title: Mu- and delta-opioid receptor densities in respiratory-related brainstem regions of neonatal swine.
abstract: The piglet displays similar postnatal development in respiration and sleep-wake behavior to the human. To shed light on the possible influence of opioid systems on these functions, this study assessed the density of mu- and delta-opioid receptors in brainstems of 2-3 and 5-7 (young), 14-17 (intermediate) and 20-21 (older) day-old piglets, using quantitative autoradiography. Serial 10 microns sections from fresh-frozen brains were incubated with either mu-(125I-DAGO) or delta-(125I-DPDPE) opioid ligands. The binding characteristics of each receptor remained unchanged over the age-range studied. delta-opioid receptor density was minimal in the young piglets, and increased over the age-range studied in all brainstem regions. mu-opioid receptor density exceeded delta-opioid density in all brainstem regions in young and older piglets, and remained unchanged with age. We conclude that, as in other species, the development of delta-opioid receptors in swine lags behind that of mu-opioid receptors, and that the distribution of each in the piglet's brainstem is distinct. The present findings help explain the changing influence of the mu- and delta-opioid systems on breating and state during postnatal development.
authors.affiliation: Department of Pediatrics, McGill University, Montreal, Quebec, Canada.
authors.forename: A
authors.initials: A
authors.lastname: Laferrière
authors.forename: J K
authors.initials: JK
authors.lastname: Liu
authors.forename: I R
authors.initials: IR
authors.lastname: Moss
mesh_terms: D000700:Analgesics / Q000378:metabolism; D000701:Analgesics, Opioid / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D001665:Binding Sites / Q000502:physiology; D001933:Brain Stem / Q000378:metabolism / Q000502:physiology*; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D020881:Enkephalin, D-Penicillamine (2,5)-; D004745:Enkephalins / Q000378:metabolism; D017465:Receptors, Opioid, delta / Q000378:metabolism*; D017450:Receptors, Opioid, mu / Q000378:metabolism*; D012143:Respiratory Physiological Phenomena; D013552:Swine / Q000378:metabolism*; D013556:Swine, Miniature