Epilepsy is a serious neurological condition affecting one in every 100 people in the UK, according to the British Epilepsy Association. Having it can mean losing out on education, independence, income and employment, and both patients and scientists are eager for new treatments to be found.

Many people with epilepsy manage their condition well. Seizures – sudden and prolonged bursts of electrical activity between brain cells – are the main symptom, and medication usually reduces their severity or stops them entirely. When drugs don’t work, there are surgical options, including a procedure to remove a small part of the brain that causes the seizures.

But for some individuals – particularly children with the chronic neurological disorder – symptoms remain stubbornly drug resistant. For these people, seizures can be a daily occurrence and often neither drugs nor surgery have any effect.

In a perfect world, effective treatments would eradicate symptoms completely rather than just manage seizures, with a person effectively being cured of epilepsy soon after they experience their first seizure.

Networks of nerve cells

Some types of epilepsy are related to genetic abnormalities, brain injury or developmental disorders, but for many patients, the cause remains unknown.

One area of epilepsy research focuses on the development of the nervous system in its earliest days – in particular, trying to identify the biological processes that can go wrong in the foetal brain at the start of life, as well as the DNA glitches that may trigger epilepsy.

Some biologists limit their investigations to isolated nerve cells, growing these cells in the lab and observing them as they mature. However, work of this sort is of limited value, as petri-dish nerve cells don’t behave the way cells do in a living organism.

“In the developing body, nerve cells don’t act in isolation but work in intricate ways with other nerve cells to form neural circuits or networks,” explains Dr Nikolas Nikolaou, a developmental neurobiologist from the Department of Life Sciences at the University of Bath.

“What is needed now is a better understanding of how nerve cells are wired together, and how this wiring diagram is influenced by genes.”

Dr Nikolaou has just received grant funding from the Royal Society for a new research project on childhood epilepsy. His end goal is to fix the broken biological processes that give rise to epilepsy.

Many childhood epilepsies have a genetic link, with mutations found in genes encoding voltage-gated sodium channels (pores in the cell membrane that conduct sodium ions) and inhibitory neurotransmitter receptor subunits (proteins that are responsible for communication between brain cells and play a crucial role in inhibiting neuronal activity within the brain).

“My team is interested in understanding the role these proteins play during brain development and how disease variants lead to uncontrolled excitability in the brain,” said Dr Nikolaou.

“Ultimately, we want to identify better therapeutics that suppress seizures.”

Zebrafish develop fast – meaning research can progress at pace

Dr Nikolaou ‘s research uses zebrafish. These small freshwater minnows are increasingly being used to study brain development and function from embryos into adulthood.

There are several major benefits to studying zebrafish to investigate neurological disorders affecting people.

Firstly, zebrafish develop fast. A zebrafish egg is fertilised externally (i.e., after being released by the adult female into the water) and 48 to 72 hours later, the embryo hatches and becomes a free-swimming larva. Within the next two days, the fish starts to behave like a mini adult, hunting for itself and avoiding predators.

Dr Nikolaou is most interested in the changes that occur in the first few days of a fish’s life, during which nerve cells develop into functional brain networks.

Elaborating, he said: “Within 24 hours of fertilisation, cells have already differentiated into nerve cells (differentiation is the process where stem cells – cells that have the potential to become any cell type – specialise into a given lineage) and two to three days later, the fish has recognisable behaviours that we can study to assess the function of the nervous system.”

He added: “In comparison, the first nerve cells in humans appear several weeks after fertilisation, and behaviour relating to the nervous system is not observed until after birth.”

In other words, researchers can closely observe a zebrafish with a known genetic mutation from the moment its nerve cells start to form to its full development as a swimmer, all within the span of four days.

“A lot can be learnt in those four days about the role played by genes that are linked to disorders affecting humans,” said Dr Nikolaou.

Another major advantage in studying zebrafish is that they are prolific breeders. A female zebrafish can lay up to 200 eggs per week. This high fecundity means scientists can study the effects of a genetic mutation quickly and extensively by observing her (plentiful) offspring.

It also means Dr Nikolaou’s lab doesn’t need to keep many adult fish – a handful of adults per genetically altered line are sufficient to produce all the eggs his lab needs to make its observations.

A further benefit to studying genetic mutations in zebrafish is that the embryos and larvae remain virtually transparent for several days after fertilisation, meaning their organs can be seen taking shape through their skin (the fish later go on to develop their distinctive black-and-yellow stripes).

To study how the nervous system develops, Dr Nikolaou and his team anaesthetise the young fish and observe nerve cells using specialised microscopes fixed with submergible objectives (the fish are in water at all times). Once the anaesthetic wears off, the fish swim away, unharmed.

Glowing proteins

The way Dr Nikolaou and his group study neural networks is by breeding genetically modified zebrafish.

The researchers make small changes to the genome of embryos by micro-injecting new DNA sequences into the fertilised egg. These sequences insert themselves into the fish genome, and the impact of these modified sequences on the fish’s developing neural circuits is then observed.

The segments of DNA inserted by the team correspond precisely to mutations that can occur spontaneously in humans, and that are known to cause epilepsy.

Dr Nikolaou says the mutant fish variants created for the upcoming epilepsy study, “will be watched closely for any symptoms that suggest seizures. These seizures are not expected to cause any long-lasting harm to the animals but they can provide valuable insights into the underlying causes of genetic epilepsy.”

What makes it easier for the Bath biologists to observe the effects of new genetic material at a cellular level is that the proteins coded for by the inserted DNA are designed to fluoresce. When an embryo’s nerve cells glow green, it’s a whole lot easier to visualise and track them as the cells mature and form connections called synapses with other cells in the developing nervous system.

The five-day cut-off

Dr Nikolaou’s work with zebrafish ends before his fish reach their fifth day of life post-fertilisation – and before they become fully independent.

At this point, with the exception of a handful of genetically altered fish that go on to become breeders, the genetically modified larvae are humanely killed. An overdose of anaesthesia is added to their water, and they die quickly and without pain.

“For the duration of their lives, we ensure our fish are healthy and stress-free,” said Dr Nikolaou. “Being humane matters a lot to us as people, and it’s also important from a science point of view.

"Fish that are handled correctly are more fecund and their offspring show no signs of developmental defects. This means our experimental observations aren't biased by external factors and we can focus on those important genetic alterations.”

Ending childhood epilepsy

Dr Nikolaou is hopeful that his forthcoming study will eventually lead to a new drug being found that will inhibit seizures entirely in children.

“Though we’re just starting out, we have very promising data showing that zebrafish mimic humans closely in the way epilepsy is caused at the genetic level. Thanks to the high fecundity of these fish, we’ll soon be able to conduct large-scale chemical screens to identify new drugs that could alleviate or completely abolish the symptoms of epilepsy in children.

“We feel hopeful that childhood epilepsy will become a thing of the past one day – in the meantime, these experiments will give us a better understanding of the molecular mechanisms that trigger epilepsy and could lead to new treatments.”