MorphineInjections, SpinalEnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, LeucineEnkephalin, MethionineAnalgesics, OpioidEnkephalin, D-Penicillamine (2,5)-Enkephalin, Leucine-2-AlanineNaloxoneMorphine DerivativesPain, PostoperativePruritusAnesthesia, SpinalEndorphinsReceptors, Opioid, muPain MeasurementDrug ToleranceAnalgesia, ObstetricalInfusion Pumps, ImplantableReceptors, OpioidNarcotic AntagonistsMorphine DependenceAnalgesicsAnalgesiaReceptors, Opioid, deltaPainNalbuphinePain, IntractableSpinal CordMorphinansDose-Response Relationship, DrugReceptors, Neurokinin-3PirinitramideAnalgesia, Patient-ControlledAnesthesia, ObstetricalBupivacaineRats, Sprague-DawleyLabor PainAntipruriticsClonidinePostoperative Nausea and VomitingPreanesthetic MedicationCesarean SectionNarcoticsNeurokinin BEthylketocyclazocineFentanylHyperalgesiaCyclazocineTachykininsReceptors, TachykininSpinal NervesReceptors, Opioid, kappaDextromethorphanSubstance PD-Ala(2),MePhe(4),Met(0)-ol-enkephalinMuscle SpasticityUrinary RetentionDouble-Blind MethodNaltrexoneDynorphinsNeurokinin AReceptors, Neurokinin-2Hot TemperatureInjections, SubcutaneousOpioid PeptidesMuscle Relaxants, CentralDrug SynergismSufentanilHalothaneTime FactorsRNA, Transfer, GlyBenzomorphansAnesthesia, Generalbeta-EndorphinPain ThresholdVomitingRespirationSubstance Withdrawal SyndromeBenzeneacetamidesCarboxypeptidase HBaclofenGuinea PigsDrug Administration ScheduleDiprenorphineReceptors, N-Methyl-D-AspartateNeurokinin-1 Receptor AntagonistsEtorphineBehavior, AnimalAnesthetics, LocalInfusions, SpinalDrug Therapy, CombinationInjections, IntraventricularNociceptorsReceptors, Neurokinin-1Subarachnoid SpaceOligopeptidesPregnancyCodeine