GRIP1, the subcellular distribution of GRIP1 was altered in ALS2(-/-) spinal motor neurons, which correlates with a significant reduction of AMPA-type glutamate receptor subunit 2 (GluR2) at the synaptic/cell surface of ALS2(-/-) neurons. The decrease of calcium-impermeable GluR2-containing AMPA receptors at the cell/synaptic surface rendered ALS2(-/-) neurons more susceptible to glutamate receptor-mediated neurotoxicity. Our findings reveal a novel function of alsin in AMPA receptor trafficking and provide a novel pathogenic link between ALS2-deficiency and motor neuron degeneration, suggesting a protective role of alsin in maintaining the survival of motor neurons.
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Affiliation(s)
- Chen Lai
- Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, Maryland 20892
| | - Chengsong Xie
- Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, Maryland 20892
| | - Stefanie G. McCormack
- Department of Pharmacology and Neuroscience Graduate Program, University of Virginia School of Medicine, Charlottesville, Virginia 22908
| | | | - Marta K. Michalak
- Department of Pharmacology and Neuroscience Graduate Program, University of Virginia School of Medicine, Charlottesville, Virginia 22908
- Biotechnology Graduate Program, Technical University of Łódź, 90-924 Łódź, Poland
| | - Xian Lin
- Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, Maryland 20892
| | - Jayanth Chandran
- Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, Maryland 20892
| | - Hoon Shim
- Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, Maryland 20892
| | - Mika Shimoji
- Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, Maryland 20892
| | - Mark R. Cookson
- Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, Maryland 20892
| | - Richard L. Huganir
- Neuroscience, and
- Howard Hughes Medical Institute, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, and
| | | | | | | | | | - J. Julius Zhu
- Department of Pharmacology and Neuroscience Graduate Program, University of Virginia School of Medicine, Charlottesville, Virginia 22908
| | - Huaibin Cai
- Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, Maryland 20892
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412
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Holman D, Henley JM. A novel method for monitoring the cell surface expression of heteromeric protein complexes in dispersed neurons and acute hippocampal slices. J Neurosci Methods 2006; 160:302-8. [PMID: 17083981 PMCID: PMC3314503 DOI: 10.1016/j.jneumeth.2006.09.018] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2006] [Revised: 09/25/2006] [Accepted: 09/26/2006] [Indexed: 12/01/2022]
Abstract
The subunit composition of multimeric protein complexes is critical in determining their trafficking and functional properties. Despite there being multiple techniques to investigate the trafficking events of individual subunits there are currently limited means to monitor the trafficking properties of heteromeric protein complexes. Here, we combine surface biotinylation with co-immunoprecipitation to monitor the cell surface expression of native, heteromeric AMPA receptor complexes. Using this method, we demonstrate that the surface levels of GluR1/2 and GluR2/3 complexes are reduced following NMDA-evoked long-term depression (NMDA-LTD) in acute hippocampal slices. Finally, we discuss how this method can be adapted to monitor the cell surface expression of other heteromeric protein complexes.
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Affiliation(s)
- David Holman
- MRC Centre for Synaptic Plasticity, Department of Anatomy, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK.
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413
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Lisman J, Raghavachari S. A unified model of the presynaptic and postsynaptic changes during LTP at CA1 synapses. ACTA ACUST UNITED AC 2006; 2006:re11. [PMID: 17033044 DOI: 10.1126/stke.3562006re11] [Citation(s) in RCA: 162] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Long-term potentiation (LTP) has been studied extensively at CA1 synapses of the hippocampus, and there is evidence implicating both postsynaptic and presynaptic changes in this process. These changes include (i) addition of AMPA channels to the extrasynaptic membrane and diffusional equilibrium of extrasynaptic receptors with synaptic receptors, (ii) sudden addition of AMPA channels to the synapse in large groups, (iii) a change in the mode of glutamate release (presumably from kiss-and-run to full fusion), and (iv) a delayed increase in the number of vesicles released. However, it remains unclear whether (or how) these changes work together. We have incorporated all of these processes into a structural model of the synapse. We propose that the synapse is composed of transsynaptic modules that function quasi-independently in AMPA-mediated transmission. Under basal conditions, synapses are partially silent; some modules are AMPA-silent (but contribute to NMDA-mediated transmission), whereas others are functional (and contribute to both AMPA- and NMDA-mediated transmission). During LTP, there is both a rapid change in the mode of vesicle fusion and a rapid insertion of a postsynaptic complex (a hyperslot) containing many proteins (slots) capable of binding AMPA channels. The combined effect of these pre- and postsynaptic changes is to convert AMPA-silent modules into functional modules. Slot filling is transiently enhanced by a rapid increase in extrasynaptic GluR1, a form of the AMPA-type receptor. A slower transsynaptic growth process adds AMPA-silent modules to the synapse, enhancing the number of vesicles released and thereby enhancing the NMDA response. This model accounts for a broad range of data, including the LTP-induced changes in quantal parameters. The model also provides a coherent explanation for the diverse effects of GluR1 knockout on basal transmission, LTP, and distance-dependent scaling.
