301
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Abstract
A central assumption in neurobiology holds that changes in the strength of individual synapses underlie changes in behavior. This concept is widely accepted in the case of learning and memory where LTP and LTD are the most compelling cellular models. It is therefore of great interest to understand, on a molecular level, how the brain regulates the strength of neuronal connections. We review a large body of evidence in support of the very straightforward regulation of synaptic strength by changing the number of postsynaptic receptors, and discuss the molecular machinery required for insertion and removal of AMPA receptors.
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Affiliation(s)
- C Lüscher
- Dept of Pharmacology (APSIC), University of Geneva, 1211 4, Geneva, Switzerland.
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302
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Affiliation(s)
- Y N Jan
- Howard Hughes Medical Institute, Department of Physiology, University of California, San Francisco, California 94143-0725, USA.
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303
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Ziv NE, Garner CC. Principles of glutamatergic synapse formation: seeing the forest for the trees. Curr Opin Neurobiol 2001; 11:536-43. [PMID: 11595485 DOI: 10.1016/s0959-4388(00)00246-4] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
General principles regarding glutamatergic synapse formation in the central nervous system are beginning to emerge. These principles concern the specific roles that dendrites and axons play in the induction of synaptic differentiation, the modes of presynaptic and postsynaptic assembly, the time course of synapse formation and maturation, and the roles of synaptic activity in these processes.
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Affiliation(s)
- N E Ziv
- Rappaport Institute and the Departmentof Anatomy and Cell Biology, Bruce Rappaport Faculty of Medicine, Technion, PO Box 9649, Bat Galim, Haifa 31096, Israel.
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304
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Plitzko D, Rumpel S, Gottmann K. Insulin promotes functional induction of silent synapses in differentiating rat neocortical neurons. Eur J Neurosci 2001; 14:1412-5. [PMID: 11703469 DOI: 10.1046/j.0953-816x.2001.01740.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Long-term synaptic plasticity is thought to underlie synaptic reorganization phenomena that occur during neocortical development. Recently, it has been proposed, that the functional induction of AMPA receptors at silent glutamatergic synapses is of major importance in activity-dependent, developmental plasticity. To investigate the mechanisms involved in the developmental regulation of silent synapses, we analysed the functional maturation of the thalamocortical projection in culture. A large proportion of the thalamocortical synapses were functionally silent at an early stage in vitro. During further differentiation, the incidence of silent synapses decreased drastically, indicating a conversion of silent into functional synapses. Chronic blockade of spontaneous network activity by addition of tetrodotoxin to the culture medium strongly impaired this developmental maturation. Moreover, the developmental decline in the proportion of silent synapses was dramatically accelerated by chronic addition of the neurotrophic factor, insulin. This effect of insulin was partly dependent on spontaneous activity. Thus, insulin appears to be involved in the modulation of long-term developmental plasticity at immature glutamatergic synapses.
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Affiliation(s)
- D Plitzko
- Lehrstuhl für Zellphysiologie, Ruhr-Universität Bochum, D-44780 Bochum, Germany
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305
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Passafaro M, Piëch V, Sheng M. Subunit-specific temporal and spatial patterns of AMPA receptor exocytosis in hippocampal neurons. Nat Neurosci 2001; 4:917-26. [PMID: 11528423 DOI: 10.1038/nn0901-917] [Citation(s) in RCA: 492] [Impact Index Per Article: 21.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Using a thrombin cleavage assay in cultured hippocampal neurons, we studied the kinetics, regulation and site of AMPA receptor surface delivery. Surface insertion of the GluR1 subunit occurs slowly in basal conditions and is stimulated by NMDA receptor activation and insulin, whereas GluR2 exocytosis is constitutively rapid. Although both subunits ultimately concentrate in synapses, GluR1 and GluR2 show different spatial patterns of surface accumulation, consistent with GluR1 being inserted initially at extrasynaptic sites and GluR2 being inserted more directly at synapses. The spatiotemporal pattern of surface accumulation is determined by the cytoplasmic tails of GluR subunits, and in heteromeric receptors, GluR1 acts dominantly over GluR2. We propose that GluR1 controls the exocytosis and GluR2/3, the recycling and endocytosis of AMPA receptors.
