MorphineDrug ToleranceMorphine DependenceAnalgesics, OpioidInjections, SpinalPain MeasurementReceptors, Opioid, muNarcoticsNaloxoneMorphine DerivativesNarcotic AntagonistsPeriaqueductal GrayAnalgesiaSubstance Withdrawal SyndromePainSpinal CordImmune ToleranceAnalgesicsRats, Sprague-DawleyPhysiological ProcessesMononeuropathiesMSH Release-Inhibiting HormoneHyperalgesiaAgmatineReceptors, N-Methyl-D-AspartateReceptors, Opioid, deltaHyperesthesiaNaltrexoneInjections, IntraventricularOpioid PeptidesDose-Response Relationship, DrugPain ThresholdInjections, SubcutaneousBehavior, AnimalEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Receptors, OpioidDizocilpine MaleateReceptors, Opioid, kappaExcitatory Amino Acid AntagonistsDrug InteractionsGlucose Tolerance TestPosterior Horn CellsFormaldehydeMice, Inbred ICRTransplantation ToleranceNeuralgiaReaction TimeHot TemperatureCodeineOligonucleotides, AntisenseDrug Administration ScheduleMice, Inbred C57BLNeurogliaPain, PostoperativeAnalysis of VarianceTime FactorsMice, KnockoutProtein Kinase CNeuronsDisease Models, AnimalRats, WistarSelf ToleranceInflammationNalorphineAnalgesia, Patient-ControlledFentanylHeroinHydromorphoneOxycodoneGlucose IntoleranceEnkephalinsPentazocineMorphinansSalt-ToleranceNalbuphineMeperidineAdaptation, PhysiologicalExercise ToleranceBlood Glucose