In situ hybridization for HSD17B4 in P5 and adult zebra finch song nuclei. (A, B) Hybridization of P5 male (A) and P5 female (B) brain sections with sense-configured HSD17B4 riboprobe. Absence of detectable labeling demonstrates specificity of hybridization. (C, D) Comparison of HSD17B4 hybridization in P5 male (C) and female (D) brains with antisense-configured riboprobe shows label in the nidopallium where song nucleus LMAN (arrows) is located in adult males. In this region, HSD17B4 shows a significant (p = 0.021) sex difference in expression level. (E) HSD17B4 hybridization was also detected in the song nucleus HVC in adult males (arrows). (F) HVC was not visible in adult females (arrows denote area of HVC but no detectable hybridization), but the telencephalic levels of HSD17B4 expression were significantly (p = 0.016) higher in adult males than females. Scale bar in A = 1 mm (applies to A-D), scale bar in E = 1 mm (applies to E, F).