Veratrine blocks the lamotrigine-induced swimming increase and immobility decrease in the modified forced swimming test

Lamotrigine exhibits an anti-immobility effect in the modified forced swimming test, increasing swimming and climbing, behaviors that are related to serotonergic and noradrenergic effects, respectively. However, these effects could be secondary to lamotrigine blockade of Na+ sensitive channel. Thus, this study investigated the influence of veratrine (0.1 mg/kg, ip, 10 min before each lamotrigine administration), an Na+ channel activator, in the effect of lamotrigine (20 mg/kg, ip, 24, 5, 1 h before the test session) in the modified forced swimming test. Veratrine pre-treatment blocked lamotrigine-induced immobility decrease and swimming increase but it did not change the effect of lamotrigine on climbing. These results suggest that the serotonergic effect of lamotrigine in the modified forced swimming test is dependent on Na+ voltage sensitive channel blockade, whereas its noradrenergic effect is not.