Functional structure of the mitral cell dendritic tuft in the rat olfactory bulb

Author Posting. © Society for Neuroscience, 2008. This article is posted here by permission of Society for Neuroscience for personal use, not for redistribution. The definitive version was published in Journal of Neuroscience 28 (2008): 4057-4068, doi:10.1523/JNEUROSCI.5296-07.2008.The input–output transform performed by mitral cells, the principal projection neurons of the olfactory bulb, is one of the key factors in understanding olfaction. We used combined calcium and voltage imaging from the same neuron and computer modeling to investigate signal processing in the mitral cells, focusing on the glomerular dendritic tuft. The main finding was that the dendritic tuft functions as a single electrical compartment for subthreshold signals within the range of amplitudes detectable by voltage-sensitive dye recording. These evoked EPSPs had uniform characteristics throughout the glomerular tuft. The Ca2+ transients associated with spatially uniform subthreshold synaptic potentials were comparable but not equal in amplitude in all regions. The average range of normalized amplitudes of the EPSP-driven Ca2+ signals from different locations on dendritic branches in the glomerular tuft was relatively narrow and appeared to be independent of the dendritic surface-to-volume ratio. The computer simulations constrained by the imaging data indicated that a synchronized activation of ~100 synapses randomly distributed on tuft branches was sufficient to generate spatially homogenous EPSPs. This number of activated synapses is consistent with the data from anatomical studies. Furthermore, voltage attenuation of the EPSP along the primary dendrite at physiological temperature was weak compared with other cell types. In the model, weak attenuation of the EPSP along the primary dendrite could be accounted for by passive electrical properties of the mitral cell.This work was supported by National Institutes of Health Grant NS4273

Voltage imaging from dendrites of mitral cells : EPSP attenuation and spike trigger zones

Author Posting. © Society for Neuroscience, 2004. This article is posted here by permission of Society for Neuroscience for personal use, not for redistribution. The definitive version was published in Journal of Neuroscience 24 (2004): 6703-6714, doi:10.1523/JNEUROSCI.0307-04.2004.To obtain a more complete description of individual neurons, it is necessary to complement the electrical patch pipette measurements with technologies that permit a massive parallel recording from many sites on neuronal processes. This can be achieved by using voltage imaging with intracellular dyes. With this approach, we investigated the functional structure of a mitral cell, the principal output neuron in the rat olfactory bulb. The most significant finding concerns the characteristics of EPSPs at the synaptic sites and surprisingly small attenuation along the trunk of the primary dendrite. Also, the experiments were performed to determine the number, location, and stability of spike trigger zones, the excitability of terminal dendritic branches, and the pattern and nature of spike initiation and propagation in the primary and secondary dendrites. The results show that optical data can be used to deduce the amplitude and shape of the EPSPs evoked by olfactory nerve stimulation at the site of origin (glomerular tuft) and to determine its attenuation along the entire length of the primary dendrite. This attenuation corresponds to an unusually large mean apparent "length constant" of the primary dendrite. Furthermore, the images of spike trigger zones showed that an action potential can be initiated in three different compartments of the mitral cell: the soma-axon region, the primary dendrite trunk, and the terminal dendritic tuft, which appears to be fully excitable. Finally, secondary dendrites clearly support the active propagation of action potentialsThis work was supported by National Institutes of Health Grants NS4273 and DC03918. W.R.C. was also supported by the Whitehall Foundation

PAK1 phosphorylation of MEK1 regulates fibronectin-stimulated MAPK activation

Activation of the Ras–MAPK signal transduction pathway is necessary for biological responses both to growth factors and ECM. Here, we provide evidence that phosphorylation of S298 of MAPK kinase 1 (MEK1) by p21-activated kinase (PAK) is a site of convergence for integrin and growth factor signaling. We find that adhesion to fibronectin induces PAK1-dependent phosphorylation of MEK1 on S298 and that this phosphorylation is necessary for efficient activation of MEK1 and subsequent MAPK activation. The rapid and efficient activation of MEK and phosphorylation on S298 induced by cell adhesion to fibronectin is influenced by FAK and Src signaling and is paralleled by localization of phospho-S298 MEK1 and phospho-MAPK staining in peripheral membrane–proximal adhesion structures. We propose that FAK/Src-dependent, PAK1-mediated phosphorylation of MEK1 on S298 is central to the organization and localization of active Raf–MEK1–MAPK signaling complexes, and that formation of such complexes contributes to the adhesion dependence of growth factor signaling to MAPK

