Immunocytochemical evidence for noradrenergic regulation of estrogen receptor concentrations in the guinea pig hypothalamus.

The noradrenergic system interacts with steroid hormones to influence female sexual behavior and gonadotropin release in rodents. Using a double label immunocytochemical procedure for estrogen receptors and dopamine-beta-hydroxylase, we investigated the anatomical relationships between noradrenergic neurons and estrogen receptor-immunoreactive (ER-IR) cells in the brain of ovariectomized female guinea pigs. Dopamine-beta-hydroxylase-immunoreactive (DBH-IR) varicosities were closely associated with ER-IR cells throughout the hypothalamus and preoptic area. This anatomical relationship was observed with almost 80% of the ER-IR cells in the ventrolateral hypothalamus (VLH), an area involved in the regulation of female sexual behavior in guinea pigs. Furthermore, the presence of closely associated DBH-IR varicosities was related to staining intensity of ER-IR neurons. In the rostral VLH, ER-IR neurons with closely associated DBH-IR varicosities stained more darkly than ER-IR neurons lacking this association, suggesting noradrenergic regulation of basal levels of cellular estrogen receptors. These findings provide neuroanatomical evidence suggestive of noradrenergic regulation of estrogen receptor levels in the hypothalamus of female guinea pigs.