MorphineMorphine DependenceMorphine DerivativesAnalgesics, OpioidDrug ToleranceNarcoticsNaloxoneReceptors, Opioid, muNarcotic AntagonistsSubstance Withdrawal SyndromeAnalgesiaPain MeasurementInjections, SpinalCodeinePain, PostoperativeNaltrexoneAnalgesicsDose-Response Relationship, DrugPainReceptors, OpioidTobacco Use DisorderAlcoholismHeroinNalorphineRats, Sprague-DawleyAnalgesia, Patient-ControlledHydromorphoneOpioid-Related DisordersEnkephalin, Ala(2)-MePhe(4)-Gly(5)-FentanylPeriaqueductal GrayEnkephalinsPentazocineMorphinansOxycodoneHeroin DependenceReceptors, Opioid, deltaNalbuphineKineticsTime FactorsMethadoneBehavior, AnimalMeperidinePain ThresholdBuprenorphineThebaineSubstance-Related DisordersOpiumOxymorphoneAnalgesia, EpiduralReceptors, Opioid, kappaDrug InteractionsEndorphinsHydrogen-Ion ConcentrationSpinal CordDouble-Blind MethodTemperatureLevallorphanInjections, SubcutaneousLocus CoeruleusInjections, IntraventricularEtorphineTramadolCocaine-Related DisordersHyperalgesiaPapaverInjections, IntravenousMembrane PotentialsMarijuana AbuseSubstance Abuse DetectionClonidinePain, IntractableBupivacaineBrainMotor ActivityLevorphanolNeuronsAgmatineBehavior, AddictivePruritusCalciumEnkephalin, D-Penicillamine (2,5)-NociceptorsOpioid Peptides