Receptors, Opioid, muReceptors, Opioid, deltaAnalgesics, OpioidReceptors, OpioidReceptors, Opioid, kappaNarcotic AntagonistsMorphinansEnkephalin, Ala(2)-MePhe(4)-Gly(5)-Enkephalin, D-Penicillamine (2,5)-Opioid PeptidesNaltrexoneDose-Response Relationship, DrugCannabinoid Receptor AgonistsBenzeneacetamidesNarcoticsNaloxoneEnkephalinsMorphinePyrrolidinesSelective Estrogen Receptor ModulatorsBuprenorphineEtorphineEstrogen AntagonistsLigandsPiperidinesOpioid-Related DisordersRats, Sprague-DawleyRaloxifeneEnkephalin, Leucine-2-AlanineLevorphanolReceptor, Cannabinoid, CB1Receptor, Adenosine A1BenzomorphansEndorphinsDynorphinsCannabinoidsFentanylNalbuphineMethadoneAnalgesicsDrug ToleranceMethadyl AcetateBinding, CompetitiveEnkephalin, LeucineDiprenorphineHydromorphoneEthylketocyclazocineNeurokinin-1 Receptor AntagonistsEstrogen Receptor betaTamoxifenDiterpenes, ClerodanePain MeasurementAzocinesPainEnkephalin, MethionineStructure-Activity RelationshipMorphine DerivativesEstrogen Receptor alphaReceptors, EstrogenDopamine AgonistsOligopeptidesOxycodoneD-Ala(2),MePhe(4),Met(0)-ol-enkephalinSignal TransductionPeriaqueductal GrayDrug InteractionsCell LineEstradiolRadioligand AssayCells, CulturedAmino Acid SequenceMolecular Sequence DataPiperazinesButorphanolBinding SitesProtein Bindingbeta-EndorphinSubstance Withdrawal SyndromeDopamine AntagonistsHormone AntagonistsHeroinModels, MolecularGuanosine 5'-O-(3-Thiotriphosphate)Opiate Substitution TreatmentRats, WistarGuinea PigsExcitatory Amino Acid AntagonistsBenzamidesBehavior, AnimalVas DeferensGABA AgonistsHyperalgesiaInjections, SpinalAnalgesics, Non-NarcoticSpiro CompoundsMorphine DependenceMuscarinic AntagonistsHistamine H2 AntagonistsSelf StimulationPurinergic P1 Receptor Agonists