title: 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.
  
  
  CONCLUSIONS
  Estradiol upregulates the ARH OFQ/N-ORL-1 system projecting to the MPN that regulates lordosis.
authors.affiliation: Department of Biological Sciences, California State University, Long Beach, Long Beach, Calif., USA.
authors.forename: Nayna M
authors.initials: NM
authors.lastname: Sanathara
authors.forename: Justine
authors.initials: J
authors.lastname: Moreas
authors.forename: Matthew
authors.initials: M
authors.lastname: Mahavongtrakul
authors.forename: Kevin
authors.initials: K
authors.lastname: Sinchak
mesh_terms: D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000502:physiology*; D004958:Estradiol / Q000008:administration & dosage / Q000378:metabolism*; D004967:Estrogens / Q000008:administration & dosage / Q000378:metabolism; D005260:Female; D009434:Neural Pathways / Q000502:physiology; D009474:Neurons / Q000502:physiology; D018847:Opioid Peptides / Q000378:metabolism*; D010052:Ovariectomy; D011187:Posture / Q000502:physiology; D011301:Preoptic Area / Q000502:physiology*; D011333:Pro-Opiomelanocortin / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020318:Rats, Long-Evans; D011957:Receptors, Opioid / Q000378:metabolism*; D011980:Receptors, Progesterone / Q000378:metabolism*; D012726:Sexual Behavior, Animal / Q000502:physiology; D000094942:Nociceptin Receptor; D000097629:Nociceptin
chemical_list: D004958:Estradiol; D004967:Estrogens; D018847:Opioid Peptides; D011333:Pro-Opiomelanocortin; D012333:RNA, Messenger; D011957:Receptors, Opioid; D011980:Receptors, Progesterone; D000094942:Nociceptin Receptor; D000097629:Nociceptin; C000722285:Oprl1 protein, rat