MorphineAnalgesics, OpioidMorphine DependenceMorphine DerivativesNarcoticsDrug ToleranceNaloxoneReceptors, Opioid, muPain, PostoperativePain MeasurementAnalgesia, EpiduralNarcotic AntagonistsAnalgesiaInjections, SpinalAnesthetics, IntravenousAnalgesia, Patient-ControlledBupivacaineSufentanilPainAlfentanilAnalgesicsPreanesthetic MedicationAdjuvants, AnesthesiaAnesthesia, IntravenousAdministration, CutaneousAnalgesia, ObstetricalDose-Response Relationship, DrugAnesthesia, GeneralDouble-Blind MethodAnesthetics, CombinedSubstance Withdrawal SyndromeMeperidinePropofolReceptors, OpioidAnesthetics, LocalCodeineNaltrexoneOxycodoneHydromorphoneMidazolamAnesthesia Recovery PeriodDrug InteractionsNalbuphineNitrous OxideBreakthrough PainEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Anesthesia, EpiduralHeroinAnesthesia, ObstetricalOxymorphoneReceptors, Opioid, deltaInjections, IntravenousRats, Sprague-DawleyPeriaqueductal GrayPentazocineNalorphineAnesthesia, SpinalPostoperative Nausea and VomitingMorphinansAnesthesiaIsofluraneDroperidolAnesthetics, InhalationPain ThresholdHypnotics and SedativesFentanylConscious SedationInfusions, IntravenousAnesthesia, InhalationKetamineCesarean SectionBuprenorphineMethyl EthersAdministration, BuccalMethadoneClonidineTramadolReceptors, Opioid, kappaEnkephalinsLevallorphanPain, IntractableInfusion PumpsKetorolacRespirationAnestheticsSpinal CordPiperidinesEndorphinsEtorphineBehavior, AnimalSubstance Abuse DetectionTime FactorsOpioid-Related DisordersThebaineNociceptorsTransdermal PatchHemodynamicsLidocaineInjections, SubcutaneousEnflurane