NaloxoneNarcotic AntagonistsReceptors, OpioidMorphineEndorphinsReceptors, Opioid, muDose-Response Relationship, DrugHormone AntagonistsEnkephalin, MethionineAnalgesics, OpioidNarcoticsBuprenorphineDopamine AntagonistsOpioid PeptidesExcitatory Amino Acid AntagonistsRats, Sprague-DawleyEnkephalinsNeurokinin-1 Receptor AntagonistsNaltrexoneMorphine DependenceHistamine H2 AntagonistsReceptors, Opioid, kappaPiperidinesInterleukin 1 Receptor Antagonist ProteinAnalgesicsEnkephalin, LeucineMuscarinic Antagonistsbeta-EndorphinGABA AntagonistsSubstance Withdrawal SyndromeReceptors, Opioid, deltaHistamine H1 AntagonistsRats, WistarPurinergic P1 Receptor AntagonistsOpioid-Related DisordersHistamine AntagonistsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Drug OverdoseNicotinic AntagonistsMorphinansAdenosine A2 Receptor AntagonistsAdrenergic alpha-1 Receptor AntagonistsPurinergic P2 Receptor AntagonistsInjections, IntraventricularDrug ToleranceAdrenergic alpha-AntagonistsSerotonin 5-HT3 Receptor AntagonistsPyrrolidinesGuinea PigsSerotonin 5-HT2 Receptor AntagonistsDrug InteractionsAdrenergic alpha-2 Receptor AntagonistsElectric StimulationAdenosine A1 Receptor AntagonistsDynorphinsPainLeukotriene AntagonistsInjections, SpinalAngiotensin Receptor AntagonistsPentazocineBehavior, AnimalRadioligand AssayEnkephalin, Leucine-2-AlanineNalorphineTime FactorsLevorphanolCyclazocineBinding, CompetitiveEnkephalin, D-Penicillamine (2,5)-Pain MeasurementLoperamideLevallorphanAdrenergic AntagonistsGABA-A Receptor AntagonistsReceptors, SerotoninReceptors, N-Methyl-D-AspartateHistamine H3 AntagonistsOligopeptidesRats, Inbred StrainsSubstance PYohimbineCells, CulturedSerotoninBenzazepinesDizocilpine MaleateCalcium Channel BlockersMuscle ContractionReceptors, EndothelinOxycodoneAdrenergic beta-2 Receptor AntagonistsNeuronsDiprenorphineSpinal CordAzepinesFentanylNociceptorsHeroinAdministration, SublingualNorepinephrineClonidine