Autoradiographic evidence for two classes of mu opioid binding sites in rat brain using [I]FK33824 |
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Authors: | Richard B Rothman Arthur E Jacobson Kenner C Rice and Miles Herkenham |
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Institution: | * Laboratory of Preclinical Pharmacology, NIMH, St. Elizabeths Hospital, Washington, DC 20032, USA ? Laboratory of Chemistry, NIDDK, Bethesda, MD 20892, USA ? Unit on Functional Neuroanatomy, NIMH, Bethesda, MD 20892, USA |
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Abstract: | Previous studies demonstrated that pretreatment of brain membranes with the irreversible mu antagonist, beta-funaltrexamine (beta-FNA), partially eliminated mu binding sites 25,35], consistent with the existence of two mu binding sites distinguished by beta-FNA. This paper tests the hypothesis that the FNA-sensitive and FNA-insensitive mu binding sites have different anatomical distributions in rat brain. Prior to autoradiographic visualization of mu binding sites, 3H]oxymorphone, 3H]D-ala2-MePhe4, Gly-ol5-enkephalin (DAGO), and 125I]D-ala2-Me-Phe4-met(o)-ol]enkephalin (FK33824) were shown to selectively label mu binding sites using slide mounted sections of molded minced rat brain. As found using membranes, beta-FNA eliminated only a portion of mu binding sites. Autoradiographic visualization of mu binding sites using the mu-selective ligand 125I]FK33824 in control and FNA-treated sections of rat brain demonstrated that the proportion of mu binding sites sensitive to beta-FNA varied across regions of the brain, particularly the dorsal thalamus, ventrobasal complex and the hypothalamus, providing anatomical data supporting the existence of two classes of mu binding sites in rat brain. |
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Keywords: | Opiate receptors Autoradiography Beta-FNA |
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