AnalgesicsAnalgesics, OpioidReceptors, Opioid, muReceptors, OpioidSleep, REMReceptors, Opioid, deltaReceptors, Opioid, kappaOpioid PeptidesAnalgesics, Non-NarcoticMorphineNarcotic AntagonistsPainAnalgesiaNaloxonePain MeasurementSleep DeprivationOpioid-Related DisordersElectroencephalographyNaltrexoneSleepSleep StagesWakefulnessPain, PostoperativeEnkephalinsTramadolNarcoticsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Drug TolerancePharmacovigilanceBuprenorphineEndorphinsEnkephalin, D-Penicillamine (2,5)-FentanylDynorphinsPhenacetinBrain WavesAcetaminophenElectromyographyPain ThresholdHydromorphoneElectrooculographyRats, Sprague-DawleyEnkephalin, LeucineMorphinansDextropropoxypheneCodeineArousalInjections, SpinalEnkephalin, Leucine-2-AlanineHyperalgesiabeta-EndorphinAnti-Inflammatory Agents, Non-SteroidalMeperidinePain ManagementPentazocineDose-Response Relationship, DrugMethadoneBenzeneacetamidesPain, IntractableDiprenorphineRats, WistarButorphanolAnesthetics, LocalHydrocodoneChronic PainHypothalamusPolysomnographyOxymorphoneTime FactorsMorphine DerivativesRisk ManagementDouble-Blind MethodDipyroneAnalgesia, EpiduralLevorphanolAnalgesia, Patient-ControlledBenzomorphansBupivacaineOxycodoneNociceptorsAlfentanilCyclazocineNociceptionNalbuphineSubstance Withdrawal SyndromePrescription DrugsBrain StemPyrrolidinesHeroinNeuralgiaTolmetinAnalysis of VarianceCarrageenanKetoprofenSufentanilMeptazinolKetorolacAcupuncture AnalgesiaBrainCircadian Rhythm