Abstract: Ipalbidine(Ipa)is a photoactive alkaloid isolated from the seeds of ipomoea hardwickki Hemsl.The analgesic effects of Ipa were determined by rat tail flick method.A dose-dependent analgesic effect was found after sc or icv administration of Ipa,but no analgesia wasobserved after intrathecal injection,indicating that the analgesic effect of Ipa is central in origin,and itacts mainly on supraspinal substrate.The analgesic effect induced by Ipa(60 mg·kg^-1,sc)was markedly reduced by reserpine(2mg·kg^-1,ip)given 24 h before Ipa, which was reversed by combined administration with icvnorepinephrine(NE).In addition, Ipa-induced analgesia was significantly attenuated by electrolyticlesion of bilateral destruction of locus coeruleus.and combined administration withdiethyldithiocarbamate(200 mg·kg^-1,ip),phentolamine(10 mg·kg^-1,ip or icv),and prazosin(3mg·kg^-1,sc).But no influence was observed on the analgesia of Ipa after administration ofyohimbine(5 mg·kg^-1,sc) or propranolol(10 mg·kg^-1,ip).These results suggest that the analgesiacaused by Ipa is closely related to the function of the central norepinephrinergic system,and probablymediated by indirectly acting on α₁ receptors,but not α₂ orβreceptors.