Apoptosis assays on dre-oprm1 morphants. TUNEL staining on control and dre-oprm1 morphants of 24 and 48 hpf. The apoptotic nuclei are positive for peroxidase labeling. Lateral views are shown, and embryos are oriented anterior toward the left and posterior toward the right. A total of 25 embryos were used for each treatment and for each time point, and the experiment was repeated three times.