%0 Journal Article
%T Genetically Encoded Green Fluorescent Ca2+ Indicators with Improved Detectability for Neuronal Ca2+ Signals
%A Masamichi Ohkura
%A Takuya Sasaki
%A Junko Sadakari
%A Keiko Gengyo-Ando
%A Yuko Kagawa-Nagamura
%A Chiaki Kobayashi
%A Yuji Ikegaya
%A Junichi Nakai
%J PLOS ONE
%D 2012
%I Public Library of Science (PLoS)
%R 10.1371/journal.pone.0051286
%X Imaging the activities of individual neurons with genetically encoded Ca2+ indicators (GECIs) is a promising method for understanding neuronal network functions. Here, we report GECIs with improved neuronal Ca2+ signal detectability, termed G-CaMP6 and G-CaMP8. Compared to a series of existing G-CaMPs, G-CaMP6 showed fairly high sensitivity and rapid kinetics, both of which are suitable properties for detecting subtle and fast neuronal activities. G-CaMP8 showed a greater signal (Fmax/Fmin = 38) than G-CaMP6 and demonstrated kinetics similar to those of G-CaMP6. Both GECIs could detect individual spikes from pyramidal neurons of cultured hippocampal slices or acute cortical slices with 100% detection rates, demonstrating their superior performance to existing GECIs. Because G-CaMP6 showed a higher sensitivity and brighter baseline fluorescence than G-CaMP8 in a cellular environment, we applied G-CaMP6 for Ca2+ imaging of dendritic spines, the putative postsynaptic sites. By expressing a G-CaMP6-actin fusion protein for the spines in hippocampal CA3 pyramidal neurons and electrically stimulating the granule cells of the dentate gyrus, which innervate CA3 pyramidal neurons, we found that sub-threshold stimulation triggered small Ca2+ responses in a limited number of spines with a low response rate in active spines, whereas supra-threshold stimulation triggered large fluorescence responses in virtually all of the spines with a 100% activity rate.
%U http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0051286