THE ACTIVITY AND EXPRESSION OF AROMATASE IN SONGBIRDS

Songbirds have emerged as extremely important animals for investigatin g sex steroid hormone effects on the central nervous system, The mascu linizing effects of exogenous estrogen on the neural circuits controll ing song in female zebra finches are well documented, There is evidenc e that estrogens are necessary for the full activation of singing beha vior in several species. These kinds of studies have led us and others to investigate the mechanisms whereby estrogens are made available to the brains of songbirds during development and adulthood. In this art icle, I review results of some of these studies examining the estrogen synthetic enzyme aromatase and its expression and activity in brain a nd in other tissues of songbirds, I will discuss some results and thou ghts we have about the interactions of aromatase with the two remainin g androgen-metabolizing enzymes in the avian brain, 5 alpha-reductase, the enzyme that converts T into the active androgen 5 alpha-dihydrote stosterone (DHT); and 5 beta-reductase, the enzyme that converts T int o the inactive 5 beta-DHT. Finally, I will consider some ideas raised by these studies concerning potential sources of the androgen substrat e for brain aromatization as well as some possible new functions that aromatase might be playing in the songbird telencephalon. (C) 1997 Els evier Science Inc.