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 BEthylketocyclazocineCyclazocineOpioid PeptidesTachykininsAnalgesiaPain MeasurementReceptors, TachykininDose-Response Relationship, DrugReceptors, Opioid, kappaD-Ala(2),MePhe(4),Met(0)-ol-enkephalinNucleus AccumbensPainSubstance PNeurokinin AReceptors, Neurokinin-2Behavior, AnimalHyperalgesiaDynorphinsSpinal CordAdenylate CyclaseBrainOpioid-Related DisordersTime FactorsNeuronsAnalgesicsInjections, SpinalArrestinsRNA, Transfer, GlyG Protein-Coupled Inwardly-Rectifying Potassium ChannelsBenzomorphansDrug Administration ScheduleCyclic AMP-Dependent Protein KinasesCyclic AMPbeta-EndorphinMotor ActivityMice, Inbred C57BLBenzeneacetamidesCarboxypeptidase HMorphinansGuinea PigsGTP-Binding Protein beta SubunitsRats, WistarDiprenorphineEtorphineRNA, MessengerExcitatory Postsynaptic PotentialsReceptors, N-Methyl-D-AspartateSynaptic TransmissionNeurokinin-1 Receptor AntagonistsCodeineInhibitory Postsynaptic PotentialsMice, KnockoutPain, PostoperativeOligopeptidesExcitatory Amino Acid AntagonistsGlycineFentanylAnalysis of VarianceReceptors, Neurokinin-1ThiorphanPiperidinesAmino Acid SequenceProtein PrecursorsSignal TransductionPhosphorylationInjections, IntraventricularMolecular Sequence DataPyrrolidinesBlotting, WesternPentazocineIleumGene Expression RegulationPeptide FragmentsAnalgesia, Patient-Controlled