Sites of aromatization of [H]testosterone in forebrain of male, female and androgen receptor-deficient Tfm mice: an autoradiographic study

The distribution of radioactivity after injection of 3H]testosterone was studied in the forebrain of adult mice by thaw-mount autoradiography. Nuclear labeling was high in neurons in the dorsal part of the medial nucleus of the amygdala and in the dorsocaudal part of the bed nucleus of the stria terminalis. Low nuclear uptake occurred in the medial preoptic nucleus, in mediobasal hypothalamic nuclei and in the ventromedial amygdala. Nuclear concentration of radioactivity was not influenced by competition with dihydrotestosterone and was present in androgen receptor deficient Tfm mice. It was totally abolished by competition with estradiol. This indicates that in the brain 3H]testosterone is converted to estrogenic metabolites which bind to estrogen receptors. Nuclear labeling after 3H]testosterone was restricted to a few of the brain nuclei, known to contain estrogen receptors indicating that aromatization occurs only in select regions. The results suggest that testosterone acts on the brain via estrogen receptors.