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Affiliation(s)
- M Passafaro
- Department of Neurobiology and Howard Hughes Medical Institute, Massachusetts General Hospital and Harvard Medical School, 50 Blossom Street, Boston, Massachusetts 02114, USA
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306
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Abstract
Several morphological changes of synapses have been reported to be associated with the induction of long-term potentiation (LTP) in the CA1 hippocampus, including an transient increase in the proportion of synapses with perforated postsynaptic densities (PSDs) and a later occurrence of multiple spine boutons (MSBs) in which the two spines arise from the same dendrite. To investigate the functional significance of these modifications, we analyzed single sections and reconstructed 134 synapses labeled via activity using a calcium precipitation approach. Analyses of labeled spine profiles showed changes of the spine head area, PSD length, and proportion of spine profiles containing a coated vesicle that reflected variations in the relative proportion of different types of synapses. Three-dimensional reconstruction indicated that the increase of perforated spine profiles observed 30 min after LTP induction essentially resulted from synapses exhibiting segmented, completely partitioned PSDs. These synapses had spine head and PSD areas approximately three times larger than those of simple synapses. They contained coated vesicles in a much higher proportion than that of any other type of synapse and exhibited large spinules associated with the PSD. Also the MSBs with two spines arising from the same dendrite that were observed 1-2 hr after LTP induction included a spine that was smaller and a PSD that was smaller than those of simple synapses. These results support the idea that LTP induction is associated with an enhanced recycling of synaptic membrane and that this process could underlie the formation of synapses with segmented PSDs and eventually result in the formation of a new, immature spine.
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307
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Mack V, Burnashev N, Kaiser KM, Rozov A, Jensen V, Hvalby O, Seeburg PH, Sakmann B, Sprengel R. Conditional restoration of hippocampal synaptic potentiation in Glur-A-deficient mice. Science 2001; 292:2501-4. [PMID: 11431570 DOI: 10.1126/science.1059365] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Plasticity of mature hippocampal CA1 synapses is dependent on l-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptors containing the glutamate receptor A (GluR-A) subunit. In GluR-A-deficient mice, plasticity could be restored by controlled expression of green fluorescent protein (GFP)-tagged GluR-A, which contributes to channel formation and displayed the developmental redistribution of AMPA receptors in CA1 pyramidal neurons. Long-term potentiation (LTP) induced by pairing or tetanic stimulation was rescued in adult GluR-A(-/-) mice when (GFP)GluR-A expression was constitutive or induced in already fully developed pyramidal cells. This shows that GluR-A-independent forms of synaptic plasticity can mediate the establishment of mature hippocampal circuits that are prebuilt to express GluR-A-dependent LTP.
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Affiliation(s)
- V Mack
- Department of Molecular Neurobiology, Max-Planck-Institute for Medical Research, D-69120 Heidelberg, Germany
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308
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Affiliation(s)
- M Sheng
- Department of Neurobiology and Howard Hughes Medical Institute, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA.
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309
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Kaech S, Parmar H, Roelandse M, Bornmann C, Matus A. Cytoskeletal microdifferentiation: a mechanism for organizing morphological plasticity in dendrites. Proc Natl Acad Sci U S A 2001; 98:7086-92. [PMID: 11416192 PMCID: PMC34627 DOI: 10.1073/pnas.111146798] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Experimental evidence suggests that microfilaments and microtubules play contrasting roles in regulating the balance between motility and stability in neuronal structures. Actin-containing microfilaments are associated with structural plasticity, both during development when their dynamic activity drives the exploratory activity of growth cones and after circuit formation when the actin-rich dendritic spines of excitatory synapses retain a capacity for rapid changes in morphology. By contrast, microtubules predominate in axonal and dendritic processes, which appear to be morphologically relatively more stable. To compare the cytoplasmic distributions and dynamics of microfilaments and microtubules we made time-lapse recordings of actin or the microtubule-associated protein 2 tagged with green fluorescent protein in neurons growing in dispersed culture or in tissue slices from transgenic mice. The results complement existing evidence indicating that the high concentrations of actin present in dendritic spines is a specialization for morphological plasticity. By contrast, microtubule-associated protein 2 is limited to the shafts of dendrites where time-lapse recordings show little evidence for dynamic activity. A parallel exists between the partitioning of microfilaments and microtubules in motile and stable domains of growing processes during development and between dendrite shafts and spines at excitatory synapses in established neuronal circuits. These data thus suggest a mechanism, conserved through development and adulthood, in which the differential dynamics of actin and microtubules determine the plasticity of neuronal structures.
