A dose–response study of estradiol's effects on the developing zebra finch song system

Abstract

To gauge the sensitivity of the female zebra finch song system to estradiol (E2), we used subcutaneous implants to administer various doses of E2 to hatchling female zebra finches. Four different doses of E2 were administered: 50, 15, 5 and 0 μg via subcutaneous silicon "ropes" at hatching, and the brains were examined in adulthood. Further, we examined whether masculinization was all-or-none once a threshold was reached or if the morphology of the song system would show a graded response to the various doses of E2. Finally, we asked if the various dependent measures-volume of song nuclei, neuron size, and neuron number-would show differential sensitivity to E2.Fifteen micrograms was sufficient to masculinize many aspects of the song system and was often as effective as 50 μg, causing a dramatic difference relative to the 0 μg group. Different aspects of the song system seemed differentially sensitive to the effects of E2: volumes of song control nuclei, the size of RA neurons, and the number of HVC neurons were significantly masculinized by 15 μg E2, but the number of RA neurons and HVC and lMAN soma sizes required 50 μg. The results suggest that several developmental processes are influenced by E2, possibly because of multiple sites of action or multiple processes that respond to E2.

The effects of estradiol on 17β-hydroxysteroid dehydrogenase type IV and androgen receptor expression in the developing zebra finch song system

“…In addition to considering different developmental time points (day 11 vs. day 25 in the present study), our study also used a lower dose of E2 (50 μg) than did the earlier study (83 μg), which may account for this difference. Nonetheless, another study found that our dosage was sufficient to masculinize many morphological measures in the song regions of females (Grisham et al, 2008), and increased AR mRNA expression in HVC in the present study. AR mRNA in Area X may therefore be less responsive to E2.…”

Masculinisation of the Zebra Finch Song System: Roles of Oestradiol and the Z‐chromosome Gene Tubulin‐Specific Chaperone Protein A

“…In addition, because we are unaware of any report of the effects of early E 2 on juvenile LMAN volume [but, for adult brains, see Grisham et al . (], the volume of this region was quantified in all individuals. Cross‐sectional areas were determined by tracing the border of LMAN on each side of the brain using imagej in each section that it was visible.…”

Sex differences and rapid estrogen signaling: A look at songbird audition

“…The major portion of sexual differentiation in young zebra finches occurs during the incubation and post-hatching periods, which has allowed particular accessibility to manipulations during critical windows of differentiation and song learning. Treatment with E2 in the first two weeks of hatching is a potent manipulation that can masculinize female hatchlings via organizational actions, leading to females that are able to sing in adulthood (Adkins-Regan et al , 1994, Grisham et al , 2008, Gurney & Konishi, 1980, Konishi & Akutagawa, 1988, Nordeen et al , 1986, Thompson et al , 2011). …”