A. Representative confocal images from EGFP-GSK3α FRAP experiments. Upper left panel ('Baseline') shows EGFP-GSK3α expression in a dendrite and dendritic spine of organotypic slices cultured from rat hippocampus. The spine was bleached ('Bleach'; yellow dashed circle) and its fluorescence partially recovered 90 s later ('Recovery'). Single dendritic spines were imaged once per second for 10 seconds prior to, and for 90 seconds following, spine photobleaching. Such single FRAP experiments were performed on different spines during basal conditions ('basal'; upper panels), immediately after cLTD induction with 20 µM NMDA for 5 minutes ('cLTD'; middle panels), and immediately following 10 minutes of washout ('washout'; lower panels). Scale bars = 1 µm. B. Time course of fluorescence recovery during FRAP experiments described in A. White circles ('basal') show the average spine/dendrite fluorescence of FRAP on EGFP-GSK3α-expressing spines in slices prior to cLTD induction. Pink circles ('cLTD') show fluorescence in spines in which cLTD had been induced using 20 µM NMDA. Green circles ('washout') represent the average of spine fluorescence after NMDA washout for 10 minutes. Recovery trajectories for the three conditions are fitted with two-phase exponential curves (red lines). C, D. As A, B but for spines expressing EGFP-GSK3β. Scale bars = 1 µm. 