Genome–brain–behavior interdependencies as a framework to understand hormone effects on learned behavior

Dynamic variation in forebrain estradiol levels during song learning

“…If the sex difference in baseline E2 levels that emerges in the late juvenile/subadult stage is involved in the emergence and/or maintenance of masculinized song circuitry, the rising neuroestrogen tone in the brain of males is undoubtedly acting in concert with other hormonal and neurogenetic factors during this developmental timeline (Jin and Clayton, ; London et al, ; Tomaszycki et al, ; London, ). There is abundant evidence that E2 acts during a developmental time period (i.e., within the first 2 weeks) to masculinize the song system, and the masculinizing effects of E2 on select song system nuclei can still be observed up to ∼45 dph (Konishi and Akutagawa, ).…”

“…A role for brain‐derived estrogens in the developmental masculinization of the zebra finch forebrain has been suggested by three primary lines of evidence. First, the enzymes necessary for the synthesis of 17‐beta‐estradiol (E2) de novo from cholesterol are expressed in the brain of juvenile zebra finches from hatching onward (Shen et al, ; Jacobs et al, ; London et al, ; London and Schlinger, ; London, ). Second, although female zebra finches ordinarily do not sing, treatment with exogenous E2 within the first 2 weeks after hatching can potently masculinize the brain, resulting in females that are able to sing in adulthood (Gurney and Konishi, ; Nordeen et al, ; Konishi and Akutagawa, ; Adkins‐Regan et al, ; Grisham et al, ; Thompson et al, ).…”