AnalgesicsAnalgesics, OpioidReceptors, Opioid, muDexmedetomidineAnalgesiaAnalgesics, Non-NarcoticPainPeptidesReceptors, OpioidPain MeasurementMorphineNaloxoneReceptors, Opioid, deltaReceptors, Opioid, kappaPain ThresholdHypnotics and SedativesHyperalgesiaOpioid PeptidesKetamineDose-Response Relationship, DrugRats, Sprague-DawleyPlant ExtractsNarcotic AntagonistsBehavior, AnimalPeptide FragmentsOpioid-Related DisordersPeptide LibraryNaltrexoneEnkephalinsAntimicrobial Cationic PeptidesEndorphinsPain, PostoperativeNarcoticsOligopeptidesPeptides, CyclicEnkephalin, Ala(2)-MePhe(4)-Gly(5)-TramadolDrug ToleranceBuprenorphineEnkephalin, D-Penicillamine (2,5)-FentanylDynorphinsPeptide MappingEnkephalin, LeucineAmino Acid SequencePhenacetinAcetaminophenHydromorphonebeta-EndorphinMorphinansDextropropoxypheneCodeineEnkephalin, Leucine-2-AlanineInjections, SpinalNatriuretic Peptide, BrainAnti-Inflammatory Agents, Non-SteroidalCalcitonin Gene-Related PeptidePain ManagementMeperidinePentazocineMethadoneProtein BindingMolecular Sequence DataBenzeneacetamidesVasoactive Intestinal PeptidePain, IntractableDiprenorphineCell-Penetrating PeptidesButorphanolAnesthetics, LocalStructure-Activity RelationshipChronic PainHydrocodoneOxymorphoneDouble-Blind MethodPeptide BiosynthesisMorphine DerivativesPeptide YYBinding SitesModels, MolecularProtein PrecursorsDipyroneAnalgesia, EpiduralLevorphanolAnalgesia, Patient-ControlledBenzomorphansPeptide Nucleic AcidsNociceptorsNatriuretic Peptide, C-TypeBupivacaineKineticsChromatography, High Pressure LiquidProtein ConformationNociceptionOxycodoneTime FactorsNatriuretic PeptidesProtein Structure, SecondaryAlfentanilCyclazocine