MorphineEnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, MethionineEnkephalin, LeucineMorphine DependenceReceptors, Opioid, muAnalgesics, OpioidNarcoticsDrug ToleranceEnkephalin, D-Penicillamine (2,5)-NaloxoneEnkephalin, Leucine-2-AlanineReceptors, OpioidReceptors, Opioid, deltaNarcotic AntagonistsMorphine DerivativesSubstance Withdrawal SyndromeEndorphinsNaltrexoneLocus CoeruleusReceptors, Neurokinin-3LevallorphanPeriaqueductal GrayRats, Sprague-DawleyNeurokinin BEthylketocyclazocineDose-Response Relationship, DrugOpioid PeptidesCyclazocineTachykininsPain MeasurementAnalgesiaReceptors, TachykininReceptors, Opioid, kappaD-Ala(2),MePhe(4),Met(0)-ol-enkephalinNucleus AccumbensPainSubstance PNeurokinin ABehavior, AnimalReceptors, Neurokinin-2Time FactorsHyperalgesiaDynorphinsBrainAdenylate CyclaseSpinal CordNeuronsAnalgesicsOpioid-Related DisordersInjections, SpinalDrug Administration ScheduleCyclic AMPArrestinsBenzomorphansG Protein-Coupled Inwardly-Rectifying Potassium ChannelsCyclic AMP-Dependent Protein KinasesRNA, Transfer, GlyRats, WistarMice, Inbred C57BLMotor Activitybeta-EndorphinGuinea PigsBenzeneacetamidesRNA, MessengerMorphinansCarboxypeptidase HGTP-Binding Protein beta SubunitsDiprenorphineEtorphineExcitatory Postsynaptic PotentialsReceptors, N-Methyl-D-AspartateSynaptic TransmissionNeurokinin-1 Receptor AntagonistsMice, KnockoutOligopeptidesCodeineInhibitory Postsynaptic PotentialsSignal TransductionExcitatory Amino Acid AntagonistsPain, PostoperativeAnalysis of VariancePhosphorylationInjections, IntraventricularGlycinePiperidinesFentanylReceptors, Neurokinin-1Blotting, WesternAmino Acid SequenceThiorphanProtein PrecursorsPyrrolidinesMolecular Sequence DataDrug InteractionsKineticsGene Expression RegulationRats, Inbred StrainsPeptide Fragments