title: Comparison of genetically encoded calcium indicators for monitoring action potentials in mammalian brain by two-photon excitation fluorescence microscopy.
abstract: Imaging calcium transients associated with neuronal activity has yielded important insights into neural physiology. Genetically encoded calcium indicators (GECIs) offer conspicuous potential advantages for this purpose, including exquisite targeting. While the catalogue of available GECIs is steadily growing, many newly developed sensors that appear promising in vitro or in model cells appear to be less useful when expressed in mammalian neurons. We have, therefore, evaluated the performance of GECIs from two of the most promising families of sensors, G-CaMPs [Nat. Biotechnol.2(2), 137-141 (2001)] and GECOs [Science2(2), 1888-1891 (2011)], for monitoring action potentials in rat brain. Specifically, we used two-photon excitation fluorescence microscopy to compare calcium transients detected by G-CaMP3; GCaMP6f; G-CaMP7; Green-GECO1.0, 1.1 and 1.2; Blue-GECO; Red-GECO; Rex-GECO0.9; Rex-GECO1; Carmine-GECO; Orange-GECO; and Yellow-GECO1s. After optimizing excitation wavelengths, we monitored fluorescence signals associated with increasing numbers of action potentials evoked by current injection in CA1 pyramidal neurons in rat organotypic hippocampal slices. Some GECIs, particularly Green-GECO1.2, GCaMP6f, and G-CaMP7, were able to detect single action potentials with high reliability. By virtue of greatest sensitivity and fast kinetics, G-CaMP7 may be the best currently available GECI for monitoring calcium transients in mammalian neurons.
authors.affiliation: Dalhousie University , Department of Physiology and Biophysics, Halifax, Nova Scotia B3H 4R2, Canada.
authors.forename: Borbala
authors.initials: B
authors.lastname: Podor
authors.affiliation: Dalhousie University , Department of Physiology and Biophysics, Halifax, Nova Scotia B3H 4R2, Canada.
authors.forename: Yi-Ling
authors.initials: YL
authors.lastname: Hu
authors.affiliation: Saitama University , Brain Science Institute, Saitama 338-8570, Japan.
authors.forename: Masamichi
authors.initials: M
authors.lastname: Ohkura
authors.affiliation: Saitama University , Brain Science Institute, Saitama 338-8570, Japan.
authors.forename: Junichi
authors.initials: J
authors.lastname: Nakai
authors.affiliation: Dalhousie University , Department of Physiology and Biophysics, Halifax, Nova Scotia B3H 4R2, Canada.
authors.forename: Roger
authors.initials: R
authors.lastname: Croll
authors.affiliation: Dalhousie University , Department of Physiology and Biophysics, Halifax, Nova Scotia B3H 4R2, Canada.
authors.forename: Alan
authors.initials: A
authors.lastname: Fine
keywords: G-CaMP; GECO; calcium transients; genetically encoded calcium indicators; organotypic hippocampal slice; two-photon microscopy