Receptors, Opioid, kappaDiterpenes, ClerodaneBenzeneacetamidesReceptors, Opioid, muDynorphinsPyrrolidinesReceptors, OpioidReceptors, Opioid, deltaNaltrexoneEnkephalin, D-Penicillamine (2,5)-Analgesics, OpioidEnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Narcotic AntagonistsMorphinansNaloxoneOpioid PeptidesBenzomorphansMorphineAnalgesicsDiprenorphineEthylketocyclazocineNarcoticsEndorphinsCyclazocineButorphanolLevorphanolSalviaEnkephalin, Leucine-2-AlanineSpiro CompoundsEnkephalin, LeucineD-Ala(2),MePhe(4),Met(0)-ol-enkephalinRats, Sprague-DawleyDose-Response Relationship, DrugOligopeptidesEtorphineFentanylRadioligand AssayPain MeasurementPainDrug ToleranceBenzylidene CompoundsGuanosine 5'-O-(3-Thiotriphosphate)Immobility Response, TonicGuinea PigsDrug InteractionsCricetulusAnalgesics, Non-NarcoticCHO CellsCricetinaePiperidinesHyperalgesiaEnkephalin, MethionineBehavior, AnimalRats, WistarLigandsTetrahydroisoquinolinesSpinal CordInjections, SpinalG-Protein-Coupled Receptor Kinase 3Purinergic P1 Receptor AgonistsSelf StimulationLoperamideStructure-Activity RelationshipMotor ActivitySerotonin Receptor AgonistsSubstance Withdrawal SyndromeCocaineDopamine AgonistsElectric StimulationNeurokinin-1 Receptor AntagonistsSelf AdministrationPiperazinesNeuronsSerotonin 5-HT1 Receptor AgonistsBinding, CompetitiveConditioning, OperantVas Deferensbeta-EndorphinBenzofuransDiterpenesSerotonin 5-HT2 Receptor AgonistsProtein PrecursorsBenzamidesAdenosine A1 Receptor AgonistsSwimmingMolecular Sequence DataBrainNalbuphineAdenylate CyclaseOpioid-Related DisordersMice, Inbred C57BLIleumAmino Acid SequenceCell LineCocaine-Related DisordersSignal TransductionStereoisomerismCyclic AMPNucleus Accumbens