Estradiol Upregulates Progesterone Receptor and Orphanin FQ Colocalization in Arcuate Nucleus Neurons and Opioid Receptor-Like Receptor-1 Expression in Proopiomelanocortin Neurons That Project to the Medial Preoptic Nucleus in the Female Rat

Abstract

Background: Ovarian steroids regulate sexual receptivity in the female rat by acting on neurons that converge on proopiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus (ARH) that project to the medial preoptic nucleus (MPN). Estradiol rapidly activates these neurons to release β-endorphin that activates MPN μ-opioid receptors (MOP) to inhibit lordosis. Lordosis is facilitated by the subsequent action of progesterone that deactivates the estradiol-induced MPN MOP activation. Orphanin FQ (OFQ/N; also known as nociceptin) infusions into the ARH, like progesterone, deactivate MPN MOP and facilitate lordosis in estradiol-primed rats. OFQ/N reduces the activity of ARH β-endorphin neurons through post- and presynaptic mechanisms via its cognate receptor, ORL-1. Methods: We tested the hypotheses that progesterone receptors (PR) are expressed in ARH OFQ/N neurons by immunohistochemistry and ORL-1 is expressed in POMC neurons that project to the MPN by combining Fluoro-Gold injection into the MPN and double-label fluorescent in situ hybridization (FISH). We also hypothesized that estradiol increases coexpression of PR-OFQ/N and ORL-1-POMC in ARH neurons of ovariectomized rats. Results: The number of PR- and OFQ/N-immunopositive ARH neurons was increased as was their colocalization by estradiol treatment. FISH for ORL-1 and POMC mRNA revealed a subpopulation of ARH neurons that was triple labeled, indicating these neurons project to the MPN and coexpress ORL-1 and POMC mRNA. Estradiol was shown to upregulate ORL-1 and POMC expression in MPN-projecting ARH neurons. Conclusion: Estradiol upregulates the ARH OFQ/N-ORL-1 system projecting to the MPN that regulates lordosis.

Orphanin FQ-ORL-1 Regulation of Reproduction and Reproductive Behavior in the Female

“…An example of a priming effect of estradiol is the upregulation of progesterone receptor (PR) in the VMH, ARH, and medial preoptic nucleus of the hypothalamus (MPN) (Alves et al, 2000;Blaustein & Feder, 1979;MacLusky & McEwen, 1978Moguilewsky & Raynaud, 1979;Sanathara et al, 2014;Shughrue, Lubahn, NegroVilar, Korach, & Merchenthaler, 1997). Estradiol-induction of PR synthesis takes about 20 h and is why progesterone treatment must be given at least 20-24 h after EB priming for facilitation of lordosis and why progesterone follows the rise in estradiol in the rat estrous cycle (Alves et al, 2000;Shughrue et al, 1997;Sinchak & Micevych, 2001).…”

“…Estradiol-induction of PR synthesis takes about 20 h and is why progesterone treatment must be given at least 20-24 h after EB priming for facilitation of lordosis and why progesterone follows the rise in estradiol in the rat estrous cycle (Alves et al, 2000;Shughrue et al, 1997;Sinchak & Micevych, 2001). Estradiol also induces OFQ/N and ORL-1 mRNA and protein expression in several brain regions that are important for sexual receptivity (Sanathara et al, 2014;Sinchak et al, 2006). In addition to upregulating enzymes, ligands and receptors (Dohanich, Witcher, Weaver, & Clemens, 1982;Luine, Khylchevskaya, & McEwen, 1975;Luine, Park, Joh, Reis, & McEwen, 1980;Rainbow, Degroff, Luine, & McEwen, 1980), estradiol concurrently modulates receptor signaling pathways (Kellert, Nguyen, Nguyen, Nguyen, & Wagner, 2009;Kelly, Loose, & Ronnekleiv, 1992;Lagrange, Ronnekleiv, & Kelly, 1994;Qiu et al, 2003;Tang, Tran, & Wagner, 2005).…”

“…1; reviewed in Micevych & Sinchak, 2013;Sinchak & Wagner, 2012). All of the steroid priming paradigms that facilitate lordosis converge to regulate the output of ARH β-endorphin (β-END) neurons that project to the MPN (Borgquist et al, 2013(Borgquist et al, , 2014Cheung & Hammer, 1995;Christensen, Dewing, & Micevych, 2011;Christensen & Micevych, 2012Dewing et al, 2007;Dewing, Christensen, Bondar, & Micevych, 2008;Long, Chhorvann, & Sinchak, 2012;Long et al, 2013Long et al, , 2014Micevych, Rissman, Gustafsson, & Sinchak, 2003;Mills, Sohn, & Micevych, 2004;Sanathara et al, 2011Sanathara et al, , 2014Sinchak et al, 2013;Sinchak & Micevych, 2001;Sinchak, Shahedi, Dewing, & Micevych, 2005; Fig. 1).…”

“…Following estradiol priming, progesterone also deactivates this circuit to facilitate lordosis. Although PR are expressed in OFQ/N neuron, OFQ/N is not necessary for deactivating MPN MOP and progesterone may induce the release of other inhibitory neurotransmitters such as GABA to inhibit β-END release to facilitate lordosis (Borgquist et al, 2013(Borgquist et al, , 2014Dewing et al, 2007Dewing et al, , 2008Eckersell et al, 1998;Mills et al, 2004;Sanathara et al, 2011Sanathara et al, , 2014Sinchak et al, 2007;Sinchak & Micevych, 2001;Wagner et al, 1998). receptivity ( Fig.…”

“…Shortly afterward, the heptadecapeptide, orphanin FQ (OFQ/N; aka nociceptin) was determined to be the endogenous ligand for the orphan receptor, ORL-1 (Meunier et al, 1995;Reinscheid et al, 1995;Saito et al, 1996;Saito, Maruyama, Saido, & Kawashima, 1995). Both OFQ/N and ORL-1 are expressed in steroid hormone-responsive brain regions that are important for the integrative control of the HPO axis and reproductive behavior in females (Neal, Mansour, Reinscheid, Nothacker, Civelli, Akil, et al, 1999;Neal, Mansour, Reinscheid, Nothacker, Civelli, & Watson, 1999;Sanathara, Moraes, Mahavongtrakul, & Sinchak, 2014;Sinchak, Romeo, & Micevych, 2006). The initial ORL-1 mapping studies were performed in the male rat and demonstrated that ORL-1 was highly expressed in the ventromedial hypothalamus (VMH) (Neal, Mansour, Reinscheid, Nothacker, Civelli, et al, 1999;Neal, Mansour, Reinscheid, Nothacker, Civelli, & Watson, 1999), indicating the potential for regulation of reproductive behavior.…”