Hormonal priming and triggering of maternal behavior in the rat with special reference to the relations between estrogen receptor binding and ER mRNA in specific brain regions.

Estrogen stimulation of maternal behavior during pregnancy in the rat has been studied at several levels of analysis. These include (a) changes in maternal responsiveness during pregnancy; (b) hormonal stimulation of maternal behavior; and (c) correlation between nuclear binding of estradiol in the medial preoptic area and the stimulation of maternal behavior (i.e., in pregnancy-terminated, ovariectomized females treated with estradiol benzoate). These studies have given rise to the concepts of hormonal priming and triggering of maternal behavior during pregnancy and at parturition. More recently, using in situ hybridization, ER mRNA was measured during pregnancy (also diestrus and postpartum) in brain regions in which binding previously had been studied, to investigate further the regulation of hormonal priming. Steady state levels of ER mRNA per cell and cell densities of ER mRNA produced a measure of total ER mRNA per brain region which was then compared to nuclear estrogen receptor binding. The relation between binding and ER mRNA is presented for one of the brain regions, the rostral medial preoptic nucleus. The results indicate that ER transcription is regulated during pregnancy, but regulation is specific to each brain region and there is no simple relation between ER mRNA and nuclear estrogen receptor binding.