351
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Eggermont JJ. Correlated neural activity as the driving force for functional changes in auditory cortex. Hear Res 2007; 229:69-80. [PMID: 17296278 DOI: 10.1016/j.heares.2007.01.008] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/03/2006] [Revised: 10/31/2006] [Accepted: 01/03/2007] [Indexed: 10/23/2022]
Abstract
The functional role of neural synchrony is reflected in cortical tonotopic map reorganization and in the emergence of pathological phenomena such as tinnitus. First of all experimenter-centered and subject-centered views of neural activity will be contrasted; this argues against the use of stimulus-correction procedures and favors the use of a correction procedure based on neural activity without reference to stimulus timing. Within a cortical column neurons fired synchronously with on average about 6% of their spikes in a 1 ms bin and occasionally showing 30% or more of such coincident spikes. For electrode separations exceeding 200 microm the average peak correlation strength only occasionally reached 3%. The experimental evidence for coincidence of neural activity, neural correlation and neural synchrony shows that horizontal fibers activity can induce strong neural correlations. Cortico-cortical connections for a large part connect cell groups with characteristic frequencies differing by more than one octave. Such neurons have generally non-overlapping receptive fields but still can have sizeable peak cross-correlations. Correlated neural activity and heterotopic neural interconnections are presented as the substrates for cortical reorganization; increased neural synchrony and tonotopic map reorganization go hand in hand. This links cortical reorganization with hypersynchrony that can be considered as an important driving force underlying tinnitus.
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Affiliation(s)
- Jos J Eggermont
- Department of Physiology and Biophysics, University of Calgary, Calgary, Alberta, Canada.
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352
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Crozier RA, Wang Y, Liu CH, Bear MF. Deprivation-induced synaptic depression by distinct mechanisms in different layers of mouse visual cortex. Proc Natl Acad Sci U S A 2007; 104:1383-8. [PMID: 17227847 PMCID: PMC1783104 DOI: 10.1073/pnas.0609596104] [Citation(s) in RCA: 131] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Long-term depression (LTD) induced by low-frequency synaptic stimulation (LFS) was originally introduced as a model to probe potential mechanisms of deprivation-induced synaptic depression in visual cortex. In hippocampus, LTD requires activation of postsynaptic NMDA receptors, PKA, and the clathrin-dependent endocytosis of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. It has long been assumed that LTD induced in visual cortical layer 2/3 by LFS of layer 4 uses similar mechanisms. Here we show in mouse visual cortex that this conclusion requires revision. We find that LTD induced in layer 2/3 by LFS is unaffected by inhibitors of PKA or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor endocytosis but is reliably blocked by an endocannabinoid CB1 receptor antagonist. Conversely, LFS applied to synapses on layer 4 neurons produces LTD that appears mechanistically identical to that in CA1 and is insensitive to CB1 blockers. Occlusion experiments suggest that both mechanisms contribute to the loss of visual responsiveness after monocular deprivation.
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Affiliation(s)
- Robert A. Crozier
- *Howard Hughes Medical Institute, The Picower Institute for Learning and Memory, Department of Brain and Cognitive Science, Massachusetts Institute of Technology, 177 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Yun Wang
- Division of Neurology Research, Caritas St. Elizabeth's Medical Center, Tufts University, Boston, MA 02135
| | - Cheng-Hang Liu
- *Howard Hughes Medical Institute, The Picower Institute for Learning and Memory, Department of Brain and Cognitive Science, Massachusetts Institute of Technology, 177 Massachusetts Avenue, Cambridge, MA 02139; and
| | - Mark F. Bear
- *Howard Hughes Medical Institute, The Picower Institute for Learning and Memory, Department of Brain and Cognitive Science, Massachusetts Institute of Technology, 177 Massachusetts Avenue, Cambridge, MA 02139; and
- To whom correspondence should be addressed. E-mail:
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353
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Deshmukh S, Onozuka K, Bender KJ, Bender VA, Lutz B, Mackie K, Feldman DE. Postnatal development of cannabinoid receptor type 1 expression in rodent somatosensory cortex. Neuroscience 2007; 145:279-87. [PMID: 17210229 PMCID: PMC1850104 DOI: 10.1016/j.neuroscience.2006.11.033] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2006] [Revised: 11/17/2006] [Accepted: 11/20/2006] [Indexed: 11/19/2022]
Abstract
Endocannabinoids are powerful modulators of synaptic transmission that act on presynaptic cannabinoid receptors. Cannabinoid receptor type 1 (CB1) is the dominant receptor in the CNS, and is present in many brain regions, including sensory cortex. To investigate the potential role of CB1 receptors in cortical development, we examined the developmental expression of CB1 in rodent primary somatosensory (barrel) cortex, using immunohistochemistry with a CB1-specific antibody. We found that before postnatal day (P) 6, CB1 receptor staining was present exclusively in the cortical white matter, and that CB1 staining appeared in the gray matter between P6 and P20 in a specific laminar pattern. CB1 staining was confined to axons, and was most prominent in cortical layers 2/3, 5a, and 6. CB1 null (-/-) mice showed altered anatomical barrel maps in layer 4, with enlarged inter-barrel septa, but normal barrel size. These results indicate that CB1 receptors are present in early postnatal development and influence development of sensory maps.
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Affiliation(s)
- Suvarna Deshmukh
- Division of Biological Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0357
| | - Kaori Onozuka
- Division of Biological Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0357
| | - Kevin J. Bender
- Division of Biological Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0357
| | - Vanessa A. Bender
- Division of Biological Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0357
| | - Beat Lutz
- Department of Physiological Chemistry, Johannes Gutenberg-University Mainz, Duesbergweg 6, 55099 Mainz, Germany
| | - Ken Mackie
- Department of Anesthesiology, University of Washington School of Medicine, Seattle, WA 98195-6540
| | - Daniel E. Feldman
- Division of Biological Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0357
- Corresponding author: phone 858-822-4271, fax 858-534-7309,
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354
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Bartlett TE, Bannister NJ, Collett VJ, Dargan SL, Massey PV, Bortolotto ZA, Fitzjohn SM, Bashir ZI, Collingridge GL, Lodge D. Differential roles of NR2A and NR2B-containing NMDA receptors in LTP and LTD in the CA1 region of two-week old rat hippocampus. Neuropharmacology 2007; 52:60-70. [PMID: 16904707 DOI: 10.1016/j.neuropharm.2006.07.013] [Citation(s) in RCA: 201] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2006] [Revised: 07/05/2006] [Accepted: 07/06/2006] [Indexed: 10/24/2022]
Abstract
The role of NMDA receptors in the induction of long-term potentiation (LTP) and long-term depression (LTD) is well established but which particular NR2 subunits are involved in these plasticity processes is still a matter of controversy. We have studied the effects of subtype selective NMDA receptor antagonists on LTP induced by high frequency stimulation (100 Hz for 1s) and LTD induced by low frequency stimulation (1 Hz for 15 min) in the CA1 region of hippocampal slices from 14 day old Wistar rats. Against recombinant receptors in HEK293 cells NVP-AAM077 (NVP) was approximately 14-fold selective for NR2A vs NR2B receptors, whilst Ro 25-6981 (Ro) was highly selective for NR2B receptors. On NMDA receptor-mediated EPSCs from Schaffer collaterals in CA1 neurones, NVP and Ro both reduced the amplitude but differentially affected the time constant of decay. The data are compatible with the selective effect of NVP (0.1 microM) and Ro (4 microM) on native NR2A and NBR2B receptors, respectively. NVP reduced both LTP and LTD whereas Ro reduced only LTP. Thus, LTP was reduced by 63% at 0.1 microM NVP and almost completely at 0.4 microM whereas 5 microM Ro reduced LTP by 45%. These data are consistent with a role for both NR2A and NR2B in the induction of LTP, under our experimental conditions. In comparison, LTD was unaffected by Ro (5 microM) even in the presence of a glutamate uptake inhibitor threo-beta-benzylaspartic acid (TBOA) to increase the concentration of glutamate at NR2B containing receptors. NVP (0.2-0.4 microM), however, produced a concentration dependent inhibition of LTD which was complete at 0.4 microM. The lack of effect of 0.1 microM NVP on LTD contrasts with its marked effect on LTP and raises the possibility that different NVP-sensitive NR2 subunit-containing NMDA receptors are required for LTP and LTD in this preparation.
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Affiliation(s)
- Thomas E Bartlett
- MRC Centre for Synaptic Plasticity, Department of Anatomy, University of Bristol, School of Medical Sciences, University Walk, Bristol, BS8 1TD, UK
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355
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Li YH, Han TZ. Glycine Binding Sites of Presynaptic NMDA Receptors May Tonically Regulate Glutamate Release in the Rat Visual Cortex. J Neurophysiol 2007; 97:817-23. [PMID: 17093111 DOI: 10.1152/jn.00980.2006] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In the CNS, activation of N-methyl-d-aspartate receptor (NMDA-R) glycine binding sites is a prerequisite for activation of postsynaptic NMDA-Rs by the excitatory neurotransmitter glutamate. Here we provide electrophysiological evidence that the glycine binding sites of presynaptic NMDA-Rs regulate glutamate release in layer II/III pyramidal neurons of the rat visual cortex. Specifically, our results reveal that the frequency of miniature excitatory postsynaptic currents is significantly reduced by 7-chloro-kynurenic acid (7-Cl KYNA), a NMDA-R glycine binding site antagonist, and glycine or d-serine reverses this effect. Similar results are obtained when the open-channel NMDA receptor blocker, MK-801, is included in the recording pipette. Our data indicate that the glycine binding site of postsynaptic NMDA-Rs is not saturated. Moreover, they suggest that presynaptic NMDA-Rs are located in layer II/III pyramidal neurons of the rat visual cortex and that the glycine binding site of presynaptic NMDA-Rs tonically regulates glutamate release.
