MorphineAnalgesics, OpioidAnalgesicsReceptors, Opioid, muReceptors, OpioidReceptors, Opioid, deltaSleep, REMMorphine DerivativesMorphine DependenceReceptors, Opioid, kappaNaloxoneOpioid PeptidesNarcotic AntagonistsAnalgesics, Non-NarcoticDrug ToleranceAnalgesiaNarcoticsPain MeasurementPainNaltrexonePain, PostoperativeOpioid-Related DisordersEnkephalin, Ala(2)-MePhe(4)-Gly(5)-EnkephalinsSleep DeprivationInjections, SpinalCodeineElectroencephalographyFentanylTramadolSleepSleep StagesEndorphinsWakefulnessBuprenorphineHydromorphoneRats, Sprague-DawleySubstance Withdrawal SyndromeEnkephalin, D-Penicillamine (2,5)-MorphinansDose-Response Relationship, DrugPain ThresholdPentazocinePharmacovigilanceAnalgesia, Patient-ControlledMeperidineDynorphinsEnkephalin, LeucineHeroinMethadoneOxycodoneHyperalgesiaNalorphineAcetaminophenOxymorphoneNalbuphineAnalgesia, EpiduralPain, IntractablePhenacetinPeriaqueductal Graybeta-EndorphinEnkephalin, Leucine-2-AlanineElectromyographyBrain WavesDextropropoxypheneDouble-Blind MethodElectrooculographyAnti-Inflammatory Agents, Non-SteroidalHydrocodoneAnesthetics, LocalTime FactorsLevorphanolArousalDiprenorphineButorphanolBupivacaineRats, WistarPain ManagementDipyroneBenzomorphansNociceptorsBenzeneacetamidesBehavior, AnimalSpinal CordKetorolacDrug InteractionsCyclazocineNociceptionHypothalamusAlfentanilChronic PainSufentanilTolmetinAnalysis of VarianceBrainOpiumPyrrolidinesInjections, IntraventricularPolysomnographyBrain Stem