Fig. 5. Recovery of cytoplasmic GFP-tau after photobleaching. (A) Fluorescence images of a GFP-tau-transfected neuron after overnight incubation at 4°C followed by nocodazole treatment (10 µg/ml, 1 hour). The first image was acquired immediately before photobleaching. The time after photobleaching is shown at the upper-right corner of each panel. The size of the bleached zone was 4 µm. No single MTs can be detected with fluorescence microscopy, and therefore fluorescence intensity reflects the concentration of cytoplasmic GFP-tau. Dark elongated structures visible throughout the entire sequence correspond to membrane organelles (most likely mitochondria) which exclude GFP-tau. (B) Fluorescence intensity of the bleached zone (I) normalized to the initial fluorescence (I_o) as a function of time.