Figure 9.

Effect of stimulus frequency and number on fluorescence responses recorded from the CA3 s. lucidum and CA1 s. radiatum of SyG37 mice. Trains of 20 stimuli were applied at a fixed voltage at frequencies between 1 Hz and 100 Hz. In panel (A) responses over time are shown for SyGCaMP2 fluorescence extracted from ROIs placed over the s. lucidum. (B) The means and SEM for the peak responses are shown alongside data recorded from CA1 (n = 6 slices from four different mice in each case). Panel (C) Examples of traces recorded at 20 Hz from CA3 and CA1 are shown. The inset shows the two responses scaled to the peak to highlight the different decay time courses. (D) The decay phases of responses were fitted with double exponential curves and the faster value of the time constant tau plotted against frequency at each region. The means and SEM from 18 separate experiments are shown. (***P = 0.0015 (20 Hz); **P = 0.0085 (50 Hz) and ****P = 0.0003 (100 Hz); Kruskall-Wallace Test with Dunn’s multiple comparisons; n = 18 in each case). Panel (E) provides an example of CA3 responses to increasing stimulus numbers delivered at a fixed intensity at 20 Hz. Data are plotted to the same scale as that in panel (A). Data pooled from six separate slices from four different mice are shown in panel (F). (G) Applications of the mGluR2 agonist DCGIV reduced both SyGCaMP2 responses and fEPSPs recorded in s. lucidum. The absolute fluorescence of both mCherry (red bars) and SyGCaMP2 (green bars) under baseline conditions are shown (H) along with the ratio of SyG:mCherry fluorescence. The means and SEM of six separate experiments from six different mice are shown (P = 0.002 (SyGCaMP2); P < 0.004 (mCherry); P = 0.22 (Ratio) Mann-Whitney U-test).