Topographic distribution of progestin target cells in hamster brain and pituitary after injection of [3H]R5020

The topographic distribution of progestin concentrating cells in the female hamster brain and pituitary was studied by thaw-mount autoradiography. Fifteen minutes after injection of [3H]R5020, a synthetic progestin, nuclear uptake and concentration of radioactivity was found in certain cells of the forebrain and midbrain, as well as in the anterior pituitary. Competition studies with unlabeled R5020 abolished and with progesterone reduced the nuclear uptake of radioactivity. In the forebrain, radioactively labeled cells are observed in n. septi lateralis, n. interstitialis striae terminalis, n. preopticus medialis and lateralis, n. periventricularis hypothalami, organum subfornicale, n. arcuatus hypothalami, n. ventromedialis hypothalami, n. dorsomedialis hypothalami and n. premammillaris ventralis. In the midbrain a few labeled cells are found in the griseum centrale. In the anterior pituitary, labeled cells are identified by immunostaining as luteinizing hormone-producing cells. The results of the autoradiographic study demonstrate nuclear progestin binding sites and suggest genomic action of progestin on the labeled structures, probably related to the modulation of gonadotropin secretion and sexual behavior in the brain and pituitary.