AnalgesicsAnalgesics, OpioidMice, KnockoutReceptors, Opioid, muDexmedetomidineAnalgesiaAnalgesics, Non-NarcoticPainReceptors, OpioidPain MeasurementMorphineNaloxoneReceptors, Opioid, deltaReceptors, Opioid, kappaPain ThresholdHypnotics and SedativesHyperalgesiaOpioid PeptidesKetamineDose-Response Relationship, DrugBehavior, AnimalRats, Sprague-DawleyNarcotic AntagonistsPlant ExtractsMice, Inbred C57BLOpioid-Related DisordersNaltrexoneGene Knockout TechniquesEnkephalinsNarcoticsPain, PostoperativeEnkephalin, Ala(2)-MePhe(4)-Gly(5)-TramadolDrug ToleranceBuprenorphineEndorphinsEnkephalin, D-Penicillamine (2,5)-FentanylDynorphinsAcetaminophenDisease Models, AnimalPhenacetinHydromorphoneEnkephalin, LeucineMorphinansDextropropoxypheneCodeineInjections, Spinalbeta-EndorphinEnkephalin, Leucine-2-AlanineAnti-Inflammatory Agents, Non-SteroidalPentazocineMeperidinePain ManagementMethadoneBenzeneacetamidesPain, IntractableDiprenorphineButorphanolAnesthetics, LocalTime FactorsHydrocodoneChronic PainMice, TransgenicOxymorphoneNociceptionSignal TransductionMorphine DerivativesBrainDouble-Blind MethodDipyroneAnalgesia, EpiduralLevorphanolNociceptorsAnalgesia, Patient-ControlledBenzomorphansSubstance Withdrawal SyndromeCells, CulturedGene TargetingBupivacaineGene DeletionNeuralgiaOxycodonePyrrolidinesMice, 129 StrainMotor ActivitySpinal CordNeuronsPhenotypeAlfentanilCyclazocineCarrageenanNalbuphinePrescription DrugsMorphine DependenceRNA, MessengerHeroinTolmetinGene Expression RegulationKetoprofen