title: Developmental sex differences in brain aromatase activity are related to androgen level.
abstract: Sex differences in the metabolism of testosterone (T) in the developing brain of quail were examined using an in vitro microassay. During each developmental stage (day before hatching, hatching and 2 days after hatching) aromatase activity was higher in hypothalamic areas than in a control neostriatal area. There was no sex difference in oestradiol-17 beta (E2) formation in the late embryonic brain or at hatching. But aromatase activity in the male preoptic-anterior hypothalamic area was 50% higher than in females by day 2. No regional differences in brain 5 beta-reductase activity were detected at any of the developmental stages sampled. There was a sex difference in production of catabolic 5 beta-reduced metabolites. Male 5 beta-reductase activity declined continuously from high embryonic levels in all areas, whereas female enzyme activity showed an increase at hatching. In contrast to plasma progesterone, levels of T were higher in the male than in the female by day 1 after hatching. We suggest that elevated circulating T in the male after hatching may account for the sexual dimorphism in brain aromatase activity.
authors.affiliation: MRC Neuroendocrine Development and Behaviour Group, Institute of Animal Physiology, Babraham, Cambridge, U.K.
authors.forename: J B
authors.initials: JB
authors.lastname: Hutchison
authors.forename: M
authors.initials: M
authors.lastname: Schumacher
authors.forename: R E
authors.initials: RE
authors.lastname: Hutchison
mesh_terms: D000728:Androgens / Q000097:blood / Q000502:physiology*; D015113:Androstane-3,17-diol / Q000378:metabolism; D000818:Animals; D001141:Aromatase / Q000378:metabolism*; D001921:Brain / Q000201:enzymology* / Q000254:growth & development; D002988:Cloaca / Q000033:anatomy & histology / Q000254:growth & development; D013196:Dihydrotestosterone / Q000378:metabolism; D004958:Estradiol / Q000378:metabolism; D004967:Estrogens / Q000096:biosynthesis; D005260:Female; D006066:Gonads / Q000033:anatomy & histology / Q000254:growth & development; D007031:Hypothalamus / Q000378:metabolism; D008297:Male; D011784:Quail; D011863:Radioimmunoassay; D012727:Sex Characteristics; D013739:Testosterone / Q000378:metabolism
chemical_list: D000728:Androgens; D004967:Estrogens; D013196:Dihydrotestosterone; D015113:Androstane-3,17-diol; D013739:Testosterone; D004958:Estradiol; D001141:Aromatase