Figure 5. Intradendritic Ca2+ transients evoked during STDP induction protocols. Analysis of Ca2+ transients elicited by the STDP induction protocol at 6 Hz in granule cells filled with 200 μm OG1. A, Top, Fluorescence image of a GrC filled with 200 μm OG1. Scale bar, 5 μm. Fluorescence intensity is color coded with arbitrary units within an interval chosen to allow the visualization of the synaptic terminals. Bottom, The series of pseudo-ratio images illustrate fluorescence changes ΔF/F0 during evoked EPSP paired with spike at Δt = ±25 ms. Yellow square represents the ROI used for measurements. Scale bar, 0.2 μm. B, Traces represent the background-subtracted kinetics of fluorescence changes (ΔF/F0)max, for different STDP induction protocols (Δt = ±25 ms). The stimulation starts 2 s after the beginning of the recording. Gray bar represents the duration of STDP protocols. Each point indicates the Ca2+ transient in response to three consecutive EPSP-AP (or AP-EPSP) pairings. It should be noted that, at the beginning of the pairing period (blue point, i.e., after 3 pairings), the Ca2+ transient was still small and attained plateau near the end of the pairing period (20th point, i.e., after 60 pairings). C, Histograms compare the (ΔF/F0)max amplitude and area, and delay of Ca2+ transients induced by evoked EPSP paired with spike at Δt = ±25 ms. D, The relationship between intracellular Ca2+ changes, [Ca2+]i, and STDP obtained during evoked EPSP paired with the spike at Δt = ±25 ms.