Cloning and expression analysis of retinoic acid receptors in the zebra finch brain

The vitamin A derivative retinoic acid is produced postembryonically in discrete portions of the songbird brain, including some of the nuclei involved in song production and song learning, and its synthesis is required for the normal maturation of song behavior. To identify the brain targets for retinoic acid action, we cloned the zebra finch homologs of the alpha, beta, and gamma classes of retinoic acid receptors (RARs). In situ hybridization analysis revealed that the mRNAs for all three RARs are expressed at different levels in several brain areas, with a broader distribution than the mRNA for retinaldehyde-specific aldehyde dehydrogenase (zRalDH), a retinoic acid-synthesizing enzyme. Detectable RAR expression was found in all nuclei of the song control system, with the most marked expression occurring within the striatal song nucleus area X. These observations are consistent with a persistent action of retinoic acid in the postembryonic and adult songbird brain and provide further evidence for an involvement of retinoic acid signaling in the control of learned vocal behavior in a songbird species. They also suggest that the striatum is a major target of retinoic acid in songbirds.