Aromatase inhibition rapidly affects in a reversible manner distinct features of birdsong

Abstract

Recent evidence has implicated steroid hormones, specifically estrogens, in the rapid modulation of cognitive processes. Songbirds have been a useful model system in the study of complex cognitive processes including birdsong, a naturally learned vocal behavior regulated by a discrete steroid-sensitive telencephalic circuitry. Singing behavior is known to be regulated by long-term actions of estrogens but rapid steroid modulation of this behavior has never been examined. We investigated if acute actions of estrogens regulate birdsong in canaries (Serinus canaria). In the morning, male canaries sing within minutes after light onset. Birds were injected with fadrozole, a potent aromatase inhibitor, or vehicle within 2-5 minutes after lights on to implement a within-subjects experimental design. This single injection of fadrozole reduced the motivation to sing as well as song acoustic stereotypy, a measure of consistency over song renditions, on the same day. By the next day, however, all song measures that were affected had returned to baseline. This study indicates that estrogens also act in a rapid fashion to regulate two distinct features of song, a learned vocal behavior.

Figure 1. Effects of acute aromatase inhibition with fadrozole on multiple measures of song.

Representative songs from a bird treated with (A) vehicle (VEH) versus (B) fadrozole (FAD). Treatment affected measures of the motivation to sing including (C) the Latency to sing, (D) % Time singing, (E) Song duration, and a measure of song stereotypy (F) Song bandwidth coefficient of variation (CV). The higher the CV, the lower the stereotypy and vice versa. Bars represent the mean of all data in the corresponding group. Asterisks indicate a significant difference. Differences were considered significant at p < 0.05.

Figure 2

Comparison of song features reflecting the motivation to sing (A,B) and the song stereotypy (C) on the baseline (BL) day and on the day after fadrozole (FAD) injection. CV = Coefficient of Variation. The higher the CV, the lower the stereotypy and vice versa. Bars represent the mean of all data in the corresponding group. In all cases differences were non-significant (ns).

Figure 3. Effects of fadrozole on aromatase activity (AA) at two different time points after injection.

Fmol/h = fentomoles per hour. The numbers within each bar represent sample size. Asterisks indicate a significant difference between the AA in the respective brain regions as indicated by Bonferroni-corrected planned comparisons at the different time points. Bars represent the means ± standard errors. Differences were considered significant at p < 0.05.