EnkephalinsMorphineEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, LeucineEnkephalin, MethionineReceptors, Opioid, muReceptors, OpioidAnalgesics, OpioidEnkephalin, D-Penicillamine (2,5)-Receptors, Opioid, deltaEnkephalin, Leucine-2-AlanineReceptors, Opioid, kappaNaloxoneEndorphinsNarcotic AntagonistsMorphine DerivativesMorphine DependenceOpioid PeptidesNarcoticsReceptors, Neurokinin-3NaltrexoneDrug ToleranceEthylketocyclazocineCyclazocineNeurokinin BDynorphinsTachykininsReceptors, TachykininAnalgesicsD-Ala(2),MePhe(4),Met(0)-ol-enkephalinBenzeneacetamidesDiprenorphineBenzomorphansSubstance Pbeta-EndorphinPain MeasurementInjections, SpinalNeurokinin ADose-Response Relationship, DrugPainOpioid-Related DisordersReceptors, Neurokinin-2AnalgesiaMorphinansRats, Sprague-DawleyEtorphineOligopeptidesPyrrolidinesSubstance Withdrawal SyndromeFentanylPeriaqueductal GrayGuinea PigsRNA, Transfer, GlySomatostatinCarboxypeptidase HBuprenorphineSpinal CordCodeineMethadoneGuanosine 5'-O-(3-Thiotriphosphate)Pain, PostoperativeHydromorphoneLocus CoeruleusInjections, IntraventricularNeurokinin-1 Receptor AntagonistsHeroinDrug InteractionsPain ThresholdBrainPiperidinesBehavior, AnimalNeuronsOxymorphoneAmino Acid SequenceProtein PrecursorsMicroinjectionsHyperalgesiaNociceptorsGlycineReceptors, Neurokinin-1PentazocineMolecular Sequence DataThiorphanIleumPeptide FragmentsAnalgesics, Non-NarcoticAnalgesia, Patient-ControlledElectric StimulationNucleus AccumbensBinding, CompetitiveBenzylidene CompoundsRadioligand AssayKineticsVas DeferensNalbuphineSubstantia GelatinosaMedulla OblongataNeurotransmitter AgentsNalorphineNeprilysin