Developmental regulation of the distribution of aromatase- and estrogen-receptor-mRNA-expressing cells in the zebra finch brain

Strong evidence exists for the masculinizing effects of estrogen on the neu ral network that controls song learning and behavior in zebra finches. Howe ver, the mechanisms by which estrogen acts to influence the development of this circuitry are not well understood, In this study, we used in situ hybr idization to detect the distribution of cells expressing mRNAs for AROM and ER alpha at postnatal days 5-25 (P5-25). Our findings revealed development al regulation of both mRNAs in the neostriatum, archistriatum, hippocampus, diencephalon and midbrain. Within the vocal control circuitry, cells expre ssing ER alpha mRNA were found in the medial HVC (P10-25), archistriatum la teral to the RA (Ad; P25), in the ICo (P5-25), and along the fiber tract co ntaining efferents from the RA. High levels of AROM mRNA were found in the neostriatum, including both the lateral and mMAN and along their projection s to the RA and HVC, respectively, (P5-25), in the archistriatum (P18-25) a nd around RA (P18). Codistribution of the two mRNAs occurred along the bord er of the HVC suggesting that in this region, local synthesis of estrogen m ay be acting through its nuclear receptor to regulate gene transcription. T aken together, our findings show that the neural circuitry controlling song may be exposed to the effects of estrogen during early postnatal developme nt. However, in most of the song control regions, these mRNAs were! not exp ressed together either temporally or spatially, indicating that AROM may ha ve a role in the development of the song system independent of ER alpha. Co pyright (C) 2000 S. Karger AG, Basel.