Ontogeny of 17B-estradiol (E2)- and estrogen receptor (ER)- immunostained cells in the hypothalamus and adenohyophyseal pars distalis of the chick embryo.

Brain sections of 6.5-18.5 day-old (stages 30-45: Hamburger and Hamilton, 1951) male and female chick embryos were examined immunocytochemically for the presence of 17B-estradiol (E2)- and estrogen receptor (ER)-containing cells in the hypothalamus and adenohypophyseal pars distalis. Single (E2 or ER)- and double (E2 and ER)-immunostained cells were observed in five nuclei of the anterior-, mid-, and posterior-hypothalamus and in the rostral and caudal pars distalis. The number of E2-immunostained cells were determined in each of these brain areas from Days 10.5 through 18.5 (stages 37 through 45); during this time period no differences were noted between the cell counts of males and females. In both sexes there was a significant increase (P<0.05) from Days 10.5 through 12.5-13.5 (stages 37 through 39-40) in the mean number of E2-immunoreactive cells. These findings agree with the observations of Wilson and Glick (1970) that prior to the 13th day of embryonic development E2 contributes, via its effect on the hypothalamic neural circuitry (organization) to posthatch mating behavior.