Immunocytochemical localization of aromatase-containing neurons in the rat brain during pre- and postnatal development.

The present immunohistochemical study demonstrates the ontogenetic appearance of aromatase-immunoreactive neurons in several discrete regions of the hypothalamus and limbic system in the rat brain, using a purified antibody against human placental aromatase cytochrome P450. Immunoreactive cells were first detected in the preoptic area on the 13th day of embryonic life (E13), and additionally in the bed nucleus of the stria terminalis on E15. Labeled cells were also found in the medial amygdaloid nucleus and the ventromedial nucleus on E16, and some were detected in the arcuate nucleus on E19. As gestation progressed, the number and the immunoreactivity of these cells gradually increased and peaked within definite periods of perinatal life and thereafter declined or disappeared. The immunoreactive cells were also found in the central amygdaloid nucleus and the lateral septal nucleus, and in the ventral pallidum, after the 14th day of postnatal life (P14) and 30th day (P30), respectively. The distribution of aromatase-immunoreactive neurons was similar between the sexes, while the immunoreactivity was higher in males than in females after late gestational days. No immunoreaction was detectable in other regions of the telencephalon or midbrain at any time periods studied. The aromatase-immunoreactive neurons in the specific regions may be involved in the sexual differentiation of the brain.