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13 Publications

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    Looger Lab
    10/18/12 | Imaging neural activity using Thy1-GCaMP transgenic mice.
    Chen Q, Cichon J, Wang W, Qiu L, Lee SR, Campbell NR, DeStefino N, Fu Z, Yasuda R, Looger LL, Arenkiel BR, Gan W, Feng G
    Neuron. 2012 Oct 18;76(2):297-308. doi: 10.1016/j.neuron.2012.07.011

    The ability to chronically monitor neuronal activity in the living brain is essential for understanding the organization and function of the nervous system. The genetically encoded green fluorescent protein based calcium sensor GCaMP provides a powerful tool for detecting calcium transients in neuronal somata, processes, and synapses that are triggered by neuronal activities. Here we report the generation and characterization of transgenic mice that express improved GCaMPs in various neuronal subpopulations under the control of the Thy1 promoter. In vitro and in vivo studies show that calcium transients induced by spontaneous and stimulus-evoked neuronal activities can be readily detected at the level of individual cells and synapses in acute brain slices, as well as in awake behaving animals. These GCaMP transgenic mice allow investigation of activity patterns in defined neuronal populations in the living brain, and will greatly facilitate dissecting complex structural and functional relationships of neural networks.

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    10/03/12 | Optimization of a GCaMP calcium indicator for neural activity imaging.
    Akerboom J, Chen T, Wardill TJ, Marvin JS, Mutlu S, Carreras Caldero N, Esposti F, Borghuis BG, Sun XR, Gordus A, Orger MB, Portugues R, Engert F, Macklin JJ, Filosa A, Aggarwal A, Kerr R, Takagi R, Kracun S, Shigetomi E, Khakh BS, Baier H, Lagnado L, Wang SS, Bargmann C, Kimmel B, Jayaraman V, Svoboda K, Kim DS, Schreiter ER, Looger LL
    The Journal of Neuroscience. 2012 Oct 3;32:13819-40. doi: 10.1523/​JNEUROSCI.2601-12.2012

    Genetically encoded calcium indicators (GECIs) are powerful tools for systems neuroscience. Recent efforts in protein engineering have significantly increased the performance of GECIs. The state-of-the art single-wavelength GECI, GCaMP3, has been deployed in a number of model organisms and can reliably detect three or more action potentials in short bursts in several systems in vivo . Through protein structure determination, targeted mutagenesis, high-throughput screening, and a battery of in vitro assays, we have increased the dynamic range of GCaMP3 by severalfold, creating a family of “GCaMP5” sensors. We tested GCaMP5s in several systems: cultured neurons and astrocytes, mouse retina, and in vivo in Caenorhabditis chemosensory neurons, Drosophila larval neuromuscular junction and adult antennal lobe, zebrafish retina and tectum, and mouse visual cortex. Signal-to-noise ratio was improved by at least 2- to 3-fold. In the visual cortex, two GCaMP5 variants detected twice as many visual stimulus-responsive cells as GCaMP3. By combining in vivo imaging with electrophysiology we show that GCaMP5 fluorescence provides a more reliable measure of neuronal activity than its predecessor GCaMP3.GCaMP5allows more sensitive detection of neural activity in vivo andmayfind widespread applications for cellular imaging in general.

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    Looger LabSvoboda Lab
    09/13/12 | Activity in motor-sensory projections reveals distributed coding in somatosensation.
    Petreanu L, Gutnisky DA, Huber D, Xu N, O’Connor DH, Tian L, Looger L, Svoboda K
    Nature. 2012 Sep 13;489:299-303. doi: 10.1038/nature11321

    Cortical-feedback projections to primary sensory areas terminate most heavily in layer 1 (L1) of the neocortex, where they make synapses with tuft dendrites of pyramidal neurons. L1 input is thought to provide ‘contextual’ information, but the signals transmitted by L1 feedback remain uncharacterized. In the rodent somatosensory system, the spatially diffuse feedback projection from vibrissal motor cortex (vM1) to vibrissal somatosensory cortex (vS1, also known as the barrel cortex) may allow whisker touch to be interpreted in the context of whisker position to compute object location. When mice palpate objects with their whiskers to localize object features, whisker touch excites vS1 and later vM1 in a somatotopic manner. Here we use axonal calcium imaging to track activity in vM1–>vS1 afferents in L1 of the barrel cortex while mice performed whisker-dependent object localization. Spatially intermingled individual axons represent whisker movements, touch and other behavioural features. In a subpopulation of axons, activity depends on object location and persists for seconds after touch. Neurons in the barrel cortex thus have information to integrate movements and touches of multiple whiskers over time, key components of object identification and navigation by active touch.

