PROGESTIN RECEPTOR-CELLS IN THE 8-DAY-OLD MALE AND FEMALE MOUSE CEREBRAL-CORTEX - AUTORADIOGRAPHIC EVIDENCE FOR A SEXUAL DIMORPHISM IN TARGET-CELL NUMBER

The present study examined the number and distribution of progestin receptor cells in the 8-day-old-male and female cortex and compared cortical labeling with that in the preoptic area and central hypothalamus. Eight-day postnatal mice (four males and four females), treated with estradiol, were each sc injected with 0.32-mu-g/100 g BW [I-125]progestin (SA,2200 Ci/mM). Brains were frozen 2 hours after injection of [I-125] progestin, sectioned, and processed for thaw-mount autoradiography. Cells with a nuclear concentration of radioactivity were localized in lamina VI of the lateral cortical regions of the male and female brain, while only a few cortical cells were seen in laminae II,III, and V of the suprarhinal, lateral, and cingulate/paracingulate regions. Comparison of the number of labeled cells revealed that the female cortex contained significantly more labeled cells than the male at three of the four levels investigated. Similarly. the number of target cells was higher in the female medial preoptic nucleus, but not in the arcuate nucleus and ventromedial hypothalamic nucleus, while the distributions of labeled cells in the male and female preoptic/hypothalamic regions were comparable. Injection of unlabeled progesterone or R5020 1 h before [I-125]progestin reduced the nuclear concentration of radioactivity in all target regions and verified the specificity of [I-125]protestin for the progestin receptor. The results of these studies indicate that mouse 8-day-old cortex and preoptic area in the female animal have more progestin receptor cells than those in the male and demonstrate that progestin receptor cells are localized in a region of the cortex known to contain few estrogen target cells. These results further suggest that a sexual dimorphism in progestin cell number may result in a differential effect of progestin on the cortex and preoptic area of the mouse, perhaps establishing a dimorphism in development and function.