AROMATASE-IMMUNOREACTIVITY IS LOCALIZED SPECIFICALLY IN NEURONS IN THE DEVELOPING MOUSE HYPOTHALAMUS AND CORTEX

Local formation of oestrogens from androgens by aromatase cytochrome P -450 within brain cells is crucial for the sexual differentiation of t he mammalian CNS. Aromatase activity has been detected in several brai n regions of the developing rodent brain. In the present study, we use d a mouse-specific, peptide-generated, polyclonal aromatase antibody t o determine whether neurones and/or glial cells in the developing brai n are involved in androgen aromatization and if aromatase-immunoreacti ve (Arom-IR) cells exhibit a sex-specific distribution and regional-sp ecific morphological characteristics. For these experiments, gender-sp ecific cell cultures were prepared from embryonic day 15 mouse hypotha lamus and cortex. Specificity of the immunoreaction was confirmed by W estern-blot analysis and by inhibition of aromatase activity using tis sue homogenates from mouse ovaries and male newborn hypothalamus and f rom male hypothalamic cultures with known aromatase activity, respecti vely. Arom-IR cells were found in both hypothalamic and cortical cultu res. Double-labeling experiments revealed that Arom-IR cells co-staine d only for the neuronal marker MAP II, but never for glial markers. Th erefore aromatase immunoreactivity is specifically neuronal. Regional differences in the morphology of Arom-IR neurones were observed betwee n both brain regions. In hypothalamic cultures, IR-neurones represente d a heterologeous population of phenotypes (magnocellular, small bipol ar and multipolar neurones with long processes showing varicose-like s tructures or without processes). Cortical Arom-IR neurones were always oval in shape with short or no IR-processes. Sexual dimorphisms in nu mbers of Arom-IR neurones were found in the hypothalamus with signific antly higher cell numbers in male cultures. In the cortex, numbers of Arom-IR neurones were low compared to the hypothalmus and no sex diffe rences were observed. These data provide the first direct evidence tha t aromatase is localised specifically in neurones of the developing mo use brain. Furthermore, we describe distinct regional and sexual dimor phisms in numbers and morphological characteristics of Arom-IR cells b etween the cortex and hypothalamus.