Estrogen receptors in quail brain: a functional relationship to aromatase and aggressiveness

Estradiol (E2) mediates many of the activational effects of testosterone (T) on masculine reproductive and aggressive behaviors. Using Japanese quail (Coturnix coturnix japonica) as an animal model, together with a newly devised procedure for quantifying aggressiveness, we recently showed that aggression is E2-dependent and that individual differences in behavioral intensity are correlated with aromatase in the hypothalamus/preoptic area (HPOA). In this study we characterized estrogen receptors (ER) in quail brain and tested the hypothesis that aromatase in brain regulates T-induced behavioral responsiveness by regulating the quantity of E2 available for receptor binding. Based on standard binding assays and Sephadex LH-20 chromatography, quail brain ER was shown to be estrogen-specific, of high affinity (Kd = 0.88 nM), and of limited capacity with highest concentrations in limbic brain areas (Bmax 23-27 fmoles/gm HPOA). In addition, this ER adhered to DNA-cellulose under activating conditions. The quantitative relationship between aromatization, ER, and aggressiveness was tested in reproductively inactive (nonaggressive) males by treatment with T +/- the aromatase inhibitor 4-hydroxyandrostenedione (OHA). After 5 days, T markedly stimulated aggressiveness, and elevated aromatase and nuclear (occupied) ER in HPOA. Simultaneous treatment with OHA blocked effects on aggressiveness and aromatase, and lowered nuclear ER, but increased cytosolic (empty) ER. Total ER (nuclear plus cytosolic) was higher after T treatment whether or not OHA was administered, suggesting that androgen per se induces ER in quail HPOA.