Opioid-Related DisordersAnalgesics, OpioidNarcoticsMorphineNaloxoneEnkephalin, MethionineNarcotic AntagonistsReceptors, OpioidOpioid PeptidesPainOxycodoneEnkephalin, Ala(2)-MePhe(4)-Gly(5)-FentanylReceptors, Opioid, kappaEnkephalinsEndorphinsMolecular Sequence DataSignal TransductionCells, CulturedAnalgesicsCell LineHydromorphoneDose-Response Relationship, DrugReceptors, Opioid, deltaPain MeasurementNaltrexoneChronic PainTime FactorsEnkephalin, D-Penicillamine (2,5)-KineticsPrescription DrugsCalciumAlfentanilOxymorphoneAnalgesiaMice, Inbred C57BLBuprenorphinePain, IntractableAmino Acid SequenceProtein BindingDynorphinsMutationDrug ToleranceRats, Sprague-DawleyEnkephalin, LeucinePhosphorylationMice, KnockoutBase Sequencebeta-EndorphinPrescription Drug MisuseCodeineSufentanilDNA-Binding ProteinsRNA, MessengerBenzeneacetamidesMethadoneEnzyme ActivationTranscription, GeneticHydrocodoneModels, BiologicalGene Expression RegulationInjections, SpinalTranscription FactorsTransfectionBinding SitesTramadolNeuronsEnkephalin, Leucine-2-AlaninePromoter Regions, GeneticEnzyme InhibitorsCarrier ProteinsApoptosisRecombinant ProteinsPyrrolidinesHeroinMorphine DerivativesCell MembraneHydrogen-Ion ConcentrationMeperidineCell Line, TumorOpiate AlkaloidsEtorphineMembrane ProteinsBlotting, WesternRecombinant Fusion ProteinsBacterial ProteinsHeLa CellsDrug InteractionsNuclear ProteinsTumor Cells, CulturedBiological Transport