7 results on '"Volker Scheuss"'
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2. Quantitative Analysis of the Spatial Organization of Synaptic Inputs on the Postsynaptic Dendrite
- Author
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Volker Scheuss
- Subjects
synaptic input ,dendritic integration ,dendrite ,spatial organization ,synapse cluster ,quantitative analysis ,Neurosciences. Biological psychiatry. Neuropsychiatry ,RC321-571 - Abstract
The spatial organization of synaptic inputs on the dendritic tree of cortical neurons is considered to play an important role in the dendritic integration of synaptic activity. Active electrical properties of dendrites and mechanisms of dendritic integration have been studied for a long time. New technological developments are now enabling the characterization of the spatial organization of synaptic inputs on dendrites. However, quantitative methods for the analysis of such data are lacking. In order to place cluster parameters into the framework of dendritic integration and synaptic summation, these parameters need to be assessed rigorously in a quantitative manner. Here I present an approach for the analysis of synaptic input clusters on the dendritic tree that is based on combinatorial analysis of the likelihoods to observe specific input arrangements. This approach is superior to the commonly applied analysis of nearest neighbor distances between synaptic inputs comparing their distribution to simulations with random reshuffling or bootstrapping. First, the new approach yields exact likelihood values rather than approximate numbers obtained from simulations. Second and more importantly, the new approach identifies individual clusters and thereby allows to quantify and characterize individual cluster properties.
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- 2018
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3. Clusters of synaptic inputs on dendrites of layer 5 pyramidal cells in mouse visual cortex
- Author
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Onur Gökçe, Tobias Bonhoeffer, and Volker Scheuss
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synapse mapping ,synapse cluster ,optogenetics ,2-photon calcium imaging ,visual cortex ,spatial cluster analysis ,Medicine ,Science ,Biology (General) ,QH301-705.5 - Abstract
The spatial organization of synaptic inputs on the dendritic tree of cortical neurons plays a major role for dendritic integration and neural computations, yet, remarkably little is known about it. We mapped the spatial organization of glutamatergic synapses between layer 5 pyramidal cells by combining optogenetics and 2-photon calcium imaging in mouse neocortical slices. To mathematically characterize the organization of inputs we developed an approach based on combinatorial analysis of the likelihoods of specific synapse arrangements. We found that the synapses of intralaminar inputs form clusters on the basal dendrites of layer 5 pyramidal cells. These clusters contain 4 to 14 synapses within ≤30 µm of dendrite. According to the spatiotemporal characteristics of synaptic summation, these numbers suggest that there will be non-linear dendritic integration of synaptic inputs during synchronous activation.
- Published
- 2016
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4. Characterization and subcellular targeting of GCaMP-type genetically-encoded calcium indicators.
- Author
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Tianyi Mao, Daniel H O'Connor, Volker Scheuss, Junichi Nakai, and Karel Svoboda
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Medicine ,Science - Abstract
Genetically-encoded calcium indicators (GECIs) hold the promise of monitoring [Ca(2+)] in selected populations of neurons and in specific cellular compartments. Relating GECI fluorescence to neuronal activity requires quantitative characterization. We have characterized a promising new genetically-encoded calcium indicator-GCaMP2-in mammalian pyramidal neurons. Fluorescence changes in response to single action potentials (17+/-10% DeltaF/F [mean+/-SD]) could be detected in some, but not all, neurons. Trains of high-frequency action potentials yielded robust responses (302+/-50% for trains of 40 action potentials at 83 Hz). Responses were similar in acute brain slices from in utero electroporated mice, indicating that long-term expression did not interfere with GCaMP2 function. Membrane-targeted versions of GCaMP2 did not yield larger signals than their non-targeted counterparts. We further targeted GCaMP2 to dendritic spines to monitor Ca(2+) accumulations evoked by activation of synaptic NMDA receptors. We observed robust DeltaF/F responses (range: 37%-264%) to single spine uncaging stimuli that were correlated with NMDA receptor currents measured through a somatic patch pipette. One major drawback of GCaMP2 was its low baseline fluorescence. Our results show that GCaMP2 is improved from the previous versions of GCaMP and may be suited to detect bursts of high-frequency action potentials and synaptic currents in vivo.
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- 2008
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5. Inducing different neuronal subtypes from astrocytes in the injured mouse cerebral cortex
- Author
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Nicola Mattugini, Volker Scheuss, Chu Lan Lao, Olof Torper, Magdalena Götz, Riccardo Bocchi, and Gianluca Luigi Russo
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0301 basic medicine ,Genetic Vectors ,Inflammation ,Nerve Tissue Proteins ,Wounds, Stab ,Biology ,Article ,White matter ,03 medical and health sciences ,Mice ,reactive gliosis ,Aav ,Astrocytes ,Axonal Projection ,Cerebral Cortex ,Cortical Layers ,Electrophysiology ,Lentivirus ,Reactive Gliosis ,Reprogramming ,0302 clinical medicine ,lentivirus ,Brain Injuries, Traumatic ,Nuclear Receptor Subfamily 4, Group A, Member 2 ,medicine ,Basic Helix-Loop-Helix Transcription Factors ,Animals ,Cellular Reprogramming Techniques ,Neurogenin-2 ,Gliosis ,Gray Matter ,Neurons ,General Neuroscience ,Pyramidal Cells ,astrocytes ,reprogramming ,AAV ,cortical layers ,Dependovirus ,electrophysiology ,White Matter ,030104 developmental biology ,medicine.anatomical_structure ,Cerebral cortex ,inflammation ,Mouse Cerebral Cortex ,medicine.symptom ,axonal projection ,Neuroscience ,030217 neurology & neurosurgery ,Astrocyte - Abstract
Summary Astrocytes are particularly promising candidates for reprogramming into neurons, as they maintain some of the original patterning information from their radial glial ancestors. However, to which extent the position of astrocytes influences the fate of reprogrammed neurons remains unknown. To elucidate this, we performed stab wound injury covering an entire neocortical column, including the gray matter (GM) and white matter (WM), and targeted local reactive astrocytes via injecting FLEx switch (Cre-On) adeno-associated viral (AAV) vectors into mGFAP-Cre mice. Single proneural factors were not sufficient for adequate reprogramming, although their combination with the nuclear receptor-related 1 protein (Nurr1) improved reprogramming efficiency. Nurr1 and Neurogenin 2 (Ngn2) resulted in high-efficiency reprogramming of targeted astrocytes into neurons that develop lamina-specific hallmarks, including the appropriate long-distance axonal projections. Surprisingly, in the WM, we did not observe any reprogrammed neurons, thereby unveiling a crucial role of region- and layer-specific differences in astrocyte reprogramming., Graphical Abstract, Highlights • AAV can be targeted to reactive astrocytes upon stab wound injury • Expression of Ngn2 and Nurr1 in these astrocytes induces pyramidal neurons • Induced pyramidal neurons acquire correct layer identity and axonal projections • Neurons cannot be induced in the white matter, Neurons dying after brain injury cannot be replaced. Mattugini, Bocchi, et al. show that local astrocytes can be converted into functional neurons acquiring appropriate layer identity and connectivity by expression of neurogenic factors in a mouse model of traumatic brain injury.
