Figure 2.

The effects of stimulus intensity on optical and electrophysiogical responses recorded from the CA1 region of the hippocampus in SyG37 mice. Bursts of 20 stimuli over a range of intensities were delivered at 20 Hz via a patch pipette placed in the s. radiatum of CA3. Images of SyGCaMP2 (green) and mCherry fluorescence (red) are shown along with the ratio of the two and images illustrating the difference in fluorescence for each fluorophore and their ratio before and during stimulation at each intensity labeled (A). The positions of the recording and stimulating electrodes are marked with upper and lower asterisks respectively. Abbreviations: pcl; pyramidal cell layer; sr; s. radiatum. The horizontal scale bar represents 100 μm. Responses over time are shown (B) for SyGCaMP2 and mCherry fluorescence extracted from regions of interest (ROIs) placed over the s radiatum (sr). The ratios of SyGCaMP2:mCherry fluorescence at each intensity are shown in blue. Increasing intensities are depicted with darker hues. The mean and standard errors of the mean (SEM) peak (C), initial slope (D) and decay time constant (E) of SyGCaMP2 fluorescence responses and the N2 component of fEPSPs (F) are plotted against intensity. The relationship between SyGCaMP2 and N2 peak responses is shown in panel (G). A line of best fit was plotted for values measured below 50 V where the relationship was linear. Data were obtained from six separate hippocampal slices taken from four different mice.