Conversion of androgen to estrogen in the rat brain is catalyzed by aromatase enzymes. The maximum concentrations of these enzymes are found within the hypothalamus and amygdala, where they appear to play an important role in the process by which androgens affect both behavior and neuroendocrine function. In the present study, we measured the levels of aromatase activity (AA) in 20 nuclei and brain regions of the adult rat brain. Individual nuclei were microdissected from 600-μm frozen sections. Tissues from 3 animals were pooled, and AA was measured by an in vitro radiometric assay that quantifies the stereospecific production of 3H2O from [1β-3H]androstenedione as an index of estrogen formation. Our results provide a quantitative profile of AA in specific hypothalamic and limbic nuclei of the rat brain as well as information on the control of AA within these discrete regions.
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