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-AlaninePainDiprenorphineAbnormalities, Multiplebeta-EndorphinBenzeneacetamidesAnalgesicsDrug ToleranceMorphinansFentanylMethadonePain MeasurementChromosome AberrationsHydromorphoneBenzomorphansPyrrolidinesSubstance Withdrawal SyndromeAnalgesiaBrainCongenital AbnormalitiesOpiate Substitution TreatmentChromosome DisordersDose-Response Relationship, DrugEye AbnormalitiesHeroinKaryotypingChronic PainMagnetic Resonance ImagingPrescription Drug MisuseLevorphanolRats, Sprague-DawleyMorphine DependenceButorphanolPrescription DrugsHeroin DependenceDiterpenes, ClerodaneTime FactorsOxymorphoneEthylketocyclazocineInjections, SpinalMorphine DerivativesOligopeptidesPregnancyPain, IntractablePain ThresholdDrug OverdoseCardiovascular AbnormalitiesBenzylidene CompoundsCraniofacial AbnormalitiesCyclazocinePeriaqueductal GrayAnalgesics, Non-NarcoticHyperalgesiaDisease Models, AnimalPhenotypeSyndromeMutationBehavior, AnimalD-Ala(2),MePhe(4),Met(0)-ol-enkephalinSkin AbnormalitiesRetrospective StudiesSpinal CordUrogenital AbnormalitiesAlfentanilNalbuphineHydrocodoneTrisomyAnalysis of VarianceDrug InteractionsMice, KnockoutTramadolChronic DiseaseMusculoskeletal AbnormalitiesGuanosine 5'-O-(3-Thiotriphosphate)In Situ Hybridization, FluorescenceRadioligand AssaySufentanilInfant, NewbornLoperamideTooth AbnormalitiesMice, Inbred C57BL