Receptors, Opioid, muReceptors, Opioid, deltaAnalgesics, OpioidReceptors, OpioidProtein MultimerizationReceptors, Opioid, kappaOpioid PeptidesReceptors, Dopamine D2Receptors, Dopamine D1HEK293 CellsProtein Structure, QuaternaryNarcotic AntagonistsReceptors, G-Protein-CoupledNaloxoneProtein BindingOpioid-Related DisordersChondroitin Sulfate ProteoglycansNaltrexoneEnkephalinsLigandsMolecular Sequence DataEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Amino Acid SequenceMorphineCell LineNarcoticsSignal TransductionEnkephalin, D-Penicillamine (2,5)-EndorphinsDynorphinsNeuronsBuprenorphineEnkephalin, LeucineEnkephalin, Leucine-2-AlanineDiprenorphinePainbeta-EndorphinBenzeneacetamidesAnalgesicsDrug ToleranceMorphinansFentanylMethadonePain MeasurementHydromorphoneBenzomorphansPyrrolidinesAnalgesiaSubstance Withdrawal SyndromeOpiate Substitution TreatmentHeroinChronic PainPrescription Drug MisuseLevorphanolDose-Response Relationship, DrugMorphine DependenceButorphanolPrescription DrugsDiterpenes, ClerodaneHeroin DependenceOxymorphoneEthylketocyclazocineMorphine DerivativesInjections, SpinalRats, Sprague-DawleyPain, IntractableOligopeptidesBenzylidene CompoundsDrug OverdosePain ThresholdCyclazocineAnalgesics, Non-NarcoticPeriaqueductal GrayD-Ala(2),MePhe(4),Met(0)-ol-enkephalinHyperalgesiaAlfentanilNalbuphineHydrocodoneTramadolGuanosine 5'-O-(3-Thiotriphosphate)Drug InteractionsRadioligand AssaySufentanilLoperamideOpiate AlkaloidsPain, PostoperativePain ManagementMethadyl AcetateCodeineAzocinesNociceptorsSpinal CordPiperidinesPentazocineSomatostatinBehavior, AnimalMeperidineMeptazinolDihydromorphineBrain