Two-photon imaging of spontaneous hippocampal CA1 circuit activity in anesthetized TRE-G-CaMP7 x CaMKII-tTA mice at 4 months of age.

<p><b>A</b>, Different subcellular compartments of pyramidal neurons expressing G-CaMP7 (left) and DsRed2 (right) were imaged in the dorsal CA1 hippocampus 50, 95 and 140 μm from the hippocampal surface. Scale bar = 50 μm. <b>B</b>, The positions and numbers of 12 active neurons selected for analysis are indicated in an average G-CaMP7 fluorescence image acquired at a depth of 145 μm. <b>C</b>, Baseline-normalized G-CaMP7 fluorescence time traces of the 12 active cells. <b>D</b>, A cross-correlation matrix of G-CaMP7 fluorescence time traces of the 12 active cells. <b>E</b>, Example time-lapse images of G-CaMP7 fluorescence during spontaneous network activity in the CA1 hippocampus. Cells 7 and 2 (as designated in <b>B</b>) were sequentially activated multiple times. Only two out of nine total sequential activation events are shown here. Time stamps are indicated at the bottom of the images. Δt represents the image sampling interval (0.43 s). Active cells 7 and 2 are indicated by red arrows.