Dopaminergic mechanisms involved in estrogen modulation of the prolactin response to Orphanin FQ/Nociceptin

The role of estrogen in modulating Orphanin FQ/Nocicpetin (OFQ/N) induced prolactin secretion and the involvement of hypothalamic dopaminergic neurons involved in this response were investigated.In ovariectomized Sprague-Dawley rats, estrogen treatment produced an increase in basal circulating prolactin levels and pituitary prolactin content.The prolactin response to OFQ/N was 6-8 times greater in estrogen-replaced rats compared to placebo-treated controls.Also, OFQ/N produced a rapid, transient inhibition of tuberoinfundibular dopaminergic (TIDA) neuronal activity which preceded the prolactin secretory response in the estrogen-replaced rats only.The results of this study indicate that estrogen is necessary for the prolactin response to OFQ/N and estrogen mediates this effect at the pituitary and hypothalamic levels by increasing pituitary prolactin content and sensitizing TIDA neurons to OFQ/N-induced inhibition of activity.These results suggest that estrogen is responsible for the gender differences in the prolactin response to OFQ/N.