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- 2019
6. Allosteric modulation of the presynaptic Ca2+ sensor for vesicle fusion
- Author
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Volker Scheuss, Ralf Schneggenburger, and Xuelin Lou
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Vesicle fusion ,Chromaffin Cells ,Allosteric regulation ,Presynaptic Terminals ,In Vitro Techniques ,Synaptic vesicle ,Membrane Fusion ,Models, Biological ,Synaptic Transmission ,Allosteric Regulation ,Animals ,Calcium Signaling ,Protein kinase C ,Phorbol 12,13-Dibutyrate ,Physics ,Neurotransmitter Agents ,Multidisciplinary ,SNAP25 ,Excitatory Postsynaptic Potentials ,Long-term potentiation ,Kiss-and-run fusion ,Cell biology ,Rats ,Synapses ,Calcium ,Calyx of Held ,Brain Stem - Abstract
Neurotransmitter release is triggered by an increase in the cytosolic Ca2+ concentration ([Ca2+]i), but it is unknown whether the Ca2+-sensitivity of vesicle fusion is modulated during synaptic plasticity. We investigated whether the potentiation of neurotransmitter release by phorbol esters, which target presynaptic protein kinase C (PKC)/munc-13 signalling cascades, exerts a direct effect on the Ca2+-sensitivity of vesicle fusion. Using direct presynaptic Ca2+-manipulation and Ca2+ uncaging at a giant presynaptic terminal, the calyx of Held, we show that phorbol esters potentiate transmitter release by increasing the apparent Ca2+-sensitivity of vesicle fusion. Phorbol esters potentiate Ca2+-evoked release as well as the spontaneous release rate. We explain both effects by an increased fusion 'willingness' in a new allosteric model of Ca2+-activation of vesicle fusion. In agreement with an allosteric mechanism, we observe that the classically high Ca2+ cooperativity in triggering vesicle fusion (approximately 4) is gradually reduced below 3 microM [Ca2+]i, reaching a value of
- Published
- 2005
7. Rapid Functional Maturation of Nascent Dendritic Spines
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Graham Knott, Karen Zito, Volker Scheuss, Travis C. Hill, and Karel Svoboda
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musculoskeletal diseases ,Dendritic spine ,Patch-Clamp Techniques ,Time Factors ,Neuroscience(all) ,Dendritic Spines ,Long-Term Potentiation ,Synaptic Membranes ,Glutamic Acid ,AMPA receptor ,Hippocampal-Neurons ,Biology ,Hippocampal formation ,Hippocampus ,Synaptic Transmission ,Article ,MOLNEURO ,Postnatal-Development ,Actin remodeling of neurons ,Organ Culture Techniques ,Microscopy, Electron, Transmission ,Animals ,Immunogold Localization ,Calcium Signaling ,Receptors, AMPA ,Cortex In-Vivo ,Microscopy, Confocal ,Neuronal Plasticity ,General Neuroscience ,Pyramidal Cells ,Long-term potentiation ,Cell Differentiation ,musculoskeletal system ,Individual Excitatory Synapses ,Cell biology ,Dendritic filopodia ,Rats ,Spine (zoology) ,Nmda Receptors ,Postsynaptically Silent Synapses ,Synaptic plasticity ,Synapses ,Calcium ,Neuroscience ,Synaptic Plasticity ,Dependent Plasticity - Abstract
Spine growth and retraction with synapse formation and elimination plays an important role in shaping brain circuits during development and in the adult brain. Yet the temporal relationship between spine morphogenesis and the formation of functional synapses remains poorly defined. We imaged hippocampal pyramidal neurons to identify spines of different ages. We then used two-photon glutamate uncaging, whole-cell recording, and Ca2+ imaging to analyze the properties of nascent spines and their older neighbors. We found that new spines expressed glutamate sensitive currents that were indistinguishable from mature spines of comparable volumes. Some spines exhibited negligible AMPA receptor-mediated responses, but the occurrence of these ‘silent’ spines was uncorrelated with spine age. In contrast, NMDA receptor-mediated Ca2+ accumulations were significantly lower in new spines. New spines reconstructed using electron microscopy made synapses. Our data support a model in which outgrowth and enlargement of nascent spines is tightly coupled to formation and maturation of glutamatergic synapses.
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