EnkephalinsMorphineEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, LeucineEnkephalin, MethionineEnkephalin, D-Penicillamine (2,5)-Enkephalin, Leucine-2-AlanineEndorphinsReceptors, Opioid, muReceptors, OpioidMorphine DependenceMorphine DerivativesNaloxoneAnalgesics, OpioidReceptors, Opioid, deltaReceptors, Neurokinin-3Narcotic AntagonistsNeurokinin BEthylketocyclazocineNarcoticsCyclazocineTachykininsReceptors, TachykininDrug ToleranceReceptors, Opioid, kappaD-Ala(2),MePhe(4),Met(0)-ol-enkephalinSubstance PNeurokinin ANaltrexoneReceptors, Neurokinin-2DynorphinsAnalgesicsInjections, SpinalRNA, Transfer, GlyBenzomorphansDose-Response Relationship, DrugAnalgesiaMolecular Sequence DataPain Measurementbeta-EndorphinOpioid PeptidesAmino Acid SequenceBenzeneacetamidesCarboxypeptidase HMorphinansGuinea PigsSubstance Withdrawal SyndromeDiprenorphineEtorphineRats, Sprague-DawleyProtein BindingBinding SitesOligopeptidesPainNeurokinin-1 Receptor AntagonistsCodeinePain, PostoperativeGlycineKineticsPeriaqueductal GrayFentanylReceptors, Neurokinin-1Peptide FragmentsThiorphanPiperidinesBrainProtein PrecursorsBinding, CompetitiveInjections, IntraventricularBase SequenceModels, MolecularPyrrolidinesLocus CoeruleusSpinal CordPentazocineIleumMutagenesis, Site-DirectedNeprilysinAnalgesia, Patient-ControlledNalorphineTioproninAlanineAdrenal MedullaBehavior, AnimalPeptidesProtein ConformationSomatostatinRats, Inbred StrainsNeuronsHeroinOxymorphoneVas DeferensPain ThresholdIrisHydromorphoneCell LineMutationDrug InteractionsAmino Acid SubstitutionOxycodone