title: Beta-endorphin cells in the arcuate nucleus: projections to the supraoptic nucleus and changes in expression during pregnancy and parturition.
abstract: Supraoptic nucleus oxytocin neurone activity and secretion are inhibited in late pregnancy and parturition by endogenous opioids. Here, we investigated alterations in the projections and gene expression of beta-endorphin/pro-opiomelanocortin neurones in the arcuate nucleus in the pregnant rat. All regions of the arcuate nucleus were found to contain cells immunoreactive for beta-endorphin fluorescent microbeads retrogradely transported from the supraoptic nucleus, and double-labelled neurones (beta-endorphin plus microbeads), showing that beta-endorphin neurones throughout the arcuate nucleus project to the supraoptic nucleus. There was an increase in the number of beta-endorphin-immunoreactive cells in the arcuate nucleus and an increase in the density of beta-endorphin fibres within the supraoptic nucleus and peri-supraoptic region in late pregnancy and parturition, suggesting enhanced expression of beta-endorphin and increased beta-endorphin innervation of the supraoptic nucleus. Pro-opiomelanocortin mRNA expression in the arcuate nucleus increased in late compared to early pregnancy: the number of positive neurones significantly increased in the caudal region. Fos expression (an indicator of neuronal activation) in the arcuate nucleus was colocalized in beta-endorphin neurones in both proestrus and parturient rats, but the number of positive cells did not increase during parturition, suggesting lack of activation of beta-endorphin neurones at birth. Thus, beta-endorphin cells in the arcuate nucleus project to the supraoptic nucleus and increased innervation during pregnancy may explain the enhanced endogenous opioid inhibition of oxytocin neurones.
authors.affiliation: Division of Biomedical Sciences, University of Edinburgh, George Square, Edinburgh, UK. alison.j.douglas@ed.ac.uk
authors.forename: A J
authors.initials: AJ
authors.lastname: Douglas
authors.forename: R J
authors.initials: RJ
authors.lastname: Bicknell
authors.forename: G
authors.initials: G
authors.lastname: Leng
authors.forename: J A
authors.initials: JA
authors.lastname: Russell
authors.forename: S L
authors.initials: SL
authors.lastname: Meddle
mesh_terms: D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000166:cytology*; D005260:Female; D015870:Gene Expression / Q000502:physiology; D009434:Neural Pathways; D009474:Neurons / Q000737:chemistry / Q000502:physiology; D036801:Parturition / Q000502:physiology*; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D011333:Pro-Opiomelanocortin / Q000235:genetics; D016760:Proto-Oncogene Proteins c-fos / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D013495:Supraoptic Nucleus / Q000166:cytology*; D001615:beta-Endorphin / Q000032:analysis / Q000235:genetics*
chemical_list: D016760:Proto-Oncogene Proteins c-fos; D001615:beta-Endorphin; D011333:Pro-Opiomelanocortin