Receptors, Opioid, muReceptors, OpioidAnalgesics, OpioidReceptors, Opioid, deltaReceptors, Opioid, kappaOpioid PeptidesNarcotic AntagonistsNaloxoneOpioid-Related DisordersNaltrexoneEnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-MorphineNarcoticsEnkephalin, D-Penicillamine (2,5)-EndorphinsDynorphinsBuprenorphineEnkephalin, LeucineProtein BindingEnkephalin, Leucine-2-AlanineDiprenorphinePainMolecular Sequence Databeta-EndorphinBinding SitesBenzeneacetamidesAnalgesicsMorphinansDrug ToleranceFentanylMethadoneAmino Acid SequencePain MeasurementHydromorphoneBenzomorphansPyrrolidinesSubstance Withdrawal SyndromeAnalgesiaDose-Response Relationship, DrugOpiate Substitution TreatmentBase SequenceBinding, CompetitiveHeroinLigandsChronic PainLevorphanolPrescription Drug MisuseCell LineProtein Structure, TertiaryOligopeptidesMorphine DependenceButorphanolPrescription DrugsModels, MolecularRats, Sprague-DawleyKineticsDiterpenes, ClerodaneDNA-Binding ProteinsHeroin DependenceOxymorphoneEthylketocyclazocineMorphine DerivativesInjections, SpinalRecombinant ProteinsPain, IntractableBenzylidene CompoundsDrug OverdoseCyclazocinePain ThresholdAnalgesics, Non-NarcoticRecombinant Fusion ProteinsTranscription FactorsRadioligand AssayCHO CellsPeriaqueductal GrayCarrier ProteinsD-Ala(2),MePhe(4),Met(0)-ol-enkephalinSequence Homology, Amino AcidCricetinaeGuanosine 5'-O-(3-Thiotriphosphate)HyperalgesiaAlfentanilNalbuphineHydrocodonePromoter Regions, GeneticTransfectionTramadolDrug InteractionsDNAMutationSignal TransductionProtein ConformationBrainCloning, MolecularSufentanilLoperamideTime FactorsOpiate AlkaloidsPiperidines