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Affiliation(s)
- Yan-Hai Li
- Dept. of Physiology, School of Medicine, Xi'an Jiaotong University, Zhuque Dajie 205, Xi'an, Shaanxi 710061, PR China
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356
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Walz C, Jüngling K, Lessmann V, Gottmann K. Presynaptic Plasticity in an Immature Neocortical Network Requires NMDA Receptor Activation and BDNF Release. J Neurophysiol 2006; 96:3512-6. [PMID: 17110740 DOI: 10.1152/jn.00018.2006] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Activity-dependent developmental maturation of the neocortical network is thought to involve the stabilization and potentiation of immature synapses. In particular, N-methyl-d-aspartate (NMDA) receptor-dependent long-term plasticity that is expressed presynaptically appears to be crucial for the selection of functionally adequate synapses. However, presynaptic expression of long-term plasticity in neocortical neurons has mainly been studied indirectly by electrophysiological techniques. Here we analyzed presynaptic plasticity directly by repeated imaging of actively cycling presynaptic vesicles with the styryl dye FM4-64 in cultured neocortical neurons at 34°C. To monitor long-term changes, stimulation-induced saturating FM4-64 staining and subsequent destaining was performed twice with an interval of 1.5 h between stainings and with the first staining serving as a plasticity stimulus. In the vast majority of presynaptic release sites, we found an increase in the mean fluorescence intensity after the second staining indicating an enhanced number of cycling synaptic vesicles. Most intriguingly, we additionally observed the appearance of new active release sites. As demonstrated by the addition of the NMDA receptor antagonist d-2-amino-5-phosphonopentanoic acid (d-AP5), both plasticity phenomena were strictly dependent on NMDA receptor activation. This suggests that a subpopulation of release sites was functionally silent during the first round of staining. Moreover, we studied a potential role of brain-derived neurotrophic factor (BDNF) in this type of presynaptic plasticity by imaging BDNF-deficient neocortical neurons. The increase in fluorescence intensity was strongly inhibited in BDNF-knockout neurons and was absent in wild-type neurons in the presence of BDNF scavenging trkB receptor bodies. These results indicate that BDNF might play an important role as a plasticity-related messenger molecule in neocortical neurons.
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Affiliation(s)
- Corinna Walz
- Institut für Neuro- und Sinnesphysiologie, Heinrich-Heine-Universität Düsseldorf, Universitätsstrasse 1, D-40225 Düsseldorf, Germany
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357
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Abstract
Calcium is a second messenger, which can trigger the modification of synaptic efficacy. We investigated the question of whether a differential rise in postsynaptic Ca2+ ([Ca2+]i) alone is sufficient to account for the induction of long-term potentiation (LTP) and long-term depression (LTD) of EPSPs in the basal dendrites of layer 2/3 pyramidal neurons of the somatosensory cortex. Volume-averaged [Ca2+]i transients were measured in spines of the basal dendritic arbor for spike-timing-dependent plasticity induction protocols. The rise in [Ca2+]i was uncorrelated to the direction of the change in synaptic efficacy, because several pairing protocols evoked similar spine [Ca2+]i transients but resulted in either LTP or LTD. The sequence dependence of near-coincident presynaptic and postsynaptic activity on the direction of changes in synaptic strength suggested that LTP and LTD were induced by two processes, which were controlled separately by postsynaptic [Ca2+]i levels. Activation of voltage-dependent Ca2+ channels before metabotropic glutamate receptors (mGluRs) resulted in the phospholipase C-dependent (PLC-dependent) synthesis of endocannabinoids, which acted as a retrograde messenger to induce LTD. LTP required a large [Ca2+]i transient evoked by NMDA receptor activation. Blocking mGluRs abolished the induction of LTD and uncovered the Ca2+-dependent induction of LTP. We conclude that the volume-averaged peak elevation of [Ca2+]i in spines of layer 2/3 pyramids determines the magnitude of long-term changes in synaptic efficacy. The direction of the change is controlled, however, via a mGluR-coupled signaling cascade. mGluRs act in conjunction with PLC as sequence-sensitive coincidence detectors when postsynaptic precede presynaptic action potentials to induce LTD. Thus presumably two different Ca2+ sensors in spines control the induction of spike-timing-dependent synaptic plasticity.
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Affiliation(s)
- Thomas Nevian
- Department of Cell Physiology, Max-Planck Institute for Medical Research, D-69120 Heidelberg, Germany.
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358
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Czarnecki A, Birtoli B, Ulrich D. Cellular mechanisms of burst firing-mediated long-term depression in rat neocortical pyramidal cells. J Physiol 2006; 578:471-9. [PMID: 17082228 PMCID: PMC2075152 DOI: 10.1113/jphysiol.2006.123588] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
During wakefulness and sleep, neurons in the neocortex emit action potentials tonically or in rhythmic bursts, respectively. However, the role of synchronized discharge patterns is largely unknown. We have recently shown that pairings of excitatory postsynaptic potentials (EPSPs) and action potential bursts or single spikes lead to long-term depression (burst-LTD) or long-term potentiation, respectively. In this study, we elucidate the cellular mechanisms of burst-LTD and characterize its functional properties. Whole-cell patch-clamp recordings were obtained from layer V pyramidal cells in somatosensory cortex of juvenile rats in vitro and composite EPSPs and EPSCs were evoked extracellularly in layers II/III. Repetitive burst-pairings led to a long-lasting depression of EPSPs and EPSCs that was blocked by inhibitors of metabotropic glutamate group 1 receptors, phospholipase C, protein kinase C (PKC) and calcium release from the endoplasmic reticulum, and that required an intact machinery for endocytosis. Thus, burst-LTD is induced via a Ca2+- and phosphatidylinositol-dependent activation of PKC and expressed through phosphorylation-triggered endocytosis of AMPA receptors. Functionally, burst-LTD is inversely related to EPSP size and bursts dominate single spikes in determining the sign of synaptic plasticity. Thus burst-firing constitutes a signal by which coincident synaptic inputs are proportionally downsized. Overall, our data thus suggest a mechanism by which synaptic weights can be reconfigured during non-rapid eye movement sleep.
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Affiliation(s)
- Antonny Czarnecki
- Department of Physiology, University of Bern, Bühlplatz 5, 3012 Bern, Switzerland
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359
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Abstract
Given the extensive attenuation that can occur along dendritic cables, location within the dendritic tree might appear to be a dominant factor in determining the impact of a synapse on the postsynaptic response. By this reasoning, distal synapses should have a smaller effect than proximal ones. However, experimental evidence from several types of neurons, such as CA1 pyramidal cells, indicates that a compensatory strengthening of synapses counteracts the effect of location on synaptic efficacy. A form of spike-timing-dependent plasticity (STDP), called anti-STDP, combined with non-Hebbian activity-dependent plasticity can account for the equalization of synaptic efficacies. This result, obtained originally in models with unbranched passive cables, also arises in multi-compartment models with branched and active dendrites that feature backpropagating action potentials, including models with CA1 pyramidal morphologies. Additionally, when dendrites support the local generation of action potentials, anti-STDP prevents runaway dendritic spiking and locally balances the numbers of dendritic and backpropagating action potentials. Thus in multiple ways, anti-STDP eliminates the location dependence of synapses and allows Hebbian plasticity to operate in a more “democratic” manner.
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Affiliation(s)
- Clifton C Rumsey
- The University of Texas at Austin, Center for Learning and Memory, 1 University Station C7000, Austin, TX 78712, USA.
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360
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Varshney LR, Sjöström PJ, Chklovskii DB. Optimal Information Storage in Noisy Synapses under Resource Constraints. Neuron 2006; 52:409-23. [PMID: 17088208 DOI: 10.1016/j.neuron.2006.10.017] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2005] [Revised: 04/27/2006] [Accepted: 10/10/2006] [Indexed: 11/25/2022]
Abstract
Experimental investigations have revealed that synapses possess interesting and, in some cases, unexpected properties. We propose a theoretical framework that accounts for three of these properties: typical central synapses are noisy, the distribution of synaptic weights among central synapses is wide, and synaptic connectivity between neurons is sparse. We also comment on the possibility that synaptic weights may vary in discrete steps. Our approach is based on maximizing information storage capacity of neural tissue under resource constraints. Based on previous experimental and theoretical work, we use volume as a limited resource and utilize the empirical relationship between volume and synaptic weight. Solutions of our constrained optimization problems are not only consistent with existing experimental measurements but also make nontrivial predictions.
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Affiliation(s)
- Lav R Varshney
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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361
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Zhang XL, Zhou ZY, Winterer J, Müller W, Stanton PK. NMDA-dependent, but not group I metabotropic glutamate receptor-dependent, long-term depression at Schaffer collateral-CA1 synapses is associated with long-term reduction of release from the rapidly recycling presynaptic vesicle pool. J Neurosci 2006; 26:10270-80. [PMID: 17021182 PMCID: PMC6674623 DOI: 10.1523/jneurosci.3091-06.2006] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Postsynaptic alterations have been suggested to account for NMDA receptor (NMDAR)-dependent long-term depression (LTD) and long-term potentiation of synaptic strength, although there is substantial evidence supporting changes in presynaptic release. Direct chemical activation of either NMDA or group I metabotropic glutamate receptor (mGluR1) elicits LTD of similar magnitudes, but it is unknown whether they share common expression mechanisms. Using dual-photon laser-scanning microscopy of FM1-43 [N-(3-triethylammoniumpropyl)-4-(4-(dibutylamino)styryl)pyridinium dibromide] to directly visualize presynaptic vesicular release from the rapidly recycling vesicle pool (RRP) at Schaffer collateral terminals in field CA1 of rat hippocampal slices, we found that a persistent reduction in vesicular release from the RRP is induced by NMDA-LTD but not by mGluR1-LTD. Variance-mean analyses of Schaffer collateral release probability (P(r)) at varying extracellular calcium concentrations confirmed that NMDA-LTD was associated with reduced P(r), whereas mGluR1-LTD was not. Pharmacological isolation of NMDAR-dependent and mGluR-dependent forms of stimulus-evoked LTD revealed that both are composed of a combination of presynaptic and postsynaptic alterations. However, when group I mGluR-dependent LTD was isolated by combining an NMDAR blocker with a group II mGluR antagonist, this form of LTD was purely postsynaptic. The nitric oxide synthase inhibitor N omega-nitro-L-arginine blocked the induction of NMDA-LTD but did not alter mGluR-LTD, consistent with a selective role for nitric oxide as a retrograde messenger mediating NMDA-LTD. These data demonstrate that single synapses can express multiple forms of LTD with different sites of expression, that NMDA-LTD is a combination of presynaptic and postsynaptic alterations, but that group I mGluR-LTD appears to be expressed entirely postsynaptically.
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Affiliation(s)
| | | | - Jochen Winterer
- Neuroscience Research Institute and
- Department of Psychiatry, Charité, Humboldt University, D-10117 Berlin, Germany, and
| | - Wolfgang Müller
- Departments of Neurosurgery, Neurology, and Neuroscience, University of New Mexico School of Medicine, Albuquerque, New Mexico 87131
| | - Patric K. Stanton
- Departments of Cell Biology and Anatomy and
- Neurology, New York Medical College, Valhalla, New York 10595
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362
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Scheuber A, Rudge R, Danglot L, Raposo G, Binz T, Poncer JC, Galli T. Loss of AP-3 function affects spontaneous and evoked release at hippocampal mossy fiber synapses. Proc Natl Acad Sci U S A 2006; 103:16562-7. [PMID: 17056716 PMCID: PMC1637621 DOI: 10.1073/pnas.0603511103] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Synaptic vesicle (SV) exocytosis mediating neurotransmitter release occurs spontaneously at low intraterminal calcium concentrations and is stimulated by a rise in intracellular calcium. Exocytosis is compensated for by the reformation of vesicles at plasma membrane and endosomes. Although the adaptor complex AP-3 was proposed to be involved in the formation of SVs from endosomes, whether its function has an indirect effect on exocytosis remains unknown. Using mocha mice, which are deficient in functional AP-3, we identify an AP-3-dependent tetanus neurotoxin-resistant asynchronous release that can be evoked at hippocampal mossy fiber (MF) synapses. Presynaptic targeting of the tetanus neurotoxin-resistant vesicle soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) tetanus neurotoxin-insensitive vesicle-associated membrane protein (TI-VAMP) is lost in mocha hippocampal MF terminals, whereas the localization of synaptobrevin 2 is unaffected. In addition, quantal release in mocha cultures is more frequent and more sensitive to sucrose. We conclude that lack of AP-3 results in more constitutive secretion and loss of an asynchronous evoked release component, suggesting an important function of AP-3 in regulating SV exocytosis at MF terminals.
