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 secretary patterns of hypothalamic GnRH, pituitary gonadotropins, and/or ovarian steroids. 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 cycles, and old (16-19 months) and very old (20-21 months) rats, exhibiting repeated pseudopregnancies, were bilaterally ovariectomized. They were implanted with Silastic capsules containing estradiol-17β one week later, and killed 2 days after capsule implantation. Changes in prolactin receptor gene expression were assessed using in situ hybridization. The level of prolactin receptor mRNA in choroid plexus, periventricular area of the preoptic nucleus, and arcuate nucleus increased significantly by the time the animals were old. In the lateral ventromedial nucleus, prolactin receptor gene expression did not change significantly during aging, even in the oldest group of rats. These findings suggest that changes in the prolactin receptor gene may influence the ability of prolactin to exert effects and may allow older animals to the more responsive to prolactin than young rats.