Analgesics, OpioidEnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, LeucineEnkephalin, MethionineAnalgesiaAnalgesia, EpiduralEnkephalin, Leucine-2-AlanineEnkephalin, D-Penicillamine (2,5)-Analgesia, ObstetricalEndorphinsReceptors, OpioidReceptors, Opioid, muMorphineNaloxoneAnalgesia, Patient-ControlledReceptors, Opioid, deltaReceptors, Neurokinin-3NarcoticsEthylketocyclazocineCyclazocineNarcotic AntagonistsNeurokinin BPain, PostoperativeTachykininsAnalgesicsReceptors, TachykininPain MeasurementReceptors, Opioid, kappaOpiate AlkaloidsD-Ala(2),MePhe(4),Met(0)-ol-enkephalinFentanylBupivacaineSubstance PNaltrexoneAnesthetics, LocalDynorphinsNeurokinin AOpioid-Related DisordersAcupuncture AnalgesiaReceptors, Neurokinin-2EtorphineMorphine DerivativesOpioid PeptidesPainBenzomorphansbeta-EndorphinInjections, SpinalMeperidineSufentanilDrug ToleranceDihydromorphineDiprenorphineAnesthesia, EpiduralRNA, Transfer, GlyCodeineHeroinMorphinansLabor PainBenzeneacetamidesMethadoneDose-Response Relationship, DrugCarboxypeptidase HMorphine DependenceNerve BlockGuinea PigsSubstance Withdrawal SyndromeOpiumPiperidinesLabor, ObstetricAnesthesia, ObstetricalPain ThresholdBuprenorphineAmidesOligopeptidesHydromorphoneTramadolDouble-Blind MethodNeurokinin-1 Receptor AntagonistsAnalgesics, Non-NarcoticRats, Sprague-DawleyAnesthesia, SpinalReceptors, Neurokinin-1BrainPentazocineHeroin DependenceGlycineLocus CoeruleusPyrrolidinesProtein PrecursorsOxymorphoneAmino Acid SequenceClonidineSpinal CordSubstance Abuse DetectionThiorphanOxycodoneCesarean SectionPostoperative Nausea and VomitingMolecular Sequence Data