The Contribution Of Genes And Hormones To The Sexual Differention Of The Zebra Finch Song System

Recent studies in the zebra finch suggest the sexual differentiation of the song system and singing behavior may not be solely driven by steroid hormones organizing the brain, and may be genetically driven. In fact, genes and hormones might act together to produce sexual differentiation of the brain. To test this hypothesis, animals were implanted with a 1mm pellet containing 50ug of 17b-estradiol or a blank pellet on the third day post-hatching. At post-hatch day 25, the brains were collected and a double label fluorescence in situ hybridization protocol using biotin and digoxigenin-tagged mRNA probes was used to simultaneously label androgen receptor mRNA CK313884 mRNA (the gene coding for 17β-Hydroxysteroid Dehydrogenase type IV) in three areas of the song system. Estradiol treatments increased the number of cells expressing of CK313884 in the HVC of the female zebra finch, but did not increase co-localization of 17BHSD4 and AR. For male zebra finches estradiol treatment decreased the number of cells expressing AR and 17BHSD4 in HVC and the number of cells expressing AR in Area X. This suggests a limit to which estradiol will contribute to masculinization. These results lend further evidence to support the hypothesis that genes and hormones act in concert to sexually differentiate the song system in the zebra finch