MorphineMethadoneEnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, LeucineEnkephalin, MethionineMorphine DerivativesNarcoticsMorphine DependenceAnalgesics, OpioidEnkephalin, D-Penicillamine (2,5)-Enkephalin, Leucine-2-AlanineReceptors, Opioid, muNaloxoneEndorphinsReceptors, OpioidNarcotic AntagonistsDrug ToleranceReceptors, Opioid, deltaOpioid-Related DisordersOpiate Substitution TreatmentReceptors, Neurokinin-3Heroin DependenceEthylketocyclazocineCyclazocineNeurokinin BNaltrexoneHeroinMethadyl AcetateSubstance Withdrawal SyndromeBuprenorphineReceptors, Opioid, kappaTachykininsReceptors, TachykininInjections, SpinalAnalgesiaPain MeasurementAnalgesicsDose-Response Relationship, DrugCodeineD-Ala(2),MePhe(4),Met(0)-ol-enkephalinSubstance PPainNeonatal Abstinence SyndromeNeurokinin ADynorphinsPain, PostoperativeReceptors, Neurokinin-2PyrrolidinesMorphinansRats, Sprague-DawleyDiprenorphineBenzomorphansSubstance Abuse DetectionFentanylHydromorphoneNalorphineEtorphineOpioid Peptidesbeta-EndorphinOpiumPeriaqueductal GrayDrug InteractionsRNA, Transfer, GlyOxycodonePentazocineAnalgesia, Patient-ControlledBenzeneacetamidesGuinea PigsCarboxypeptidase HMeperidineInjections, IntraventricularBehavior, AnimalPain ThresholdDrug OverdoseNeurokinin-1 Receptor AntagonistsSpinal CordOxymorphoneLocus CoeruleusNalbuphineOligopeptidesStreet DrugsBrainSubstance-Related DisordersTime FactorsPain, IntractablePiperidinesThebaineDextropropoxypheneGlycineReceptors, Neurokinin-1StereoisomerismIleumAnalgesia, EpiduralTramadolDouble-Blind MethodHyperalgesiaThiorphanProtein PrecursorsInjections, Subcutaneous