Sex steroids act on the developing veloping zebra finch telencephalon. Cultures were and adult telencephalon of songbirds to organize and treated for 0-72 h with sex steroids (T, E 2 , 5a-DHT, activate the neural circuits required for the learning and 5b-DHT) or with dibutyryl cAMP. Afterward, and production of song. Presumably, the availability activities of aromatase, 5a-, and 5b-reductase were of active androgens and estrogens to steroid-sensitive determined or total RNA was extracted for Northern neural circuits controlling song is modulated by the analysis. Treatments with cAMP increased both local expression of androgen-metabolizing enzymes.
aromatase activity and aromatase mRNA levels by Two enzymes, 5a-and 5b-reductase, are expressed 220%. E 2 significantly reduced aromatase activity by widely in the songbird telencephalon, as they are in the an average of 65%, whereas 5a-and 5b-DHT had no telencephalons of other avian species. These enzymes effect on aromatase activity. Compared to untreated convert circulating testosterone (T) into the active controls, E 2 treatment decreased aromatase mRNA and inactive metabolites, 5a-and 5b-dihydrotestoslevels by 56%. None of these treatments consistently terone (DHT), respectively. A third enzyme, aromaaffected either 5a-or 5b-reductase activities. These tase, converts T into estradiol (E 2 ) and is expressed at results suggest that telencephalic E 2 may regulate its unusually high levels in several regions of the songbird own synthesis by repression of aromatase expression, telencephalon. In many tissues, including the brain, whereas factors that upregulate cAMP in the telenthe regulation of expression of one or more of these cephalon can increase the local concentrations of E 2 . enzymes can be a critical feature of their ability to