EnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, D-Penicillamine (2,5)-Enkephalin, LeucineEnkephalin, MethionineReceptors, Opioid, deltaEnkephalin, Leucine-2-AlanineReceptors, Opioid, muReceptors, OpioidAnalgesicsAnalgesics, OpioidEndorphinsNaloxoneNarcotic AntagonistsMorphineReceptors, Opioid, kappaPain MeasurementInjections, SpinalNaltrexoneReceptors, Neurokinin-3Opioid PeptidesEthylketocyclazocineDynorphinsNeurokinin BCyclazocineDrug TolerancePainInjections, IntraventricularAnalgesiabeta-EndorphinTachykininsReceptors, TachykininBenzeneacetamidesBenzomorphansDose-Response Relationship, DrugNarcoticsD-Ala(2),MePhe(4),Met(0)-ol-enkephalinPain ThresholdOligopeptidesSubstance PNociceptorsPyrrolidinesPeriaqueductal GrayRats, Sprague-DawleySpinal CordNeurokinin AAnalgesics, Non-NarcoticMorphinansReceptors, Neurokinin-2DiprenorphineNociceptionMice, Inbred ICRBenzylidene CompoundsEtorphineHyperalgesiaPiperidinesRNA, Transfer, GlyGuinea PigsAdrenergic alpha-2 Receptor AgonistsNeurokinin-1 Receptor AntagonistsCarboxypeptidase HSomatostatinMorphine DerivativesMicroinjectionsReceptors, Adrenergic, alpha-2PentazocineNociceptive PainReaction TimeDrug InteractionsClonidineBehavior, AnimalFormaldehydeHot TemperatureBrainFentanylReceptors, Neurokinin-1Rats, WistarAdrenergic alpha-AgonistsMedulla OblongataTetrahydroisoquinolinesBuprenorphineGlycineButorphanolTailMorphine DependenceCannabinoidsBinding, CompetitiveDronabinolNeprilysinElectric StimulationThiorphanNeuronsAmino Acid SequencePeptide FragmentsProtein PrecursorsAcetic AcidDrug SynergismLocus CoeruleusAdrenergic alpha-AntagonistsBenzamides