Opioid PeptidesReceptors, OpioidCycloheptanesNaloxoneNarcotic AntagonistsSpiro CompoundsDynorphinsReceptors, Opioid, kappaReceptors, Opioid, muAnalgesics, OpioidEnkephalin, D-Penicillamine (2,5)-Enkephalin, Ala(2)-MePhe(4)-Gly(5)-NarcoticsInjections, SpinalRats, Sprague-DawleyAcenaphthenesBenzimidazolesPiperidinesGuanosine 5'-O-(3-Thiotriphosphate)NaltrexoneBuprenorphineEtorphineDiprenorphineDose-Response Relationship, DrugLatency Period (Psychology)Receptors, Opioid, deltaAzabicyclo CompoundsCHO CellsEnkephalin, MethionineInjections, IntraventricularPainMorphineElectroacupuncturePain MeasurementConsummatory BehaviorBinding, CompetitiveCricetinaeSpinal CordCapsaicinVasodilator AgentsVas DeferensOtolaryngologyHyperalgesiaExcitatory Amino AcidsLigandsAnalgesicsSulfur RadioisotopesCausalgiaAutonomic PathwaysFentanylLocus CoeruleusRats, WistarPeptide FragmentsSubstance PPhenalenesGuinea PigsPeriaqueductal GrayOligopeptidesMedulla OblongataTachykininsMice, Inbred ICRBrainDrug InteractionsDibutyl PhthalateGABA AgentsCentral Nervous System DepressantsElectric Stimulationgamma-Aminobutyric AcidProtein PrecursorsVisceral AfferentsHydrochloric AcidBenzeneacetamidesEnkephalinsSynaptic TransmissionMolecular Sequence DataSalamandridaeAmygdalaImidazolesAmino Acid SequenceEnkephalin, LeucineBehavior, AnimalReceptors, GABAInjections, IntradermalMotor ActivityDrug ToleranceAcetic AcidReceptors, PresynapticVirulence Factors, BordetellaPain ThresholdNeuronsPruritusTerfenadineCorticotropin-Releasing HormoneAnalgesiaCerebral CortexBee VenomsStructure-Activity RelationshipCardiovascular SystemCyclic AMPNeuropeptides