NaloxoneNarcotic AntagonistsNaltrexoneReceptors, OpioidReceptors, Opioid, muAnalgesics, OpioidReceptors, Opioid, deltaReceptors, Opioid, kappaOpioid PeptidesEndorphinsMorphineNarcoticsEnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, MethionineEnkephalin, LeucineDynorphinsOpioid-Related DisordersEnkephalin, D-Penicillamine (2,5)-Diprenorphinebeta-EndorphinEnkephalin, Leucine-2-AlanineMorphinansBuprenorphineAnalgesicsDose-Response Relationship, DrugBenzeneacetamidesMorphine DependenceSubstance Withdrawal SyndromeAzocinesPyrrolidinesPain MeasurementBenzomorphansPainRats, Sprague-DawleyFentanylLevorphanolDrug ToleranceHeroinOxymorphoneMeptazinolEtorphinePiperidinesBenzylidene CompoundsInjections, IntraventricularInjections, SpinalDrug InteractionsAnalgesics, Non-NarcoticPruritusOligopeptidesAnalgesiaDiterpenes, ClerodanePeriaqueductal GrayBehavior, AnimalDrug Inverse AgonismRats, WistarNociceptorsAntipruriticsHormone AntagonistsTetrahydroisoquinolinesGuinea PigsDopamine AntagonistsPain ThresholdSpinal CordExcitatory Amino Acid AntagonistsConditioning, OperantTime FactorsNeurokinin-1 Receptor AntagonistsElectric StimulationHyperalgesiaMotor ActivityInjections, SubcutaneousStereoisomerismEthanolMice, Inbred ICRSomatostatinDrug OverdoseRats, Inbred StrainsHistamine H2 AntagonistsLuteinizing HormoneBrainSelf AdministrationHallucinogensReflexInterleukin 1 Receptor Antagonist ProteinCapsaicinAnalysis of VarianceGABA AntagonistsMuscarinic AntagonistsLigandsMethadoneInjections, IntraperitonealNeuronsCyclazocineHistamine H1 AntagonistsPurinergic P1 Receptor AntagonistsQuaternary Ammonium CompoundsRadioligand AssayPentazocineLoperamide