Oestradiol, sexual receptivity and cytosol progestin receptors in rat hypothalamus

Abstract

Oestradiol and progesterone regulate feminine reproductive behaviour in rodents. Their administration induces changes of biosynthetic activity in the hypothalamus¹, one of which—the induction of progestin receptors—is correlated with the induction of sexual receptivity^2–4, conveniently indicated (in the rat) by the lordosis reflex of the mounted female. We have attempted to define what might be considered as a minimal regime of oestradiol administration—one which is just ‘sufficient’ for activating the lordosis reflex—and have used this paradigm to measure associated changes in nuclear oestrogen (NOER) and cytosol progestin (CPRs) receptors in the mediobasal hypothalamus–preoptic area (MBH-POA) of the rat brain. We find that two 1-h exposures to oestradiol are sufficient to induce the lordosis reflex and to increase significantly CPRs in the MBH-POA. An essentially discontinuous pattern of NOERs in MBH-POA can promote these changes.