Receptors, Opioid, kappaNarcotic AntagonistsNaltrexoneDynorphinsBenzeneacetamidesDiterpenes, ClerodaneReceptors, OpioidReceptors, Opioid, muNaloxoneAnalgesics, OpioidReceptors, Opioid, deltaOpioid PeptidesEndorphinsMorphineNarcoticsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-EnkephalinsDose-Response Relationship, DrugMorphinansEnkephalin, D-Penicillamine (2,5)-Enkephalin, LeucineDiprenorphineAnalgesicsPyrrolidinesRats, Sprague-DawleyEnkephalin, Leucine-2-AlanineEnkephalin, MethionineAzocinesBenzomorphansOpioid-Related Disordersbeta-EndorphinPiperidinesHormone AntagonistsSubstance Withdrawal SyndromePain MeasurementPainDopamine AntagonistsNeurokinin-1 Receptor AntagonistsBuprenorphineExcitatory Amino Acid AntagonistsMorphine DependenceFentanylHistamine H2 AntagonistsOxymorphoneInterleukin 1 Receptor Antagonist ProteinDrug InteractionsLevorphanolDrug ToleranceMuscarinic AntagonistsRats, WistarHeroinBenzylidene CompoundsAnalgesics, Non-NarcoticGABA AntagonistsAnalgesiaInjections, IntraventricularOligopeptidesInjections, SpinalTetrahydroisoquinolinesHistamine H1 AntagonistsBehavior, AnimalPurinergic P1 Receptor AntagonistsEtorphineDrug Inverse AgonismPruritusGuinea PigsHistamine AntagonistsMeptazinolNicotinic AntagonistsAdenosine A2 Receptor AntagonistsAntipruriticsAdrenergic alpha-1 Receptor AntagonistsPurinergic P2 Receptor AntagonistsTime FactorsSerotonin 5-HT3 Receptor AntagonistsNociceptorsSerotonin 5-HT2 Receptor AntagonistsRadioligand AssayPeriaqueductal GrayConditioning, OperantMotor ActivitySpinal CordLigandsElectric StimulationAdenosine A1 Receptor AntagonistsHyperalgesiaEthanolLeukotriene AntagonistsAngiotensin Receptor AntagonistsAdrenergic alpha-2 Receptor AntagonistsMice, Inbred ICRStereoisomerismBrainCapsaicinAdrenergic alpha-AntagonistsNeuronsGABA-A Receptor AntagonistsAdrenergic AntagonistsAnalysis of VariancePain Threshold