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Affiliation(s)
- Anita Scheuber
- *Institut National de la Santé et de la Recherche Médicale, Université Pierre et Marie Curie–Paris 6, Unité Mixte de Recherche 739, Cortex and Epilepsy, F-75013 Paris, France
| | - Rachel Rudge
- Membrane Traffic in Neuronal and Epithelial Morphogenesis, Institut National de la Santé et de la Recherche Médicale Avenir Team, F-75005 Paris, France
- Institut Jacques Monod, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7592, Université Paris 6, Université Paris 7, F-75005 Paris, France
| | - Lydia Danglot
- Membrane Traffic in Neuronal and Epithelial Morphogenesis, Institut National de la Santé et de la Recherche Médicale Avenir Team, F-75005 Paris, France
- Institut Jacques Monod, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7592, Université Paris 6, Université Paris 7, F-75005 Paris, France
| | - Graca Raposo
- Structure and Membrane Compartments, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 144, Institut Curie, F-75005 Paris, France; and
| | - Thomas Binz
- Institute of Biochemistry, Medical School Hannover, D-30625 Hannover, Germany
| | - Jean-Christophe Poncer
- *Institut National de la Santé et de la Recherche Médicale, Université Pierre et Marie Curie–Paris 6, Unité Mixte de Recherche 739, Cortex and Epilepsy, F-75013 Paris, France
| | - Thierry Galli
- Membrane Traffic in Neuronal and Epithelial Morphogenesis, Institut National de la Santé et de la Recherche Médicale Avenir Team, F-75005 Paris, France
- To whom correspondence should be addressed. E-mail:
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363
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Cai Y, Gavornik JP, Cooper LN, Yeung LC, Shouval HZ. Effect of stochastic synaptic and dendritic dynamics on synaptic plasticity in visual cortex and hippocampus. J Neurophysiol 2006; 97:375-86. [PMID: 17035360 DOI: 10.1152/jn.00895.2006] [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] [Indexed: 11/22/2022] Open
Abstract
Various forms of synaptic plasticity, including spike timing-dependent plasticity, can be accounted for by calcium-dependent models of synaptic plasticity. However, recent results in which synaptic plasticity is induced by multi-spike protocols cannot simply be accounted for by linear superposition of plasticity due to spike pairs or by existing calcium-dependent models. In this paper, we show that multi-spike protocols can be accounted for if, in addition to the dynamics of back-propagating action potentials, stochastic synaptic dynamics are taken into account. We show that a stochastic implementation can account for the data better than a deterministic implementation and is also more robust. Our results demonstrate that differences between experimental results obtained in hippocampus and visual cortex can be accounted for by the different synaptic and dendritic dynamics in these two systems.
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Affiliation(s)
- Yidao Cai
- Department of Neurobiology and Anatomy, The University of Texas Medical School, Houston, TX 77030, USA
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364
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Desai NS, Casimiro TM, Gruber SM, Vanderklish PW. Early Postnatal Plasticity in Neocortex of Fmr1 Knockout Mice. J Neurophysiol 2006; 96:1734-45. [PMID: 16823030 DOI: 10.1152/jn.00221.2006] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Fragile X syndrome is produced by a defect in a single X-linked gene, called Fmr1, and is characterized by abnormal dendritic spine morphologies with spines that are longer and thinner in neocortex than those from age-matched controls. Studies using Fmr1 knockout mice indicate that spine abnormalities are especially pronounced in the first month of life, suggesting that altered developmental plasticity underlies some of the behavioral phenotypes associated with the syndrome. To address this issue, we used intracellular recordings in neocortical slices from early postnatal mice to examine the effects of Fmr1 disruption on two forms of plasticity active during development. One of these, long-term potentiation of intrinsic excitability, is intrinsic in expression and requires mGluR5 activation. The other, spike timing-dependent plasticity, is synaptic in expression and requires N-methyl-d-aspartate receptor activation. While intrinsic plasticity was normal in the knockout mice, synaptic plasticity was altered in an unusual and striking way: long-term depression was robust but long-term potentiation was entirely absent. These findings underscore the ideas that Fmr1 has highly selective effects on plasticity and that abnormal postnatal development is an important component of the disorder.
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MESH Headings
- Action Potentials/genetics
- Action Potentials/physiology
- Animals
- Animals, Newborn/genetics
- Animals, Newborn/physiology
- Fragile X Mental Retardation Protein/genetics
- Fragile X Mental Retardation Protein/physiology
- Fragile X Syndrome/genetics
- Fragile X Syndrome/physiopathology
- Gene Expression Regulation, Developmental/genetics
- Gene Expression Regulation, Developmental/physiology
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Neocortex/growth & development
- Neocortex/physiology
- Neuronal Plasticity/genetics
- Neuronal Plasticity/physiology
- Receptor, Metabotropic Glutamate 5
- Receptors, Metabotropic Glutamate/genetics
- Receptors, Metabotropic Glutamate/physiology
- Receptors, N-Methyl-D-Aspartate/genetics
- Receptors, N-Methyl-D-Aspartate/physiology
- Synapses/genetics
- Synapses/physiology
- Synaptic Transmission/genetics
- Synaptic Transmission/physiology
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Affiliation(s)
- Niraj S Desai
- The Neurosciences Fine Institute, San Diego, CA 92121, USA.
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365
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Czaja K, Ritter RC, Burns GA. Vagal afferent neurons projecting to the stomach and small intestine exhibit multiple N-methyl-D-aspartate receptor subunit phenotypes. Brain Res 2006; 1119:86-93. [PMID: 16989781 DOI: 10.1016/j.brainres.2006.08.042] [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: 05/31/2006] [Revised: 08/08/2006] [Accepted: 08/11/2006] [Indexed: 01/30/2023]
Abstract
Previous reports suggest that NMDA receptors participate in control of food intake via vagal afferent neurons that innervate the upper gastrointestinal (GI) tract. While messenger RNA coding for the NR1 NMDA receptor subunit is present in a majority of vagal afferent neurons of nodose ganglia (NG), immunoreactivity for other NMDA receptor subunits (NR2B, NR2C and NR2D) are expressed in more limited subpopulations of vagal afferents. To determine whether vagal afferent neurons that project to the stomach or duodenum exhibit distinct NMDA receptor subunit phenotypes, we examined immunoreactivity (IR) for NMDA receptor NR1, NR2B, NR2C and NR2D subunits in NG neurons that were labeled by injections of the retrograde tracer Fast Blue (FB) into the wall of the stomach or duodenum. FB injections into the fundus or corpus of the stomach labeled comparable numbers of neurons in both the left and right NG, while proximal duodenal injections labeled only neurons of left NG. NR1-IR expression was observed in most neurons innervating the upper GI tract (fundus, 97%; corpus, 95%; duodenum, 98%). Likewise, most neurons that innervated the upper GI tract expressed NR2B-IR (fundus, 98%; corpus, 85%; duodenum, 81%). NR2C-IR was observed in only 52%, 46% and 32% of FB-positive neurons projecting to the fundus, corpus or duodenum respectively, while NR2D-IR occurred in an even more restricted FB-labeled subpopulation (fundus, 13%; corpus, 26%; and duodenum, 18%). Our observations indicate that different subpopulations of vagal afferents express distinct NMDA receptor subunit phenotypes. However, the neuronal distribution of NMDA receptor subunits is not correlated with innervation of either the stomach or duodenum.
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Affiliation(s)
- Krzysztof Czaja
- Department of Veterinary, Comparative Anatomy, Pharmacology, and Physiology, College of Veterinary Medicine, Washington State University, Pullman, WA 99163-6520, USA
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366
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Abstract
Classically, a high-power association relates the neurotransmitter release probability to the concentration of presynaptic Ca2+. Activated by the action potential waveform, voltage-gated Ca2+ channels mediate Ca2+entry into presynaptic terminals. Inside the terminal, Ca2+ ions rapidly bind to endogenous intracellular buffers and could trigger Ca2+ release from internal Ca2+ stores. The resulting space-time profile of free Ca2+ determines the time course and probability of neurotransmitter release through the interaction with molecular release triggers strategically located in the vicinity of release sites. Following a rapid concentration transient, excess Ca2+ has to be removed from the cytosol through the process involving Ca2+ uptake by the endoplasmatic reticulum stores, sequestration by mitochondria, and/or extrusion into the extracellular medium. The ongoing synaptic activity could affect any of the multiple factors that shape presynaptic Ca2+ dynamics, thus arbitrating use-dependent modification of the neurotransmitter release probability. Here we present an overview of major players involved in Ca2+-dependent presynaptic regulation of neurotransmitter release and discuss the relationships arising between their actions.
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367
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Safo PK, Cravatt BF, Regehr WG. Retrograde endocannabinoid signaling in the cerebellar cortex. THE CEREBELLUM 2006; 5:134-45. [PMID: 16818388 DOI: 10.1080/14734220600791477] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
The regulation of Purkinje cell activity is important for motor behavior and motor learning. As the sole output cell of the cerebellar cortex, Purkinje cell firing is controlled by parallel fibers and climbing fiber synapses, and by inhibitory interneurons. Depolarization of Purkinje cells evokes endocannabinoid release that activates cannabinoid CB1 receptors expressed on boutons of its synaptic inputs to transiently decrease neurotransmitter release. In addition, associative activation of the excitatory inputs can liberate endocannabinoids to decrease synaptic strength for a prolonged duration. Here we review the different mechanisms of evoking endocannabinoid release and discuss the physiological role of endocannabinoids in mediating global modulation of synaptic strength, localized short-term associative plasticity and cerebellar long term depression.
