Receptors, Opioid, kappaAnalgesicsAnalgesics, OpioidReceptors, Opioid, muReceptors, OpioidReceptors, Opioid, deltaAnalgesics, Non-NarcoticPainNaloxoneAnalgesiaDynorphinsDexmedetomidineNaltrexoneOpioid PeptidesNarcotic AntagonistsPain MeasurementMorphineBenzeneacetamidesDiterpenes, ClerodaneMorphinansEnkephalinsPain ThresholdHyperalgesiaPyrrolidinesHypnotics and SedativesEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, D-Penicillamine (2,5)-Dose-Response Relationship, DrugNarcoticsKetamineEndorphinsOpioid-Related DisordersSalviaRats, Sprague-DawleyDiprenorphineBehavior, AnimalLevorphanolPlant ExtractsFentanylDrug ToleranceButorphanolBuprenorphineEthylketocyclazocineNalbuphineEnkephalin, LeucineCyclazocineImmobility Response, TonicEnkephalin, Leucine-2-AlaninePain, PostoperativeTramadolInjections, SpinalSpiro CompoundsSubstance Withdrawal Syndromebeta-EndorphinHydromorphoneTetrahydroisoquinolinesImmunoglobulin kappa-ChainsGuanosine 5'-O-(3-Thiotriphosphate)MethadoneRadioligand AssayBenzomorphansDrug InteractionsSelf AdministrationCHO CellsNociceptorsG-Protein-Coupled Receptor Kinase 3EtorphineCodeinePiperidinesLigandsAcetaminophenChronic PainSpinal CordOligopeptidesCocaineAntipruriticsPhenacetinConditioning, OperantPain, IntractableDextropropoxyphenePain ManagementPentazocineProtein PrecursorsOxymorphoneMorphine DerivativesMeperidineCricetulusGuinea PigsHeroinHydrocodoneInjections, IntraventricularCricetinaeDiterpenesCocaine-Related DisordersAnti-Inflammatory Agents, Non-SteroidalPrescription DrugsBrainOpiate Substitution TreatmentMorphine DependenceBenzofurans