What makes the Muller cell GFAP response so dramatic is the fact that these filamentous proteins are almost exclusively localized to the endfoot region in a normal retina (red/yellow labeling, Fig. 23A), and in some species such as rats and mice, barely detectable by current immunocytochemical technology (Figs. 23C, Bignami and Dahl, 1979; Eisenfeld et al., 1984; Sarthy and Ripps, 2001).