PROLACTIN RECEPTORS IN THE RAT HYPOTHALAMUS - AUTORADIOGRAPHIC LOCALIZATION AND CHARACTERIZATION

A precise mapping of prolactin (PRL) receptors in the rat brain has be en achieved. Localization of binding sites for both I-125-human growth hormone (I-125-hGH) and I-125-Monoclonal anti-PRL receptor (I-125-U5) was studied by in vitro autoradiography on brain sections in female r ats (n = 7). The analysis of autoradiograms generated from 12 adjacent sections at 11 different brain levels (bregma 0.2 to -4.8 mm) reveale d 9 distinctive localizations for I-125-hGH binding sites: preoptic su prachiasmatic nucleus, medial preoptic area, periventricular, supraopt ic, paraventricular, arcuate and vetromedial nuclei and also the media n eminence and the infundibulum. Specificity for PRL binding was asses sed by competition experiment of I-125-hGH with unlabeled hGH and ovin e PRL. Binding sites were similarly localized by I-125-U5 indicating t he presence of PRL receptors moiety. The quantitative analysis with 0. 6 nM I-125-hGH demonstrated maximal densities in the preoptic suprachi asmatic and arcuate nuclei and minimal densities in the median eminenc e and the infundibulum. Due to ample antero-posterior variations no si gnificant changes were observed during the estrous cycle. Saturation a nalysis of binding in the arcuate nucleus indicated a single class of high affinity (K(d) from 0.9 to 2.2 nM) receptors (B(max) from 34 to 4 4 fmol/mg of proteins). The present data provide the hypothalamic cart ography of PRL receptors in the female rat brain and support all the p hysiological evidence for the existence of a direct action of PRL in t he hypothalamus.