Chloroquine, a 4-aminoquinoline derivative, has long been used for the treatment of malaria and rheumatological disorders, including rheumatoid arthritis and systemic lupus erythematosus. Accumulating evidence now suggests potential use of chloroquine as a neuroprotectant. Studies have shown that nitric oxide (NO) pathway is involved in the chloroquine actions. Considering the fact that nitrergic neurotransmission plays a crucial role in the central nervous system functioning, in the present study we evaluated whether nitrergic system is involved in the anticonvulsant effects of chloroquine in a model of clonicseizure in mice.

Clonic seizure threshold was determined by infusion of pentylenetetrazole (PTZ, 0.5%) at a constant rate of 1mL/min into the tail vein of male Swiss mice (23–29g). Minimal dose of PTZ (mg/kg of mice weight) needed to induce clonicseizure was considered as an index of seizure threshold.

Chloroquine (5mg/kg, acutely 30min before test, intraperitoneally), i.p significantly increased the seizure threshold. Acute co-administration of a non-effective dose of the non-selective NO synthase (NOS) inhibitor, L-NAME (L-NG-Nitro-L-arginine methyl ester hydrochloride,5mg/kg, i.p.) or the selective inhibitor of neuronal NOS, 7-NI (7-nitroindazole, 40mg/kg, i.p.) with an effective dose of chloroquine (5mg/kg) inhibited its anticonvulsant effects. Co-administration of a non-effective dose the selective inducible NOS inhibitor, aminoguanidine (100mg/kg, i.p.) with chloroquine 5mg/kg did not alter its anticonvulsant effects.

Chloroquine increases the PTZ-induced clonic seizure threshold in mice. We demonstrated for the first time that nitric oxide signaling probably through neuronal NOS could be involved in the anticonvulsant effects of chloroquine in this model of seizure in mice.