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. 2006 Aug 15;4(9):e271. doi: 10.1371/journal.pbio.0040271

Figure 2. Synapsin I Lost from One Bouton Is Incorporated into Adjacent Boutons.

Figure 2

An axonal segment expressing both CFP (A) and PA-GFP:Synapsin I (B).

(C) Higher magnification of region enclosed in rectangle in (B). PA-GFP:Synapsin I within a single bouton was photoactivated by selective illumination of this bouton at 405 nm (t = 0). Within 10 min of photoactivation, fluorescence at this bouton had decreased, whereas fluorescence at adjacent boutons (distances of 8 to 21 μm) had increased significantly. PA-GFP:Synapsin I fluorescence encoded in pseudo-color as in Figure 1.

(D) Quantification of fluorescence changes following photoactivation at photoactivated and adjacent boutons. Note the rapid reduction of fluorescence at the photoactivated site and the concomitant (but transient) increases recorded at adjacent boutons that were most prominent at boutons nearest to the photoactivation site.

(E) Synapsin lost from one bouton is incorporated into the presynaptic matrix of adjacent boutons. Two presynaptic boutons along an axonal segment expressing PA-GFP:Synapsin I. At time t = 0, PA-GFP:Synapsin I within one bouton (arrowhead) was photoactivated by selective illumination at 405 nm, and the redistribution of the photoactivated material was followed by time-lapse microscopy. At 21 min after photoactivation, a brief (20s@20Hz) stimulation train was delivered, leading to the transient dispersion of PA-GFP:Synapsin I at the photoactivated bouton as well as at the second bouton that had incorporated some of photoactivated PA-GFP:Synapsin I (arrow). PA-GFP:Synapsin I fluorescence encoded in pseudocolor as in Figure 1.

(F) FM4–64 labeling at the end of the experiment confirmed that both sites were functional presynaptic boutons. Bar, 5 μm.

(G) Normalized fluorescence of both boutons before, during, and after the stimulation episode. Note that PA-GFP:Synapsin I in the neighboring bouton exhibited activity induced dispersion just like Synapsin in the photoactivated bouton, indicating that the PA-GFP:Synapsin that had migrated to it had become incorporated into its presynaptic matrix.