MorphineEnkephalinsReceptors, Opioid, muEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Analgesics, OpioidEnkephalin, MethionineEnkephalin, LeucineMorphine DependenceEnkephalin, D-Penicillamine (2,5)-Receptors, Opioid, deltaNaloxoneNarcotic AntagonistsReceptors, Opioid, kappaNarcoticsDrug ToleranceNaltrexoneEnkephalin, Leucine-2-AlanineReceptors, OpioidMorphine DerivativesSubstance Withdrawal SyndromeDose-Response Relationship, DrugEndorphinsPain MeasurementDrug Partial AgonismLocus CoeruleusReceptors, Neurokinin-3Rats, Sprague-DawleyLevallorphanPeriaqueductal GrayOpioid PeptidesEthylketocyclazocineNeurokinin BCyclazocineTachykininsReceptors, TachykininAnalgesiaD-Ala(2),MePhe(4),Met(0)-ol-enkephalinNucleus AccumbensBehavior, AnimalPainSubstance PDopamine AgonistsAdenylate CyclaseNeurokinin ACyclic AMPReceptors, Neurokinin-2BrainNeuronsTime FactorsNicotinic AgonistsHyperalgesiaDynorphinsGuinea PigsOpioid-Related DisordersAnalgesicsArrestinsSpinal CordRats, WistarBenzeneacetamidesRadioligand AssayMotor ActivityMorphinansXamoterolMice, Inbred C57BLBenzomorphansDrug Administration ScheduleGABA AgonistsBenzylidene CompoundsCyclic AMP-Dependent Protein KinasesBinding, CompetitiveInjections, SpinalG Protein-Coupled Inwardly-Rectifying Potassium ChannelsLigandsReceptors, N-Methyl-D-AspartateRNA, Transfer, GlyOligopeptidesPiperidinesGlycineGABA-A Receptor Agonistsbeta-EndorphinRNA, MessengerAdrenergic beta-AgonistsAzocinesSynaptic TransmissionEtorphineDiprenorphineGuanosine 5'-O-(3-Thiotriphosphate)Signal TransductionCycloserineAnabasineMice, KnockoutSerotonin 5-HT1 Receptor AgonistsCarboxypeptidase HStructure-Activity RelationshipAdrenergic beta-1 Receptor AgonistsPyrrolidinesAmino Acid SequenceExcitatory Amino Acid AntagonistsDrug InteractionsGTP-Binding Protein beta Subunits