Abstract

Introduction

Materials & Methods

Results

Discussion & Conclusion

References

Discussion
Board

We have previously described the presence of immunoreactive prolactin receptors in all three dopaminergic neuron populations involved in the hypothalamic control of prolactin (PRL) secretion. In non-neural tissues it has been shown that Stat5 protein is phosphorylated, dimerized and translocated to the nucleus as a result of activation of the prolactin receptor. The aim of this study was to determine whether the same mechanisms was present in neuroendocrine dopaminergic neurons and to assess the time-course of the nuclear translocation of Stat5 in these neurons. Ovariectomized female rats were injected subcutaneously with ovine prolactin (oPRL). Controls received saline only. The animals were sacrificed 1,2 or 4 h after injection and perfused with fixative. The levels of oPRL in serum was measured with RIA. Double label fluorescence immunocytochemistry for Stat5 and tyrosine hydroxylase (TH) was performed on hypothalamic sections and examined by confocal microscopy. One hour after oPRL injection there was a significant increase in serum oPRL levels and the number of Stat5-stained nuclei in the dopaminergic neurons of the rostral and dorsomedial portions of the arcuate nucleus (THDA and TIDA neurons, respectively), when compared to the respective controls. Two hours after injection similar nuclear translocation of Stat5 was observed in the periventricular dopaminergic (PHDA) neurons. By 4 h there was no difference in the cellular distribution of Stat5 in the oPRL-treated and control rats. Conclusions: (1) TIDA and THDA neurons are targeted directly by the circulating prolactin, and (2) these neurons play a pivotal role in regulating PRL secretion through the PRL autofeedback mechanism. Supported by NIDDK43200

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Poster Number PAlerant 0748
Keywords: hypothalamus, dopamine, prolactin, PRL-receptor, Stat