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Accueil > Agenda > Les séminaires Jean Roche > Neuronal activity and the dynamics of dendritic spines.

Neuronal activity and the dynamics of dendritic (...)

Lundi 28 octobre 2005,11h, salle Lissitzky.

Bibliographie

1 : Richards, DA ; Mateos, JM ; Hugel, S ; de Paola, V ; Caroni, P ; Gahwiler, BH ; McKinney, RA. 2005.

Glutamate induces the rapid formation of spine head protrusions in hippocampal slice cultures.

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 102 (17) : 6166-6171.

Abstract : Synaptic plasticity at neuronal connections has been well characterized functionally by using electrophysiological approaches, but the structural basis for this phenomenon remains controversial. We have studied the dynamic interactions between presynaptic and postsynaptic structures labeled with FM 4-64 and a membrane-targeted GFP, respectively, in hippocampal slices. Under conditions of reduced neuronal activity (1 mu M tetrodotoxin), we observed extension of glutamate receptor-dependent processes from dendritic spines of CA1 pyramidal cells to presynaptic boutons. The formation of these spine head protrusions is blocked by alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor antagonists and by agents that reduce the release of glutamate from presynaptic terminals. Moreover, spine head protrusions form in response to exogenously applied glutamate, with clear directionality toward the glutamate electrode. Our results suggest that spontaneously released glutamate is sufficient to activate nearby spines, which can then lead to the growth of new postsynaptic processes connecting to a presynaptic site. Spines thus can compare their recent history with that of neighboring synapses and modify local connectivity accordingly.

http://www.pnas.org/cgi/content/full/102/17/6166?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=Glutamate+induces+the+rapid+formation+of+spine+head+protrusions+in+hippocampal+slice+cultures.+&searchid=1129742941194_7703&stored_search=&FIRSTINDEX=0&journalcode=pnas

2 Mori, M ; Abegg, MH ; Gahwiler, BH ; Gerber, U. 2004.

A frequency-dependent switch from inhibition to excitation in a hippocampal unitary circuit.

NATURE 431 (7007) : 453-456.

Abstract : The hippocampus, a brain structure essential for memory and cognition, is classically represented as a trisynaptic excitatory circuit. Recent findings challenge this view, particularly with regard to the mossy fibre input to CA3, the second synapse in the trisynaptic pathway(1). Thus, the powerful mossy fibre input to CA3 pyramidal cells might mediate both synaptic excitation and inhibition(2,3). Here we show, by recording from connected cell pairs in rat entorhinal - hippocampal slice cultures, that single action potentials in a dentate granule cell evoke a net inhibitory signal in a pyramidal cell. The hyperpolarization is due to disynaptic feedforward inhibition, which overwhelms monosynaptic excitation. Interestingly, this net inhibitory synaptic response changes to an excitatory signal when the frequency of presynaptic action potentials increases. The process responsible for this switch involves the facilitation of monosynaptic excitatory transmission coupled with rapid depression of inhibitory circuits. This ability to immediately switch the polarity of synaptic responses constitutes a novel synaptic mechanism, which might be crucial to the state-dependent processing of information in associative hippocampal networks.

http://www.nature.com/nature/journal/v431/n7007/full/nature02854.html

3 Voelker, CCJ ; Garin, N ; Taylor, JSH ; Gahwiler, BH ; Hornung, JP ; Molnar, Z. 2004.

Selective neurofilament (SMI-32, FNP-7 and N200) expression in subpopulations of layer V pyramidal neurons in vivo and in vitro.

CEREBRAL CORTEX 14 (11) : 1276-1286.

