MorphineMorphine DependenceMorphine DerivativesAnalgesics, OpioidDrug ToleranceNarcoticsVapor PressureNaloxoneVolatilizationReceptors, Opioid, muNarcotic AntagonistsAnalgesiaInjections, SpinalPain MeasurementSubstance Withdrawal SyndromeCodeinePain, PostoperativeAnalgesicsPainReceptors, OpioidNaltrexoneDose-Response Relationship, DrugAnalgesia, Patient-ControlledNalorphineHeroinRats, Sprague-DawleyHydromorphoneSteamFentanylEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Periaqueductal GrayGasesOxycodonePentazocineMorphinansEnkephalinsNalbuphineReceptors, Opioid, deltaMercuryMeperidineThebaineBehavior, AnimalPain ThresholdOxymorphoneAnalgesia, EpiduralOpiumEndorphinsHumidityMethadoneReceptors, Opioid, kappaInjections, SubcutaneousSpinal CordDrug InteractionsTime FactorsInjections, IntraventricularMercury PoisoningPapaverDouble-Blind MethodLevallorphanLocus CoeruleusHyperalgesiaPain, IntractableEtorphineTramadolBupivacaineInjections, IntravenousPruritusClonidineBuprenorphineMiosis