Developmental Regulation of the Distribution of Aromatase- and Estrogen-Receptor- mRNA-Expressing Cells in the Zebra Finch Brain

Abstract

Strong evidence exists for the masculinizing effects of estrogen on the neural network that controls song learning and behavior in zebra finches. However, the mechanisms by which estrogen acts to influence the development of this circuitry are not well understood. In this study, we used in situ hybridization to detect the distribution of cells expressing mRNAs for AROM and ERα at postnatal days 5–25 (P5–25). Our findings revealed developmental regulation of both mRNAs in the neostriatum, archistriatum, hippocampus, diencephalon and midbrain. Within the vocal control circuitry, cells expressing ERα mRNA were found in the medial HVC (P10–25), archistriatum lateral to the RA (Ad; P25), in the ICo (P5–25), and along the fiber tract containing efferents from the RA. High levels of AROM mRNA were found in the neostriatum, including both the lateral and mMAN and along their projections to the RA and HVC, respectively, (P5–25), in the archistriatum (P18–25) and around RA (P18). Codistribution of the two mRNAs occurred along the border of the HVC suggesting that in this region, local synthesis of estrogen may be acting through its nuclear receptor to regulate gene transcription. Taken together, our findings show that the neural circuitry controlling song may be exposed to the effects of estrogen during early postnatal development. However, in most of the song control regions, these mRNAs were not expressed together either temporally or spatially, indicating that AROM may have a role in the development of the song system independent of ERα.

ParallelFoxP1andFoxP2Expression in Songbird and Human Brain Predicts Functional Interaction

“…Analysis of FoxP gene expression was performed essentially as described by Jacobs et al (1999), except that frozen sections were thaw-mounted on Superfrost Plus microscope slides (Fisher Scientific, Pittsburgh, PA) and postfixed with 4% paraformaldehyde, pH 7.4. Briefly, a series of 20 m thick coronal or sagittal sections were hybridized with […”

Mismatch in sexual dimorphism of developing song and song control system in blue-capped cordon-bleus, a songbird species with singing females and males

“…Initial sex differences in the size of HVC and RA neuron pools of zebra finches are likely genetically determined (Wade and Arnold, 1996;Gahr et al, 1998;Agate et al, 2003) suggesting a similar explanation for the early sex differences of cordonbleu song areas. The subsequent ontogenetic development of the song system might be linked to gonadal hormone activity although clear proof for this is missing in any songbird species except for the observation that androgen receptors are expressed in the developing HVC and RA (Gahr, 1996;Gahr and Metzdorf, 1999;Jacobs et al, 1999;Kim et al, 2004) and that estrogen receptors occur in the juvenile HVC (Gahr and Konishi, 1988;Gahr, 1996). Gonadal hormones are likely to promote the survival of song neurons to a developmental stage that allows the intra-song system connectivity to form, which is thought necessary for song learning and development.…”

Zebra finch sexual differentiation: The aromatization hypothesis revisited

“…After 2 weeks in vitro, high levels of aromatase activity were detected in these cultures, but no sex differences. The development of aromatase expression was also investigated by in situ hybridization in the telencephalic song control nuclei on post-hatching days 5, 10, 18, and 25 (Jacobs et al, 1999). Aromatase mRNA was expressed in lMAN at all ages.…”

“…In general, relatively few neurons containing estrogen receptors have been observed within their song control regions, although more were detected in HVC when the protein was investigated than when binding of 3H-E2 was assessed (Gahr and Konishi, 1988;Nordeen et al, 1987). The distribution of cells containing estrogen receptor mRNA was investigated in developing males and females, and HVC was the only region that showed substantial labeling (posthatching days 5-25), but without any obvious sex differences (Jacobs et al, 1999). These results suggest that, while it is possible that estradiol acts at other sites to influence development of the telencephalic song circuit, it is unlikely that it is a primary mechanism for directly modulating sexual differentiation of that system.…”