Embryonic rodent brain contains estrogen receptors.

Estradiol-binding proteins with the properties of putative estrogen receptors are present in cytosol extracts of embryonic mouse hypothalamus and other brain regions. These embryonic estrogen receptors are adultlike in their high affinity and limited capacity for estradiol, sensitivity to diethylstilbestrol, ability to adhere to DNA, and behavior during DNA-cellulose affinity chromatography. As early as 4 days before birth, mouse hypothalamus has approximately 40 percent of the adult concentration of hypothalamic estrogen receptors with these properties. These observations raise the possibility that embryonic rodent brain has the biochemical potential to respond to sex hormones and that the critical period of brain sexual differentiation could be initiated prenatally.