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15 Publications

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    07/29/19 | Kilohertz frame-rate two-photon tomography.
    Kazemipour A, Novak O, Flickinger D, Marvin JS, Abdelfattah AS, King J, Borden P, Kim J, Al-Abdullatif S, Deal P, Miller E, Schreiter E, Druckmann S, Svoboda K, Looger L, Podgorski K
    Nature Methods. 2019 Jul 29;16(8):778-86. doi: 10.1101/357269

    Point-scanning two-photon microscopy enables high-resolution imaging within scattering specimens such as the mammalian brain, but sequential acquisition of voxels fundamentally limits imaging speed. We developed a two-photon imaging technique that scans lines of excitation across a focal plane at multiple angles and uses prior information to recover high-resolution images at over 1.4 billion voxels per second. Using a structural image as a prior for recording neural activity, we imaged visually-evoked and spontaneous glutamate release across hundreds of dendritic spines in mice at depths over 250 microns and frame-rates over 1 kHz. Dendritic glutamate transients in anaesthetized mice are synchronized within spatially-contiguous domains spanning tens of microns at frequencies ranging from 1-100 Hz. We demonstrate high-speed recording of acetylcholine and calcium sensors, 3D single-particle tracking, and imaging in densely-labeled cortex. Our method surpasses limits on the speed of raster-scanned imaging imposed by fluorescence lifetime.

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    07/15/19 | A genetically encoded fluorescent sensor for in vivo imaging of GABA.
    Marvin JS, Shimoda Y, Magloire V, Leite M, Kawashima T, Jensen TP, Kolb I, Knott EL, Novak O, Podgorski K, Leidenheimer NJ, Rusakov DA, Ahrens MB, Kullmann DM, Looger LL
    Nature Methods. 2019 Jul 15;16(8):763-770. doi: 10.1038/s41592-019-0471-2

    Current techniques for monitoring GABA (γ-aminobutyric acid), the primary inhibitory neurotransmitter in vertebrates, cannot follow transients in intact neural circuits. To develop a GABA sensor, we applied the design principles used to create the fluorescent glutamate receptor iGluSnFR. We used a protein derived from a previously unsequenced Pseudomonas fluorescens strain and performed structure-guided mutagenesis and library screening to obtain intensity-based GABA sensing fluorescence reporter (iGABASnFR) variants. iGABASnFR is genetically encoded, detects GABA release evoked by electric stimulation of afferent fibers in acute brain slices and produces readily detectable fluorescence increases in vivo in mice and zebrafish. We applied iGABASnFR to track mitochondrial GABA content and its modulation by an anticonvulsant, swimming-evoked, GABA-mediated transmission in zebrafish cerebellum, GABA release events during interictal spikes and seizures in awake mice, and found that GABA-mediated tone decreases during isoflurane anesthesia.

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    11/01/18 | Stability, affinity and chromatic variants of the glutamate sensor iGluSnFR.
    Marvin JS, Scholl B, Wilson DE, Podgorski K, Kazemipour A, Mueller JA, Schoch-McGovern S, Wang SS, Quiroz FJ, Rebola N, Bao H, Little JP, Tkachuk AN, Hantman AW, Chapman ER, Dietrich D, DiGregorio DA, Fitzpatrick D, Looger LL
    Nature Methods. 2018 Nov;15(11):9386-9. doi: 10.1038/s41592-018-0171-3

    Single-wavelength fluorescent reporters allow visualization of specific neurotransmitters with high spatial and temporal resolution. We report variants of intensity-based glutamate-sensing fluorescent reporter (iGluSnFR) that are functionally brighter; detect submicromolar to millimolar amounts of glutamate; and have blue, cyan, green, or yellow emission profiles. These variants could be imaged in vivo in cases where original iGluSnFR was too dim, resolved glutamate transients in dendritic spines and axonal boutons, and allowed imaging at kilohertz rates.

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    Druckmann LabPodgorski Lab
    04/16/18 | Multiplicative updates for optimization problems with dynamics.
    Abbas Kazemipour , Behtash Babadi , wu m, Podgorski K, Shaul Druckmann
    IEEE Xplore. 2018 Apr 16:. doi: 10.1109/ACSSC.2017.8335723

    We consider the problem of optimizing general convex objective functions with nonnegativity constraints. Using the Karush-Kuhn-Tucker (KKT) conditions for the nonnegativity constraints we will derive fast multiplicative update rules for several problems of interest in signal processing, including non-negative deconvolution, point-process smoothing, ML estimation for Poisson Observations, nonnegative least squares and nonnegative matrix factorization (NMF). Our algorithm can also account for temporal and spatial structure and regularization. We will analyze the performance of our algorithm on simultaneously recorded neuronal calcium imaging and electrophysiology data.

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    Magee LabPodgorski Lab
    06/08/16 | Brain heating induced by near infrared lasers during multi-photon microscopy.
    Podgorski K, Ranganathan GN
    Journal of Neurophysiology. 2016 Jun 8;116(3):1012-23. doi: 10.1152/jn.00275.2016

    Two-photon imaging and optogenetic stimulation rely on high illumination powers, particularly for state-of-the-art applications that target deeper structures, achieve faster measurements, or probe larger brain areas. However, little information is available on heating and resulting damage induced by high-power illumination in the brain. Here we used thermocouple probes and quantum dot nanothermometers to measure temperature changes induced by two-photon microscopy in the neocortex of awake and anaesthetized mice. We characterized heating as a function of wavelength, exposure time, and distance from the center of illumination. Although total power is highest near the surface of the brain, heating was most severe hundreds of microns below the focal plane, due to heat dissipation through the cranial window. Continuous illumination of a 1mm2 area produced a peak temperature increase of approximately 1.8°C/100mW. Continuous illumination with powers above 250 mW induced lasting damage, detected with immunohistochemistry against Iba1, GFAP, heat shock proteins, and activated Caspase-3. Higher powers were usable in experiments with limited duty ratios, suggesting an approach to mitigate damage in high-power microscopy experiments.

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