title: Visualizing activation of opioid circuits by internalization of G protein-coupled receptors.
abstract: Mu-opioid receptor (MOR) and opioid receptor-like receptor (ORL-1) circuits in the limbic hypothalamic system are important for the regulation of sexual receptivity in the female rat. Sexual receptivity is tightly regulated by the sequential release of estrogen and progesterone from the ovary suggesting ovarian steroids regulate the activity of these neuropeptide systems. Both MOR and ORL-1 distributions overlap with the distribution of estrogen and progesterone receptors in the hypothalamus and limbic system providing a morphological substrate for interaction between steroids and the opioid circuits in the brain. Both MOR and ORL-1 are receptors that respond to activation by endogenous ligands with internalization into early endosomes. This internalization is part of the mechanism of receptor desensitization or down regulation. Although receptor activation and internalization are separate events, internalization can be used as a temporal measure of circuit activation by endogenous ligands. This review focuses on the estrogen and progesterone regulation of MOR and ORL-1 circuits in the medial preoptic nucleus and ventromedial nucleus of the hypothalamus that are central to modulating sexual receptivity.
authors.affiliation: Department of Neurobiology, David Geffen School of Medicine at UCLA and the Laboratory of Neuroendocrinology of the Brain Research Institute UCLA, Los Angeles, CA 90095-1763, USA. sinchak@mednet.ucla.edu
authors.forename: Kevin
authors.initials: K
authors.lastname: Sinchak
authors.forename: Paul
authors.initials: P
authors.lastname: Micevych
mesh_terms: D000818:Animals; D004705:Endocytosis / Q000502:physiology; D004967:Estrogens / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism; D006801:Humans; D007031:Hypothalamus / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D009434:Neural Pathways / Q000166:cytology / Q000378:metabolism*; D018847:Opioid Peptides / Q000378:metabolism; D011374:Progesterone / Q000378:metabolism*; D011957:Receptors, Opioid / Q000378:metabolism*; D017450:Receptors, Opioid, mu / Q000378:metabolism*; D000094942:Nociceptin Receptor
chemical_list: D004967:Estrogens; D018847:Opioid Peptides; D011957:Receptors, Opioid; D017450:Receptors, Opioid, mu; D011374:Progesterone; D019204:GTP-Binding Proteins; D000094942:Nociceptin Receptor; C000722283:OPRL1 protein, human