NaloxoneNarcotic AntagonistsReceptors, OpioidReceptors, Opioid, muOpioid PeptidesAnalgesics, OpioidReceptors, Opioid, deltaNaltrexoneReceptors, Opioid, kappaEndorphinsMorphineEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, Methioninebeta-EndorphinAnalgesicsEnkephalin, LeucineEnkephalinsNarcoticsDose-Response Relationship, DrugPainPain MeasurementDynorphinsEnkephalin, Leucine-2-AlanineEnkephalin, D-Penicillamine (2,5)-Rats, Sprague-DawleyBenzeneacetamidesEtorphineSubstance Withdrawal SyndromePyrrolidinesOpioid-Related DisordersAnalgesics, Non-NarcoticDiprenorphineMorphinansBuprenorphineAnalgesiaHypnosis, AnestheticInjections, IntraventricularInjections, SpinalMorphine DependenceAzocinesPiperidinesNociceptorsBenzomorphansDrug InteractionsBehavior, AnimalPain ThresholdFentanylRats, WistarOligopeptidesLevorphanolDrug ToleranceInjections, SubcutaneousSpinal CordHeroinOxymorphoneElectric StimulationGuinea PigsMeptazinolBenzylidene CompoundsTime FactorsLuteinizing HormoneRats, Inbred StrainsPruritusBrainDiterpenes, ClerodanePeriaqueductal GrayDrug Inverse AgonismNeuronsAntipruriticsHormone AntagonistsHot TemperatureTetrahydroisoquinolinesDopamine AntagonistsExcitatory Amino Acid AntagonistsConditioning, OperantNeurokinin-1 Receptor AntagonistsHyperalgesiaMotor ActivityStereoisomerismEthanolMice, Inbred ICRSomatostatinDrug OverdoseHistamine H2 Antagonists