Androgen‐Dependent and ‐Independent Aromatase Activity Coexists with Androgen Receptors in Male Guinea‐Pig Brain

Using a microdissection technique we localized androgen receptors and aromatase activity (AA) in the brain of male guinea‐pigs. In addition, we evaluated the effects of castration and androgen replacement on androgen receptor dynamics and induction of AA. In the castrate animal, cytosolic androgen receptor content was highest in the basal hypothalamus, specifically in the median eminence‐arcuate nucleus (> 15 fmol mg protein ¹), while lesser levels were found in the preoptic regions and amygdala. Nuclear receptor content was highest (> 150 fmol mg DNA ⁻¹) in the median eminence‐arcuate nucleus, periventricular region of the preoptic area and cortical amygdala. All regions investigated showed a significant decrease in nuclear receptors following castration and an increase with androgen replacement. However, reciprocal changes in cytosolic androgen receptors were not always evident. Aromatase activity was high in the cortical amygdala, medial amygdala, periventricular region of the preoptic area and bed nucleus of the stria terminalis. Castration and androgen replacement had significant stimulatory effects on AA in the ventral medial hypothalamus, median eminence‐arcuate nucleus, cortical amygdala and periventricular regions of the preoptic area and anterior hypothalamus. Thus, androgen receptors and AA are unevenly distributed throughout the subcortical regions of the male guinea‐pig brain and respond differently to endocrine stimuli. Our data demonstrate that AA is androgen‐dependent in some subcortical regions which contain androgen receptors. Even though nuclear receptors in all brain regions were affected by castration and dihydrotestosterone treatment, the events were not always linked to AA regulation. Due to this difference in regulation, AA may serve divergent functions in guinea‐pig brain.