EnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Receptors, Opioid, muEnkephalin, LeucineEnkephalin, MethionineReceptors, OpioidEnkephalin, D-Penicillamine (2,5)-Analgesics, OpioidReceptors, Opioid, deltaReceptors, Opioid, kappaEnkephalin, Leucine-2-AlanineNarcotic AntagonistsNaloxoneMorphineEndorphinsNaltrexoneAnalgesicsOpioid PeptidesNarcoticsBenzeneacetamidesPain MeasurementDynorphinsEthylketocyclazocineDrug TolerancePyrrolidinesBuprenorphinePainEtorphineInjections, SpinalDose-Response Relationship, DrugBenzomorphansReceptors, Neurokinin-3MorphinansD-Ala(2),MePhe(4),Met(0)-ol-enkephalinbeta-EndorphinPeriaqueductal GrayOpioid-Related DisordersFentanylAnalgesiaCyclazocineRats, Sprague-DawleyLevorphanolDiprenorphinePain ThresholdNeurokinin BInjections, IntraventricularOligopeptidesNociceptorsMorphine DerivativesNalbuphineAnalgesics, Non-NarcoticTachykininsMethadoneReceptors, TachykininSpinal CordMethadyl AcetateSubstance PHyperalgesiaNeurokinin-1 Receptor AntagonistsHydromorphoneButorphanolAzocinesDiterpenes, ClerodaneDrug InteractionsOxycodoneNeurokinin AAdrenergic alpha-2 Receptor AgonistsGuinea PigsReceptors, Neurokinin-2PentazocinePiperidinesGuanosine 5'-O-(3-Thiotriphosphate)Behavior, AnimalSubstance Withdrawal SyndromeNociceptionMorphine DependenceBenzamidesRadioligand AssayVas DeferensMice, Inbred ICRHeroinRats, WistarDopamine AgonistsAdrenergic alpha-AgonistsPiperazinesSomatostatinReaction TimeBinding, CompetitiveHot TemperatureRNA, Transfer, GlyReceptors, Adrenergic, alpha-2MicroinjectionsOpiate Substitution TreatmentLocus CoeruleusIleumBrainClonidineNeuronsLigandsCarboxypeptidase H