EnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, LeucineEnkephalin, MethionineEnkephalin, D-Penicillamine (2,5)-Enkephalin, Leucine-2-AlanineReceptors, Opioid, muReceptors, OpioidEndorphinsReceptors, Opioid, deltaAnalgesicsNaloxoneMorphineAnalgesics, OpioidNarcotic AntagonistsReceptors, Opioid, kappaReceptors, Neurokinin-3Pain MeasurementInjections, SpinalNaltrexoneNeurokinin BCyclazocinePainEthylketocyclazocineAnalgesiaOpioid PeptidesTachykininsDynorphinsReceptors, TachykininDrug ToleranceInjections, IntraventricularD-Ala(2),MePhe(4),Met(0)-ol-enkephalinbeta-EndorphinPain ThresholdSubstance PDose-Response Relationship, DrugNociceptorsPeriaqueductal GrayNeurokinin AAnalgesics, Non-NarcoticMorphinansReceptors, Neurokinin-2BenzomorphansSpinal CordNociceptionRats, Sprague-DawleyNarcoticsOligopeptidesBenzeneacetamidesHyperalgesiaPiperidinesRNA, Transfer, GlyMice, Inbred ICRAdrenergic alpha-2 Receptor AgonistsNeurokinin-1 Receptor AntagonistsPyrrolidinesCarboxypeptidase HMorphine DerivativesGuinea PigsMicroinjectionsReceptors, Adrenergic, alpha-2PentazocineNociceptive PainReaction TimeDrug InteractionsClonidineBehavior, AnimalFormaldehydeHot TemperatureDiprenorphineFentanylReceptors, Neurokinin-1Adrenergic alpha-AgonistsMedulla OblongataBuprenorphineGlycineButorphanolTailMorphine DependenceCannabinoidsEtorphineBrainSomatostatinDronabinolNeprilysinRats, WistarThiorphanBenzylidene CompoundsAmino Acid SequencePeptide FragmentsProtein PrecursorsAcetic AcidDrug SynergismLocus CoeruleusAdrenergic alpha-AntagonistsBenzamidesMolecular Sequence DataRats, Inbred StrainsReceptor, Cannabinoid, CB1Dihydroergocristine