AnalgesicsAnalgesics, OpioidReceptors, Opioid, muDexmedetomidineAnalgesiaAnalgesics, Non-NarcoticPainReceptors, OpioidPain MeasurementMorphineNaloxoneReceptors, Opioid, deltaPain ThresholdReceptors, Opioid, kappaHypnotics and SedativesHyperalgesiaOpioid PeptidesKetamineDose-Response Relationship, DrugPlant ExtractsNarcotic AntagonistsRats, Sprague-DawleyBehavior, AnimalOpioid-Related DisordersNaltrexonePain, PostoperativeEnkephalinsTramadolNarcoticsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Drug ToleranceBuprenorphineEndorphinsEnkephalin, D-Penicillamine (2,5)-FentanylDynorphinsPhenacetinAcetaminophenHydromorphoneEnkephalin, LeucineMorphinansDextropropoxypheneCodeineInjections, SpinalEnkephalin, Leucine-2-Alaninebeta-EndorphinAnti-Inflammatory Agents, Non-SteroidalMeperidinePain ManagementPentazocineMethadoneBenzeneacetamidesPain, IntractableDiprenorphineButorphanolAnesthetics, LocalHydrocodoneChronic PainOxymorphoneMorphine DerivativesDouble-Blind MethodDipyroneAnalgesia, EpiduralLevorphanolAnalgesia, Patient-ControlledBenzomorphansBupivacaineOxycodoneNociceptorsAlfentanilCyclazocineNociceptionNalbuphineSubstance Withdrawal SyndromePrescription DrugsPyrrolidinesHeroinNeuralgiaTolmetinCarrageenanKetoprofenSufentanilMeptazinolKetorolacAcupuncture AnalgesiaMorphine DependenceNalorphineKidney Papillary NecrosisNociceptive PainDrug OverdoseAcute PainPeriaqueductal GrayNefopamPrescription Drug MisuseSpinal CordCyclohexanecarboxylic AcidsIbuprofenOpiate Substitution TreatmentDrug InteractionsAnalgesia, Obstetrical