Abstract : There are two main types of layer V pyramidal neurons in rat cortex. Type I neurons have tufted apical dendrites extending into layer I, produce bursts of action potentials and project to subcortical targets (spinal cord, superior colliculus and pontine nuclei). Type II neurons have apical dendrites, which arborize in layers II-IV, do not produce bursts of action potentials and project to ipsilateral and contralateral cortex. The specific expression of different genes and proteins in these two distinct layer V neurons is unknown. To distinguish between distinct subpopulations, fluorescent microspheres were injected into subcortical targets (labeling type I neurons) or primary somatosensory cortex (labeling type II neurons) of adult rats. After transport, cortical sections were processed for immunohistochemistry using various antibodies. This study demonstrated that antigens recognized by SMI-32, N200 and FNP-7 antibodies were only expressed in subcortical (type I) - but not in contralateral (type II) - projecting neurons. NR1, NR2a/b, PLCbeta(1), BDNF, NGF and TrkB antigens were highly expressed in all neuronal subpopulations examined. Organotypic culture experiments demonstrated that the development of neurofilament expression and laminar specificity does not depend on the presence of the subcortical targets. This study suggests specific markers for the subcortical projecting layer V neuron subpopulations. Record 3 of 13 Mori, M ; Abegg, MH ; Gahwiler, BH ; Gerber, U. 2004. A frequency-dependent switch from inhibition to excitation in a hippocampal unitary circuit. NATURE 431 (7007) : 453-456. Abstract : The hippocampus, a brain structure essential for memory and cognition, is classically represented as a trisynaptic excitatory circuit. Recent findings challenge this view, particularly with regard to the mossy fibre input to CA3, the second synapse in the trisynaptic pathway(1). Thus, the powerful mossy fibre input to CA3 pyramidal cells might mediate both synaptic excitation and inhibition(2,3). Here we show, by recording from connected cell pairs in rat entorhinal - hippocampal slice cultures, that single action potentials in a dentate granule cell evoke a net inhibitory signal in a pyramidal cell. The hyperpolarization is due to disynaptic feedforward inhibition, which overwhelms monosynaptic excitation. Interestingly, this net inhibitory synaptic response changes to an excitatory signal when the frequency of presynaptic action potentials increases. The process responsible for this switch involves the facilitation of monosynaptic excitatory transmission coupled with rapid depression of inhibitory circuits. This ability to immediately switch the polarity of synaptic responses constitutes a novel synaptic mechanism, which might be crucial to the state-dependent processing of information in associative hippocampal networks.

4 Richards, DA ; de Paola, V ; Caroni, P ; Gahwiler, BH ; McKinney, RA. 2004.

AMPA-receptor activation regulates the diffusion of a membrane marker in parallel with dendritic spine motility in the mouse hippocampus.

JOURNAL OF PHYSIOLOGY-LONDON 558 (2) : 503-512.

Abstract : Dendritic spines are the site of most excitatory connections in the hippocampus. We have investigated the diffusibility of a membrane-bound green fluorescent protein (mGFP) within the inner leaflet of the plasma membrane using Fluorescence Recovery After Photobleaching. In dendritic spines the diffusion of mGFP was significantly retarded relative to the dendritic shaft. In parallel, we have assessed the motility of dendritic spines, and found an inverse correlation between spine motility and the rate of diffusion of mGFP. We then tested the influence of glutamate receptor activation or blockade, and the involvement of the actin cytoskeleton (using latrunculin A) on spine motility and mGFP diffusion. These results show that glutamate receptors regulate the mobility of molecules in the inner leaflet of the plasma membrane through an action upon the actin cytoskeleton, suggesting a novel mechanism for the regulation of postsynaptic receptor density and composition.

http://www.blackwell-synergy.com/doi/full/10.1113/jphysiol.2004.062091?prevSearch=allfield%3A%28AMPA-receptor+activation+regulates+the+diffusion+of+a+membrane+marker+in+parallel+with+dendritic+spine+motility+in+the+mouse+hippocampus.%29

5 Raineteau, O ; Rietschin, L ; Gradwohl, G ; Guillemot, F ; Gahwiler, BH. 2004.

Neurogenesis in hippocampal slice cultures.

MOLECULAR AND CELLULAR NEUROSCIENCE 26 (2) : 241-250.

Abstract : A major challenge in studying neurogenesis in the adult brain is gaining access to neural stem cells for experimental manipulation. We developed an approach utilizing mouse hippocampal organotypic cultures to characterize neurogenesis under controlled conditions. After 2 weeks in culture, double immunostaining using the mitotic marker BrdU and cell type-specific markers revealed persistent proliferation of various cell types. The birth of new neurons was restricted to a third subgranular germinal zone as shown by analysis of the expression pattern of the proneural transcription factor neurogenin-2 and colocalization of BrdU with neuronal phenotypic markers. The regional distribution of newly born neurons closely resembled that observed in vivo in the adult hippocampus. Furthermore, neurogenesis was increased by chronic application of epidermal growth factor (EGF) and abolished by adding serum to the culture medium. Our study therefore establishes the hippocampal slice culture as a promising ex vivo model for investigating neurogenesis. (C) 2004 Elsevier Inc. All rights reserved.

http://www.sciencedirect.com/science?_ob=ArticleURL&_aset=V-WA-A-W-A-MsSAYZA-UUA-U-AABWBBYBWE-AAWEEAEAWE-VACVZUYCB-A-U&_rdoc=1&_fmt=full&_udi=B6WNB-4C604X6-1&_coverDate=06%2F30%2F2004&_cdi=6958&_orig=search&_st=13&_sort=d&view=c&_acct=C000009002&_version=1&_urlVersion=0&_userid=113324&md5=52ace4045e81b064af111022eac8097d

6 Abegg, MH ; Savic, N ; Ehrengruber, MU ; McKinney, RA ; Gahwiler, BH. 2004.

Epileptiform activity in rat hippocampus strengthens excitatory synapses.

