title: Modulation of lordosis behavior of female rats by naloxone, beta-endorphin and its antiserum in the mesencephalic central gray: possible mediation via GnRH.
abstract: The role of endogenous opiate peptides in the mesencephalic central gray (MCG) and their possible interactions with gonadotropin-releasing hormone (GnRH) in the regulation of lordosis behavior was assessed in ovariectomized, estrogen-treated and estrogen-progesterone-treated female rats. Lordosis behavior triggered by male mounting was enhanced by microinfusion of naloxone and anti-beta-endorphin-globulin (anti-beta-end-G) but not by anti-met-enkephalin-globulin or anti-dynorphin-globulin into the MCG in both estrogen-treated and estrogen- (low dose) progesterone-treated females. The potentiating effects of naloxone and anti-beta-end-G could be blocked by a preinfusion of either anti-GnRH-globulin or an antagonist analog of GnRH directly into the MCG. However, two potent antagonist analogs of GnRH were not effective in blocking lordosis indicating a dissociation between their neural actions and their known inhibitory effects on luteinizing hormone release. Conversely, beta-endorphin but not met-enkephalin or dynorphin infused into the MCG inhibited lordosis behavior in both estrogen-treated and estrogen-progesterone-treated rats. This beta-endorphin-induced inhibition of lordosis in the estrogen-treated rats could be overcome by GnRH microinfused directly into the MCG which potentiated lordosis to high levels. These observations provide evidence that beta-endorphin may be the sole opiate peptide in the MCG involved in the control of lordosis behavior and also suggests a functional relationship with GnRH systems in the MCG in such a regulatory mechanism.
mesh_terms: D000818:Animals; D004399:Dynorphins / Q000494:pharmacology; D004723:Endorphins / Q000494:pharmacology*; D004744:Enkephalin, Methionine / Q000494:pharmacology; D004967:Estrogens / Q000494:pharmacology; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology*; D010487:Periaqueductal Gray / Q000378:metabolism*; D010906:Pituitary Hormone-Releasing Hormones / Q000502:physiology*; D011374:Progesterone / Q000494:pharmacology; D011761:Pyrrolidonecarboxylic Acid / Q000031:analogs & derivatives; D051381:Rats; D011919:Rats, Inbred Strains; D012726:Sexual Behavior, Animal / Q000187:drug effects*; D001615:beta-Endorphin; D005719:gamma-Globulins / Q000494:pharmacology
chemical_list: D004723:Endorphins; D004967:Estrogens; D010906:Pituitary Hormone-Releasing Hormones; D005719:gamma-Globulins; D007987:Gonadotropin-Releasing Hormone; D009270:Naloxone; D011374:Progesterone; D004744:Enkephalin, Methionine; D001615:beta-Endorphin; C037232:LHRH, Phe(2)-Pro(3)-Phe(6)-; C034511:LHRH, pGlu(1)-Phe(2)-Trp(3,6)-; D004399:Dynorphins; C033548:LHRH, Ac-dehydro-Pro(1)-4-Cl-Phe(2)-Trp(3,6)-; D011761:Pyrrolidonecarboxylic Acid