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Affiliation(s)
- Patrick K Safo
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA
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368
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Abstract
Changes in synaptic efficacy are thought to be crucial to experience-dependent modifications of neural function. The diversity of mechanisms underlying these changes is far greater than previously expected. In the last five years, a new class of use-dependent synaptic plasticity that requires retrograde signaling by endocannabinoids (eCB) and presynaptic CB1 receptor activation has been identified in several brain structures. eCB-mediated plasticity encompasses many forms of transient and long-lasting synaptic depression and is found at both excitatory and inhibitory synapses. In addition, eCBs can modify the inducibility of non-eCB-mediated forms of plasticity. Thus, the eCB system is emerging as a major player in synaptic plasticity. Given the wide distribution of CB1 receptors in the CNS, the list of brain structures and synapses expressing eCB-mediated plasticity is likely to expand.
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Affiliation(s)
- Vivien Chevaleyre
- Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York 10461, USA
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369
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van Beugen BJ, Nagaraja RY, Hansel C. Climbing fiber-evoked endocannabinoid signaling heterosynaptically suppresses presynaptic cerebellar long-term potentiation. J Neurosci 2006; 26:8289-94. [PMID: 16899723 PMCID: PMC6673796 DOI: 10.1523/jneurosci.0805-06.2006] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Endocannabinoid signaling has been demonstrated to mediate depolarization-induced suppression of excitation at climbing fiber (CF) and parallel fiber (PF) synapses onto cerebellar Purkinje cells. Here, we show that CF-evoked release of cannabinoids (CBs) additionally suppresses a presynaptic form of long-term potentiation (LTP) at PF synapses. PF-LTP can be induced by 8 Hz PF tetanization but is blocked when the PF tetanization is paired with 4 or 1 Hz CF coactivation. CF activity can be substituted for by bath application of the CB receptor agonist WIN55,212-2 [R(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrrolo[1,2,3-de]-1,4-benzoxazinyl]-(1-naphthalenyl) methanone]. In the presence of the CB1 receptor antagonist AM251 [N-1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-1-piperidinyl-1H-pyrazole-3-carboxamide], CF activity no longer suppresses PF-LTP. Presynaptic potentiation can also be obtained by the adenylyl cyclase activator forskolin. WIN55,212-2 blocked this forskolin-mediated enhancement, showing that CB1 receptor activation interferes with the adenylyl cyclase-protein kinase A cascade, which participates in LTP induction. CF activity has been described to promote the induction of postsynaptic PF-long-term depression (LTD) and to impair postsynaptic PF-LTP. Our observation that CF activity blocks the induction of presynaptic LTP suggests that the CF input controls all forms of presynaptic and postsynaptic PF plasticity and that CF activity provides a "safety lock" to prevent an enhancement of transmitter release while postsynaptic AMPA receptor function is downregulated during LTD.
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370
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Sjöström PJ, Häusser M. A cooperative switch determines the sign of synaptic plasticity in distal dendrites of neocortical pyramidal neurons. Neuron 2006; 51:227-38. [PMID: 16846857 DOI: 10.1016/j.neuron.2006.06.017] [Citation(s) in RCA: 282] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2006] [Revised: 05/02/2006] [Accepted: 06/19/2006] [Indexed: 11/19/2022]
Abstract
Pyramidal neurons in the cerebral cortex span multiple cortical layers. How the excitable properties of pyramidal neuron dendrites allow these neurons to both integrate activity and store associations between different layers is not well understood, but is thought to rely in part on dendritic backpropagation of action potentials. Here we demonstrate that the sign of synaptic plasticity in neocortical pyramidal neurons is regulated by the spread of the backpropagating action potential to the synapse. This creates a progressive gradient between LTP and LTD as the distance of the synaptic contacts from the soma increases. At distal synapses, cooperative synaptic input or dendritic depolarization can switch plasticity between LTD and LTP by boosting backpropagation of action potentials. This activity-dependent switch provides a mechanism for associative learning across different neocortical layers that process distinct types of information.
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Affiliation(s)
- Per Jesper Sjöström
- Wolfson Institute for Biomedical Research, Department of Physiology, University College London, London WC1E 6BT, United Kingdom.
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371
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Sjöström PJ, Turrigiano GG, Nelson SB. Multiple forms of long-term plasticity at unitary neocortical layer 5 synapses. Neuropharmacology 2006; 52:176-84. [PMID: 16895733 DOI: 10.1016/j.neuropharm.2006.07.021] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2006] [Revised: 07/11/2006] [Accepted: 07/12/2006] [Indexed: 11/19/2022]
Abstract
Long-term potentiation and depression (LTP and LTD) are cellular plasticity phenomena expressed at a variety of central synapses, and are thought to contribute to learning and developmental changes in circuitry. Recurrent neocortical layer-5 synapses are thought to express a presynaptic form of LTP that influences the short-term plasticity of the synapse. Here we show that changes in synaptic strength elicited by pairing high frequency pre- and postsynaptic firing at this synapse result from a mixture of presynaptic and postsynaptic forms of plasticity, as assessed by the analysis of changes in coefficient of variation, short-term plasticity, and NMDA:AMPA current ratios. Pharmacological dissection of this plasticity revealed that block of presynaptic LTD with an endocannabinoid inhibitor enhanced LTP, while the apparently presynaptic component of LTP could be prevented by induction in the presence of blockers of nitric oxide. These data suggest that correlated high-frequency firing at layer-5 synapses simultaneously induces a mixture of presynaptic LTD, presynaptic LTP, and postsynaptic LTP.
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Affiliation(s)
- Per Jesper Sjöström
- Department of Biology and Center for Behavioral Genomics, Brandeis University, Waltham, MA 02454, USA
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372
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Abstract
Information in the nervous system may be carried by both the rate and timing of neuronal spikes. Recent findings of spike timing-dependent plasticity (STDP) have fueled the interest in the potential roles of spike timing in processing and storage of information in neural circuits. Induction of long-term potentiation (LTP) and long-term depression (LTD) in a variety of in vitro and in vivo systems has been shown to depend on the temporal order of pre- and postsynaptic spiking. Spike timing-dependent modification of neuronal excitability and dendritic integration was also observed. Such STDP at the synaptic and cellular level is likely to play important roles in activity-induced functional changes in neuronal receptive fields and human perception.
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Affiliation(s)
- Yang Dan
- Division of Neurobiology, Department of Molecular and Cell Biology, and Helen Wills Neuroscience Institute, University of California, Berkeley, California 94720, USA.
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373
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Shah NT, Yeung LC, Cooper LN, Cai Y, Shouval HZ. A biophysical basis for the inter-spike interaction of spike-timing-dependent plasticity. BIOLOGICAL CYBERNETICS 2006; 95:113-21. [PMID: 16691393 DOI: 10.1007/s00422-006-0071-y] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2005] [Accepted: 03/08/2006] [Indexed: 05/09/2023]
Abstract
Although spike-timing-dependent plasticity (STDP) is well characterized when pre- and postsynaptic spikes are paired with a given time lag, how this generalizes for more complex spike-trains is unclear. Recent experiments demonstrate that contributions to synaptic plasticity from different spike pairs within a spike train do not add linearly. In the visual cortex conditioning with spike triplets shows that the effect of the first spike pair dominates over the second. Using a previously proposed calcium-dependent plasticity model, we show that short-term synaptic dynamics and interaction between successive back-propagating action potentials (BPAP) may jointly account for the nonlinearities observed. Paired-pulse depression and attenuation of BPAPs are incorporated into the model through the use-dependent depletion of pre- and postsynaptic resources, respectively. Simulations suggest that these processes may play critical roles in determining how STDP operates in the context of natural spike-trains.
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Affiliation(s)
- Neel T Shah
- Institute for Brain and Neural Systems, Brown University, Providence, RI 02912, USA
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374
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Kampa BM, Stuart GJ. Calcium spikes in basal dendrites of layer 5 pyramidal neurons during action potential bursts. J Neurosci 2006; 26:7424-32. [PMID: 16837590 PMCID: PMC6674200 DOI: 10.1523/jneurosci.3062-05.2006] [Citation(s) in RCA: 112] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Patch-clamp recording from dendrites has lead to a significant increase in our understanding of the mechanisms underlying signal integration and propagation in neurons. The majority of synaptic input to neurons, however, is made onto small-diameter dendrites, currently beyond the scope of patch-clamp recording techniques. Here we use both calcium and voltage imaging to investigate propagation of action potentials (APs) in fine basal dendrites of cortical layer 5 pyramidal neurons. High-frequency (200 Hz) AP bursts caused supralinear increases in dendritic calcium at distal, but not proximal, basal locations. Supralinear increases in dendritic calcium were also observed at distal basal locations during AP trains above a critical frequency (approximately 100 Hz). Using voltage imaging, we show that single APs undergo significant attenuation as they propagate into basal dendrites, whereas AP bursts lead to generation of dendritic calcium spikes. Focal and bath application of 4-AP increased the amplitude of calcium transients evoked by APs at distal, but not proximal, locations, suggesting that A-type potassium channels regulate AP backpropagation into basal dendrites. Finally, we show that pairing EPSPs with AP bursts is an effective means of activating synaptic NMDA receptors in basal dendrites. The experimental observations on the role of A-type potassium channels in regulation of AP backpropagation in basal dendrites, as well as the generation of dendritic calcium spikes during AP bursts, were reproduced in a morphologically realistic neuronal model with uniform distributions of dendritic sodium, calcium, and potassium channels. Together, these findings have important implications for understanding dendritic integration and synaptic plasticity in cortical basal dendrites.
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Affiliation(s)
- Björn M Kampa
- Division of Neuroscience, John Curtin School of Medical Research, Australian National University, Canberra, Australian Capital Territory 0200, Australia.
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375
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Hardingham N, Fox K. The role of nitric oxide and GluR1 in presynaptic and postsynaptic components of neocortical potentiation. J Neurosci 2006; 26:7395-404. [PMID: 16837587 PMCID: PMC6674184 DOI: 10.1523/jneurosci.0652-06.2006] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
In this study, we investigated the mechanisms underlying synaptic plasticity at the layer IV to II/III pathway in barrel cortex of mice aged 6-13 weeks. This pathway is one of the likely candidates for expression of experience-dependent plasticity in the barrel cortex and may serve as a model for other IV to II/III synapses in the neocortex. We found that postsynaptic autocamtide-2-inhibitory peptide is sufficient to block long-term potentiation (LTP) (IC50 of 500 nm), implicating postsynaptic calcium/calmodulin-dependent kinase II in LTP induction. AMPA receptor subunit 1 (GluR1) knock-out mice also showed LTP in this pathway, but potentiation was predominantly presynaptic in origin as determined by paired-pulse analysis, coefficient of variation analysis, and quantal analysis, whereas wild types showed a mixed presynaptic and postsynaptic locus. Quantal analysis at this synapse was validated by measuring uniquantal events in the presence of strontium. The predominantly presynaptic LTP in the GluR1 knock-outs was blocked by postsynaptic antagonism of nitric oxide synthase (NOS), either with intracellular N-omega-nitro-L-arginine methyl ester or N-nitro-L-arginine, providing the first evidence for a retrograde transmitter role for NO at this synapse. Antagonism of NOS in wild types significantly reduced but did not eliminate LTP (group average reduction of 50%). The residual LTP formed a variable proportion of the total LTP in each cell and was found to be postsynaptic in origin. We found no evidence for silent synapses in this pathway at this age. Finally, application of NO via a donor induced potentiation in layer II/III cells and caused an increase in frequency but not amplitude of miniature EPSPs, again implicating NO in presynaptic plasticity.
