Fig. 1. Temporal and spatial correlation of astrocyte differentiation and vascularization in the developing optic nerve. Longitudinal cryosections of developing rat optic nerves from E17 (A–C), E18 (D–F), E19 (G–I), E20 (J–L), and P1 (M–O) were stained by a GFAP antiserum (A, D, G,J, M), which is a specific marker of astrocytes. GFAP staining was scarce at E17 but was first detected near the surface of the nerve at E18. The intensity of the staining increased with age, extending more deeply into the nerve. The staining extended throughout the nerve by P1. Optic nerve sections of the same ages were double by two endothelial-specific markers, a VWF antiserum (B, E, H,K, N) and rhodamine-conjugated BSLI (C, F, I,L, O). VWF and BSLI labeling colocalized and displayed a similar time course and pattern to the GFAP staining. Scale bar, 100 μm