Receptors, Opioid, kappaMorphinansNarcotic AntagonistsNaltrexoneReceptors, Opioid, muReceptors, OpioidNaloxoneReceptors, Opioid, deltaAnalgesics, OpioidDynorphinsOpioid PeptidesBenzeneacetamidesDiterpenes, ClerodaneEnkephalinsEndorphinsPyrrolidinesEnkephalin, Ala(2)-MePhe(4)-Gly(5)-NarcoticsEnkephalin, D-Penicillamine (2,5)-DiprenorphineMorphineAnalgesicsLevorphanolDose-Response Relationship, DrugSalviaEnkephalin, LeucineEnkephalin, Leucine-2-AlanineEnkephalin, MethionineAzocinesOpioid-Related DisordersPain MeasurementSubstance Withdrawal SyndromeBenzomorphansRats, Sprague-Dawleybeta-EndorphinFentanylPainAnalgesics, Non-NarcoticEtorphineTetrahydroisoquinolinesAntipruriticsBuprenorphineDrug TolerancePiperidinesDrug InteractionsMorphine DependenceOxymorphoneEthylketocyclazocineInjections, IntraventricularHeroinOligopeptidesConditioning, OperantBehavior, AnimalInjections, SpinalImmobility Response, TonicSelf AdministrationBenzylidene CompoundsButorphanolGuinea PigsNalbuphineSpiro CompoundsRadioligand AssayAnalgesiaRats, WistarLigandsMeptazinolHallucinogensNociceptorsPain ThresholdPruritusDrug Inverse AgonismImmunoglobulin kappa-ChainsEthanolMotor ActivitySpinal CordStereoisomerismHyperalgesiaCyclazocineHormone AntagonistsBrainGuanosine 5'-O-(3-Thiotriphosphate)CHO CellsAnalysis of VariancePeriaqueductal GrayTime FactorsNeurokinin-1 Receptor AntagonistsDopamine AntagonistsExcitatory Amino Acid AntagonistsElectric StimulationCocaineBinding, CompetitiveG-Protein-Coupled Receptor Kinase 3Histamine H2 AntagonistsCricetinaeNeuronsCricetulusInterleukin 1 Receptor Antagonist ProteinInjections, SubcutaneousSomatostatinBenzofurans