EnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, LeucineEnkephalin, MethionineEnkephalin, D-Penicillamine (2,5)-Enkephalin, Leucine-2-AlanineReceptors, Opioid, muReceptors, OpioidEndorphinsNaloxoneMorphineReceptors, Opioid, deltaAnalgesicsAnalgesics, OpioidNarcotic AntagonistsReceptors, Opioid, kappaNarcoticsPain MeasurementReceptors, Neurokinin-3NaltrexoneCyclazocineInjections, SpinalEthylketocyclazocineAnalgesiaPainNeurokinin BDrug ToleranceDynorphinsOpioid PeptidesTachykininsReceptors, Tachykininbeta-EndorphinOpiate AlkaloidsInjections, IntraventricularDose-Response Relationship, DrugD-Ala(2),MePhe(4),Met(0)-ol-enkephalinPain ThresholdMorphinansBenzomorphansNociceptorsSubstance PMorphine DerivativesPeriaqueductal GrayNeurokinin AAnalgesics, Non-NarcoticRats, Sprague-DawleyOpioid-Related DisordersReceptors, Neurokinin-2Spinal CordOligopeptidesNociceptionEtorphineBenzeneacetamidesBuprenorphineMorphine DependencePiperidinesHyperalgesiaDiprenorphineRNA, Transfer, GlyMice, Inbred ICRSubstance Withdrawal SyndromePentazocinePyrrolidinesMethadoneHeroinAdrenergic alpha-2 Receptor AgonistsGuinea PigsDihydromorphineFentanylNeurokinin-1 Receptor AntagonistsCarboxypeptidase HClonidineMicroinjectionsBehavior, AnimalReceptors, Adrenergic, alpha-2Drug InteractionsCodeineReaction TimeLocus CoeruleusNociceptive PainBrainHot TemperatureAdrenergic alpha-AgonistsMedulla OblongataReceptors, Neurokinin-1FormaldehydeButorphanolCannabinoidsOxymorphoneTailDronabinolRats, Inbred StrainsHeroin DependenceGlycineSomatostatinRats, WistarOpiumProtein PrecursorsLoperamideSubstance Abuse Detection