JOURNAL OF PHYSIOLOGY-LONDON 554 (2) : 439-448.

Abstract : Although epileptic seizures are characterized by excessive excitation, the role of excitatory synaptic transmission in the induction and expression of epilepsy remains unclear. Here, we show that epileptiform activity strengthens excitatory hippocampal synapses by increasing the number of functional (RS)-alpha-amino-3hydroxy-5methyl-4-isoxadepropionate (AMPA)-type glutamate receptors in CA3-CA1 synapses. This form of synaptic strengthening occludes long-term potentiation (LTP) and enhances long-term depression (LTD), processes involved in learning and memory. These changes in synaptic transmission and plasticity, which are fully blocked with N-methyl-D-aspartate (NMDA) receptor antagonists, may underlie epilepsy induction and seizure-associated memory deficits.

http://www.blackwell-synergy.com/doi/full/10.1113/jphysiol.2003.052662?prevSearch=allfield%3A%28Epileptiform+activity+in+rat+hippocampus+strengthens+excitatory+synapses.%29

7 Hennou, S ; Kato, A ; Schneider, EM ; Lundstrom, K ; Gahwiler, BH ; Inokuchi, K ; Gerber, U ; Ehrengruber, MU. 2003.

Homer-1a/Vesl-1S enhances hippocampal synaptic transmission.

EUROPEAN JOURNAL OF NEUROSCIENCE 18 (4) : 811-819.

Abstract : Homer/Vesl proteins are involved in regulating metabotropic glutamate receptors, synaptogenesis, dendritic spine development and axonal pathfinding. We investigated the potential modulation of glutamatergic synaptic transmission by the immediate early gene product Homer-1 a/Vesl-1S and by the constitutively expressed long-form Homer-1 c/Vest-1L in CA1 pyramidal cells from cultured rat hippocampal slices. Semliki Forest virus vector-mediated overexpression of Homer-1 a enhanced alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor function, but did not detectably affect N-methyl-D-aspartate (NMDA) receptor function and presynaptic glutamate release. Overexpression of Homer-1c, by contrast, did not alter synaptic transmission. To corroborate our electrophysiological results obtained in slice cultures, we performed quantitative immunocytochemistry in cultures of dissociated hippocampal neurons. Homer-1a also increased synaptic clustering of AMPA but not NMDA receptors, whereas Homer-1c had no detectable effect. Our results show that Homer-1 a potentiates synaptic AMPA receptor function, supporting a critical role for Homer-1 a in hippocampal synaptic plasticity.

http://www.blackwell-synergy.com/doi/full/10.1046/j.1460-9568.2003.02812.x?prevSearch=allfield%3A%28Homer-1a%2FVesl-1S+enhances+hippocampal+synaptic+transmission.%29

8 Savic, N ; Luthi, A ; Gahwiler, BH ; McKinney, RA. 2003

N-methyl-D-aspartate receptor blockade during development lowers long-term potentiation threshold without affecting dynamic range of CA3-CA1 synapses.

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 100 (9) : 5503-5508.

Abstract : During development, excitatory synapses in the CA1 region of the hippocampus undergo activity-dependent and N-methyl-D-aspartate (NMDA) receptor-dependent long-lasting changes in synaptic efficacy. These bidirectional changes occur between limits that determine the dynamic range within which synapses operate. It is unknown whether the dynamic range itself is also activity-dependent and NMDA receptor-dependent. Here, we show that chronic blockade of NMDA receptors in hippocampal slice cultures during early postnatal development does not affect the dynamic range but results in a lower threshold for the induction of long-term potentiation. Thus, the dynamic range of CA3-CA1 synapses, unlike long-term potentiation threshold, is NMDA receptor-independent, thereby providing functional stability to the hippocampal network during development.

http://www.pnas.org/cgi/content/full/100/9/5503?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=N-methyl-D-aspartate+receptor+blockade+during+development+lowers+long-term+potentiation+threshold+without+affecting+dynamic+range+of+CA3-CA1+synapses.&searchid=1129742544762_7627&stored_search=&FIRSTINDEX=0&journalcode=pnas

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