Journal of Neuroscience, Vol 6, 734-738, Copyright © 1986 by Society for Neuroscience
Estrogen establishes sex differences in androgen accumulation in zebra finch brain
KW Nordeen, EJ Nordeen and AP Arnold
In zebra finches, androgens stimulate the production of a learned courtship
song in males but not in females. Corresponding to this behavioral
dimorphism, neural regions controlling the learning and production of song
are much larger in males than in females. In two of these song-related
brain regions, magnocellular nucleus of the anterior neostriatum (MAN) and
hyperstriatum ventrale pars caudale (HVc), males have a larger percentage
of androgen-accumulating cells than females. Since sex differences in the
capacity for song and in the size of songrelated nuclei are established by
gonadal hormones shortly after hatching, we determined whether the early
hormonal environment also establishes sex differences in androgen
accumulation within MAN and HVc. Newly hatched female zebra finches
received either estradiol (E2) or cholesterol (Ch). Three to six months
later, E2-females, Ch-females, and normal adult males were gonadectomized
and injected 24 hr later with 3H-dihydrotestosterone. Autoradiograms were
prepared, and the incidence of androgen-labeled cells was determined for
MAN, HVc, and a control region, the lateral septal nucleus (SL). In
females, early E2 exposure dramatically increases the percentage of
androgen-accumulating cells in MAN and HVc, without influencing androgen
accumulation in SL. In MAN and HVc, the percentage of
androgen-concentrating cells in E2- females approximates that observed in
normal adult males. Cells also tended to be more densely labeled in
E2-females than in Ch-females. Since early E2 exposure renders the female
song system neuroanatomically and functionally responsive to androgens, we
suggest that E2 establishes this responsiveness by regulating the number of
androgen target neurons within MAN and HVc.