Is seizure a consequence of altered neural development?

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The incidence of epilepsy in humans is a significant clinical problem which is exacerbated by the fact that up to one third of patients fail to respond to current drug treatment. The cause of epilepsy is both varied and in many cases unknown. However, what is known is that epilepsy results from incorrect function of nerve cells that make up the central nervous system. The human central nervous system is composed of many different types of nerve cells which must communicate with one another. These cells differ in the targets that they contact, the signalling chemicals (neurotransmitters) that they release, and the way in which they are able to fire electrical action potentials - the basis of signalling in the brain. Two recent studies highlight the possibility that some epilepsies may arise as a consequence of altered neural development due to the occurrence of abnormal patterns of activity. In essence self-reinforcing cycles of aberrant activity may be sufficient to destabilise the formation of neural circuits, the consequence of which is seizures in later life. If so, then such seizures may be treatable through early intervention to break the cycle of aberrant activity. This research proposal will exploit the fruitfly, Drosophila melanogaster, because it is very amenable to genetic analysis, the complete genome has been sequenced, and because it provides a simple model of the human nervous system. We intend to use a characterised mutant of the fly that exhibits seizures that are remarkably similar to those in humans. Our previous study shows that this mutant, termed slamdance, can be effectively 'cured' by treating the early embryo with an established antiepileptic drug. The present proposal seeks to use a relatively new set of genetic tools in order to use light to manipulate activity in an early developing nervous system (optogenetics). We hope to determine whether a critical period exists during which aberrant activity is sufficient to destabilise neural circuit formation and leave an individual prone to seizures in later life. If proven this outcome may have significant implications for the way heritable-forms of epilepsies are treated in humans.