MorphineDrug ToleranceMorphine DependenceMorphine DerivativesAnalgesics, OpioidImmune ToleranceNarcoticsNaloxoneGlucose Tolerance TestReceptors, Opioid, muNarcotic AntagonistsTransplantation ToleranceAnalgesiaPain MeasurementInjections, SpinalSubstance Withdrawal SyndromeCodeinePain, PostoperativeAnalgesicsPainDose-Response Relationship, DrugReceptors, OpioidNaltrexoneSelf ToleranceRats, Sprague-DawleyEnkephalin, Ala(2)-MePhe(4)-Gly(5)-NalorphineAnalgesia, Patient-ControlledPeriaqueductal GrayFentanylHeroinHydromorphoneOxycodoneReceptors, Opioid, deltaGlucose IntoleranceEnkephalinsPentazocinePain ThresholdMorphinansSalt-ToleranceNalbuphineTime FactorsMeperidineMice, Inbred C57BLBehavior, AnimalAdaptation, PhysiologicalInjections, SubcutaneousExercise ToleranceBlood GlucoseThebaineDroughtsDouble-Blind MethodStress, PhysiologicalOxymorphoneDrug InteractionsSpinal CordAnalgesia, EpiduralReceptors, Opioid, kappaPeripheral ToleranceEndorphinsOpiumInjections, IntravenousMethadoneHyperalgesiaInjections, IntraventricularEtorphineHot TemperatureLocus CoeruleusSodium ChlorideSkin TransplantationAcclimatizationDrug Administration ScheduleMotor ActivityMice, KnockoutLevorphanolAdministration, OralPapaverLevallorphanPain, IntractableOpioid-Related DisordersTramadolInjections, IntraperitonealEnkephalin, D-Penicillamine (2,5)-ClonidineSalt-Tolerant PlantsOpioid PeptidesMice, TransgenicAgmatineInsulin ResistanceBupivacaineAnalgesics, Non-NarcoticNociceptorsBuprenorphineRats, WistarAnalysis of VarianceT-Lymphocytes, RegulatoryDisease Models, AnimalMice, Inbred BALB CPruritus