NaloxoneNarcotic AntagonistsReceptors, OpioidOpioid PeptidesReceptors, Opioid, muMorphineEndorphinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Analgesics, OpioidEnkephalin, LeucineEnkephalin, MethionineNaltrexoneReceptors, Opioid, kappabeta-EndorphinEnkephalinsDynorphinsNarcoticsReceptors, Opioid, deltaEnkephalin, Leucine-2-AlanineHypnosis, AnestheticEnkephalin, D-Penicillamine (2,5)-EtorphineAnalgesicsDose-Response Relationship, DrugBenzeneacetamidesRats, Sprague-DawleyPainAnalgesics, Non-NarcoticPain MeasurementPyrrolidinesSubstance Withdrawal SyndromePiperidinesAnalgesiaInjections, IntraventricularInjections, SpinalNociceptorsRats, WistarBehavior, AnimalPain ThresholdDrug InteractionsInjections, SubcutaneousSpinal CordElectric StimulationHormone AntagonistsOligopeptidesGuinea PigsBuprenorphineDopamine AntagonistsExcitatory Amino Acid AntagonistsTime FactorsLuteinizing HormoneNeurokinin-1 Receptor AntagonistsRats, Inbred StrainsMorphine DependenceHistamine H2 AntagonistsNeuronsInterleukin 1 Receptor Antagonist ProteinBrainMuscarinic AntagonistsGABA AntagonistsHot TemperatureHistamine H1 AntagonistsOpioid-Related DisordersPurinergic P1 Receptor AntagonistsHistamine AntagonistsDrug OverdoseMorphinansNicotinic AntagonistsAdenosine A2 Receptor AntagonistsAdrenergic alpha-1 Receptor AntagonistsPurinergic P2 Receptor AntagonistsDrug ToleranceSerotonin 5-HT3 Receptor AntagonistsAdrenergic alpha-AntagonistsSerotonin 5-HT2 Receptor AntagonistsAdrenergic alpha-2 Receptor AntagonistsAdenosine A1 Receptor AntagonistsLeukotriene AntagonistsAngiotensin Receptor AntagonistsPentazocineNalorphineLevorphanolCyclazocineRadioligand AssayLoperamideLevallorphanAdrenergic AntagonistsBinding, CompetitiveGABA-A Receptor Antagonists