EnkephalinsMorphineReceptors, OpioidEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Receptors, Opioid, muEnkephalin, LeucineEnkephalin, MethionineReceptors, Opioid, deltaEnkephalin, D-Penicillamine (2,5)-Analgesics, OpioidReceptors, Opioid, kappaEnkephalin, Leucine-2-AlanineNaloxoneNarcotic AntagonistsEndorphinsNaltrexoneOpioid PeptidesMorphine DerivativesMorphine DependenceNarcoticsDynorphinsDiprenorphineEthylketocyclazocineCyclazocineDrug ToleranceBenzeneacetamidesReceptors, Neurokinin-3MorphinansBenzomorphansAnalgesicsbeta-EndorphinEtorphineD-Ala(2),MePhe(4),Met(0)-ol-enkephalinNeurokinin BTachykininsPain MeasurementPyrrolidinesReceptors, TachykininAnalgesiaPainInjections, SpinalDose-Response Relationship, DrugFentanylSubstance PBenzylidene CompoundsOligopeptidesOpioid-Related DisordersRats, Sprague-DawleySubstance Withdrawal SyndromeNeurokinin ADiterpenes, ClerodaneLevorphanolReceptors, Neurokinin-2Guinea PigsPeriaqueductal GrayBuprenorphineHeroinGuanosine 5'-O-(3-Thiotriphosphate)Injections, IntraventricularSomatostatinSpinal CordRNA, Transfer, GlyPain ThresholdButorphanolRadioligand AssayMethadoneBrainPiperidinesHydromorphoneBehavior, AnimalHyperalgesiaNeurokinin-1 Receptor AntagonistsCarboxypeptidase HNociceptorsLigandsAmino Acid SequenceProtein PrecursorsBinding, CompetitiveDrug InteractionsIleumPain, PostoperativeMolecular Sequence DataVas DeferensCodeineAnalgesics, Non-NarcoticDihydromorphineLocus CoeruleusOxymorphoneNalbuphinePentazocineCHO CellsStructure-Activity RelationshipNeuronsRats, WistarLoperamideMicroinjectionsThiorphanReceptors, Neurokinin-1KineticsNucleus Accumbens