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376
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Czaja K, Ritter RC, Burns GA. N-methyl-D-aspartate receptor subunit phenotypes of vagal afferent neurons in nodose ganglia of the rat. J Comp Neurol 2006; 496:877-85. [PMID: 16628619 PMCID: PMC2834225 DOI: 10.1002/cne.20955] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Most vagal afferent neurons in rat nodose ganglia express mRNA coding for the NR1 subunit of the heteromeric N-methyl-D-aspartate (NMDA) receptor ion channel. NMDA receptor subunit immunoreactivity has been detected on axon terminals of vagal afferents in the dorsal hindbrain, suggesting a role for presynaptic NMDA receptors in viscerosensory function. Although NMDA receptor subunits (NR1, NR2B, NR2C, and NR2D) have been linked to distinct neuronal populations in the brain, the NMDA receptor subunit phenotype of vagal afferent neurons has not been determined. Therefore, we examined NMDA receptor subunit (NR1, NR2B, NR2C, and NR2D) immunoreactivity in vagal afferent neurons. We found that, although the left nodose contained significantly more neurons (7,603), than the right (5,978), the proportions of NMDA subunits expressed in the left and right nodose ganglia were not significantly different. Immunoreactivity for NMDA NR1 subunit was present in 92.3% of all nodose neurons. NR2B immunoreactivity was present in 56.7% of neurons; NR2C-expressing nodose neurons made up 49.4% of the total population; NR2D subunit immunoreactivity was observed in just 13.5% of all nodose neurons. Double labeling revealed that 30.2% of nodose neurons expressed immunoreactivity to both NR2B and NR2C, whereas NR2B and NR2D immunoreactivities were colocalized in 11.5% of nodose neurons. NR2C immunoreactivity colocalized with NR2D in 13.1% of nodose neurons. Our results indicate that most vagal afferent neurons express NMDA receptor ion channels composed of NR1, NR2B, and NR2C subunits and that a minority phenotype that expresses NR2D also expresses NR1, NR2B, and NR2C.
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Affiliation(s)
- Krzysztof Czaja
- Programs in Neuroscience and Department of Veterinary, Comparative Anatomy, Pharmacology, and Physiology, College of Veterinary Medicine, Washington State University, Pullman, 99163-6520, USA.
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377
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Katona I, Urbán GM, Wallace M, Ledent C, Jung KM, Piomelli D, Mackie K, Freund TF. Molecular composition of the endocannabinoid system at glutamatergic synapses. J Neurosci 2006; 26:5628-37. [PMID: 16723519 PMCID: PMC1698282 DOI: 10.1523/jneurosci.0309-06.2006] [Citation(s) in RCA: 386] [Impact Index Per Article: 21.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Endocannabinoids play central roles in retrograde signaling at a wide variety of synapses throughout the CNS. Although several molecular components of the endocannabinoid system have been identified recently, their precise location and contribution to retrograde synaptic signaling is essentially unknown. Here we show, by using two independent riboprobes, that principal cell populations of the hippocampus express high levels of diacylglycerol lipase alpha (DGL-alpha), the enzyme involved in generation of the endocannabinoid 2-arachidonoyl-glycerol (2-AG). Immunostaining with two independent antibodies against DGL-alpha revealed that this lipase was concentrated in heads of dendritic spines throughout the hippocampal formation. Furthermore, quantification of high-resolution immunoelectron microscopic data showed that this enzyme was highly compartmentalized into a wide perisynaptic annulus around the postsynaptic density of axospinous contacts but did not occur intrasynaptically. On the opposite side of the synapse, the axon terminals forming these excitatory contacts were found to be equipped with presynaptic CB1 cannabinoid receptors. This precise anatomical positioning suggests that 2-AG produced by DGL-alpha on spine heads may be involved in retrograde synaptic signaling at glutamatergic synapses, whereas CB1 receptors located on the afferent terminals are in an ideal position to bind 2-AG and thereby adjust presynaptic glutamate release as a function of postsynaptic activity. We propose that this molecular composition of the endocannabinoid system may be a general feature of most glutamatergic synapses throughout the brain and may contribute to homosynaptic plasticity of excitatory synapses and to heterosynaptic plasticity between excitatory and inhibitory contacts.
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378
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Rancz EA, Häusser M. Dendritic calcium spikes are tunable triggers of cannabinoid release and short-term synaptic plasticity in cerebellar Purkinje neurons. J Neurosci 2006; 26:5428-37. [PMID: 16707795 PMCID: PMC5886360 DOI: 10.1523/jneurosci.5284-05.2006] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Understanding the relationship between dendritic excitability and synaptic plasticity is vital for determining how dendrites regulate the input-output function of the neuron. Dendritic calcium spikes have been associated with the induction of long-term changes in synaptic efficacy. Here we use direct recordings from cerebellar Purkinje cell dendrites to show that synaptically activated local dendritic calcium spikes are potent triggers of cannabinoid release, producing a profound and short-term reduction in synaptic efficacy at parallel fiber synapses. Enhancing dendritic excitability by modulating dendritic large-conductance calcium-activated potassium (BK) channels improves the spread of dendritic calcium spikes and enhances cannabinoid release at the expense of spatial specificity. Our findings reveal that dendritic calcium spikes provide a local and tunable coincidence detection mechanism that readjusts synaptic gain when synchronous activity reaches a threshold, and they reveal a tight link between the regulation of dendritic excitability and the induction of synaptic plasticity.
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Affiliation(s)
- Ede A Rancz
- Wolfson Institute for Biomedical Research, Department of Physiology, University College London, London WC1E 6BT, United Kingdom
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379
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Duguid I, Sjöström PJ. Novel presynaptic mechanisms for coincidence detection in synaptic plasticity. Curr Opin Neurobiol 2006; 16:312-22. [PMID: 16713246 DOI: 10.1016/j.conb.2006.05.008] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2006] [Accepted: 05/05/2006] [Indexed: 11/28/2022]
Abstract
Long-term plasticity typically relies on postsynaptic NMDA receptors to detect the coincidence of pre- and postsynaptic activity. Recent studies, however, have revealed forms of plasticity that depend on coincidence detection by presynaptic NMDA receptors. In the amygdala, cortical afferent associative presynaptic long-term potentiation (LTP) requires activation of presynaptic NMDA receptors by simultaneous thalamic and cortical afferents. Surprisingly, both types of afferent can also undergo postsynaptically induced NMDA-receptor-dependent LTP. In the neocortex, spike-timing-dependent long-term depression (LTD) requires simultaneous activation of presynaptic NMDA autoreceptors and retrograde signalling by endocannabinoids. In cerebellar LTD, presynaptic NMDA receptor activation suggests that similar presynaptic mechanisms may exist. Recent studies also indicate the existence of presynaptic coincidence detection that is independent of NMDA receptors, suggesting that such mechanisms have a widespread role in plasticity.
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Affiliation(s)
- Ian Duguid
- Wolfson Institute for Biomedical Research and Department of Physiology, University College London, Gower Street, London WC1E 6BT, UK
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380
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Bender KJ, Allen CB, Bender VA, Feldman DE. Synaptic basis for whisker deprivation-induced synaptic depression in rat somatosensory cortex. J Neurosci 2006; 26:4155-65. [PMID: 16624936 PMCID: PMC3070309 DOI: 10.1523/jneurosci.0175-06.2006] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Whisker deprivation weakens excitatory layer 4 (L4) inputs to L2/3 pyramidal cells in rat primary somatosensory (S1) cortex, which is likely to contribute to whisker map plasticity. This weakening has been proposed to represent long-term depression (LTD) induced by sensory deprivation in vivo. Here, we studied the synaptic expression mechanisms for deprivation-induced weakening of L4-L2/3 inputs and assessed its similarity to LTD, which is known to be expressed presynaptically at L4-L2/3 synapses. Whisker deprivation increased the paired pulse ratio at L4-L2/3 synapses and slowed the use-dependent block of NMDA receptor currents by MK-801 [(5S,10R)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate], indicating that deprivation reduced transmitter release probability at these synapses. In contrast, deprivation did not alter either miniature EPSC amplitude in L2/3 neurons or the amplitude of quantal L4-L2/3 synaptic responses measured in strontium, indicating that postsynaptic responsiveness was unchanged. In young postnatal day 12 (P12) rats, at least 4 d of deprivation were required to significantly weaken L4-L2/3 synapses. Similar weakening occurred when deprivation began at older ages (P20), when synapses are mostly mature, indicating that weakening is unlikely to represent a failure of synaptic maturation but instead represents a reduction in the strength of existing synapses. Thus, whisker deprivation weakens L4-L2/3 synapses by decreasing presynaptic function, similar to known LTD mechanisms at this synapse.
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Affiliation(s)
- Kevin J Bender
- Division of Biological Sciences, University of California San Diego, La Jolla, California 92093-0357, USA.
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381
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Bender VA, Bender KJ, Brasier DJ, Feldman DE. Two coincidence detectors for spike timing-dependent plasticity in somatosensory cortex. J Neurosci 2006; 26:4166-77. [PMID: 16624937 PMCID: PMC3071735 DOI: 10.1523/jneurosci.0176-06.2006] [Citation(s) in RCA: 305] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Many cortical synapses exhibit spike timing-dependent plasticity (STDP) in which the precise timing of presynaptic and postsynaptic spikes induces synaptic strengthening [long-term potentiation (LTP)] or weakening [long-term depression (LTD)]. Standard models posit a single, postsynaptic, NMDA receptor-based coincidence detector for LTP and LTD components of STDP. We show instead that STDP at layer 4 to layer 2/3 synapses in somatosensory (S1) cortex involves separate calcium sources and coincidence detection mechanisms for LTP and LTD. LTP showed classical NMDA receptor dependence. LTD was independent of postsynaptic NMDA receptors and instead required group I metabotropic glutamate receptors and calcium from voltage-sensitive channels and IP3 receptor-gated stores. Downstream of postsynaptic calcium, LTD required retrograde endocannabinoid signaling, leading to presynaptic LTD expression, and also required activation of apparently presynaptic NMDA receptors. These LTP and LTD mechanisms detected firing coincidence on approximately 25 and approximately 125 ms time scales, respectively, and combined to implement the overall STDP rule. These findings indicate that STDP is not a unitary process and suggest that endocannabinoid-dependent LTD may be relevant to cortical map plasticity.
