Positive effects of substituted phenol compounds on the TSA-POD reaction. Lateral views of 1-dpf zebrafish embryos hybridized with a digoxigenin-labeled antisense RNA probe specific for nkx6.1 are shown with anterior to the left. (A) Control (CTL); (B, C) vanillin added; (D, E) 4-iodophenol added. In all embryos shown, dextran sulfate was included in the hybridization and TSA-POD reaction. Above each panel signal-to-noise ratios (s/n) and compound concentrations are indicated. Black and white pictures were recorded with identical exposure times. Images were false-colored with help of the ImageJ software and no further adjustments or other image processing were performed. Scale bar = 100 μm.