Reversal of the sexually dimorphic distribution of serotonin-immunoreactive fibers in the medial preoptic nucleus by treatment with perinatal androgen.

The effect of perinatal androgen exposure on the sexually dimorphic distribution of serotonin (5-HT)-immunoreactive fibers in the medial preoptic nucleus (MPN) of the rat was evaluated with an indirect immunohistochemical method. Female animals treated with testosterone propionate (TP) perinatally, postnatally or with oil vehicle alone were gonadectomized as adults and the 5-HT fiber distributions compared with those of intact male and female animals. In the adult female rat, the TP treatments resulted in a significant masculinization of both the 5-HT-stained fiber distribution and the sexually dimorphic cytoarchitectonic features of the MPN. This masculinization appears to be complete only in the animals exposed to TP perinatally, suggesting that the critical period for the sexual differentiation of this nucleus may extend into the late prenatal period.