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    Looger Lab
    05/08/12 | Optogenetic analysis of a nociceptor neuron and network reveals ion channels acting downstream of primary sensors.
    Husson SJ, Costa WS, Wabnig S, Stirman JN, Watson JD, Spencer WC, Akerboom J, Looger LL, Treinin M, Miller DM, Lu H, Gottschalk A
    Current Biology. 2012 May 8;22(9):743-52. doi: 10.1016/j.cub.2012.02.066

    Nociception generally evokes rapid withdrawal behavior in order to protect the tissue from harmful insults. Most nociceptive neurons responding to mechanical insults display highly branched dendrites, an anatomy shared by Caenorhabditis elegans FLP and PVD neurons, which mediate harsh touch responses. Although several primary molecular nociceptive sensors have been characterized, less is known about modulation and amplification of noxious signals within nociceptor neurons. First, we analyzed the FLP/PVD network by optogenetics and studied integration of signals from these cells in downstream interneurons. Second, we investigated which genes modulate PVD function, based on prior single-neuron mRNA profiling of PVD.

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    Looger LabSvoboda Lab
    04/26/12 | Multiple dynamic representations in the motor cortex during sensorimotor learning.
    Huber D, Gutnisky DA, Peron S, O’Connor DH, Wiegert JS, Tian L, Oertner TG, Looger L, Svoboda K
    Nature. 2012 Apr 26;484(7395):473-8. doi: 10.1038/nature11039

    The mechanisms linking sensation and action during learning are poorly understood. Layer 2/3 neurons in the motor cortex might participate in sensorimotor integration and learning; they receive input from sensory cortex and excite deep layer neurons, which control movement. Here we imaged activity in the same set of layer 2/3 neurons in the motor cortex over weeks, while mice learned to detect objects with their whiskers and report detection with licking. Spatially intermingled neurons represented sensory (touch) and motor behaviours (whisker movements and licking). With learning, the population-level representation of task-related licking strengthened. In trained mice, population-level representations were redundant and stable, despite dynamism of single-neuron representations. The activity of a subpopulation of neurons was consistent with touch driving licking behaviour. Our results suggest that ensembles of motor cortex neurons couple sensory input to multiple, related motor programs during learning.

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    Looger LabLavis Lab
    04/01/12 | A genetically encoded fluorescent protein in echinoderms marks the history of neuronal activity.
    Verdecia MA, Looger LL, Lavis L, Graumann J, Mandel G, Brehm P
    Luminescence. 2012 Apr;27:170

    Since the original identification of GFP from jellyfish and corals, the genetically encoded fluorescent proteins have become mainstream indicators for imaging. Functionally homologous candidates exist in more highly evolved bioluminescent invertebrates, including echinoderms. For example, in brittlestars, stimulus-evoked bioluminescence is transient, lasting seconds, and emanates from specialized cells (photocytes). Prior to light emission, we observe little or no green fluorescence. However, concurrent with light emission, an intense green, calcium-dependent fluorescence develops that persists indefinitely.

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    Sternson LabLooger LabLavis Lab
    03/27/12 | Selective esterase-ester pair for targeting small molecules with cellular specificity.
    Tian L, Yang Y, Wysocki LM, Arnold AC, Hu A, Ravichandran B, Sternson SM, Looger LL, Lavis LD
    Proceedings of the National Academy of Sciences of the United States of America. 2012 Mar 27;109:4756-61. doi: 10.1073/pnas.1111943109

    Small molecules are important tools to measure and modulate intracellular signaling pathways. A longstanding limitation for using chemical compounds in complex tissues has been the inability to target bioactive small molecules to a specific cell class. Here, we describe a generalizable esterase-ester pair capable of targeted delivery of small molecules to living cells and tissue with cellular specificity. We used fluorogenic molecules to rapidly identify a small ester masking motif that is stable to endogenous esterases, but is efficiently removed by an exogenous esterase. This strategy allows facile targeting of dyes and drugs in complex biological environments to label specific cell types, illuminate gap junction connectivity, and pharmacologically perturb distinct subsets of cells. We expect this approach to have general utility for the specific delivery of many small molecules to defined cellular populations.

