OVARIAN-STEROIDS DIFFERENTIALLY REGULATE THE EXPRESSION OF PRL-R IN NEUROENDOCRINE DOPAMINERGIC NEURON POPULATIONS - A DOUBLE-LABEL CONFOCAL MICROSCOPIC STUDY

The aims of this study were (1) to identify the possible hypothalamic targets for a short prolactin (PRL) feedback in the adult female rat b y identifying DAergic neuron populations expressing PRL receptor (PRL- R); (2) to describe the effect of ovarian steroids on the expression o f PRC-R and (3) to compare the distribution of both the extracellular (EC) and ligand binding (LB) domains of the PRL-R on the hypothalamic dopaminergic neurons by applying double label immunocytochemistry for the different domains of PRL-R and for tyrosine hydroxylase (TH). Five - to six-month-old female rats were ovariectomized (OVX) and implanted with either 17 beta-estradiol (E-2), progesterone (P-4) or received a n E-2 and a P-4 implant (E-2 + P-4) at the same time. In the periventr icular nucleus and in the dorsomedial portion of the middle arcuate nu cleus, a dramatic increase in PRL-R-EC immunoreactivity was observed i n E-2 implanted rats. This increase was attenuated in E-2 + P-4 rats, but P-4 treatment alone had no effect. Changes in PRL-R-EC expression were paralleled by changes in serum PRL levels. Interestingly, PRL-R-E C expression in the rostral arcuate nucleus decreased in P-4 implanted rats, however, P-4 did not attenuate the E-2-induced increase in PRL- R-EC density. PRL-R-EC immunostaining was observed on the membrane, in the cytoplasm and in the nucleus. PRL-R, immunoreactivity was also de tectable in the TH positive neurons, but no nuclear staining was obser ved with this antibody. However, we found a strong PRL-R, immunostaini ng in the ependymal lining of the 3rd ventricle and in the processes o f tanycytes projecting to the median eminence. These data indicate tha t (1) all neuroendocrine DAergic cells can be targets for PRL, (2) exp ression of PRL-R is differentially affected by ovarian steroids in the different TH cell populations, (3) PRL-R-LB domain may be involved in trafficking PRL in the median eminence. (C) 1998 Elsevier Science B.V . All rights reserved.