Fluorescence photomicrographs of adult-formed neurons in Area X, the hippocampus, and high vocal center (HVC) from an adult male zebra finch. Row 1: BrdU⁺ cell nuclei in Area X, the hippocampus, and HVC visualized using a FITC filter. Row 2: The same fields of view showing BrdU⁺/Hu⁺ neurons, revealed with a dual FITC-rhodamine filter to show colocalization of the two markers. Row 3: The same fields of view showing Hu⁺ neuronal label in the cytoplasm, visualized with a rhodamine filter. Scale bars, 10 µm. The fluorophore used for visualizing BrdU was Alexa 488 (Molecular Probes); the neuron-specific protein Hu was labeled with Cy-3 (Jackson ImmunoResearch Laboratories). From Pytte et al. 2007; reprinted with permission from Wiley Periodicals, Inc.