An autoradiographic study of changes in the uptake of tritiated estradiol in the anterior hypothalamus during the estrous cycle of the rat.

In cycling rats exposed to a controlled light schedule of 12 h of light daily from 22.00 to 10.00 h the concentration of estradiol in the anterior hypothalamus at 5.00-6.00 h on the day of proestrus was significantly higher than those at 0.00-1.00 h on day 1 of diestrus and estrus, and was about twofold higher than serum estradiol concentration, which reached a peak at 5.00-6.00 h on the same day. Autoradiographically, the uptake of tritiated estradiol by the nuclei of neurons in the nucleus (n.) preopticus, pars suprachiasmatica (POSC), n. preopticus periventricularis (POP), and anterior part of n. anterior hypothalami (AAH) was significantly higher at 1.00 h on the day of diestrus 1 than at 6.00 h on the day of proestrus and at 1.00 h on the day of estrus. These results suggest that the POSC, POP and AAH may be target sites in the anterior hypothalamus of estradiol for its feedback action.