MorphineEnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-AnalgesicsAnalgesics, OpioidEnkephalin, LeucineEnkephalin, MethionineMorphine DerivativesAnalgesiaReceptors, Opioid, muEndorphinsDrug ToleranceReceptors, OpioidMorphine DependenceEnkephalin, D-Penicillamine (2,5)-Enkephalin, Leucine-2-AlanineHydromorphoneAnalgesics, Non-NarcoticNaloxonePain MeasurementPainNarcoticsReceptors, Opioid, deltaNarcotic AntagonistsBupivacaineDose-Response Relationship, DrugReceptors, Neurokinin-3CyclazocineEthylketocyclazocinePain, PostoperativeInjections, SpinalNeurokinin BReceptors, Opioid, kappaNaltrexoneTachykininsReceptors, TachykininCodeineD-Ala(2),MePhe(4),Met(0)-ol-enkephalinSubstance PSubstance Withdrawal SyndromeMorphinansFentanylNeurokinin ADynorphinsRats, Sprague-DawleyReceptors, Neurokinin-2PentazocineOpioid PeptidesTramadolBenzomorphansAnalgesia, Patient-ControlledNalorphinePain ThresholdOxycodonebeta-EndorphinPeriaqueductal GrayEtorphineMeperidineGuinea PigsBenzeneacetamidesRNA, Transfer, GlyOxymorphoneAnalgesia, EpiduralHyperalgesiaHeroinDiprenorphineNalbuphineSpinal CordBehavior, AnimalInjections, IntraventricularDrug InteractionsPiperidinesOligopeptidesCarboxypeptidase HDouble-Blind MethodAcetaminophenAnesthetics, LocalLocus CoeruleusNociceptorsNeurokinin-1 Receptor AntagonistsBrainAnti-Inflammatory Agents, Non-SteroidalDipyronePain, IntractableMethadonePhenacetinTime FactorsPyrrolidinesGlycineKetorolacDextropropoxypheneHydrocodoneBuprenorphineReceptors, Neurokinin-1IleumAmino Acid SequenceOpiumThebaineStructure-Activity RelationshipInjections, Subcutaneous