PROLACTIN RECEPTOR GENE-EXPRESSION IN SPECIFIC HYPOTHALAMIC NUCLEI INCREASES WITH AGE

Increasing prolactin levels or increasing responsiveness to prolactin may contribute to reproductive aging by influencing the secretory patt erns of hypothalamic GnRH, pituitary gonadotropins, and/or ovarian ste roids. Some studies have documented changes in the levels of prolactin in peripheral plasma. The goal of this study was to determine whether prolactin receptor mRNA levels in the brain change with aging, which may lead to increasing responsiveness to prolactin. Young (2-4 months) and middle-aged (9-11 months), demonstrating 3 consecutive estrous cy cles, and old (16-19 months) and very old (20-21 months) rats, exhibit ing repeated pseudopregnancies, were bilaterally ovariectomized. They were implanted with Silastic capsules containing estradiol-17 beta one week later, and killed 2 days after capsule implantation. Changes in prolactin receptor gene expression were assessed using in situ hybridi zation. The level of prolactin receptor mRNA in choroid plexus, perive ntricular area of the preoptic muscles, and arcuate nucleus increased significantly by the time the animals were old. In the lateral ventrom edial nucleus, prolactin receptor gene expression did not change signi ficantly during aging, even in the oldest group of rats. These finding s suggest that changes in the prolactin receptor gene may influence th e ability of prolactin to exert effects and may allow animals to be mo re responsive to prolactin than young rats.