Receptors, Opioid, muReceptors, OpioidAnalgesics, OpioidReceptors, Opioid, deltaReceptors, Opioid, kappaOpioid PeptidesNarcotic AntagonistsNaloxoneOpioid-Related DisordersNaltrexoneEnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-MorphineNarcoticsEnkephalin, D-Penicillamine (2,5)-EndorphinsDynorphinsBuprenorphineEnkephalin, LeucineEnkephalin, Leucine-2-AlanineDiprenorphinePainbeta-EndorphinBenzeneacetamidesAnalgesicsDrug ToleranceMorphinansFentanylMethadonePain MeasurementHydromorphoneBenzomorphansPyrrolidinesAnalgesiaSubstance Withdrawal SyndromeOpiate Substitution TreatmentHeroinChronic PainPrescription Drug MisuseLevorphanolDose-Response Relationship, DrugMorphine DependenceButorphanolPrescription DrugsDiterpenes, ClerodaneHeroin DependenceOxymorphoneEthylketocyclazocineMorphine DerivativesInjections, SpinalRats, Sprague-DawleyPain, IntractableOligopeptidesBenzylidene CompoundsDrug OverdosePain ThresholdCyclazocineAnalgesics, Non-NarcoticPeriaqueductal GrayD-Ala(2),MePhe(4),Met(0)-ol-enkephalinHyperalgesiaAlfentanilNalbuphineHydrocodoneTramadolGuanosine 5'-O-(3-Thiotriphosphate)Drug InteractionsRadioligand AssaySufentanilLoperamideOpiate AlkaloidsPain, PostoperativePain ManagementMethadyl AcetateCodeineAzocinesNociceptorsSpinal CordPiperidinesLigandsPentazocineSomatostatinBehavior, AnimalMeperidineMeptazinolDihydromorphineBrainGuinea PigsSubstance-Related DisordersInjections, IntraventricularDrug PrescriptionsVas DeferensCHO CellsRats, WistarBinding, CompetitiveSalviaChronic DiseaseSelf AdministrationTime FactorsSubstance Abuse Detection