Receptors, OpioidReceptors, Opioid, muReceptors, Opioid, deltaReceptors, Opioid, kappaAnalgesics, OpioidNarcotic AntagonistsNaltrexoneOpioid PeptidesNaloxoneEnkephalin, Ala(2)-MePhe(4)-Gly(5)-EnkephalinsEnkephalin, D-Penicillamine (2,5)-MorphineDiprenorphineDynorphinsEnkephalin, LeucineEnkephalin, Leucine-2-AlanineBenzeneacetamidesNarcoticsMorphinansBenzomorphansAnalgesicsEndorphinsPyrrolidinesEtorphinebeta-EndorphinDose-Response Relationship, DrugDiterpenes, ClerodaneOpioid-Related DisordersRats, Sprague-DawleyEthylketocyclazocineDrug ToleranceCyclazocineBenzylidene CompoundsPainLevorphanolFentanylPain MeasurementOligopeptidesEnkephalin, MethionineBuprenorphineRadioligand AssayAnalgesiaPiperidinesNeurokinin-1 Receptor AntagonistsDopamine AntagonistsGuanosine 5'-O-(3-Thiotriphosphate)LigandsHormone AntagonistsExcitatory Amino Acid AntagonistsMorphine DerivativesButorphanolInjections, SpinalRats, WistarBinding, CompetitiveHeroinSubstance Withdrawal SyndromeCHO CellsMorphine DependenceGuinea PigsPeriaqueductal GrayDrug InteractionsInjections, IntraventricularHistamine H2 AntagonistsHyperalgesiaGABA AntagonistsCricetinaeSomatostatinBehavior, AnimalInterleukin 1 Receptor Antagonist ProteinLoperamideSpinal CordMethadoneNociceptorsMuscarinic AntagonistsSpiro CompoundsPain ThresholdAnalgesics, Non-NarcoticBrainCricetulusPiperazinesHistamine H1 AntagonistsStructure-Activity RelationshipPurinergic P1 Receptor AntagonistsMicroinjectionsAzocinesNeuronsSalviaOpiate AlkaloidsElectric StimulationHydromorphoneVas DeferensNicotinic AntagonistsCyclic AMPHistamine AntagonistsAdrenergic alpha-2 Receptor AntagonistsSignal TransductionTime FactorsAdenosine A2 Receptor AntagonistsCell Line