Fig. 3.

Axon engulfment by OPCs. (A) OPC process in pink ingests an excitatory axon bouton (gray) at its tip. (Scale bar, 500 nm.) (B) 3D reconstruction reveals a small excitatory axon fragment (Ax) encapsulated within the OPC (pink) at the tip (white line, arrow). (Scale bar, 500 nm.) (C) 3D reconstruction shows the same axon (Ax)(arrow) without OPC surrounding it. The bouton tip is visible. (Scale bar, 500 nm.) (D) Ultrathin section slice of a large section of an inhibitory axon (Ax) collateral branch (white line) in gray ingested within the cytoplasm of the OPC (pink). Two PL (one in dashed circle) are adjacent to the ingested axon. (Scale bar, 500 nm.) (E) 3D rendered axon collateral branch encapsulated within the cytoplasm of the OPC (arrow, white line and outline) and phagolysosome within the cytoplasm (dashed circle). (Scale bar, 1μm.) (F) 3D reconstruction of the axon (Ax) in gray shows encapsulated branch (white line, arrow) without the surrounding OPC. (Scale bar, 1μm.) (G) Bar graph of ten individual isolated main branches (one each) of ten OPC cells were analyzed for ingestion events and categorized as either phagosome (PS)(pink) or phagolysosome (PL)(purple). (H) Bar graph of the same ten OPCs showing axons partially ingested typed as excitatory (E), inhibitory (I) or unsure (U). Excitatory axons were the most prevalent type ingested at 85.9% versus 7.7% for inhibitory.