EnkephalinsMorphineEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, LeucineEnkephalin, MethionineEnkephalin, D-Penicillamine (2,5)-Receptors, Opioid, muEnkephalin, Leucine-2-AlanineEndorphinsReceptors, OpioidAnalgesics, OpioidNaloxoneReceptors, Opioid, deltaMorphine DerivativesMorphine DependenceNarcotic AntagonistsReceptors, Neurokinin-3NarcoticsReceptors, Opioid, kappaEthylketocyclazocineDrug ToleranceNeurokinin BCyclazocineTachykininsReceptors, TachykininNaltrexoneD-Ala(2),MePhe(4),Met(0)-ol-enkephalinSubstance PAnalgesicsOpioid PeptidesNeurokinin ADynorphinsReceptors, Neurokinin-2BenzeneacetamidesDiprenorphineInjections, SpinalBenzomorphansEtorphinePain MeasurementDose-Response Relationship, Drugbeta-EndorphinRNA, Transfer, GlyRats, Sprague-DawleyAnalgesiaOligopeptidesGuinea PigsPeriaqueductal GrayCarboxypeptidase HMorphinansPyrrolidinesSubstance Withdrawal SyndromePainSomatostatinLocus CoeruleusNeurokinin-1 Receptor AntagonistsFentanylSpinal CordCodeineInjections, IntraventricularPain, PostoperativeGuanosine 5'-O-(3-Thiotriphosphate)GlycineAmino Acid SequenceBrainReceptors, Neurokinin-1NeuronsThiorphanDrug InteractionsPiperidinesProtein PrecursorsBehavior, AnimalMolecular Sequence DataMicroinjectionsPeptide FragmentsPain ThresholdSubstantia GelatinosaNociceptorsElectric StimulationPentazocineKineticsIleumAnalgesia, Patient-ControlledNalorphineNucleus AccumbensNeprilysinTioproninHyperalgesiaBinding, CompetitiveNeurotransmitter AgentsAdrenal MedullaMedulla OblongataHeroinOxymorphoneAlanineVas DeferensHydromorphoneIrisRats, Inbred StrainsPeptidesMethadone