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    Looger LabSvoboda LabLeonardo LabGENIE
    02/29/12 | A Cre-dependent GCaMP3 reporter mouse for neuronal imaging in vivo.
    Zariwala HA, Borghuis BG, Hoogland TM, Madisen L, Tian L, De Zeeuw CI, Zeng H, Looger LL, Svoboda K, Chen T
    The Journal of Neuroscience. 2012 Feb 29;32:3131-41. doi: 10.1523/JNEUROSCI.4469-11.2012

    Fluorescent calcium indicator proteins, such as GCaMP3, allow imaging of activity in genetically defined neuronal populations. GCaMP3 can be expressed using various gene delivery methods, such as viral infection or electroporation. However, these methods are invasive and provide inhomogeneous and nonstationary expression. Here, we developed a genetic reporter mouse, Ai38, which expresses GCaMP3 in a Cre-dependent manner from the ROSA26 locus, driven by a strong CAG promoter. Crossing Ai38 with appropriate Cre mice produced robust GCaMP3 expression in defined cell populations in the retina, cortex, and cerebellum. In the primary visual cortex, visually evoked GCaMP3 signals showed normal orientation and direction selectivity. GCaMP3 signals were rapid, compared with virally expressed GCaMP3 and synthetic calcium indicators. In the retina, Ai38 allowed imaging spontaneous calcium waves in starburst amacrine cells during development, and light-evoked responses in ganglion cells in adult tissue. Our results show that the Ai38 reporter mouse provides a flexible method for targeted expression of GCaMP3.

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    02/22/12 | Excitation spectra and brightness optimization of two-photon excited probes.
    Mütze J, Iyer V, Macklin JJ, Colonell J, Karsh B, Petrá\v sek Ze, Schwille P, Looger LL, Lavis LD, Harris TD
    Biophysical Journal. 2012 Feb 22;102(4):934-44. doi: 10.1016/j.bpj.2011.12.056

    Two-photon probe excitation data are commonly presented as absorption cross section or molecular brightness (the detected fluorescence rate per molecule). We report two-photon molecular brightness spectra for a diverse set of organic and genetically encoded probes with an automated spectroscopic system based on fluorescence correlation spectroscopy. The two-photon action cross section can be extracted from molecular brightness measurements at low excitation intensities, while peak molecular brightness (the maximum molecular brightness with increasing excitation intensity) is measured at higher intensities at which probe photophysical effects become significant. The spectral shape of these two parameters was similar across all dye families tested. Peak molecular brightness spectra, which can be obtained rapidly and with reduced experimental complexity, can thus serve as a first-order approximation to cross-section spectra in determining optimal wavelengths for two-photon excitation, while providing additional information pertaining to probe photostability. The data shown should assist in probe choice and experimental design for multiphoton microscopy studies. Further, we show that, by the addition of a passive pulse splitter, nonlinear bleaching can be reduced-resulting in an enhancement of the fluorescence signal in fluorescence correlation spectroscopy by a factor of two. This increase in fluorescence signal, together with the observed resemblance of action cross section and peak brightness spectra, suggests higher-order photobleaching pathways for two-photon excitation.

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    Looger Lab
    02/21/12 | Reduced release probability prevents vesicle depletion and transmission failure at dynamin mutant synapses.
    Lou X, Fan F, Messa M, Raimondi A, Wu Y, Looger LL, Ferguson SM, De Camilli P
    Proceedings of the National Academy of Sciences of the United States of America. 2012 Feb 21;109:E515-23. doi: 10.1073/pnas.1121626109

    Endocytic recycling of synaptic vesicles after exocytosis is critical for nervous system function. At synapses of cultured neurons that lack the two "neuronal" dynamins, dynamin 1 and 3, smaller excitatory postsynaptic currents are observed due to an impairment of the fission reaction of endocytosis that results in an accumulation of arrested clathrin-coated pits and a greatly reduced synaptic vesicle number. Surprisingly, despite a smaller readily releasable vesicle pool and fewer docked vesicles, a strong facilitation, which correlated with lower vesicle release probability, was observed upon action potential stimulation at such synapses. Furthermore, although network activity in mutant cultures was lower, Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) activity was unexpectedly increased, consistent with the previous report of an enhanced state of synapsin 1 phosphorylation at CaMKII-dependent sites in such neurons. These changes were partially reversed by overnight silencing of synaptic activity with tetrodotoxin, a treatment that allows progression of arrested endocytic pits to synaptic vesicles. Facilitation was also counteracted by CaMKII inhibition. These findings reveal a mechanism aimed at preventing synaptic transmission failure due to vesicle depletion when recycling vesicle traffic is backed up by a defect in dynamin-dependent endocytosis and provide new insight into the coupling between endocytosis and exocytosis.

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