In focal epilepsy, seizures are generated by localised, synchronised electrical discharges from neurons, which may spread to large portions of the brain. Research into why seizures occur is ongoing all over the world, but an important question remains: what are the earliest cellular events in the brain that start a focal seizure? Finding the answer to this is vital to understanding the mechanisms behind focal epilepsies, and for the development of new treatments for their drug-resistant forms.

Researchers led by a team from the National Research Council in Italy, have now found some exciting clues. They have shown that non-neuronal cells known as astrocytes play a crucial role in the generation of focal seizures. Astrocytes (also known as astroglia) are star-shaped cells that exist in the brain and spinal cord. They perform many functions, including the provision of nutrients to neurons and the repair of brain and spinal cord tissue after traumatic injury.

During the study, the scientists monitored the activity of neurons and astrocytes in different experimental models of epilepsy. They found that a period of hyperactivity in a restricted group of neurons triggers a large reaction among nearby astrocytes, and that the 'activated' astrocytes in turn send signals back to the neurons. This self-perpetuating 'loop' causes the neurons to become more and more excited and more and more synchronised in their activity. At a certain threshold of electrical excitement, a seizure is generated. The researchers also noticed that seizures themselves further activate the astrocytes, triggering further seizures.

These findings are very encouraging, because they show that a recurrent loop of excitation exists between neurons and astrocytes, and that this initiates and sustains epileptic seizures. Drugs that target the interaction between neurons and astrocytes could potentially be developed in the future, to help prevent seizures from starting.

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