Signaling pathways required for SDF-1-mediated RGC survival. The average number of RGCs per field 48 hr after plating is shown for each condition in four independent experiments. Each inhibitor was tested in the presence or absence of 100 ng/ml SDF-1. A, AMD3100 (20 μm), an antagonist of SDF-1 binding to CXCR4, does not affect RGC survival by itself but blocks the survival-enhancing effect of SDF-1. The Gi inhibitor PTX (100 ng/ml) does not affect RGC survival by itself but blocks the survival-enhancing effect of SDF-1. B, HxB-gp120 (100 ng/ml), anantagonist of SDF-1 binding to CXCR4, does not affect RGC survival by itself but blocks the survival-enhancing effect of SDF-1. JRFL-gp120 (100 ng/ml) does not antagonize SDF-1 binding and does not block its survival effect C, The cAMP antagonist Rp-cAMPS (20 μm) does not affect RGC survival by itself but blocks the survival-enhancing effect of SDF-1. The cGMP antagonist Rp-cGMPs (20 μm) has a lesser effect on SDF-1 activity than the cAMP antagonist. D, The PKA inhibitor PKI (200 nm) does not affect RGC survival by itself but blocks the survival-enhancing effect of SDF-1, whereas a 1 μm concentration of the PKG inhibitor KT5823 is less effective in blocking the effect of SDF-1. E, The survival effect of SDF-1 is also blocked by a 20 μm concentration of the MAP kinase inhibitor PD98059. In contrast, a 20 μm concentration of the PI-3 kinase inhibitor LY294002 does not reduce the effect of SDF-1. p values were calculated by comparing each population with the untreated one, and those with an asterisk were obtained comparing each population with the SDF-1-treated one using a two-tailed test with different variances.