EnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, LeucineEnkephalin, MethionineEnkephalin, D-Penicillamine (2,5)-Enkephalin, Leucine-2-AlanineReceptors, Opioid, muReceptors, OpioidEndorphinsReceptors, Opioid, deltaAnalgesicsNaloxoneMorphineAnalgesics, OpioidNarcotic AntagonistsReceptors, Opioid, kappaReceptors, Neurokinin-3Pain MeasurementInjections, SpinalNaltrexoneNeurokinin BCyclazocinePainEthylketocyclazocineAnalgesiaOpioid PeptidesDynorphinsTachykininsReceptors, TachykininDose-Response Relationship, DrugDrug ToleranceInjections, IntraventricularD-Ala(2),MePhe(4),Met(0)-ol-enkephalinSubstance Pbeta-EndorphinPain ThresholdNociceptorsPeriaqueductal GrayRats, Sprague-DawleyNeurokinin AMorphinansBenzomorphansAdrenergic alpha-2 Receptor AgonistsAnalgesics, Non-NarcoticReceptors, Neurokinin-2Spinal CordOligopeptidesNarcoticsBenzeneacetamidesPiperidinesNociceptionHyperalgesiaMice, Inbred ICRDopamine AgonistsPyrrolidinesGuinea PigsAdrenergic alpha-AgonistsRNA, Transfer, GlyReceptors, Adrenergic, alpha-2Neurokinin-1 Receptor AntagonistsClonidineMorphine DerivativesDrug InteractionsMicroinjectionsCarboxypeptidase HBehavior, AnimalPentazocineCannabinoidsGABA AgonistsReaction TimeRats, WistarDiprenorphineReceptors, Neurokinin-1Nociceptive PainPurinergic P1 Receptor AgonistsRadioligand AssayFentanylHot TemperatureFormaldehydeGlycineNicotinic AgonistsMedulla OblongataEtorphineBuprenorphineBenzylidene CompoundsGuanosine 5'-O-(3-Thiotriphosphate)Binding, CompetitiveReceptor, Cannabinoid, CB1Amino Acid SequenceDronabinolBrainButorphanolMuscarinic AgonistsAdrenergic alpha-AntagonistsTailSomatostatinMorphine DependencePeptide FragmentsMolecular Sequence DataDrug Synergism