EnkephalinsAnalgesiaEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Analgesics, OpioidEnkephalin, LeucineReceptors, Opioid, muEnkephalin, MethionineReceptors, OpioidAnalgesia, EpiduralMorphineReceptors, Opioid, deltaAnalgesia, ObstetricalEnkephalin, D-Penicillamine (2,5)-Enkephalin, Leucine-2-AlanineReceptors, Opioid, kappaNaloxoneOpioid PeptidesEndorphinsPain MeasurementAnalgesia, Patient-ControlledNarcotic AntagonistsFentanylPentazocineDrug TolerancePainPain, PostoperativeAnalgesicsbeta-EndorphinInjections, SpinalPain ThresholdReceptors, Neurokinin-3NarcoticsEthylketocyclazocineNeurokinin BCyclazocineNaltrexoneTachykininsReceptors, TachykininPiperidinesD-Ala(2),MePhe(4),Met(0)-ol-enkephalinDynorphinsNociceptorsSpinal CordHyperalgesiaDose-Response Relationship, DrugRats, Sprague-DawleyBupivacaineSubstance PAnesthetics, LocalAcupuncture AnalgesiaNeurokinin ABenzeneacetamidesReceptors, Neurokinin-2BenzomorphansSufentanilOpioid-Related DisordersDiprenorphineMeperidineAnesthesia, EpiduralMorphinansRNA, Transfer, GlyLabor PainCarboxypeptidase HNerve BlockBuprenorphineGuinea PigsAnalgesics, Non-NarcoticOligopeptidesHydromorphonePyrrolidinesTramadolMorphine DerivativesLabor, ObstetricAnesthesia, ObstetricalNeurokinin-1 Receptor AntagonistsDouble-Blind MethodAmidesPeriaqueductal GrayAnesthesia, SpinalEtorphineDihydromorphineProtein PrecursorsReceptors, Neurokinin-1ButorphanolAmino Acid SequenceGlycineMethadoneThiorphanMorphine DependenceBrainPain ManagementInjections, IntraventricularPostoperative Nausea and VomitingSubstance Withdrawal SyndromeMolecular Sequence DataNociceptive PainElectroacupunctureCesarean SectionAlfentanilNalbuphine