EnkephalinsEnkephalin, MethionineEnkephalin, LeucineEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Receptors, Opioid, muReceptors, OpioidEnkephalin, Leucine-2-AlanineEnkephalin, D-Penicillamine (2,5)-Receptors, Opioid, deltaAnalgesics, OpioidEndorphinsReceptors, Opioid, kappaCorpus StriatumOpioid PeptidesNaloxoneNarcotic AntagonistsDynorphinsNaltrexoneMorphineNeostriatumNarcoticsDopamineEthylketocyclazocinebeta-EndorphinCyclazocineBenzomorphansDiprenorphineOpioid-Related DisordersReceptors, Dopamine D2D-Ala(2),MePhe(4),Met(0)-ol-enkephalinAnalgesicsPyrrolidinesRats, Sprague-DawleyNeuronsCarboxypeptidase HMorphinansDrug ToleranceBrainOligopeptidesBasal GangliaGlobus PallidusHuntington DiseaseCaudate NucleusReceptors, Dopamine D1Dose-Response Relationship, DrugBuprenorphinePainProtein PrecursorsDopamine Plasma Membrane Transport ProteinsRacloprideFentanylBehavior, AnimalPain MeasurementThiorphanOxidopamineSubstantia NigraEtorphineDopamine AntagonistsSomatostatinSubstance Withdrawal SyndromeTyrosine 3-MonooxygenaseDopamine and cAMP-Regulated Phosphoprotein 32Injections, SpinalAnalgesiaBenzylidene CompoundsRadioligand AssayMorphine DerivativesSynaptosomesReceptors, DopamineNeprilysinMethadoneAdrenal MedullaGuinea Pigs3,4-Dihydroxyphenylacetic AcidElectric StimulationInjections, IntraventricularTropanesTioproninDihydromorphineRats, Inbred StrainsBenzeneacetamidesSalicylamidesIleumSubstance PMorphine DependenceMotor ActivityVas DeferensBrain ChemistryNeural PathwaysBinding, CompetitiveNucleus AccumbensRats, WistarMicrodialysisNeurotransmitter AgentsDrug InteractionsDopamine AgentsQuinolinic AcidLevodopaCatalepsyNerve Tissue Proteins