Ontogeny of immunocytochemically demonstrable androgen- and androgen receptor-containing cells in the hypothalamus and adenohypophysis of the chick embryo.

Brain sections of male chick embryos, 6.5-18.5 days of age, were examined immunocytochemically for the presence of androgen- and androgen receptor-containing cells in the hypothalamus and adenohypophyseal pars distalis. Using antibodies (Ab) against both androgens (T-Ab) and the androgen receptor (AR-Ab), single- and double-immunostained cells were located in a total of five nuclei of the anterior-, mid-, and posterior-hypothalamus, as well as in the rostral and caudal lobes of the adenohypophyseal pars distalis. From Days 9.5-12.5, the mean number of androgen-immunostained cells within the hypothalamus and pars distalis increased significantly (P < 0.01), while from Days 12.5-18.5 there was no further statistically significant increase. The results of the present investigation support previous findings which suggest that in the chick embryo the negative feedback loop of the hypothalamo-adenohypophyseal-testicular (HATest) axis is functional by the 13th day of development (Woods et al., 1989a,b). They also agree with the observations of Wilson and Glick (1970) that in the male chick embryo testosterone organizes masculine mating behavior prior to Day 13.0.