Nuclear translocation of STAT5 and increased expression of Fos related antigens (FRAs) in hypothalamic dopaminergic neurons after prolactin administration

Ample evidence indicates feedback relationships between pituitary prolactin and hypothalamic dopaminergic neurons. Since the presence of prolactin rec eptors was earlier demonstrated in hypothalamic dopaminergic neurons, our w orking hypothesis was that prolactin induced activation of prolactin recept or coupled signaling leads to increased neuronal activity in these neurons. The aim of this study was to correlate prolactin receptor mediated signali ng and prolactin induced activation in hypothalamic dopaminergic neurons. W e used nuclear translocation of STAT5 as a marker of prolactin receptor ind uced signaling and expression of Fos related antigens (FRAs) as an indicato r of neuronal activation. We performed double label immunocytochemical stud ies to determine the time course of the presence of FRAs and STAT5 in the n uclei of hypothalamic dopaminergic neurons after ovine prolactin treatment. Exogenous ovine prolactin treatment of ovariectomized rats resulted in an increase in serum ovine prolactin levels and a decrease in endogenous serum prolactin levels, indicating that ovine prolactin activated mechanisms inh ibited pituitary prolactin secretion. Indeed, ovine prolactin activated the prolactin receptors in most subpopulations of hypothalamic dopaminergic ne urons, resulting in nuclear translocation of STAT5. Also, increased neurona l activity, indicated by expression of FRAs, was observed in the same neuro n populations after ovine prolactin treatment. These results suggest that s ignal transduction mechanisms coupled to prolactin receptors in hypothalami c dopaminergic neurons resemble those observed in other tissues; and nuclea r translocation of STAT5 can be used as a marker of prolactin receptor acti vation in hypothalamic dopaminergic neurons. (C) 2001 Elsevier Science B.V. All rights reserved.