<p>A1–D2: Labeled cells in the RA at post-hatching day (P) 45 (A1, A2), the LMAN at P35 (B1, B2), the HVC at P45 (C1, C2), and in Area X at P35 (D1, D2). E-H: Comparisons of the densities of Bad mRNA-positive cells in the RA (E), LMAN (F), HVC (G) and Area X (H) between males and females. Borders of the song nuclei (dashed lines) were determined with the help of another set of Nissl-stained sections. The Nissl-defined border of the female Area X was difficult to clearly identify, and the dashed lines in D2 indicate the approximate region corresponding to the male Area X. Dorsal is up and caudal is right. Scale bar = 200 μm in A1–C2 and 300 μm in D1–D2. The data are expressed as the mean ± SEM.</p
