Kovalchuk Yuri

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In vivo functional properties of juxtaglomerular neurons in the mouse olfactory bulb

2013-02-21 , Homma, Ryota , Kovalchuk, Yuri , Konnerth, A. , Cohen, Lawrence B. , Garaschuk, Olga

Juxtaglomerular neurons represent one of the largest cellular populations in the mammalian olfactory bulb yet their role for signal processing remains unclear. We used two-photon imaging and electrophysiological recordings to clarify the in vivo properties of these cells and their functional organization in the juxtaglomerular space. Juxtaglomerular neurons coded for many perceptual characteristics of the olfactory stimulus such as (1) identity of the odorant, (2) odorant concentration, (3) odorant onset, and (4) offset. The odor-responsive neurons clustered within a narrow area surrounding the glomerulus with the same odorant specificity, with ~80% of responding cells located ≤20 μm from the glomerular border. This stereotypic spatial pattern of activated cells persisted at different odorant concentrations and was found for neurons both activated and inhibited by the odorant. Our data identify a principal glomerulus with a narrow shell of juxtaglomerular neurons as a basic odor coding unit in the glomerular layer and underline the important role of intraglomerular circuitry.

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Optimized ratiometric calcium sensors for functional in vivo imaging of neurons and T lymphocytes

2013-06 , Thestrup, Thomas , Litzlbauer, Julia , Bartholomaus, Ingo , Mues, Marsilius , Russo, Luigi , Dana, Hod , Kovalchuk, Yuri , Liang, Yajie , Kalamakis, Georgios , Lauka, Yvonne , Becker, Stefan , Witte, Gregor , Geiger, Anselm , Allen, Taylor , Rome, Lawrence C. , Chen, Tsai-Wen , Kim, Douglas S. , Garaschuk, Olga , Griesinger, Christian , Griesbeck, Oliver

The quality of genetically encoded calcium indicators (GECIs) has improved dramatically in recent years, but high-performing ratiometric indicators are still rare. Here we describe a series of fluorescence resonance energy transfer (FRET)-based calcium biosensors with a reduced number of calcium binding sites per sensor. These ‘Twitch’ sensors are based on the C-terminal domain of Opsanus troponin C. Their FRET responses were optimized by a large-scale functional screen in bacterial colonies, refined by a secondary screen in rat hippocampal neuron cultures. We tested the in vivo performance of the most sensitive variants in the brain and lymph nodes of mice. The sensitivity of the “Twitch” sensors matched that of synthetic calcium dyes and allowed visualization of tonic action potential firing in neurons and high resolution functional tracking of T lymphocytes. Given their ratiometric readout, their brightness, large dynamic range and linear response properties, Twitch sensors represent versatile tools for neuroscience and immunology.