Spinal CordEnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, LeucineEnkephalin, MethionineEnkephalin, D-Penicillamine (2,5)-Enkephalin, Leucine-2-AlanineReceptors, Opioid, muReceptors, OpioidEndorphinsReceptors, Opioid, deltaAnalgesicsNaloxoneMorphineAnalgesics, OpioidInjections, SpinalNarcotic AntagonistsSpinal Cord InjuriesReceptors, Opioid, kappaPain MeasurementReceptors, Neurokinin-3NaltrexonePainNeurokinin BCyclazocineAnalgesiaEthylketocyclazocineDynorphinsOpioid PeptidesDrug ToleranceTachykininsReceptors, TachykininNociceptorsInjections, IntraventricularPain ThresholdSubstance PD-Ala(2),MePhe(4),Met(0)-ol-enkephalinbeta-EndorphinDose-Response Relationship, DrugPeriaqueductal GrayRats, Sprague-DawleyNeurokinin AAnalgesics, Non-NarcoticMorphinansReceptors, Neurokinin-2Spinal NervesBenzomorphansHyperalgesiaNociceptionAnesthesia, SpinalNarcoticsOligopeptidesBenzeneacetamidesSpinal Cord DiseasesSpinal Nerve RootsPiperidinesMice, Inbred ICRSpinal Cord NeoplasmsRNA, Transfer, GlySpinal CanalAdrenergic alpha-2 Receptor AgonistsSpinal DiseasesSpinal Cord CompressionNeurokinin-1 Receptor AntagonistsSpinal NeoplasmsPyrrolidinesCarboxypeptidase HGuinea PigsMorphine DerivativesMicroinjectionsBehavior, AnimalReceptors, Adrenergic, alpha-2Spinal StenosisClonidineNociceptive PainReaction TimeSpinal FusionPosterior Horn CellsFormaldehydePentazocineGanglia, SpinalHot TemperatureReceptors, Neurokinin-1Drug InteractionsMedulla OblongataFentanylAdrenergic alpha-AgonistsGlycineTailDiprenorphineRats, WistarBrainNeuronsSpinal InjuriesMuscular Atrophy, SpinalBuprenorphineMorphine DependenceCannabinoidsMotor ActivityButorphanol