Abstract: AIMTo study the effect of NO on securinine-induced long-term potentiation in the dentate gyrus of anesthetized rats. METHODSThe population spike (PS) was recorded by electrophysiological techniques. Then the rat brain was homogenized, of which the NO level was detected by spectrometry at 550 nm after the catalysis of nitric acid reductase. RESULTSPretreatment with 7-nitroindazole (1 μmol·L^-1, 5 μL icv) was shown to inhibit LTP induced by securinine (0.2 nmol·L^-1, 5 μL icv) in anesthetic rats. The percentage of PS amplitude was (100±23)%, (106±16)% and (124±20)% at 15, 30 and 60 min, respectively (N=6, P<0.01). Meanwhile, the NO level was obviously higher in securinine group compared with that in 7-nitroindazole group (P<0.01). Nevertheless, L-arginine (250 mg·kg^-1, ip) was found to reverse this inhibitory effect induced by 7-nitroindazole (P<0.05). CONCLUSION Selective nNOS inhibitor 7-nitroindazole inhibited the securinine-induced LTP in anesthetic rats, which demonstrated that NO was involved in securinine-induced LTP.