Receptors, NicotinicReceptors, Opioid, muReceptors, OpioidAnalgesics, OpioidReceptors, Opioid, deltaReceptors, Opioid, kappaOpioid PeptidesNarcotic AntagonistsNaloxoneNaltrexoneDose-Response Relationship, DrugDopamine AgonistsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Opioid-Related DisordersEnkephalinsRats, Sprague-DawleyNarcoticsMorphineDopamine AntagonistsHormone AntagonistsEnkephalin, D-Penicillamine (2,5)-PiperidinesExcitatory Amino Acid AntagonistsNeurokinin-1 Receptor AntagonistsDynorphinsGABA AgonistsEndorphinsEnkephalin, LeucineRadioligand AssayMuscarinic AntagonistsHistamine H2 AntagonistsPurinergic P1 Receptor AgonistsBuprenorphinePyrrolidinesGABA AntagonistsEnkephalin, Leucine-2-AlanineRats, WistarBenzeneacetamidesPainPurinergic P1 Receptor AntagonistsInterleukin 1 Receptor Antagonist ProteinMorphinansMuscarinic AgonistsNicotinic AgonistsDiprenorphineAdrenergic alpha-2 Receptor AgonistsNicotinic AntagonistsBinding, CompetitiveHistamine AntagonistsHistamine H1 AntagonistsHistamine AgonistsLigandsAdrenergic alpha-AgonistsAnalgesicsGuinea PigsDrug InteractionsAdenosine A2 Receptor AntagonistsSerotonin 5-HT2 Receptor AgonistsPurinergic P2 Receptor AntagonistsAdrenergic AgonistsBenzomorphansOligopeptidesSerotonin 5-HT1 Receptor AgonistsPain MeasurementAdrenergic alpha-1 Receptor AntagonistsSerotonin 5-HT2 Receptor AntagonistsAdrenergic beta-Agonistsbeta-EndorphinAdrenergic alpha-AntagonistsCells, CulturedPurinergic P2 Receptor AgonistsDrug ToleranceExcitatory Amino Acid AgonistsSerotonin 5-HT3 Receptor AntagonistsFentanylSignal TransductionAdenosine A1 Receptor AntagonistsGABA-A Receptor AgonistsReceptors, Dopamine D2CHO CellsBehavior, AnimalBenzazepinesAdrenergic alpha-2 Receptor AntagonistsAdenosine A1 Receptor AgonistsPiperazinesCalciumCyclic AMPSubstance Withdrawal SyndromeTime FactorsPyridinesNeuronsGABA-A Receptor AntagonistsAdrenergic beta-2 Receptor AntagonistsCholinergic AgonistsCricetinaeAdenosineAdrenergic AntagonistsGuanosine 5'-O-(3-Thiotriphosphate)Receptors, N-Methyl-D-AspartateMethadone