Rapid Effects of 17β-estradiol on Aggressive Behavior in Songbirds: Environmental and Genetic Influences

Contribution to Special Issue on Fast effects of steroids. 17β-estradiol (E) has numerous rapid effects on the brain and behavior. This review focuses on the rapid effects of E on aggression, an important social behavior, in songbirds. First, we highlight the contributions of studies on song sparrows, which reveal that seasonal changes in the environment profoundly influence the capacity of E to rapidly alter aggressive behavior. E administration to male song sparrows increases aggression within 20 min in the non-breeding season, but not in the breeding season. Furthermore, E rapidly modulates several phosphoproteins in the song sparrow brain. In particular, E rapidly affects pCREB in the medial preoptic nucleus, in the non-breeding season only. Second, we describe studies of the white-throated sparrow, which reveal how a genetic polymorphism may influence the rapid effects of E on aggression. In this species, a chromosomal rearrangement that includes ESR1, which encodes estrogen receptor α (ERα), affects ERα expression in the brain and the ability of E to rapidly promote aggression. Third, we summarize studies showing that aggressive interactions rapidly affect levels of E and other steroids, both in the blood and in specific brain regions, and the emerging potential for steroid profiling by liquid chromatography tandem mass spectrometry (LC-MS/MS). Such studies of songbirds demonstrate the value of an ethologically informed approach, in order to reveal how steroids act rapidly on the brain to alter naturally-occurring behavior.