MorphineEnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Receptors, Opioid, muEnkephalin, MethionineEnkephalin, LeucineAnalgesics, OpioidMorphine DependenceReceptors, OpioidReceptors, Opioid, deltaNarcoticsDrug ToleranceNaloxoneEnkephalin, D-Penicillamine (2,5)-Enkephalin, Leucine-2-AlanineNarcotic AntagonistsMorphine DerivativesEndorphinsSubstance Withdrawal SyndromeReceptors, Opioid, kappaOpioid PeptidesNaltrexoneLocus CoeruleusReceptors, Neurokinin-3LevallorphanPeriaqueductal GrayRats, Sprague-DawleyEthylketocyclazocinePain MeasurementAnalgesiaOpioid-Related DisordersCyclazocineNeurokinin BPainDose-Response Relationship, DrugTachykininsReceptors, TachykininDynorphinsD-Ala(2),MePhe(4),Met(0)-ol-enkephalinNucleus AccumbensAnalgesicsSubstance PBehavior, AnimalHyperalgesiaNeurokinin Abeta-EndorphinBenzomorphansBenzeneacetamidesDiprenorphineReceptors, Neurokinin-2Spinal CordMorphinansInjections, SpinalBrainAdenylate CyclaseTime FactorsNeuronsArrestinsDrug Administration ScheduleG Protein-Coupled Inwardly-Rectifying Potassium ChannelsCyclic AMPFentanylRNA, Transfer, GlyCyclic AMP-Dependent Protein KinasesMotor ActivityGuinea PigsRats, WistarMice, Inbred C57BLCarboxypeptidase HOligopeptidesBuprenorphineGTP-Binding Protein beta SubunitsCodeinePyrrolidinesRNA, MessengerPain, PostoperativeHydromorphoneEtorphineExcitatory Postsynaptic PotentialsReceptors, N-Methyl-D-AspartateSynaptic TransmissionNeurokinin-1 Receptor AntagonistsMice, KnockoutMethadoneInhibitory Postsynaptic PotentialsHeroinPiperidinesExcitatory Amino Acid AntagonistsAnalysis of VarianceOxymorphoneInjections, IntraventricularProtein PrecursorsGlycineReceptors, Neurokinin-1PentazocinePain ThresholdAmino Acid SequenceSignal TransductionThiorphanIleum