Analysis of the transcriptional and behavioural responses to seizure onset in a zebrafish model of epilepsy.

Epilepsy is a common neurological disorder characterised by recurrent epileptic seizures. It affects approximately 0.7% of the worldwide population. Even though many patients respond to the available treatments, around a third of people with epilepsy do not respond to existing anti-epileptic drugs (AEDs). Therefore, there is a need to better understand epilepsy in order to develop new therapeutic strategies for the treatment of this disorder. In this study, a model of pharmacologically-induced epileptic seizures using young zebrafish larvae was developed and characterised. It was found that the brains of young zebrafish larvae exhibited altered PTZ-sensitivity in response to repeated seizure onset or exposure to stress hormone. In both cases, the severity of the PTZ-evoked locomotor convulsive response was enhanced, and expression of selected PTZ-induced genes was reduced. In order to identify more genes involved in the response to PTZ seizure-induction, and which might be involved in the adaptation of the CNS to seizure induction, a two-colour microarray analysis was carried out and many novel PTZ-responsive genes were identified. The function of a new epilepsy risk factor, sestrin 3, was also investigated using the zebrafish PTZ model of epileptic seizures, which revealed that sesn3 promoted locomotor convulsions and regulated expression of a subset of PTZ-induced genes. In addition to the studies of seizure mechanisms in the zebrafish, the new transgenic line NBT:GCaMP3 was created, in which expression of the fluorescent genetically encoded calcium indicator was targeted to the CNS, to visualize in vivo and in real time, seizure initiation, propagation and suppression by an antiepileptic compound. In the future, combining NBT:GCaMP3 with the new technologies to create zebrafish mutations in orthologues of genes mutated in human epilepsy, will enable novel experimental studies to investigate the pathogenetic mechanisms underlying epilepsy, and facilitate novel approaches to the discovery of anti-epileptic drugs.