EnkephalinsMorphineEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, LeucineEnkephalin, MethionineEnkephalin, D-Penicillamine (2,5)-Receptors, Opioid, muEnkephalin, Leucine-2-AlanineAnalgesics, OpioidReceptors, OpioidEndorphinsNaloxoneReceptors, Opioid, deltaMorphine DerivativesMorphine DependenceNarcotic AntagonistsNarcoticsReceptors, Neurokinin-3Drug ToleranceReceptors, Opioid, kappaEthylketocyclazocineNeurokinin BCyclazocineTachykininsNaltrexoneReceptors, TachykininAnalgesicsD-Ala(2),MePhe(4),Met(0)-ol-enkephalinPain MeasurementInjections, SpinalOpioid PeptidesSubstance PBenzeneacetamidesDose-Response Relationship, DrugNeurokinin ADynorphinsPain, PostoperativeAnalgesiaReceptors, Neurokinin-2EtorphineDiprenorphineAnalgesia, Epiduralbeta-EndorphinPainBenzomorphansRats, Sprague-DawleyAnesthetics, IntravenousAnalgesia, Patient-ControlledSufentanilRNA, Transfer, GlyPeriaqueductal GrayOligopeptidesBupivacaineGuinea PigsMorphinansPyrrolidinesDrug InteractionsAlfentanilSubstance Withdrawal SyndromeCarboxypeptidase HPreanesthetic MedicationAdjuvants, AnesthesiaAnesthesia, IntravenousAdministration, CutaneousAnalgesia, ObstetricalSpinal CordSomatostatinPiperidinesAnesthesia, GeneralDouble-Blind MethodAnesthetics, CombinedInjections, IntraventricularFentanylMeperidineLocus CoeruleusPropofolNeurokinin-1 Receptor AntagonistsAnesthetics, LocalCodeineGuanosine 5'-O-(3-Thiotriphosphate)BrainOxymorphoneOxycodonePain ThresholdHydromorphoneMidazolamNociceptorsGlycineAnesthesia Recovery PeriodNeuronsBehavior, AnimalNalbuphineAmino Acid SequencePentazocineReceptors, Neurokinin-1Nitrous OxideElectric StimulationThiorphanBreakthrough PainProtein Precursors