DESCRIPTION (applicant's abstract): Little is known about how specific noradrenergic (NA) cell groups involved in regulating ovulation and reproductive behaviors respond to estradiol and/or progesterone. Recently, it has been suggested that A1, A2, and possibly A6 brainstem NA nuclei are the major sources of NA to the preoptic area and hypothalamus. The present research is designed to examine 1) changes in tyrosine hydroxylase (TH: rate-limiting enzyme for NA synthesis) mRNA levels in relation to the onset of the preovulatory luteinizing hormone surge and the onset of female sexual behavior. In all experiments, I will use dual-label in situ hybridization histochemistry to colocalize TH mRNA and estrogen receptor (ER)-alpha, ER-beta, or progestin receptor (PR) mRNA. Additionally, I will determine changes in levels of TH mRNA at various times of the day of and the day after the LH surge and onset of lordosis behavior. The results of this project will provide new information regarding the interactions between ovarian hormones and the NA system, providing a better understanding of the mechanisms by which steroid hormones influence reproductive functions.