EnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, LeucineEnkephalin, MethionineEnkephalin, D-Penicillamine (2,5)-Enkephalin, Leucine-2-AlanineReceptors, Opioid, muReceptors, OpioidEndorphinsReceptors, Opioid, deltaAnalgesicsNaloxoneLigandsMorphineAnalgesics, OpioidNarcotic AntagonistsReceptors, Opioid, kappaReceptors, Neurokinin-3Pain MeasurementInjections, SpinalNaltrexoneNeurokinin BCyclazocinePainEthylketocyclazocineAnalgesiaOpioid PeptidesDynorphinsTachykininsReceptors, TachykininDrug ToleranceInjections, IntraventricularD-Ala(2),MePhe(4),Met(0)-ol-enkephalinDose-Response Relationship, Drugbeta-EndorphinPain ThresholdSubstance PNociceptorsPeriaqueductal GrayNeurokinin AMorphinansAnalgesics, Non-NarcoticBenzomorphansReceptors, Neurokinin-2OligopeptidesRats, Sprague-DawleySpinal CordNociceptionNarcoticsBenzeneacetamidesPiperidinesMice, Inbred ICRHyperalgesiaRNA, Transfer, GlyAdrenergic alpha-2 Receptor AgonistsPyrrolidinesNeurokinin-1 Receptor AntagonistsCarboxypeptidase HMorphine DerivativesGuinea PigsAmino Acid SequenceCD40 LigandPentazocineMolecular Sequence DataMicroinjectionsReceptors, Adrenergic, alpha-2Nociceptive PainDrug InteractionsReaction TimeBehavior, AnimalClonidineHot TemperatureDiprenorphineFormaldehydeReceptors, Neurokinin-1Fas Ligand ProteinFentanylAdrenergic alpha-AgonistsBinding, CompetitiveMedulla OblongataBinding SitesProtein BindingModels, MolecularPeptide FragmentsKineticsGlycineCannabinoidsBuprenorphineBrainButorphanolEtorphineTailRadioligand AssayMorphine DependenceRats, WistarStructure-Activity RelationshipDronabinolSomatostatinNeprilysinDrug Synergism