MorphineAnalgesiaAnalgesia, EpiduralAnesthetics, DissociativeAnalgesia, ObstetricalAnalgesics, OpioidAnalgesia, Patient-ControlledMorphine DerivativesMorphine DependencePain, PostoperativePain MeasurementAnalgesicsDrug ToleranceNaloxoneFentanylBupivacaineInjections, SpinalAnesthetics, LocalNarcoticsPainReceptors, Opioid, muAcupuncture AnalgesiaMeperidineNarcotic AntagonistsAnesthesia, EpiduralSufentanilDouble-Blind MethodDose-Response Relationship, DrugLabor PainReceptors, OpioidNerve BlockAnesthetics, CombinedPain ThresholdTramadolCodeineAnesthesia, ObstetricalXylazineAnesthesia, SpinalHydromorphoneConscious SedationAnalgesics, Non-NarcoticAnesthesia, GeneralRats, Sprague-DawleyLabor, ObstetricAnesthesia, CaudalSubstance Withdrawal SyndromePostoperative Nausea and VomitingExcitatory Amino Acid AntagonistsAmidesNaltrexoneNalbuphinePeriaqueductal GrayOxycodoneMidazolamAdjuvants, AnesthesiaPentazocineHyperalgesiaPain, IntractableAnesthesia, IntravenousCesarean SectionClonidineKetorolacHeroinLidocaineAnestheticsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Preanesthetic MedicationButorphanolAnesthesiaReceptors, Opioid, deltaKetamineInjections, IntravenousReceptors, N-Methyl-D-AspartateAlfentanilOpioid PeptidesBehavior, AnimalDrug InteractionsSpinal CordEnkephalinsMorphinansAnesthetics, IntravenousPropofolPruritusReceptors, Opioid, kappaInterpleural AnalgesiaInfusions, IntravenousPain ManagementPirinitramideDexmedetomidineThiopentalThoracotomyNociceptorsInjections, IntramuscularOpiumLabor Stage, FirstRespirationNitrous OxideTime FactorsNalorphineDrug Administration Schedule