AnalgesicsChalconeEnkephalinsHyperalgesiaEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Pain MeasurementEnkephalin, LeucineEnkephalin, MethionineEnkephalin, D-Penicillamine (2,5)-Receptors, Opioid, muReceptors, OpioidAnalgesics, OpioidEnkephalin, Leucine-2-AlanineMorphineReceptors, Opioid, deltaNaloxoneNarcotic AntagonistsEndorphinsInjections, SpinalReceptors, Opioid, kappaPainNaltrexoneAnalgesiaDrug ToleranceInjections, IntraventricularOpioid PeptidesPain ThresholdNociceptorsReceptors, Neurokinin-3Periaqueductal GrayDose-Response Relationship, DrugDynorphinsAnalgesics, Non-Narcoticbeta-EndorphinNociceptionCyclazocineSpinal CordRats, Sprague-DawleyMorphinansNeurokinin BEthylketocyclazocineTachykininsReceptors, TachykininAdrenergic alpha-2 Receptor AgonistsMice, Inbred ICRBenzomorphansSubstance POligopeptidesNarcoticsD-Ala(2),MePhe(4),Met(0)-ol-enkephalinPiperidinesReceptors, Adrenergic, alpha-2MicroinjectionsReaction TimeMorphine DerivativesBenzeneacetamidesClonidinePentazocineFormaldehydeNeurokinin AHot TemperaturePyrrolidinesReceptors, Neurokinin-2Adrenergic alpha-AgonistsDrug InteractionsBehavior, AnimalNociceptive PainBuprenorphineCannabinoidsTailPeripheral NervesButorphanolFentanylMedulla OblongataDronabinolPeripheral Nervous SystemNeurokinin-1 Receptor AntagonistsAcetic AcidRats, WistarRNA, Transfer, GlyReceptor, Cannabinoid, CB1Adrenergic alpha-AntagonistsPeripheral Nervous System DiseasesMorphine DependenceYohimbineDihydroergocristineAdrenergic alpha-2 Receptor AntagonistsGuinea PigsDrug SynergismFreund's AdjuvantBrompheniramineLoperamidePyrazolesInjections, SubcutaneousCarrageenanCarboxypeptidase HBornanesAlfentanilReceptor, Cannabinoid, CB2Motor Activity