Effects of hydrogen peroxide and dextran sulfate on Fast Red and Fast Blue detection. 24-hpf embryos were hybridized to a shha dinitrophenyl-labeled RNA probe, which was visualized by AP-Fast Blue (A-D) or AP-Fast Red (E-H) chromogenic staining for 55 min and 80 min, respectively. Lateral views of embryonic brains are shown with anterior to the left. On top of each panel it is indicated whether embryos were permeabilized with 2% hydrogen peroxide (H2O2) and whether 5% dextran sulfate (dextran-s) was added to the hybridization buffer. Strongest signals were obtained when hydrogen peroxide treated embryos were hybridized in the presence of dextran sulfate (D,H). Embryos were viewed on an Axioplan II microscope and images were recorded with an Axiocam digital camera. Scale bar is 100 μm.