NaltrexoneReceptors, OpioidNarcotic AntagonistsReceptors, Opioid, muReceptors, Opioid, kappaReceptors, Opioid, deltaNaloxoneAnalgesics, OpioidOpioid PeptidesMorphineDynorphinsEnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, D-Penicillamine (2,5)-MorphinansNarcoticsEnkephalin, LeucineBenzomorphansBenzylidene CompoundsAnalgesicsBenzeneacetamidesDose-Response Relationship, DrugRats, Sprague-Dawleybeta-EndorphinEndorphinsPyrrolidinesEthylketocyclazocineEnkephalin, MethionineMorphine DerivativesDiprenorphinePain MeasurementCyclazocinePainPiperidinesInterleukin 1 Receptor Antagonist ProteinEnkephalin, Leucine-2-AlanineSubstance Withdrawal SyndromeHeroinOpioid-Related DisordersNeurokinin-1 Receptor AntagonistsInjections, IntraventricularRats, WistarDrug ToleranceOligopeptidesFentanylPeriaqueductal GrayInjections, SpinalBehavior, AnimalDrug InteractionsAdrenergic alpha-2 Receptor AntagonistsSomatostatinElectroacupunctureLoperamideHyperalgesiaPain ThresholdEthanolGuinea PigsEtorphineBuprenorphineMicroinjectionsConditioning, OperantPurinergic P1 Receptor AntagonistsNociceptorsDopamine AntagonistsAnalgesics, Non-NarcoticSelf AdministrationExcitatory Amino Acid AntagonistsHistamine H2 AntagonistsMice, Inbred ICRSerotonin 5-HT3 Receptor AntagonistsInjections, SubcutaneousSpinal CordLevorphanolRadioligand AssayAlcoholismStereoisomerismDisease Models, AnimalDiterpenes, ClerodaneCentral Nervous System DepressantsAngiotensin Receptor AntagonistsTime FactorsCricetulusFormaldehydeElectric StimulationMotor ActivitySerotonin 5-HT2 Receptor AntagonistsAdenosine A2 Receptor AntagonistsHormone AntagonistsBrainMorphine DependenceHeroin DependenceAdenosine A1 Receptor AntagonistsNeuronsAnalgesiaButorphanolNalbuphineBinding, CompetitivePurinergic P2 Receptor AntagonistsGuanosine 5'-O-(3-Thiotriphosphate)Hydromorphone