EnkephalinsEnkephalin, Ala(2)-MePhe(4)-Gly(5)-AnalgesiaEnkephalin, LeucineEnkephalin, MethionineEnkephalin, D-Penicillamine (2,5)-Analgesia, EpiduralEnkephalin, Leucine-2-AlanineReceptors, Opioid, muAnalgesics, OpioidAnalgesia, ObstetricalAnalgesicsMorphineReceptors, OpioidEndorphinsReceptors, Opioid, deltaNaloxonePain MeasurementNarcotic AntagonistsAnalgesia, Patient-ControlledInjections, SpinalReceptors, Opioid, kappaPainReceptors, Neurokinin-3NaltrexoneDrug ToleranceOpioid PeptidesCyclazocineNeurokinin BEthylketocyclazocinePain ThresholdPain, PostoperativeDynorphinsFentanylTachykininsReceptors, TachykininAnalgesics, Non-NarcoticInjections, Intraventricularbeta-EndorphinDose-Response Relationship, DrugPeriaqueductal GrayNociceptorsD-Ala(2),MePhe(4),Met(0)-ol-enkephalinSubstance PAcupuncture AnalgesiaBupivacaineAnesthetics, LocalMorphinansSpinal CordNarcoticsNeurokinin ARats, Sprague-DawleyBenzomorphansNociceptionHyperalgesiaReceptors, Neurokinin-2PiperidinesMeperidineBenzeneacetamidesOligopeptidesMorphine DerivativesClonidineMice, Inbred ICRAdrenergic alpha-2 Receptor AgonistsPentazocineSufentanilAnesthesia, EpiduralRNA, Transfer, GlyNociceptive PainButorphanolPyrrolidinesLabor PainReceptors, Adrenergic, alpha-2Neurokinin-1 Receptor AntagonistsBehavior, AnimalCarboxypeptidase HDrug InteractionsReaction TimeMicroinjectionsGuinea PigsBuprenorphineNerve BlockAdrenergic alpha-AgonistsTramadolHot TemperatureAlfentanilFormaldehydeAnesthesia, SpinalLabor, ObstetricAnesthesia, ObstetricalMorphine DependenceReceptors, Neurokinin-1Medulla OblongataAmidesDiprenorphineCannabinoidsEtorphineLidocaineTailBrain