The brain is extremely sensitive to changes in the body and must be protected from many of the substances, such as hormones and toxins, that circulate in the blood. A structure known as the blood brain barrier (BBB) exists between the smallest blood vessels in the brain (capillaries) and the brain tissue. This filters the blood passing through, allowing only oxygen, nutrients and water to enter the brain tissue and waste products to leave.

It has already been demonstrated that damage to the BBB can cause neurons to become hyperexcitable and produce seizures. However the mechanism by which this damage occurs was previously unknown.

Researchers in the US and Italy have recently shown that substances released during the body's inflammatory and immune responses could be responsible.

Inflammation is the body's response to trauma or infection. Blood rushes to the blood vessels in the affected area, bringing immune cells called leukocytes (white blood cells) to the site. The job of these cells is to destroy any foreign materials or disease-causing organisms that they meet.

The scientists induced epileptic seizures in mouse models, using a substance called pilocarpine, to trigger inflammation and immune responses in their brains. They then examined the behaviour of leukocytes in the brains.

Upon examination, each of the brains showed the presence of chemicals known as vascular cell adhesion molecules, which were released as part of the body's response to the seizures. These chemicals caused the leukocytes to 'stick together' and remain in the blood vessels for longer than usual.

The researchers then treated some of the models with a chemical that blocked the effect of the vascular cell adhesion molecules (preventing the leukocytes from sticking together), but left others without treatment.

They found that the majority of untreated models went on to develop full epilepsy. However in the treated group, the frequency of subsequent seizures was markedly reduced.

The scientists concluded that the 'sticking together' of the leukocytes in response to a seizure, contributes to the break-down of the BBB. The neurons of the brain are then at risk of hyperexcitability, and further seizures / full epilepsy can develop. They believe that this is how a one off seizure can progress into epilepsy.

One important question that needs to be answered is whether or not other brain injuries such as trauma or infection can lead to epilepsy in the same way.

What about humans?

A recent analysis of brain tissue from humans with epilepsy, found many more leukocytes than in those without the condition, suggesting that the same mechanism might apply in humans.

This is a very exciting development. If the process is proven in humans, drugs to counteract the 'stickiness' of leukocytes seen after a brain event might be developed, and the progression of epilepsy prevented.

Read more here and here