MorphineMorphine DependenceMorphine DerivativesAnalgesics, OpioidDrug ToleranceNarcoticsNaloxoneReceptors, Opioid, muNarcotic AntagonistsAnalgesiaPain MeasurementInjections, SpinalPain, PostoperativeCodeineAnalgesicsSubstance Withdrawal SyndromePainDose-Response Relationship, DrugAnalgesia, Patient-ControlledReceptors, OpioidNaltrexoneFentanylRats, Sprague-DawleyHydromorphoneNalorphineDouble-Blind MethodOxycodoneHeroinPentazocineMorphinansEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Periaqueductal GrayMeperidineEnkephalinsNalbuphineAnalgesia, EpiduralReceptors, Opioid, deltaTime FactorsPain ThresholdDrug Administration ScheduleBehavior, AnimalDrug InteractionsThebaineTreatment OutcomeOxymorphoneInjections, SubcutaneousInjections, IntravenousPruritusDrug-Related Side Effects and Adverse ReactionsBupivacainePain, IntractableMethadoneSpinal CordTramadolOpiumReceptors, Opioid, kappaEndorphinsDrug Therapy, CombinationAdministration, OralHyperalgesiaAnalgesics, Non-NarcoticAnesthetics, LocalDelayed-Action PreparationsInjections, IntraventricularClonidineKetorolacVomitingMotor ActivityPostoperative Nausea and VomitingPapaverLocus CoeruleusLevallorphanDrug SynergismKetamineAnesthesia, SpinalBuprenorphineOpioid-Related DisordersAnti-Inflammatory Agents, Non-SteroidalInfusions, IntravenousEtorphineNauseaLevorphanolSufentanilHydrocodoneClinical Trials as TopicNociceptorsAntipsychotic AgentsProspective StudiesRats, Wistar