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Affiliation(s)
- John Lisman
- Department of Biology, Brandeis University, Waltham, MA 02454, USA.
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414
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Abstract
Considerable evidence suggests that the formation of long-term memories requires a critical period of new protein synthesis. Recently, the notion that some of these newly synthesized proteins originate through local translation in neuronal dendrites has gained some traction. Here, we review the experimental support for this idea and highlight some of the key questions outstanding in this area.
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Affiliation(s)
- Michael A Sutton
- Division of Biology 114-96, California Institute of Technology, Howard Hughes Medical Institute, Pasadena, CA 91125, USA
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415
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416
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Holman D, Feligioni M, Henley JM. Differential redistribution of native AMPA receptor complexes following LTD induction in acute hippocampal slices. Neuropharmacology 2006; 52:92-9. [PMID: 16815481 PMCID: PMC3314510 DOI: 10.1016/j.neuropharm.2006.05.022] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2006] [Revised: 05/07/2006] [Accepted: 05/17/2006] [Indexed: 11/24/2022]
Abstract
AMPAR trafficking is crucial for the expression of certain forms of synaptic plasticity. Here, using surface biotinylation of hippocampal slices and subsequent synaptosome isolation we assessed AMPAR surface expression in synaptosomes following NMDA-evoked long-term depression (NMDA-LTD). Surface levels of GluR1, GluR2 and GluR3 in synaptosomes were markedly reduced 90 min after NMDA-LTD induction. Consistent with endocytosis and degradation, whole-cell surface and total expression levels of GluR2 and GluR3 were also reduced. In contrast, whole-cell surface levels of GluR1 were unaltered at 90 min suggesting that AMPARs with different subunit composition are redistributed to different non-synaptic compartments following LTD induction in acute hippocampal slices.
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Affiliation(s)
| | | | - Jeremy M. Henley
- Corresponding author. Tel.: +44 117 954 6449; fax: +44 117 929 1687. (J.M. Henley)
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417
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Greger IH, Akamine P, Khatri L, Ziff EB. Developmentally Regulated, Combinatorial RNA Processing Modulates AMPA Receptor Biogenesis. Neuron 2006; 51:85-97. [PMID: 16815334 DOI: 10.1016/j.neuron.2006.05.020] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2005] [Revised: 11/21/2005] [Accepted: 05/25/2006] [Indexed: 11/30/2022]
Abstract
The subunit composition determines AMPA receptor (AMPA-R) function and trafficking. Mechanisms underlying channel assembly are thus central to the efficacy and plasticity of glutamatergic synapses. We previously showed that RNA editing at the Q/R site of the GluR2 subunit contributes to the assembly of AMPA-R heteromers by attenuating formation of GluR2 homotetramers. Here we report that this function of the Q/R site depends on subunit contacts between adjacent ligand binding domains (LBDs). Changes of LBD interface contacts alter GluR2 assembly properties, forward traffic, and expression at synapses. Interestingly, developmentally regulated RNA editing within the LBD (at the R/G site) produces analogous effects. Our data reveal that editing to glycine reduces the self-assembly competence of this critical subunit and slows GluR2 maturation in the endoplasmic reticulum (ER). Therefore, RNA editing sites, located at strategic subunit interfaces, shape AMPA-R assembly and trafficking in a developmentally regulated manner.
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Affiliation(s)
- Ingo H Greger
- Neurobiology Division, MRC Laboratory of Molecular Biology, Cambridge CB2 2QH, United Kingdom.
