Further evidence for the presence of specific binding sites for prolactin in the rabbit brain. Preferential distribution in the hypothalamus and substantia nigra

Distribution and Characterization of Prolactin Binding Sites in the Male and Female Rat Brain: Effects of Hypophysectomy and Ovariectomy

“…In addition to its classical effects on the mammary gland, PRL has been shown to have a number of other actions, all of which are initiated by an interaction with specific high-affinity receptors located on the plasma membrane and widely distrib uted in a number of tissues [26,27], From our data it appears evident that in the rat, as pre viously observed for other animals [6][7][8], specific binding sites for PRL are present in the hypothalamus and substantia nigra. The hormonal specificity and PRL affinity of these binding sites in the rat hypothalamus are very similar to those found in the rat liver and ovary as well as to those described by different authors in other PRL target tissues [27][28][29].…”

“…A treatment with estradiol restored the PRL binding in the ovariectomized rats to above normal levels. These results of in vitro biochemical analysis together with the experimental modula tion of hormonal status provide strong preliminary evidence for the presence of PRL binding sites in rat brain.An increasing amount of data indicates that prolactin (PRL) may play a specific role in the central nervous system (CNS) at the hypothalamic level affecting dopamine neurotransmission [1,2] and also in extrahypothalamic areas [3][4][5].The localization of specific PRL binding sites within the CNS may be able to help clarify the mechanisms responsible for the autoregulation of this hormone and its effects on other as pects of CNS activities.In accordance with these observations, over the last few years we have identified and characterized using traditional in vitro competitive binding assay specific binding sites for PRL in rabbit hypothalamus and substantia nigra [6,7] and more re cently in the hypothalamus of pig, horse, pigeon and an anuran amphibian, Xenopus laevis [8.9], Other authors have also found PRL receptors in pig hypothalamus [10] as well as in the fore brain and hypothalamus of ring dove [11] and in different brain regions from the toad, Bufo arenarum [12]. Conversely at tempts to identify PRL binding sites in rat hypothalamus by in vitro competitive binding assays have so far been unsuccessful [8,13,14], Moreover in the rat in vitro autoradiographic analy sis of whole hypothalamus [14] and in vivo autoradiographic analysis of the median eminence [15,16] have generally failed to Received: December 18, 1989 Accepted after revision: June 18, 1990 demonstrate significant specific binding for PRL.…”

Immunoreactive Prolactin in the Rat Hypothalamus: In vitro Release and Subcellular Localization

“…Both high-density peaks were maintained in tissue obtained from hypophysectomized rats and were disrupted by homogenization in hypo-osmotic med ium. Together, these data suggest that hypothalamic IR-PRL is stored in membrane-bound particles which have densities similar to those of secretory granules and is released by a calcium-dependent mechanism when the tissue is depolarized.The occurrence of prolactin sensitive neurons in the rat hypothalamus was first suggested by Clemens and Meites [3] and subsequently confirmed by a number of researchers in the rat, rabbit and guinea pig [1,2, 17, 24], Consistent with these observations, specific binding sites for prolactin (PRL) have been reported in the rabbit hypothalamus [8,9], and infusion of PRL into the rat brain has been shown to influence maternal behaviors and to induce grooming behaviors in the rat [10, 11. 15] [12, 14,[20][21][22].…”

Autoradiographic Identification of Prolactin Binding Sites in Rat Median Eminence

“…The evidence for specific receptors for prolactin in hypothalamus, however, is controversial. Results from in vitro studies using homogenates of whole hypothalami have demonstrated l25I-proIactin binding sites in rabbit (7,9] but not in rat [8]. Similarly, in vitro autoradiographic analysis failed to identify specific binding for prolactin in rat hypothala mus [10].…”