title: Rapid estradiol-17beta modulation of opioid actions on the electrical and secretory activity of rat oxytocin neurons in vivo.
abstract: During pregnancy, emergence of endogenous opioid inhibition of oxytocin neurons is revealed by increased oxytocin secretion after administration of the opioid receptor antagonist, naloxone. Here we show that prolonged estradiol-17beta and progesterone treatment (mimicking pregnancy levels) potentiates naloxone-induced oxytocin secretion in urethane-anesthetized virgin female rats. We further show that estradiol-17beta alone rapidly modifies opioid interactions with oxytocin neurons, by recording their firing rate in anesthetized rats sensitized to naloxone by morphine dependence. Naloxone-induced morphine withdrawal strongly increased the firing rate of oxytocin neurons in morphine dependent rats. Estradiol-17beta did not alter basal oxytocin neuron firing rate over 30 min, but amplified naloxone-induced increases in firing rate. Firing pattern analysis indicated that acute estradiol-17beta increased oxytocin secretion in dependent rats by increasing action potential clustering without an overall increase in firing rate. Hence, rapid estradiol-17beta actions might underpin enhanced oxytocin neuron responses to naloxone in pregnancy.
authors.affiliation: Centre for Neuroendocrinology and Department of Physiology, Otago School of Medical Sciences, University of Otago, P.O. Box 913, Dunedin, 9054, New Zealand. colin.brown@stonebow.otago.ac.nz
authors.forename: Colin H
authors.initials: CH
authors.lastname: Brown
authors.forename: Paula J
authors.initials: PJ
authors.lastname: Brunton
authors.forename: John A
authors.initials: JA
authors.lastname: Russell
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D004594:Electrophysiology; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D009021:Morphine Dependence / Q000503:physiopathology / Q000523:psychology; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D010121:Oxytocin / Q000097:blood / Q000502:physiology*; D011863:Radioimmunoassay; D051381:Rats; D017207:Rats, Sprague-Dawley; D017450:Receptors, Opioid, mu / Q000187:drug effects; D013375:Substance Withdrawal Syndrome / Q000503:physiopathology
chemical_list: D000701:Analgesics, Opioid; D009292:Narcotic Antagonists; D017450:Receptors, Opioid, mu; D009270:Naloxone; D004958:Estradiol; D010121:Oxytocin