Postnatal influence of diethylstilbestrol on the differentiation of the sexually dimorphic nucleus in the rat is as effective as perinatal treatment.

The volume of the sexually dimorphic nucleus of the preoptic area (SDN-POA) of the male rat brain is larger than that of the female. In the female rat, treatment with diethylstilbestrol (DES), either perinatally (from day 16 of gestation to postnatal day 10), or postnatally (birth to day 10) was equally effective in increasing the volume of SDN-POA compared to controls. Prenatal treatment (day 16 of gestation to birth) with DES also increased the volume of the SDN-POA but this increase was significantly smaller than that achieved with the other treatments. These results confirm the effectiveness of DES in increasing the volume of the SDN-POA in the female rat brain, and prove that the differentiating SDN-POA is very receptive to hormone influences in the early postnatal period.