Serotonin (5-HT) is thought to play an important role in the seizures of El mice because the seizure threshold of El mice correlates with the 5-HT concentration in the central nervous system. In this study, the anticonvulsant effect of a 5-HT reuptake blocker, citalopram, was evaluated behaviorally and biochemically. El mouse convulsions were inhibited by chronic administration of citalopram (80 mg/kg/day, p.o. for 2 weeks), but were not inhibited by acute administration of citalopram (80 mg/kg, i.p., 2 h after single injection). Both chronic and acute administration of citalopram decreased the concentration of 5-hydroxyindolacetic acid in the brain, whereas the concentration of 5-HT was not changed by treatment with citalopram. Tryptophan hydroxylase activity was not different between the citalopram and control groups, although the monoamine oxydase-A activity was lowered by chronic administration of citalopram. These findings suggest that both acute and chronic administration of citalopram depresses the 5-HT turnover rate, however chronic administration is necessary to inhibit El mouse convulsions.</p
