Effects of treatment with estradiol and parental experience on the number and distribution of estrogen-binding neurons in the ovariectomized mouse brain.

The effects of a treatment with estradiol benzoate alone (EB, for 2 weeks) and combined with parental experience (for 5 days) on the number and regional distribution of estrogen receptor-containing cells (ER+ cells) in the brain of ovariectomized mice were studied using an immunocytochemical staining technique. Treatment with EB alone significantly reduces the average density of ER+ cells (labeled cells/mm3) in the ventromedial hypothalamic nucleus (VMH) and in the anterior hypothalamic area (AHA). Parental experience of EB-treated females (achieved by co-caring for 12 pups together with the mother for 5 days), however, leads to a significant increase in the absolute number and relative density of ER+ cells in the VMH. Moreover, ER+ cells are found in the entorhinal and piriform cortex in experienced females only. Generally, a trend of decrease in both the number and density of labeled cells is observed after EB treatment in all regions of the brain where immunostaining is observed in ovariectomized mice (amygdaloid and hypothalamic nuclei, preoptic area), whereas an increase in the above quantitative variables is found in experienced females. The hypothesis is put forward that olfactory cues from the young, experienced during the co-caring period promote the increase in ER+ cells in the above brain regions, which all receive input from the olfactory and/or vomeronasal systems.