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Affiliation(s)
- S Kaech
- Friedrich Miescher Institute, 4058 Basel, Switzerland
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310
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Muscarinic regulation of dendritic and axonal outputs of rat thalamic interneurons: a new cellular mechanism for uncoupling distal dendrites. J Neurosci 2001. [PMID: 11160385 DOI: 10.1523/jneurosci.21-04-01148.2001] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Inhibition is crucial for sharpening the sensory information relayed through the thalamus. To understand how the interneuron-mediated inhibition in the thalamus is regulated, we studied the muscarinic effects on interneurons in the lateral posterior nucleus and lateral geniculate nucleus of the thalamus. Here, we report that activation of muscarinic receptors switched the firing pattern in thalamic interneurons from bursting to tonic. Although neuromodulators switch the firing mode in several other types of neurons by altering their membrane potential, we found that activation of muscarinic subtype 2 receptors switched the fire mode in thalamic interneurons by selectively decreasing their input resistance. This is attributable to the muscarinic enhancement of a hyperpolarizing potassium conductance and two depolarizing cation conductances. The decrease in input resistance appeared to electrotonically uncouple the distal dendrites of thalamic interneurons, which effectively changed the inhibition pattern in thalamocortical cells. These results suggest a novel cellular mechanism for the cholinergic transformation of long-range, slow dendrite- and axon-originated inhibition into short-range, fast dendrite-originated inhibition in the thalamus observed in vivo. It is concluded that the electrotonic properties of the dendritic compartments of thalamic interneurons can be dynamically regulated by muscarinic activity.
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311
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Shi S, Hayashi Y, Esteban JA, Malinow R. Subunit-specific rules governing AMPA receptor trafficking to synapses in hippocampal pyramidal neurons. Cell 2001; 105:331-43. [PMID: 11348590 DOI: 10.1016/s0092-8674(01)00321-x] [Citation(s) in RCA: 845] [Impact Index Per Article: 36.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
AMPA-type glutamate receptors (AMPA-Rs) mediate a majority of excitatory synaptic transmission in the brain. In hippocampus, most AMPA-Rs are hetero-oligomers composed of GluR1/GluR2 or GluR2/GluR3 subunits. Here we show that these AMPA-R forms display different synaptic delivery mechanisms. GluR1/GluR2 receptors are added to synapses during plasticity; this requires interactions between GluR1 and group I PDZ domain proteins. In contrast, GluR2/GluR3 receptors replace existing synaptic receptors continuously; this occurs only at synapses that already have AMPA-Rs and requires interactions by GluR2 with NSF and group II PDZ domain proteins. The combination of regulated addition and continuous replacement of synaptic receptors can stabilize long-term changes in synaptic efficacy and may serve as a general model for how surface receptor number is established and maintained.
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Affiliation(s)
- S Shi
- Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA
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312
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Carroll RC, Beattie EC, von Zastrow M, Malenka RC. Role of AMPA receptor endocytosis in synaptic plasticity. Nat Rev Neurosci 2001; 2:315-24. [PMID: 11331915 DOI: 10.1038/35072500] [Citation(s) in RCA: 329] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Activity-mediated changes in the strength of synaptic communication are important for the establishment of proper neuronal connections during development and for the experience-dependent modification of neural circuitry that is believed to underlie all forms of behavioural plasticity. Owing to the wide-ranging significance of synaptic plasticity, considerable efforts have been made to identify the mechanisms by which synaptic changes are triggered and expressed. New evidence indicates that one important expression mechanism of several long-lasting forms of synaptic plasticity might involve the physical transport of AMPA-type glutamate receptors in and out of the synaptic membrane. Here, we focus on the rapidly accumulating evidence that AMPA receptors undergo regulated endocytosis, which is important for long-term depression.
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Affiliation(s)
- R C Carroll
- Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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313
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