Dissociated rat hippocampal neurons in 24-well plates were transduced with GCaMP variants (one per well), together with nuclear mCherry29, using lentivirus-mediated gene transfer. Electrodes triggered trains of action potentials in all neurons within each well (Methods). Time-lapse images (35 Hz) of ∼800 μm fields of view containing 10-100 neurons were acquired, while delivering a series of action potential trains (Fig. 1c). Fluorescence changes extracted from single neurons were used to compare the sensitivity, dynamic range, and kinetics of individual GCaMP variants and OGB1-AM (Fig. 1d). We monitored the resting brightness of the sensor by measuring green fluorescence relative to red mCherry fluorescence.
