Testosterone regulates the activity and expression of aromatase in the canary neostriaturn

The estrogen synthesizing enzyme, P450 aromatase, plays a critical role in the regulation of vertebrate sexual behavior. Songbirds differ from other a vian species in the distribution and expression of aromatase in the telence phalon. The highest concentration of aromatase in the songbird brain is fou nd in the caudomedial neostriatum (NCM). This area surrounds the only nucle us of the neural song system that contains estrogen receptors, the high voc al center (HVC). It has been suggested that estrogen produced in NCM via ar omatization of circulating testosterone (T) is involved in song development and adult song plasticity. The modalities of regulation of aromatase in NC M are not well understood, and some studies suggest that in NCM, unlike in the preoptic-hypothalamic areas, aromatase is not regulated by androgen and /or estrogen. In this work, we studied whether the treatment of female cana ries with T, which induces the development of malelike song and the masculi nization of the song system, also induces an increase in the expression and activity of aromatase in NCM. Our results show that both the expression an d activity of aromatase in NCM increase in female canaries following T trea tment. This study provides the first direct evidence that T regulates telen cephalic aromatase in songbirds, and suggests that an increase in estrogen production in NCM might be functional in neural and behavioral plasticity d uring phases of song organization. (C) 2001 John Wiley & Sons. Inc.