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 BEthylketocyclazocineOpioid PeptidesCyclazocineTachykininsAnalgesiaPain MeasurementReceptors, TachykininDose-Response Relationship, DrugReceptors, Opioid, kappaD-Ala(2),MePhe(4),Met(0)-ol-enkephalinNucleus AccumbensPainSubstance PNeurokinin AReceptors, Neurokinin-2Behavior, AnimalHyperalgesiaDynorphinsBrainTime FactorsSpinal CordAdenylate CyclaseNeuronsOpioid-Related DisordersAnalgesicsInjections, SpinalArrestinsRNA, Transfer, GlyG Protein-Coupled Inwardly-Rectifying Potassium ChannelsBenzomorphansDrug Administration ScheduleCyclic AMP-Dependent Protein KinasesCyclic AMPMolecular Sequence DataMice, Inbred C57BLbeta-EndorphinMotor ActivityAmino Acid SequenceBenzeneacetamidesCarboxypeptidase HRNA, MessengerMorphinansGuinea PigsRats, WistarGTP-Binding Protein beta SubunitsDiprenorphineEtorphineExcitatory Postsynaptic PotentialsReceptors, N-Methyl-D-AspartateSynaptic TransmissionProtein BindingMice, KnockoutBinding SitesOligopeptidesNeurokinin-1 Receptor AntagonistsCodeineInhibitory Postsynaptic PotentialsPain, PostoperativeSignal TransductionExcitatory Amino Acid AntagonistsGlycinePhosphorylationKineticsFentanylAnalysis of VarianceReceptors, Neurokinin-1Peptide FragmentsGene Expression RegulationBlotting, WesternThiorphanPiperidinesProtein PrecursorsBinding, CompetitiveInjections, Intraventricular