Neural aromatase activity in a marsupial, the gray short-tailed opossum (Monodelphis domestica): ontogeny during postnatal development and androgen regulation in adulthood.

Neural aromatase activity (AA) was measured in gray short-tailed opossums (Monodelphis domestica) on the day of birth and at selected ages through adulthood. In adulthood, regulation by testicular androgens was examined. In mixed-sex samples of whole brain, AA was present at birth and increased until postnatal day (PD) 16. In hypothalamus-preoptic area (HPOA), significantly higher levels of AA were seen in animals on PD 16 than on PD 30 and PD 30 animals had higher levels of AA than all older ages including adults. Significant sex differences in HPOA AA with male levels higher, were seen only on PD 16 and in adulthood. While lower overall than in HPOA, AA was present also in cerebral cortex (CX). In CX, AA was higher on PDs 16 and 30 than at older ages. Significant sex differences in CX AA were observed only in adulthood. One week following castration in adulthood, AA dropped significantly in CX but not in HPOA. These findings are compared with those obtained from other marsupial and eutherian mammals with reference to the possible significance of AA in sexual differentiation of the gray opossum brain.