Receptors, OpioidReceptors, Opioid, muReceptors, Opioid, deltaReceptors, Opioid, kappaAnalgesics, OpioidNarcotic AntagonistsOpioid PeptidesNaltrexoneNaloxoneEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, D-Penicillamine (2,5)-EnkephalinsDiprenorphineMorphineDynorphinsEnkephalin, Leucine-2-AlanineEnkephalin, LeucineBenzeneacetamidesNarcoticsMorphinansBenzomorphansAnalgesicsEndorphinsEtorphinebeta-EndorphinPyrrolidinesDiterpenes, ClerodaneOpioid-Related DisordersEthylketocyclazocineCyclazocineBenzylidene CompoundsDrug ToleranceLevorphanolPainFentanylPain MeasurementBuprenorphineEnkephalin, MethionineOligopeptidesAnalgesiaDose-Response Relationship, DrugMorphine DerivativesRats, Sprague-DawleyGuanosine 5'-O-(3-Thiotriphosphate)ButorphanolLigandsProtein BindingHeroinMolecular Sequence DataRadioligand AssaySubstance Withdrawal SyndromeMorphine DependenceInjections, SpinalCHO CellsBinding, CompetitivePeriaqueductal GrayAmino Acid SequenceBinding SitesMethadoneLoperamideSomatostatinCricetinaeHyperalgesiaPain ThresholdNociceptorsAnalgesics, Non-NarcoticOpiate AlkaloidsSpinal CordSalviaCricetulusCell LineHydromorphoneInjections, IntraventricularAzocinesBrainD-Ala(2),MePhe(4),Met(0)-ol-enkephalinSpiro CompoundsGuinea PigsBehavior, AnimalDrug InteractionsG-Protein-Coupled Receptor Kinase 3ArrestinsDihydromorphineRats, WistarHeroin DependencePiperidinesMicroinjectionsKineticsBase SequenceGTP-Binding ProteinsVas DeferensNalbuphineTramadolNociceptionNucleus AccumbensSignal TransductionStructure-Activity RelationshipAdenylate CyclaseCyclic AMPStereoisomerism