UCLA

Recent studies have shown that rapid modulation of the estrogen synthesizing enzyme, aromatase, regulates estrogen production in neurons to affect behavior and cognition. In songbirds, aromatase is expressed at high levels in the hippocampus (HP), hypothalamus (HYP), and caudomedial nidopallium (NCM), where estrogens have been shown to affect learning and memory (HP), reproductive behavior (HYP), and auditory processing (NCM). Previous studies, largely in the HYP of quail, show that aromatase activity is down-regulated by Ca2+-dependent phosphorylation. Here, using zebra finches (Taeniopygia guttata), we ask if similar mechanisms are at work in the songbird HYP and if there are sex differences and differences in aromatase modulation between the HYP, HP and NCM. We quantified the conversion of [3H]androstenedione to estrone with a well-established in vitro assay to measure the effects of Ca2+, Mg2+, ATP, and an inhibitor of kinase activity in homogenates and partially purified brain fractions. We report a rapid down-regulation of aromatase activity in the presence of phosphorylating conditions across all three brain regions and both sexes. However, regional differences were seen in response to individual cofactor concentrations, some of which were improved by partial purification of the homogenates. Furthermore, while low concentrations of ATP inhibited aromatase activity, unexpectedly, inhibition was no longer seen with high ATP concentrations. These results provide evidence for a regional and temporal specificity in aromatase activity that has not been observed in songbirds.