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382
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Yashiro K, Corlew R, Philpot BD. Visual deprivation modifies both presynaptic glutamate release and the composition of perisynaptic/extrasynaptic NMDA receptors in adult visual cortex. J Neurosci 2006; 25:11684-92. [PMID: 16354927 PMCID: PMC6726025 DOI: 10.1523/jneurosci.4362-05.2005] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Use-dependent modifications of synapses have been well described in the developing visual cortex, but the ability for experience to modify synapses in the adult visual cortex is poorly understood. We found that 10 d of late-onset visual deprivation modifies both presynaptic and postsynaptic elements at the layer 4-->2/3 connection in the visual cortex of adult mice, and these changes differ from those observed in juveniles. Although visual deprivation in juvenile mice modifies the subunit composition and increases the current duration of synaptic NMDA receptors (NMDARs), no such effect is observed at synapses between layer 4 and layer 2/3 pyramidal neurons in adult mice. Surprisingly, visual deprivation in adult mice enhances the temporal summation of NMDAR-mediated currents induced by bursts of high-frequency stimulation. The enhanced temporal summation of NMDAR-mediated currents in deprived cortex could not be explained by a reduction in the rate of synaptic depression, because our data indicate that late-onset visual deprivation actually increases the rate of synaptic depression. Biochemical and electrophysiological evidence instead suggest that the enhanced temporal summation in adult mice could be accounted for by a change in the molecular composition of NMDARs at perisynaptic/extrasynaptic sites. Our data demonstrate that the experience-dependent modifications observed in the adult visual cortex are different from those observed during development. These differences may help to explain the unique consequences of sensory deprivation on plasticity in the developing versus mature cortex.
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Affiliation(s)
- Koji Yashiro
- Department of Cell and Molecular Physiology, University of North Carolina, Chapel Hill, North Carolina 27599, USA
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383
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Fujisawa S, Shirao T, Aoki C. In vivo, competitive blockade of N-methyl-D-aspartate receptors induces rapid changes in filamentous actin and drebrin A distributions within dendritic spines of adult rat cortex. Neuroscience 2006; 140:1177-87. [PMID: 16650941 PMCID: PMC2844451 DOI: 10.1016/j.neuroscience.2006.03.009] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2006] [Accepted: 03/06/2006] [Indexed: 10/24/2022]
Abstract
In vitro studies have demonstrated that prolonged N-methyl-D-aspartate receptor (NMDAR) blockade triggers a homeostatic up-regulation of NMDARs at synapses. Such upregulation can also be seen within 30 min in vivo in adult rats, implicating trafficking of reserve pools of NMDARs. Here, we evaluated the involvement of filamentous actin (F-actin), the major cytoskeletal component in spines, in this rapid in vivo homeostatic response, using biotinylated phalloidin as its probe. We also immuno-labeled spines for drebrin A, an F-actin-binding protein found at excitatory synapses and with a proposed role of modulating F-actin's cross-linking with one another and interactions with NMDARs. Quantitative 2-D analysis of ultrastructural images revealed that NMDAR blockade increased filamentous actin labeling per spine by 62.5% (P<0.005). The proportion of dendritic spines immuno-labeled for drebrin A also increased significantly, from 67.5% to 85% following NMDAR blockade (P<0.001), especially among larger spines. The frequency distributions of spine widths and postsynaptic density lengths were not affected by the D-(+)-2-amino-5-phosphonopentanoic acid (D-APV) treatment. However, the average postsynaptic density length was reduced by 25 nm among the fewer, drebrin A immuno-negative spines, indicating that drebrin A confers stability to synapse size. We propose that, in a homeostatic in vivo response, increases of drebrin A and F-actin within spines can enhance NMDAR trafficking by reducing cytoskeletal rigidity within the spine cytoplasm without changing the overt morphology of axo-spinous synapses. Alternatively or in addition, the cytoskeletal redistribution within spine cytoplasm may be triggered by the D-APV-induced, homeostatic up-regulation of NMDAR.
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Affiliation(s)
- S Fujisawa
- Center for Neural Science, New York University, 4 Washington Place #809, New York, NY 10003, USA.
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384
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Isokawa M, Alger BE. Ryanodine Receptor Regulates Endogenous Cannabinoid Mobilization in the Hippocampus. J Neurophysiol 2006; 95:3001-11. [PMID: 16467427 DOI: 10.1152/jn.00975.2005] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Endogenous cannabinoids (eCBs) are produced and mobilized in a cytosolic calcium ([Ca2+]i)–dependent manner, and they regulate excitatory and inhibitory neurotransmitter release by acting as retrograde messengers. An indirect but real-time bioassay for this process on GABAergic transmission is DSI (depolarization-induced suppression of inhibition). The magnitude of DSI correlates linearly with depolarization-induced increase of [Ca2+]ithat is thought to be initiated by Ca2+influx through voltage-gated Ca2+channels. However, the identity of Ca2+sources involved in eCB mobilization in DSI remains undetermined. Here we show that, in CA1 pyramidal cells, DSI-inducing depolarizing voltage steps caused Ca2+-induced Ca2+release (CICR) by activating the ryanodine receptor (RyR) Ca2+-release channel. CICR was reduced, and the remaining increase in [Ca2+]iwas less effective in generating DSI, when the RyR antagonists, ryanodine or ruthenium red, were applied intracellularly, or the Ca2+stores were depleted by the Ca2+-ATPase inhibitors, cyclopiazonic acid or thapsigargin. The CICR-dependent effects were most prominent in cultured or immature acute slices, but were also detectable in slices from adult tissue. Thus we suggest that voltage-gated Ca2+entry raises local [Ca2+]isufficiently to activate nearby RyRs and that the resulting CICR plays a critical role in initiating eCB mobilization. RyR may be a key molecule for the depolarization-induced production of eCBs that inhibit GABA release in the hippocampus.
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Affiliation(s)
- Masako Isokawa
- Department of Physiology, University of Maryland, Baltimore, Maryland, USA.
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385
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Shemer I, Holmgren C, Min R, Fülöp L, Zilberter M, Sousa KM, Farkas T, Härtig W, Penke B, Burnashev N, Tanila H, Zilberter Y, Harkany T. Non-fibrillar β-amyloid abates spike-timing-dependent synaptic potentiation at excitatory synapses in layer 2/3 of the neocortex by targeting postsynaptic AMPA receptors. Eur J Neurosci 2006; 23:2035-47. [PMID: 16630051 DOI: 10.1111/j.1460-9568.2006.04733.x] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Cognitive decline in Alzheimer's disease (AD) stems from the progressive dysfunction of synaptic connections within cortical neuronal microcircuits. Recently, soluble amyloid beta protein oligomers (Abeta(ol)s) have been identified as critical triggers for early synaptic disorganization. However, it remains unknown whether a deficit of Hebbian-related synaptic plasticity occurs during the early phase of AD. Therefore, we studied whether age-dependent Abeta accumulation affects the induction of spike-timing-dependent synaptic potentiation at excitatory synapses on neocortical layer 2/3 (L2/3) pyramidal cells in the APPswe/PS1dE9 transgenic mouse model of AD. Synaptic potentiation at excitatory synapses onto L2/3 pyramidal cells was significantly reduced at the onset of Abeta pathology and was virtually absent in mice with advanced Abeta burden. A decreased alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)/N-methyl-D-aspartate (NMDA) receptor-mediated current ratio implicated postsynaptic mechanisms underlying Abeta synaptotoxicity. The integral role of Abeta(ol)s in these processes was verified by showing that pretreatment of cortical slices with Abeta((25-35)ol)s disrupted spike-timing-dependent synaptic potentiation at unitary connections between L2/3 pyramidal cells, and reduced the amplitude of miniature excitatory postsynaptic currents therein. A robust decrement of AMPA, but not NMDA, receptor-mediated currents in nucleated patches from L2/3 pyramidal cells confirmed that Abeta(ol)s perturb basal glutamatergic synaptic transmission by affecting postsynaptic AMPA receptors. Inhibition of AMPA receptor desensitization by cyclothiazide significantly increased the amplitude of excitatory postsynaptic potentials evoked by afferent stimulation, and rescued synaptic plasticity even in mice with pronounced Abeta pathology. We propose that soluble Abeta(ol)s trigger the diminution of synaptic plasticity in neocortical pyramidal cell networks during early stages of AD pathogenesis by preferentially targeting postsynaptic AMPA receptors.
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Affiliation(s)
- Isaac Shemer
- Department of Neuroscience, Retzius väg 8:A3-417, Karolinska Institutet, S-17177 Stockholm, Sweden
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386
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Levy RB, Reyes AD, Aoki C. Nicotinic and muscarinic reduction of unitary excitatory postsynaptic potentials in sensory cortex; dual intracellular recording in vitro. J Neurophysiol 2006; 95:2155-66. [PMID: 16421199 PMCID: PMC1409808 DOI: 10.1152/jn.00603.2005] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We studied the cholinergic modulation of glutamatergic transmission between neighboring layer 5 regular-spiking pyramidal neurons in somatosensory cortical slices from young rats (P10-P26). Brief bath application of 5-10 microM carbachol, a nonspecific cholinergic agonist, decreased the amplitude of evoked unitary excitatory postsynaptic potentials (EPSPs). This effect was blocked by 1 microM atropine, a muscarinic receptor antagonist. Nicotine (10 microM), in contrast to carbachol, reduced EPSPs in nominally magnesium-free solution but not in the presence of 1 mM Mg+2, indicating the involvement of NMDA receptors. Likewise, when the postsynaptic cell was depolarized under voltage clamp to allow NMDA receptor activation in the presence of 1 mM Mg+2, synaptic currents were reduced by nicotine. Nicotinic EPSP reduction was prevented by the NMDA receptor antagonist D-AP5 (50 microM) and by the nicotinic receptor antagonist mecamylamine (10 microM). Both carbachol and nicotine reduced short-term depression of EPSPs evoked by 10 Hz stimulation, indicating that EPSP reduction happens via reduction of presynaptic glutamate release. In the case of nicotine, several possible mechanisms for NMDAR-dependent EPSP reduction are discussed. As a result of NMDA receptor dependence, nicotinic EPSP reduction may serve to reduce the local spread of cortical excitation during heightened sensory activity.
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Affiliation(s)
- Robert B Levy
- New York University Center for Neural Science, New York, NY 10003, USA.
