Fig. 7

Remyelination and axon survival. Six weeks after lysolecithin microinjection, normally myelinated axons, characterized by pale axoplasm, neurofilaments, microtubules, mitochondria, and smooth endoplasm reticulum, are more numerous in lesions in control (a–c) than in OPC-NG2ko (d–f) mice. Panel (a) shows a well-myelinated axon (arrow, magnified in b) and a thinly remyelinated axon (arrowhead, magnified in c). Panel (d) shows an empty axon-like structure (double arrowhead, magnified in e) and an axon with degenerated axoplasm (asterisk, magnified in f). These structures are more numerous in OPC-NG2ko mice than in control mice. Quantitative analysis of pan-neurofilament-positive axons lacking association with MBP (from data represented in Fig. 6d–f) reveals increased numbers of unmyelinated axons in OPC-NG2ko and My-NG2ko mice (g). h Plotting g values (ratio of axon diameter to myelinated axon diameter) against axon diameter (h) reveals reduced myelin thickness (increased g value) in lesions in both OPC-NG2ko and My-NG2ko mice. In comparison with lesions in control mice (i), fewer NF-positive axons of all sizes are seen in lesions in OPC-NG2ko (j) or My-NG2ko (k) animals. Blue, green, and red colors indicate axons with diameters smaller than 1 μm, between 1 and 2.5 μm, and larger than 2.5 μm, respectively, as determined with image analysis software. Scale bars indicate 2 μm (a, d), 500 nm (b, c, f), 1 μm (e), and 40 μm (i–k)