STrengthening the REporting of Genetic Association Studies (STREGA)— An Extension of the STROBE Statement

Julian Little and colleagues present the STREGA recommendations, which are aimed at improving the reporting of genetic association studies

Mesoscale Characterization of Nanoparticles Distribution Using X-ray Scattering

The properties of many functional materials depend critically on the spatial distribution of an active phase within a support. In the case of solid catalysts, controlling the spatial distribution of metal (oxide) nanoparticles at the mesoscopic scale offers new strategies to tune their performance and enhance their lifetimes. However, such advanced control requires suitable characterization methods, which are currently scarce. Here, we show how the background in small-angle X-ray scattering patterns can be analyzed to quantitatively access the mesoscale distribution of nanoparticles within supports displaying hierarchical porosity. This is illustrated for copper catalysts supported on meso- and microporous silica displaying distinctly different metal distributions. Results derived from X-ray scattering are in excellent agreement with electron tomography. Our strategy opens unprecedented prospects for understanding the properties and to guide the synthesis of a wide array of functional nanomaterials.status: publishe

Wide-field and two-photon imaging of brain activity with voltage- and calcium-sensitive dyes.: Imaging brain activity

International audienceThis chapter presents three examples of imaging brain activity with voltage- or calcium-sensitive dyes. Because experimental measurements are limited by low sensitivity, the chapter then discusses the methodological aspects that are critical for optimal signal-to-noise ratio. Two of the examples use wide-field (1-photon) imaging and the third uses two-photon scanning microscopy. These methods have relatively high temporal resolution ranging from 10 to 10,000 Hz. The three examples are the following: (1) Internally injected voltage-sensitive dye can be used to monitor membrane potential in the dendrites of invertebrate and vertebrate neurons in in vitro preparations. These experiments are directed at understanding how individual neurons convert the complex input synaptic activity into the output spike train. (2) Recently developed methods for staining many individual cells in the mammalian brain with calcium-sensitive dyes together with two-photon microscopy made it possible to follow the spike activity of many neurons simultaneously while in vivo preparations are responding to stimulation. (3) Calcium-sensitive dyes that are internalized into olfactory receptor neurons in the nose will, after several days, be transported to the nerve terminals of these cells in the olfactory bulb glomeruli. There, the population signals can be used as a measure of the input from the nose to the bulb. Three kinds of noise in measuring light intensity are discussed: (1) Shot noise from the random emission of photons from the preparation. (2) Extraneous (technical) noise from external sources. (3) Noise that occurs in the absence of light, the dark noise. In addition, we briefly discuss the light sources, the optics, and the detectors and cameras. The commonly used organic voltage and ion sensitive dyes stain all of the cell types in the preparation indiscriminately. A major effort is underway to find methods for staining individual cell types in the brain selectively. Most of these efforts center around fluorescent protein activity sensors because transgenic methods can be used to express them in individual cell types

Mesoscale Characterization of Nanoparticles Distribution Using X-ray Scattering

The properties of many functional materials depend critically on the spatial distribution of an active phase within a support. In the case of solid catalysts, controlling the spatial distribution of metal (oxide) nanoparticles at the mesoscopic scale offers new strategies to tune their performance and enhance their lifetimes. However, such advanced control requires suitable characterization methods, which are currently scarce. Here, we show how the background in small-angle Xray scattering patterns can be analyzed to quantitatively access the mesoscale distribution of nanoparticles within supports displaying hierarchical porosity. This is illustrated for copper catalysts supported on meso-and microporous silica displaying distinctly different metal distributions. Results derived from X-ray scattering are in excellent agreement with electron tomography. Our strategy opens unprecedented prospects for understanding the properties and to guide the synthesis of a wide array of functional nanomaterials