During the pruning period, RGC synaptic inputs originating from the same eye as well as between eyes compete for territory throughout the dLGN (Chen and Regehr, 2000, Hooks and Chen, 2006, Jaubert-Miazza et al., 2005 and Ziburkus and Guido, 2006). Spontaneous retinal activity plays critical role in this refinement process; however, the underlying cellular and molecular mechanisms remain poorly understood. (Del Rio and Feller, 2006, Feller, 1999, Penn et al., 1998, Shatz, 1990 and Torborg and Feller, 2005). During this robust
pruning period (P5 in mouse), we used high resolution confocal imaging to assess the interactions between microglia and synaptic GSK-3 inhibitor inputs throughout the dLGN. http://www.selleckchem.com/products/PF-2341066.html Contralateral and ipsilateral presynaptic inputs from RGCs were visualized in the dLGN by intraocular injection of anterograde tracers, cholera toxin β subunit conjugated to Alexa 594 (CTB-594) and Alexa 647 (CTB-647), respectively (Figure 1A). Microglia were labeled using the CX3CR1+/GFP mouse line in which all microglia express EGFP under the control of fractalkine receptor, CX3CR1, expression (Figure 1 and see Figures S1 and S5 available online; Cardona et al.,
2006, Jung et al., 2000 and Saederup et al., 2010). At an age consistent with robust synaptic pruning (P5), microglial processes were in close association with RGC presynaptic inputs (Figure 1B and S2A). Upon closer examination, we detected numerous fluorescently labeled RGC inputs within the processes and soma of microglia (Figure 1B; Movies S1 and S2). Internalization
was further confirmed by assessing confocal z stacks through individual microglia (Movie S2). This specific example is a microglia sampled from a region containing similar densities of overlapping ipsilateral (blue) and contralateral (red) RGC inputs (Figure 1A) which are undergoing active synaptic remodeling to establish nonoverlapping eye-specific territories (Figure 2A; Godement et al., 1984, Guido, 2008, Huberman Levetiracetam et al., 2008, Sretavan and Shatz, 1986 and Ziburkus and Guido, 2006). Consistent with simultaneous pruning of inputs from both eyes, contralateral (red) and ipsilateral (blue) RGC inputs were engulfed and localized within the microglia (Figure 1B; Movies S1 and S2). In addition, consistent with widespread pruning of RGC inputs throughout the P5 dLGN, we observed engulfment of RGC inputs in all synaptic regions (monocular and binocular). These data suggest that microglia engulf RGC inputs undergoing active synaptic remodeling. To confirm that inputs are phagocytosed by microglia, RGC inputs from both eyes were labeled with CTB-594 and colocalization with CD68, a marker of lysosomes specific to microglia, was assessed in P5 dLGN. As suggested by previous dye-labeling experiments, the majority of engulfed RGC inputs were completely colocalized within lysosomal compartments (Figures 1C–1E).