EnkephalinsReceptors, OpioidEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Receptors, Opioid, muEnkephalin, LeucineEnkephalin, MethionineAnalgesiaReceptors, Opioid, deltaEnkephalin, D-Penicillamine (2,5)-Analgesics, OpioidReceptors, Opioid, kappaEnkephalin, Leucine-2-AlanineAnalgesia, EpiduralNarcotic AntagonistsNaloxoneEndorphinsMorphineAnalgesia, ObstetricalOpioid PeptidesNaltrexoneDynorphinsAnalgesia, Patient-ControlledDiprenorphineAnalgesicsEthylketocyclazocineCyclazocineBenzeneacetamidesNarcoticsReceptors, Neurokinin-3Pain MeasurementBenzomorphansMorphinansFentanylbeta-EndorphinPainEtorphinePain, PostoperativeD-Ala(2),MePhe(4),Met(0)-ol-enkephalinNeurokinin BTachykininsDrug TolerancePyrrolidinesReceptors, TachykininInjections, SpinalSubstance PBupivacaineAcupuncture AnalgesiaDose-Response Relationship, DrugOligopeptidesAnesthetics, LocalBenzylidene CompoundsMorphine DerivativesOpioid-Related DisordersNeurokinin ADiterpenes, ClerodaneSufentanilRats, Sprague-DawleyReceptors, Neurokinin-2BuprenorphineLevorphanolGuinea PigsAnalgesics, Non-NarcoticButorphanolPain ThresholdMeperidinePeriaqueductal GrayPiperidinesGuanosine 5'-O-(3-Thiotriphosphate)Anesthesia, EpiduralTramadolMorphine DependenceSpinal CordHyperalgesiaRNA, Transfer, GlySomatostatinHeroinInjections, IntraventricularDihydromorphineHydromorphoneRadioligand AssayLabor PainSubstance Withdrawal SyndromeNociceptorsBrainCarboxypeptidase HNerve BlockAmino Acid SequenceLigandsProtein PrecursorsNeurokinin-1 Receptor AntagonistsBinding, CompetitiveElectroacupunctureMolecular Sequence DataMethadoneBehavior, AnimalLabor, ObstetricNalbuphineDouble-Blind MethodDrug InteractionsIleum