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387
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Abstract
The CB1 cannabinoid receptor has attracted much recent interest because of the observation that CB1 receptor antagonists have efficacy in treating metabolic syndrome and obesity. CB1 receptors also mediate most of the psychotropic effects of Delta9-tetrahydrocannabinol (Delta9THC), the principal psychoactive component of cannabis. In addition, they are one component of an interesting and widespread paracrine signaling system, the endocannabinoid system. The endocannabinoid system is comprised of cannabinoid receptors, endogenous cannabinoids, and the metabolic pathways responsible for their synthesis and degradation. The details of the endocannabinoid system have been most thoroughly studied in the brain. Here it has been shown to be intimately involved in several forms of neuronal plasticity. That is, activation of CB1 receptors by endocannabinoids produces either short- or long-term changes in the efficacy of synaptic transmission. The behavioral consequences of these changes are many, but some of the most striking and relevant to the current symposium are those associated with endogenous reward and consumptive behavior.
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Affiliation(s)
- K Mackie
- Department of Anesthesiology, University of Washington School of Medicine, Seattle, WA 98195-6540, USA.
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388
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Choi SY, Chang J, Jiang B, Seol GH, Min SS, Han JS, Shin HS, Gallagher M, Kirkwood A. Multiple receptors coupled to phospholipase C gate long-term depression in visual cortex. J Neurosci 2006; 25:11433-43. [PMID: 16339037 PMCID: PMC6725895 DOI: 10.1523/jneurosci.4084-05.2005] [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] [Indexed: 11/21/2022] Open
Abstract
Long-term depression (LTD) in sensory cortices depends on the activation of NMDA receptors. Here, we report that in visual cortical slices, the induction of LTD (but not long-term potentiation) also requires the activation of receptors coupled to the phospholipase C (PLC) pathway. Using immunolesions in combination with agonists and antagonists, we selectively manipulated the activation of alpha1 adrenergic, M1 muscarinic, and mGluR5 glutamatergic receptors. Inactivation of these PLC-coupled receptors prevents the induction of LTD, but only when the three receptors were inactivated together. LTD is fully restored by activating any one of them or by supplying intracellular D-myo-inositol-1,4,5-triphosphate (IP3). LTD was also impaired by intracellular application of PLC or IP3 receptor blockers, and it was absent in mice lacking PLCbeta1, the predominant PLC isoform in the forebrain. We propose that visual cortical LTD requires a minimum of PLC activity that can be supplied independently by at least three neurotransmitter systems. This essential requirement places PLC-linked receptors in a unique position to control the induction of LTD and provides a mechanism for gating visual cortical plasticity via extra-retinal inputs in the intact organism.
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Affiliation(s)
- Se-Young Choi
- Mind/Brain Institute, Department of Neurosciences, Johns Hopkins University, Baltimore, Maryland 21218, USA
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389
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Yang J, Woodhall GL, Jones RSG. Tonic facilitation of glutamate release by presynaptic NR2B-containing NMDA receptors is increased in the entorhinal cortex of chronically epileptic rats. J Neurosci 2006; 26:406-10. [PMID: 16407536 PMCID: PMC2504723 DOI: 10.1523/jneurosci.4413-05.2006] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
We have shown previously that when postsynaptic NMDA receptors are blocked, the frequency, but not amplitude, of spontaneous EPSCs (sEPSCs) at synapses in the entorhinal cortex is reduced by NMDA receptor antagonists, demonstrating that glutamate release is tonically facilitated by presynaptic NMDA autoreceptors. In the present study, we recorded sEPSCs using whole-cell voltage clamp in neurons in layer V in slices of the rat entorhinal cortex. Using specific antagonists for NR2A [(R)-[(S)-1-(4-bromo-phenyl)-ethylamino]-(2,3-dioxo-1,2,3,4-tetrahydroquinoxalin-5-yl)-methyl]-phosphonic acid] and NR2B [(alphaR, betaS)-alpha-(4-hydroxyphenyl)-beta-methyl-4-(phenylmethyl)-1-piperidinepropanol hydrochloride (Ro 25-6981)] subunit-containing receptors, we confirmed that in slices from juvenile rats (4-6 weeks of age), the autoreceptor is predominantly of the NR1-NR2B subtype. In older (4-6 months of age) control animals, the effect of the NR2B antagonist was less marked, suggesting a decline in autoreceptor function with development. In slices from rats (aged 4-6 months) exhibiting spontaneous recurrent seizures induced with a lithium-pilocarpine protocol, Ro 25-6981 again robustly reduced sEPSC frequency. The effect was equal to or greater than that seen in the juvenile slices and much more pronounced than that seen in the age-matched control animals. In all three groups, the NR2A antagonist was without effect on sEPSCs. These results suggest that there is a developmental decrease in NMDA autoreceptor function, which is reversed in a chronic epileptic condition. The enhanced autoreceptor function may contribute to seizure susceptibility and epileptogenesis in temporal lobe structures.
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Affiliation(s)
- Jian Yang
- Department of Pharmacy and Pharmacology, University of Bath, Bath BA2 7AY, United Kingdom
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390
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Nosyreva ED, Huber KM. Developmental switch in synaptic mechanisms of hippocampal metabotropic glutamate receptor-dependent long-term depression. J Neurosci 2006; 25:2992-3001. [PMID: 15772359 PMCID: PMC6725134 DOI: 10.1523/jneurosci.3652-04.2005] [Citation(s) in RCA: 138] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The presynaptic and postsynaptic properties of synapses change over the course of postnatal development. Therefore, synaptic plasticity mechanisms would be expected to adapt to these changes to facilitate alterations of synaptic strength throughout ontogeny. Here, we identified developmental changes in long-term depression (LTD) mediated by group 1 metabotropic glutamate receptors (mGluRs) and dendritic protein synthesis in hippocampal CA1 slices (mGluR-LTD). In slices prepared from adolescent rats [postnatal day 21 (P21) to P35], mGluR activation induces LTD and a long-term decrease in AMPA receptor (AMPAR) surface expression, both of which require protein synthesis. In neonatal animals (P8-P15), mGluR-LTD is independent of protein synthesis and is not associated with changes in the surface expression of AMPARs. Instead, mGluR-LTD at neonatal synapses results in large decreases in presynaptic function, measured by changes in paired-pulse facilitation and the rate of blockade by the use-dependent NMDA receptor blocker (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate. Conversely, mGluR-LTD at mature synapses results in little or no change in presynaptic function, suggesting a postsynaptic mechanism of expression. The developmental switch in the synaptic mechanisms of LTD would differentially affect synapse dynamics and perhaps information processing over the course of postnatal development.
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Affiliation(s)
- Elena D Nosyreva
- Center for Basic Neuroscience, Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9111, USA
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391
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Meliza CD, Dan Y. Receptive-field modification in rat visual cortex induced by paired visual stimulation and single-cell spiking. Neuron 2006; 49:183-9. [PMID: 16423693 DOI: 10.1016/j.neuron.2005.12.009] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2005] [Revised: 09/26/2005] [Accepted: 12/02/2005] [Indexed: 11/26/2022]
Abstract
Experience-dependent plasticity of visual cortical receptive fields (RFs) involves synaptic modifications in the underlying neural circuits, but the site and mechanism of these modifications remain to be elucidated. Using in vivo whole-cell recordings, we show that pairing visual stimulation at a given retinal location with spiking of a single neuron in developing rat visual cortex induces rapid RF modifications. The time course of the response to the visual stimulus at the paired RF location is altered, with an enhancement of the response preceding the spike time and a reduction following the spike. Such bidirectional modification is consistent with spike timing-dependent plasticity. Response modification also occurs at nearby locations, the direction and magnitude of which are correlated with the change at the paired location. In addition, changes at unpaired locations show a negative correlation with the initial strength of the response, which may facilitate rapid modification of the spatial RF profile.
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Affiliation(s)
- C Daniel Meliza
- Division of Neurobiology, Department of Molecular and Cell Biology, Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, California 94720, USA
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392
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Bodor AL, Katona I, Nyíri G, Mackie K, Ledent C, Hájos N, Freund TF. Endocannabinoid signaling in rat somatosensory cortex: laminar differences and involvement of specific interneuron types. J Neurosci 2006; 25:6845-56. [PMID: 16033894 PMCID: PMC6725346 DOI: 10.1523/jneurosci.0442-05.2005] [Citation(s) in RCA: 264] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Endocannabinoid-mediated retrograde signaling exerts powerful control over synaptic transmission in many brain areas. However, in the neocortex, the precise laminar, cellular, and subcellular localization of the type 1 cannabinoid receptor (CB1) as well as its function has been elusive. Here we combined multiple immunolabeling with whole-cell recordings to investigate the morpho-functional characteristics of cannabinoid signaling in rat somatosensory cortex. Immunostaining for CB1 revealed axonal and somatic labeling with striking layer specificity: a high density of CB1-positive fibers was seen in layers II-III, in layer VI, and in upper layer V, whereas other layers had sparse (layer IV) or hardly any (layer I) staining. Membrane staining for CB1 was only found in axon terminals, all of which contained GABA and formed symmetric synapses. Double immunostaining also revealed that CB1-positive cells formed two neurochemically distinct subpopulations: two-thirds were cholecystokinin positive and one-third expressed calbindin, each subserving specific inhibitory functions in cortical networks. In addition, cannabinoid sensitivity of GABAergic input showed striking layer specificity, as revealed by both electrophysiological and anatomical experiments. We found a unique population of large pyramidal neurons in layer VB that received much less perisomatic innervation from CB1-expressing GABAergic axon terminals and, accordingly, showed no depolarization-induced suppression of inhibition, unlike pyramidal cells in layer II, and a population of small pyramidal cells in layer V. This suggests that inhibitory control of pyramidal cells involved in intracortical or corticostriatal processing is fine-tuned by activity-dependent endocannabinoid signaling, whereas inhibition of pyramidal cells relaying cortical information to lower subcortical effector centers often lacks this plasticity.
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Affiliation(s)
- Agnes L Bodor
- Department of Cellular and Network Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, H-1450 Budapest, Hungary
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393
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Lien CC, Mu Y, Vargas-Caballero M, Poo MM. Visual stimuli–induced LTD of GABAergic synapses mediated by presynaptic NMDA receptors. Nat Neurosci 2006; 9:372-80. [PMID: 16474391 DOI: 10.1038/nn1649] [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: 12/08/2005] [Accepted: 01/24/2006] [Indexed: 11/08/2022]
Abstract
Local GABA (gamma-aminobutyric acid) circuits contribute to sensory experience-dependent refinement of neuronal connections in the developing nervous system, but whether GABAergic synapses themselves can be rapidly modified by sensory stimuli is largely unknown. Here we report that repetitive light stimuli or theta burst stimulation (TBS) of the optic nerve in the developing Xenopus retinotectal system induces long-term potentiation (LTP) of glutamatergic inputs but long-term depression (LTD) of GABAergic inputs to the same tectal neuron. The LTD is due to a reduction in presynaptic GABA release and requires activation of presynaptic NMDA (N-methyl-D-aspartate) receptors (NMDARs) and coincident high-level GABAergic activity. Thus, the presynaptic NMDAR may function as a coincidence detector for adjacent glutamatergic and GABAergic activities, leading to coordinated synaptic modification by sensory experience.
