MorphineMorphine DependenceDrug ToleranceAnalgesics, OpioidNaloxoneDependency (Psychology)LevallorphanSubstance Withdrawal SyndromeAnalgesiaNarcoticsMorphine DerivativesAminoacetonitrileAgmatineNarcotic AntagonistsPain MeasurementReceptors, Opioid, muImidazoline ReceptorsEnkephalin, MethionineDose-Response Relationship, DrugAnalgesicsPain, PostoperativePainPain ThresholdRats, Sprague-DawleyTime FactorsDrug InteractionsKineticsMolecular Sequence DataHydrogen-Ion ConcentrationInjections, SpinalCells, CulturedGlycolysisMutationCodeineSignal TransductionModels, BiologicalAmino Acid SequenceTemperatureCell LineAlgorithmsCell Line, TumorCalciumNeuronsComputer SimulationReproducibility of ResultsMice, Inbred C57BLRNA, MessengerAdenosine TriphosphateReceptors, OpioidNaltrexoneSubstrate SpecificityBase SequenceSensitivity and SpecificityAnalgesia, Patient-ControlledNalorphineGene Expression ProfilingProtein BindingEscherichia coliMitochondriaHeroinHydromorphoneFentanylSaccharomyces cerevisiaeEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Periaqueductal GrayBacterial ProteinsOxycodoneTransfectionPentazocineMorphinansEnkephalinsNalbuphineReceptors, Opioid, deltaMeperidineThebaineBehavior, AnimalOxymorphoneAnalgesia, Epidural