text: Nuclear uptake of estrogens in the male dove hypothalamus: relationship to aromatase activity and behavioral effects.
  The natural estrogen, estradiol-17 beta, and a synthetic agonist, diethyl stilbestrol (DES), accumulated selectively in cell nuclei of the male dove preoptic area and posterior hypothalamus following intramuscular injection of the corresponding 3H-labelled tracers. Nuclear incorporation of radioactivity was saturable and specific, as shown by the effect of competition doses of unlabelled estrogens. The non-aromatizable androgen, 5 alpha-dihydrotestosterone (DHT), did not compete with estrogens for nuclear binding sites, indicating that cross-reaction with androgen receptors is unlikely. Estradiol uptake was higher in the preoptic area than in the posterior hypothalamus, whereas DES uptake did not differ significantly between these areas. Although both brain areas are likely to contain specific estrogen receptors, only the preoptic area is known to be directly involved in the control of male precopulatory courtship behavior in the dove. Aromatase activity responsible for the local conversion of testosterone to biologically active estradiol-17 beta, measured in vitro, was also much higher in the preoptic and posterior hypothalamic areas than in adjacent areas of the basal forebrain and hypothalamus. The similarity in localization of aromatase activity and intranuclear uptake of estradiol indicates that the formation of estrogen may occur only within discrete brain areas containing specific estrogen receptors. Intranuclear uptake of DES in the preoptic area, which is half that of estradiol, is correlated with lower effectiveness both in inducing aromatase activity in the preoptic area and in eliciting an estrogen-dependent behavior in castrated males. The effectiveness of estrogens on behavior in the male dove is likely to depend upon characteristics of estrogen receptors in the preoptic area.