Drug screening in Scn1a zebrafish mutant identifies clemizole as a potential Dravet syndrome treatment.

Dravet syndrome is a catastrophic pediatric epilepsy with severe intellectual disability, impaired social development and persistent drug-resistant seizures. One of its primary monogenic causes are mutations in Nav1.1 (SCN1A), a voltage-gated sodium channel. Here we characterize zebrafish Nav1.1 (scn1Lab) mutants originally identified in a chemical mutagenesis screen. Mutants exhibit spontaneous abnormal electrographic activity, hyperactivity and convulsive behaviours. Although scn1Lab expression is reduced, microarray analysis is remarkable for the small fraction of differentially expressed genes (~3%) and lack of compensatory expression changes in other scn subunits. Ketogenic diet, diazepam, valproate, potassium bromide and stiripentol attenuate mutant seizure activity; seven other antiepileptic drugs have no effect. A phenotype-based screen of 320 compounds identifies a US Food and Drug Administration-approved compound (clemizole) that inhibits convulsive behaviours and electrographic seizures. This approach represents a new direction in modelling pediatric epilepsy and could be used to identify novel therapeutics for any monogenic epilepsy disorder.

A novel zebrafish model of hyperthermia-induced seizures reveals a role for TRPV4 channels and NMDA-type glutamate receptors.

Febrile seizures are the most common seizure type in children under the age of five, but mechanisms underlying seizure generation in vivo remain unclear. Animal models to address this issue primarily focus on immature rodents heated indirectly using a controlled water bath or air blower. Here we describe an in vivo model of hyperthermia-induced seizures in larval zebrafish aged 3 to 7 days post-fertilization (dpf). Bath controlled changes in temperature are rapid and reversible in this model. Acute electrographic seizures following transient hyperthermia showed age-dependence, strain independence, and absence of mortality. Electrographic seizures recorded in the larval zebrafish forebrain were blocked by adding antagonists to the transient receptor potential vanilloid (TRPV4) channel or N-methyl-d-aspartate (NMDA) glutamate receptor to the bathing medium. Application of GABA, GABA re-uptake inhibitors, or TRPV1 antagonist had no effect on hyperthermic seizures. Expression of vanilloid channel and glutamate receptor mRNA was confirmed by quantitative PCR analysis at each developmental stage in larval zebrafish. Taken together, our findings suggest a role of heat-activation of TRPV4 channels and enhanced NMDA receptor-mediated glutamatergic transmission in hyperthermia-induced seizures.