In the present study, we observed that treatment with ferulic acid increased the seizure threshold. Our findings demonstrated that nitric oxide pathway (to some extent) mediated the anticonvulsant effect of ferulic acid. To date, a number of empirical studies have shown the anticonvulsant effects of ferulic acid (21, 24, 25), which are in line with the results of the present study. In the Lin et al. study, ferulic acid showed protective effects against glutamate-induced neuronal stimulation and inhibited glutamate release from cortical synaptosomes by inhibiting voltage-dependent calcium channels in the presynaptic membrane (26).
In the present study, to determine the role of nitrergic system in the anticonvulsant effect of FA in PTZ-induced seizure, first, we showed that administration of NOS inhibitor (L-NAME) increased the onset of seizure. L-NAME also significantly decreased the nitrite levels. Consistent with the above results, it was observed in other studies that intracerebral injection of L-NAME attenuated electroconvulsive therapy (ECT) in mice (27, 28). Another study found that injection of L-NAME to mice exacerbated neural cell death and kainic acid-induced seizures and increased iNOS expression (29). According to the findings, L-NAME, a NOS inhibitor, significantly increased the seizure threshold, indicating the role of nitric oxide and the nitrergic system in the occurrence of seizures.
In the next step, mice were treated with nitric oxide precursor (L-arginine) and observed that L-arginine did not significantly change the seizure threshold. Given that L-arginine is a precursor to nitric oxide, it was expected to decrease the onset of seizures. Various studies have reported contradictory results regarding the effectiveness of L-arginine against chemical or electrical seizures. In a study by De Sarro et al, it was observed that intracerebral injection of L-arginine exacerbated seizure-induced seizures (27). In the study of Kaputlu et al., L-arginine inhibited the anticonvulsant activity of L-NAME in PTZ-treated mice (28). Another study reported that L-arginine exacerbates NMDA-induced seizures and this effect is inhibited by L-NAME (30). However, some researchers have suggested that L-arginine possessed anticonvulsant effects (31, 32). It could be concluded that the inconsistencies regarding the effects of L-arginine can be due to differences in seizure patterns, drug dosage and route of administration (intraperitoneal or intracerebral) in various researches.
In the present study, ferulic acid caused a significant decrease in the nitric oxide levels, indicating that the anticonvulsant effects of ferulic acid, partially at least, mediated through nitrergic system. Researchers have shown that ferulic acid in ischemic mice has neuroprotective effects by reducing the activity of iNOS, eNOS and nNOS; indicating that modulation of the three NOS isoforms have critical role in neuroprotective activity of this agent (18, 33). In the study of Xu et al., ferulic acid significantly decreased nitric oxide levels in reserpine-treated rats (16). In the study of Sadar et al. (2016), administration of ferulic acid (20 and 40 mg / kg) to rats with ulcerative colitis decreased nitrosative stress parameters and decreased iNOS mRNA expression (34). In another study by Ogiwara et al., it was observed that ferulic acid inhibits the production of RNS free radicals in vitro and significantly inhibits lipopolysaccharide NO production in mouse macrophage cells (35).
In the present study, in the group received sub-effective dose of ferulic acid plus L-NAME, the seizure threshold was significantly increased as well as the nitrite level in the brain significantly decreased, indicating a strengthening effect of ferulic acid in the presence of L-NAME due to L-NAME inhibition activity.