MorphineEnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, LeucineEnkephalin, MethionineMorphine DependenceAnalgesics, OpioidReceptors, Opioid, muNarcoticsEnkephalin, Leucine-2-AlanineDrug ToleranceEnkephalin, D-Penicillamine (2,5)-NaloxoneNarcotic AntagonistsReceptors, OpioidReceptors, Opioid, deltaMorphine DerivativesEndorphinsSubstance Withdrawal SyndromeLocus CoeruleusReceptors, Neurokinin-3NaltrexonePeriaqueductal GrayPain MeasurementNeurokinin BEthylketocyclazocineRats, Sprague-DawleyCyclazocineTachykininsReceptors, TachykininReceptors, Opioid, kappaDose-Response Relationship, DrugOpioid PeptidesD-Ala(2),MePhe(4),Met(0)-ol-enkephalinEtorphineOpioid-Related DisordersSubstance PPainInjections, SpinalNeurokinin APain, PostoperativeAnalgesicsAnalgesiaReceptors, Neurokinin-2Nucleus AccumbensAnalgesia, EpiduralTegmentum MesencephaliDynorphinsGuinea PigsDrug ImplantsSpinal CordDrug InteractionsBehavior, AnimalNeuronsAnesthetics, IntravenousBrainbeta-EndorphinAnalgesia, Patient-ControlledSufentanilVentral Tegmental AreaBenzeneacetamidesPain ThresholdRNA, Transfer, GlyBenzomorphansTime FactorsDrug Administration ScheduleBupivacaineOligopeptidesMorphinansArrestinsGuanosine 5'-O-(3-Thiotriphosphate)Carboxypeptidase HAdenylate CyclasePreanesthetic MedicationAdjuvants, AnesthesiaAnesthesia, IntravenousAdministration, CutaneousHyperalgesiaDiprenorphineAnalgesia, ObstetricalRats, Inbred StrainsTyrosine 3-MonooxygenaseRaphe NucleiPiperidinesAnesthesia, GeneralG Protein-Coupled Inwardly-Rectifying Potassium ChannelsDouble-Blind MethodMice, Inbred C57BLAnesthetics, CombinedLimbic SystemMotor ActivityReceptors, N-Methyl-D-AspartateCyclic AMPMeperidinePropofolNeurokinin-1 Receptor AntagonistsElectric StimulationAnesthetics, LocalCodeineRats, Wistar