Lithium-Responsive Seizure-Like Hyperexcitability Is Caused by a Mutation in the Voltage-Gated Sodium Channel Gene .

() is an X-linked dominant mutation in identified more than 40 years ago. A previous study showed that caused spontaneous tremors and defects in reactive climbing behavior, and that these phenotypes were significantly suppressed when mutants were fed food containing lithium, a mood stabilizer used in the treatment of bipolar disorder (Williamson, 1982). This unique observation suggested that the mutation affects genes involved in lithium-responsive neurobiological processes. In the present study, we identified as a novel mutant allele of the voltage-gated sodium (Na) channel gene (). Given that hypomorphic alleles and RNA interference-mediated knockdown reduced the severity of phenotypes, was classified as a hypermorphic allele. We also demonstrated that lithium could improve the behavioral abnormalities displayed by other Na mutants, including a fly model of the human generalized epilepsy with febrile seizures plus. Our electrophysiological analysis of showed that lithium treatment did not acutely suppress Na channel activity, indicating that the rescue effect of lithium resulted from chronic physiological adjustments to this drug. Microarray analysis revealed that lithium significantly alters the expression of various genes in , including those involved in innate immune responses, amino acid metabolism, and oxidation-reduction processes, raising the interesting possibility that lithium-induced modulation of these biological pathways may contribute to such adjustments. Overall, our findings demonstrate that Na channel mutants in are valuable genetic tools for elucidating the effects of lithium on the nervous system in the context of neurophysiology and behavior.