Nuclear binding of the oestrogen receptor of neonatal rat brain after injection of oestrogens and androgens; localization and sex differences.

We have investigated the nuclear binding of [3H]oestradiol in the neonatal rat brain. The nuclear bound receptor, defined as the diethylstilboestrol (DES) suppressed nuclear bound radioactivity, showed similar sedimentation properties and time course to nuclear bound steroid receptors in other target tissues. After intracerebral injection we found that nuclear binding of [3H]oestradiol was localized to the hypothalamic/ amygdaloid region with relatively little binding in cortical and cerebellar regions. After subcutaneous injection there was less difference between the hypothalamic and cortical regions, though there was still very low binding in the cerebellum. A deficit in nuclear binding of [3H]oestradiol was found in the hypothalamic amygdaloid region of the male compared to the female, which was dependent on the presence of the neonatal testis. We also found that unlabelled testosterone reduced the nuclear binding of [3H]oestradiol when given 3 h before the radioactive steroid, and this reduction was seen predominantly in the hypothalamic/amygdaloid region. The non-aromatizable androgen, 5alpha-dihydrotestosterone, was without effect on [3H]oestradiol binding. After injection of [3H]testosterone, receptor bound radioactivity was found exclusively in nuclei from the hypothalamic/amygdaloid region, this radioactivity was competed out by DES and testosterone but not by dihydrotestosterone. This study provides evidence that neurally aromatized androgen may bind to an oestrogen receptor in the neonatal hypothalamic/amygdaloid region and effect its translocation into the cell nucleus.