AnalgesicsPain MeasurementAnalgesics, OpioidMorphineReceptors, Opioid, muInjections, SpinalNarcotic AntagonistsPainAnalgesiaNaloxoneReceptors, Opioid, deltaReceptors, Opioid, kappaReceptors, OpioidNaltrexoneDrug TolerancePain ThresholdInjections, IntraventricularNociceptorsPeriaqueductal GrayAnalgesics, Non-NarcoticOpioid PeptidesEnkephalin, Ala(2)-MePhe(4)-Gly(5)-NociceptionDose-Response Relationship, DrugEnkephalin, D-Penicillamine (2,5)-EnkephalinsSpinal CordAdrenergic alpha-2 Receptor AgonistsHyperalgesiabeta-EndorphinRats, Sprague-DawleyMorphinansMice, Inbred ICRDynorphinsReceptors, Adrenergic, alpha-2ClonidineFormaldehydeReaction TimePentazocineAdrenergic alpha-AgonistsMicroinjectionsBuprenorphineHot TemperatureButorphanolTailCannabinoidsMorphine DerivativesPiperidinesDrug InteractionsOligopeptidesDronabinolBehavior, AnimalAcetic AcidNarcoticsAdrenergic alpha-AntagonistsNociceptive PainBenzomorphansFentanylReceptor, Cannabinoid, CB1DihydroergocristineYohimbineAdrenergic alpha-2 Receptor AntagonistsPyrrolidinesMedulla OblongataEnkephalin, MethionineEnkephalin, LeucineEndorphinsBrompheniramineLoperamideFreund's AdjuvantAlfentanilPyrazolesDrug SynergismBornanesCycloheptanesInjections, SubcutaneousCarrageenanReceptor, Cannabinoid, CB2Rats, WistarMyrsinaceae2-HydroxyphenethylamineSwimmingMSH Release-Inhibiting HormoneMorphine DependenceMecamylamineDrug Administration RoutesMotor ActivityZimeldineNaphthalenesBenzoxazinesDequaliniumDicyclomineFish VenomsTilidinePhysical StimulationBerberine AlkaloidsPain PerceptionBenzeneacetamidesCannabinoid Receptor ModulatorsCimetidine