Receptors, OpioidReceptors, Opioid, muReceptors, Opioid, deltaReceptors, Opioid, kappaAnalgesics, OpioidNarcotic AntagonistsOpioid PeptidesNaltrexoneNaloxoneEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, D-Penicillamine (2,5)-EnkephalinsDiprenorphineMorphineDynorphinsEnkephalin, Leucine-2-AlanineEnkephalin, LeucineBenzeneacetamidesNarcoticsMorphinansBenzomorphansAnalgesicsEndorphinsEtorphinebeta-EndorphinPyrrolidinesDiterpenes, ClerodaneOpioid-Related DisordersEthylketocyclazocineCyclazocineBenzylidene CompoundsDrug ToleranceLevorphanolPainFentanylPain MeasurementBuprenorphineEnkephalin, MethionineAnalgesiaOligopeptidesMorphine DerivativesButorphanolGuanosine 5'-O-(3-Thiotriphosphate)Dose-Response Relationship, DrugRats, Sprague-DawleyHeroinSubstance Withdrawal SyndromeMorphine DependenceInjections, SpinalRadioligand AssayLigandsPeriaqueductal GrayMethadoneLoperamideCHO CellsSomatostatinHyperalgesiaPain ThresholdNociceptorsAnalgesics, Non-NarcoticOpiate AlkaloidsSalviaSpinal CordHydromorphoneInjections, IntraventricularCricetinaeBinding, CompetitiveCricetulusD-Ala(2),MePhe(4),Met(0)-ol-enkephalinAzocinesSpiro CompoundsGuinea PigsBehavior, AnimalG-Protein-Coupled Receptor Kinase 3Drug InteractionsBrainDihydromorphineArrestinsHeroin DependenceRats, WistarPiperidinesGTP-Binding ProteinsMicroinjectionsNalbuphineTramadolVas DeferensNociceptionNucleus AccumbensStructure-Activity RelationshipAdenylate CyclaseIleumElectroacupunctureChronic PainCyclic AMPStereoisomerismOxymorphoneConditioning, OperantPertussis ToxinTetrahydroisoquinolinesBenzamides