Is seizure a consequence of altered neural development?

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.

Many forms of epilepsy are the result of heritable gene mutations that influence the activity of ion channels. Many of these are single point mutations in voltage-gated Na channels that influence open times, voltage-dependency and/or conductivity to increase excitability of neurons. Two recent studies, in rat and the fruitfly, provide evidence to suggest that such epilepsies may be effectively treated by early exposure of the developing nervous system to clinically-used antiepileptic drugs. The rationale for this effect is that aberrant patterns of activity during early neural development lead to self-reinforcing cycles of instability in neural circuit formation. The prevention of such activity, by exposure to antiepilpetics, allows the nervous system to develop and better compensate for altered channel activity caused by the specific mutation resulting in a more stable behaviour in adult life.

If proven, this observation may offer considerable promise for the treatment of some forms of idiopathic (heritable) forms of epilepsy. We will exploit the powerful molecular genetics of the fruitfly Drosophila to use optogentics to manipulate neural activity during neurogenesis to determine whether a critical period exists during which aberrant activity can destabilise circuit formation and lead to increased seizure-like activity postembryonically. There are also a number of well characterised seizure mutants of Drosophila that closely parallel the clinical manifestations of epilepsy in humans. We will also attempt to suppress seizure in these mutants through manipulation of neural activity during early development.

The work contained within this grant is basic in nature but has clear strategic relevance in relation to the treatment and possible cure for epilepsy. This work will also validate the use of an invertebrate model organism - Drosophila melanogaster - for the continued investigation of the causes and treatments for this significant disease. Thus it has the potential to reduce the usage of larger animals that are currently used for such research. As such this programme of work falls under the 3R's initiative.

The beneficiaries of this work can be divided into 2 main groupings:

1. Our published demonstration that early treatment can prevent the occurrence of seizures in a Drosophila epilepsy model has significant implications for understanding of electrical development and diseases arising when this aspect of neurogenesis is incorrect. This has significant implications to both basic Neuroscientists that are attempting to understand neural development but also to Neuroscientists in the clinic investigating the underlying causes and treatments for epilepsy.

2. The development of treatments for disease requires the involvement of large pharmaceutical companies. However, nearly all treatments currently available can have their origins traced back to basic research undertaken in Universities. We are very conscious of the roles that pharmaceutical companies play in development of treatments and our research will be of direct benefit to those companies actively pursuing treatments for this disease.

Communications & Engagement

In addition to traditional means (research publications and conferences) we will disseminate our research as follows:

1. Through direct contact with Charities such as Epilepsy Research UK and The International League Against Epilepsy. We will inform such charities of our work and to highlight, in particular, the utility of using non-mammalian animal models (which is usually under-appreciated).
2. Through contact with the Media. For example, I took part in radio 4's Material World in Nov 2008 to highlight the use of Drosophila for research in to human diseases.
3. I also have a dedicated lab website which I use to advertise the type of research that we carry out
4. As an active member of the teaching staff at Manchester, I also use and advertise my research to undergraduates through lectures and final year projects in the hope of encouraging some to consider this area of research for their future careers. For example a student in my lab this year designed and presented a workshop to 6th form students on the utility of non-mammalian models for neurological research.

Collaboration

I have recently obtained funding, from The Wellcome Trust, to develop a core-Drosophila facility at Manchester to encourage a greater degree of interactivity and collaboration between existing fly groups and those wishing to exploit this model system for the first time. Many researchers using mammalian models could benefit by incorporating this fly into their research programmes and this facility will reduce the inertia to do so.

Exploitation & Application

Drosophila offers the opportunity to develop cheap, large-scale, drug screens that are a viable alternative to using rodents. Such screens have already been undertaken for a number of diseases, including epilepsy (by Cambria Biosciences, USA, with whom I have an active collaboration).