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Affiliation(s)
- Cheng-Chang Lien
- Division of Neurobiology, Department of Molecular and Cell Biology, Helen Wills Neuroscience Institute, University of California Berkeley, California 94720-3200, USA
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394
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Kreitzer AC, Malenka RC. Dopamine modulation of state-dependent endocannabinoid release and long-term depression in the striatum. J Neurosci 2006; 25:10537-45. [PMID: 16280591 PMCID: PMC6725809 DOI: 10.1523/jneurosci.2959-05.2005] [Citation(s) in RCA: 258] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Endocannabinoids are important mediators of short- and long-term synaptic plasticity, but the mechanisms of endocannabinoid release have not been studied extensively outside the hippocampus and cerebellum. Here, we examined the mechanisms of endocannabinoid-mediated long-term depression (eCB-LTD) in the dorsal striatum, a brain region critical for motor control and reinforcement learning. Unlike other cell types, strong depolarization of medium spiny neurons was not sufficient to yield detectable endocannabinoid release. However, when paired with postsynaptic depolarization sufficient to activate L-type calcium channels, activation of postsynaptic metabotropic glutamate receptors (mGluRs), either by high-frequency tetanic stimulation or an agonist, induced eCB-LTD. Pairing bursts of afferent stimulation with brief subthreshold membrane depolarizations that mimicked down-state to up-state transitions also induced eCB-LTD, which not only required activation of mGluRs and L-type calcium channels but also was bidirectionally modulated by dopamine D2 receptors. Consistent with network models, these results demonstrate that dopamine regulates the induction of a Hebbian form of long-term synaptic plasticity in the striatum. However, this gating of plasticity by dopamine is accomplished via an unexpected mechanism involving the regulation of mGluR-dependent endocannabinoid release.
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Affiliation(s)
- Anatol C Kreitzer
- Department of Psychiatry and Behavioral Sciences, Stanford University Medical School, Palo Alto, California 94305, USA
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395
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Safo PK, Regehr WG. Endocannabinoids control the induction of cerebellar LTD. Neuron 2006; 48:647-59. [PMID: 16301180 DOI: 10.1016/j.neuron.2005.09.020] [Citation(s) in RCA: 218] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2005] [Revised: 07/25/2005] [Accepted: 09/21/2005] [Indexed: 12/20/2022]
Abstract
The long-term depression (LTD) of parallel fiber (PF) synapses onto Purkinje cells plays a central role in motor learning. Endocannabinoid release and LTD induction both depend upon activation of the metabotropic glutamate receptor mGluR1, require postsynaptic calcium increases, are synapse specific, and have a similar dependence on the associative activation of PF and climbing fiber synapses. These similarities suggest that endocannabinoid release could account for many features of cerebellar LTD. Here we show that LTD induction is blocked by a cannabinoid receptor (CB1R) antagonist, by inhibiting the synthesis of the endocannabinoid 2-arachidonyl glycerol (2-AG), and is absent in mice lacking the CB1R. Although CB1Rs are prominently expressed presynaptically at PF synapses, LTD is expressed postsynaptically. In contrast, a previously described transient form of inhibition mediated by endocannabinoids is expressed presynaptically. This indicates that Purkinje cells release 2-AG that activates CB1Rs to both transiently inhibit release and induce a postsynaptic form of LTD.
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Affiliation(s)
- Patrick K Safo
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA
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396
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Anwyl R. Induction and expression mechanisms of postsynaptic NMDA receptor-independent homosynaptic long-term depression. Prog Neurobiol 2006; 78:17-37. [PMID: 16423442 DOI: 10.1016/j.pneurobio.2005.12.001] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2005] [Revised: 11/21/2005] [Accepted: 12/01/2005] [Indexed: 12/20/2022]
Abstract
The induction of long-term depression (LTD) can be divided into two main forms, one dependent upon activation of postsynaptic NMDAR, and another independent of postsynaptic NMDAR. Non-postsynaptic NMDAR-LTD (non-NMDAR-LTD) occurs in many regions of the brain, and encompasses a wide variety of induction and expression mechanisms. In this article, the induction and expression mechanisms of such LTD in over 10 brain regions are described, with a number of common mechanisms compared across a large range of types of LTD. The article describes the involvement of different presynaptic or postsynaptic receptors in the induction of non-NMDAR-LTD, especially metabotropic glutamate receptors, cannabinoid receptors and dopamine receptors. An increase in presynaptic or postsynaptic intracellular Ca concentration is a key event in induction, commonly followed by activation of certain kinases, especially PKC, p38 MAPK and ERK. Expression mechanisms are either presynaptic via a reduction in release probability, or postsynaptic involving a decrease in AMPAR via phosphorylation of a glutamate receptor subunit, especially GluR2, followed by clathrin-mediated endocytosis. Retrograde signalling from postsynaptic to presynaptic occurs when induction is postsynaptic and expression is presynaptic.
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Affiliation(s)
- Roger Anwyl
- Department of Physiology, Trinity College, Dublin 2, Ireland.
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397
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Buonomano DV. A learning rule for the emergence of stable dynamics and timing in recurrent networks. J Neurophysiol 2005; 94:2275-83. [PMID: 16160088 DOI: 10.1152/jn.01250.2004] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Neural dynamics within recurrent cortical networks is an important component of neural processing. However, the learning rules that allow networks composed of hundreds or thousands of recurrently connected neurons to develop stable dynamical states are poorly understood. Here I use a neural network model to examine the emergence of stable dynamical states within recurrent networks. I describe a learning rule that can account both for the development of stable dynamics and guide networks to states that have been observed experimentally, specifically, states that instantiate a sparse code for time. Across trials, each neuron fires during a specific time window; by connecting the neurons to a hypothetical set of output units, it is possible to generate arbitrary spatial-temporal output patterns. Intertrial jitter of the spike time of a given neuron increases as a direct function of the delay at which it fires. These results establish a learning rule by which cortical networks can potentially process temporal information in a self-organizing manner, in the absence of specialized timing mechanisms.
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Affiliation(s)
- Dean V Buonomano
- Department of Neurobiology and Psychology, University of California, Los Angeles, 90095, USA.
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398
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Zhou YD, Acker CD, Netoff TI, Sen K, White JA. Increasing Ca2+ transients by broadening postsynaptic action potentials enhances timing-dependent synaptic depression. Proc Natl Acad Sci U S A 2005; 102:19121-5. [PMID: 16365307 PMCID: PMC1323223 DOI: 10.1073/pnas.0509856103] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Repeated induction of pre- and postsynaptic action potentials (APs) at a fixed time difference leads to long-term potentiation (LTP) or long-term depression (LTD) of the synapse, depending on the temporal order of pre- and postsynaptic activity. This phenomenon of spike-timing-dependent plasticity (STDP) is believed to arise by nonlinear processes that lead to larger calcium transients (and thus LTP) when presynaptic APs precede postsynaptic APs and smaller calcium transients (and thus LTD) when postsynaptic APs precede presynaptic APs. In contrast to predictions from such calcium-peak-detector models, we show that constitutively or artificially broadened APs in layer II/III pyramidal cells of entorhinal cortex (EC) lead to an increase in the dendritic calcium transient and shift the balance of STDP toward LTD. STDP in entorhinal pyramidal cells is NMDA-receptor-dependent and modulated by the Ca(V)1Ca(2+) channel-blocker nifedipine. Results are consistent with an elaboration of the calcium-peak-detector model in which downstream signals from voltage-dependent Ca(2+) channels suppress LTP relative to LTD. Our results suggest that modulation of AP width is a potent way to adjust the rules of synaptic plasticity in the EC.
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Affiliation(s)
- Yu-Dong Zhou
- Department of Biomedical Engineering, Center for Biodynamics, Center for Memory and Brain, Boston University, Boston, MA 02215, USA
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399
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Shin JH, Linden DJ. An NMDA Receptor/Nitric Oxide Cascade Is Involved in Cerebellar LTD But Is Not Localized to the Parallel Fiber Terminal. J Neurophysiol 2005; 94:4281-9. [PMID: 16120658 DOI: 10.1152/jn.00661.2005] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Long-term depression (LTD) of the parallel fiber-Purkinje cell synapse in the cerebellum is a cellular model system that has been suggested to underlie certain forms of motor learning. Induction of cerebellar LTD requires a postsynaptic kinase limb involving activation of mGluR1, protein kinase Cα (PKCα), and phosphorylation of ser-880 on the AMPA receptor subunit GluR2. Several lines of evidence have also implicated a complementary phosphatase limb in which N-methyl-d-aspartate (NMDA) receptor-mediated Ca2+ influx activates neuronal nitric oxide synthase (nNOS), the ultimate consequences of which are mediated by nitric oxide (NO), cGMP, and inhibition of postsynaptic protein phosphatases. However, the cellular localization of an NMDA/NO cascade has been complicated by the fact that neither functional NMDA receptors nor nNOS are expressed in Purkinje cells. This has lead to a proposal in which NMDA receptors activate nNOS in parallel fibers. Here, we confirm that pharmacological blockade of NMDA receptor or NO signaling blocks induction of LTD. However, no evidence was found for functional NMDA receptors in parallel fiber terminals: blockade of NMDA receptors did not alter either presynaptic Ca2+ transients or the frequency of miniature excitatory postsynaptic currents. NMDA receptor blockade did abolish a slow depolarization evoked by burst stimulation of parallel fiber-stellate cell synapses. The application of NMDA evoked a Ca2+ transient in stellate cell terminals but not in parallel fiber terminals. These results are consistent with the hypothesis that an NMDA receptor/NO cascade involved in cerebellar LTD is localized to interneurons rather than parallel fibers.
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Affiliation(s)
- Jung Hoon Shin
- Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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400
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Zilberter Y, Harkany T, Holmgren CD. Dendritic release of retrograde messengers controls synaptic transmission in local neocortical networks. Neuroscientist 2005; 11:334-44. [PMID: 16061520 DOI: 10.1177/1073858405275827] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The contribution of retrograde signaling to information processing in the brain has been contemplated for a long time, especially with respect to central nervous system development and long-term synaptic plasticity. During the past few years, however, the concept of retrograde signaling has been expanding to include short-term modifications of synaptic efficacy. The classic point of view on synaptic transmission represents it as a unidirectional transfer of information from presynaptic to postsynaptic sites. This paradigm has, however, been questioned in several experimental studies of neurons in different brain regions. These results suggest that a fast retrograde signal, which provides feedback, exists in active synaptic contacts. In particular, it was found that the dendritic release of retrograde messengers controls the efficacy of synaptic transmission in both excitatory and inhibitory connections between neocortical pyramidal cells and interneurons. The present review discusses these findings and the mechanisms underlying synaptic retrograde signaling.
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