MorphineNaloxoneEnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, MethionineEnkephalin, LeucineMorphine DependenceReceptors, Opioid, muAnalgesics, OpioidNarcoticsNarcotic AntagonistsDrug ToleranceEnkephalin, D-Penicillamine (2,5)-Enkephalin, Leucine-2-AlanineReceptors, OpioidReceptors, Opioid, deltaEndorphinsMorphine DerivativesSubstance Withdrawal SyndromeNaltrexoneLevallorphanLocus CoeruleusReceptors, Neurokinin-3Periaqueductal GrayOpioid PeptidesRats, Sprague-DawleyEthylketocyclazocineCyclazocineReceptors, Opioid, kappaPain MeasurementNeurokinin BDose-Response Relationship, DrugTachykininsAnalgesiaReceptors, TachykininD-Ala(2),MePhe(4),Met(0)-ol-enkephalinPainNucleus AccumbensOpioid-Related DisordersAnalgesicsSubstance PDynorphinsbeta-EndorphinBehavior, AnimalNeurokinin AHyperalgesiaInjections, SpinalSpinal CordReceptors, Neurokinin-2Time FactorsBrainMorphinansNeuronsAdenylate CyclaseDiprenorphineBenzeneacetamidesEtorphineBuprenorphineArrestinsDrug Administration ScheduleRNA, Transfer, GlyG Protein-Coupled Inwardly-Rectifying Potassium ChannelsCyclic AMPBenzomorphansMotor ActivityGuinea PigsRats, WistarCyclic AMP-Dependent Protein KinasesMice, Inbred C57BLFentanylCodeineCarboxypeptidase HPentazocineGTP-Binding Protein beta SubunitsInjections, IntraventricularNalorphineRNA, MessengerReceptors, N-Methyl-D-AspartateSynaptic TransmissionOligopeptidesExcitatory Postsynaptic PotentialsPyrrolidinesMice, KnockoutOxycodonePain, PostoperativeHeroinNeurokinin-1 Receptor AntagonistsInhibitory Postsynaptic PotentialsAnalysis of VarianceExcitatory Amino Acid AntagonistsPiperidinesThiorphanIleumGlycinePain ThresholdRats, Inbred StrainsMeperidineDrug OverdoseDrug InteractionsReceptors, Neurokinin-1