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418
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Cull-Candy S, Kelly L, Farrant M. Regulation of Ca2+-permeable AMPA receptors: synaptic plasticity and beyond. Curr Opin Neurobiol 2006; 16:288-97. [PMID: 16713244 DOI: 10.1016/j.conb.2006.05.012] [Citation(s) in RCA: 337] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2006] [Accepted: 05/08/2006] [Indexed: 12/13/2022]
Abstract
AMPA-type glutamate receptors (AMPARs) mediate most fast excitatory synaptic transmission in the brain. Diversity in excitatory signalling arises, in part, from functional differences among AMPAR subtypes. Although the rapid insertion or deletion of AMPARs is recognised as important for the expression of conventional forms of long-term synaptic plasticity--triggered, for example, by Ca2+ entry through NMDA-type glutamate receptors--only recently has attention focused on novel forms of plasticity that are regulated by, or alter the expression of, Ca2+-permeable AMPARs. The dynamic regulation of these receptors is important for normal synaptic function and in disease states.
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Affiliation(s)
- Stuart Cull-Candy
- Department of Pharmacology, University College London, Gower Street, London, WC1E 6BT, UK.
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Balland B, Lachamp P, Strube C, Kessler JP, Tell F. Glutamatergic synapses in the rat nucleus tractus solitarii develop by direct insertion of calcium-impermeable AMPA receptors and without activation of NMDA receptors. J Physiol 2006; 574:245-61. [PMID: 16690712 PMCID: PMC1817785 DOI: 10.1113/jphysiol.2006.108738] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Calcium influxes through ionotropic glutamate receptors (AMPA and NMDA receptors, AMPARs and NMDARs) are considered to be critical for the shaping and refinement of neural circuits during synaptogenesis. Using a combined morphological and electrophysiological approach, we evaluated this hypothesis at the level of the nucleus tractus solitarii (NTS), a brainstem structure that is a gateway for many visceral sensory afferent fibres. We confirmed that in the NTS, the first excitatory synapses appeared at embryonic day 18. We next characterized the biophysical properties of NTS AMPARs. Throughout perinatal development, both evoked and miniature EPSCs recorded in the presence of an NMDAR blocker were insensitive to polyamines and had linear current-voltage relationships. This demonstrated that AMPARs at NTS excitatory synapses were calcium-impermeable receptors composed of a majority of GluR2 subunits. We then investigated the influence of calcium influxes through NMDARs on the development of NTS synaptic transmission. We found that NMDAR expression at synaptic sites did not precede AMPAR expression. Moreover, NMDAR blockade in utero did not prevent the development of AMPAR synaptic currents and the synaptic clustering of GluR2 subunits. Thus, our data support an alternative model of synaptogenesis that does not depend on calcium influxes through either AMPARs or NMDARs. This model may be particularly relevant to the formation of neural networks devoted to basic behaviours required at birth for survival.
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Affiliation(s)
- Bénédicte Balland
- Laboratoire de Neurophysiologie Cellulaire, CNRS UMR 6150, IFR Jean-Roche, Faculté de Médecine, Bd Pierre Dramard, 13916 Marseille cedex 20, France
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Liu SJ, Zukin RS. Phosphorylation of the AMPA receptor GluR1 subunit is required for synaptic plasticity and retention of spatial memory. Cell 2003; 30:126-34. [PMID: 17275103 DOI: 10.1016/j.tins.2007.01.006] [Citation(s) in RCA: 416] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2006] [Revised: 12/21/2006] [Accepted: 01/18/2007] [Indexed: 10/23/2022]
Abstract
Plasticity of the nervous system is dependent on mechanisms that regulate the strength of synaptic transmission. Excitatory synapses in the brain undergo long-term potentiation (LTP) and long-term depression (LTD), cellular models of learning and memory. Protein phosphorylation is required for the induction of many forms of synaptic plasticity, including LTP and LTD. However, the critical kinase substrates that mediate plasticity have not been identified. We previously reported that phosphorylation of the GluR1 subunit of AMPA receptors, which mediate rapid excitatory transmission in the brain, is modulated during LTP and LTD. To test if GluR1 phosphorylation is necessary for plasticity and learning and memory, we generated mice with knockin mutations in the GluR1 phosphorylation sites. The phosphomutant mice show deficits in LTD and LTP and have memory defects in spatial learning tasks. These results demonstrate that phosphorylation of GluR1 is critical for LTD and LTP expression and the retention of memories.
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Affiliation(s)
- Siqiong June Liu
- Department of Biology, Pennsylvania State University, University Park, PA 16802, USA.
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