Figure 7. Incorporation Rates of Synapsin I from Somatic Sources at Remote Presynaptic Boutons.

(A) Low-magnification composite image of a neuron expressing CFP and PA-GFP:Synapsin I. Only CFP fluorescence is shown here. Parts of the axonal arbor are marked with arrowheads. Fluorescence is encoded using an inverted gray scale to increase detail clarity.

(B) Higher magnification of rectangle marked as “B” in (A). At time t = 0, PA-GFP:Synapsin I within the cell body was photoactivated by selective illumination of the soma at 405 nm. Within minutes, photoactivated PA-GFP:Synapsin was observed to spread out into the axon and, much later, to appear at presynaptic boutons in the same field of view.

(C) Higher magnification of rectangle marked as “C” in (A), enclosing a group of relatively remote presynaptic boutons. Note the gradual increase in fluorescence of these remote boutons over time.

(D) Quantification of fluorescence changes at remote boutons following photoactivation of somatic PA-GFP:Synapsin. Boutons were grouped according to distance from the soma as shown in (A). Fluorescence data for each bouton were normalized to prephotoactivation fluorescence levels at the same bouton. Bars: (A), 50 μm; (B and C), 20 μm.