AnalgesicsAnalgesics, OpioidReceptors, Opioid, muDexmedetomidineAnalgesiaAnalgesics, Non-NarcoticPainReceptors, OpioidPain MeasurementMorphineNaloxoneReceptors, Opioid, deltaPain ThresholdReceptors, Opioid, kappaHypnotics and SedativesHyperalgesiaOpioid PeptidesKetamineDose-Response Relationship, DrugPlant ExtractsRats, Sprague-DawleyNarcotic AntagonistsBehavior, AnimalOpioid-Related DisordersNaltrexonePain, PostoperativeEnkephalinsTramadolNarcoticsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Drug ToleranceBuprenorphineEndorphinsCell Adhesion MoleculesEnkephalin, D-Penicillamine (2,5)-FentanylDynorphinsPhenacetinAcetaminophenHydromorphoneEnkephalin, LeucineMorphinansDextropropoxypheneCodeineInjections, SpinalEnkephalin, Leucine-2-AlanineAnti-Inflammatory Agents, Non-Steroidalbeta-EndorphinMolecular Sequence DataMeperidinePain ManagementPentazocineMethadoneBenzeneacetamidesAmino Acid SequencePain, IntractableDiprenorphineAnesthetics, LocalButorphanolChronic PainHydrocodoneOxymorphoneSmall Molecule LibrariesMorphine DerivativesDouble-Blind MethodDipyroneAnalgesia, EpiduralLevorphanolAnalgesia, Patient-ControlledProtein BindingBenzomorphansBupivacaineOxycodoneNociceptorsNociceptionAlfentanilCyclazocineTime FactorsPyrrolidinesModels, MolecularSubstance Withdrawal SyndromeNalbuphineCell LinePrescription DrugsSignal TransductionLigandsNeuralgiaHeroinCarrageenanOligopeptidesTolmetinKetoprofenBinding SitesSufentanilMeptazinolStructure-Activity RelationshipKetorolacAcupuncture AnalgesiaKineticsCells, Cultured