The study investigated epileptic seizures in zebrafish -- a widely used model organism for modelling human brain physiology. Zebrafish contains the same cell types that are present also in human brains. Two of these cell types are glia and neurons. Neurons are primarily involved in transmitting signals. The main functions of Glial cells include maintaining a balanced environment and providing support for the neurons, assisting the immune system and increasing the speed of neural signalling.
The study found that just before an epileptic seizure, nerve cells were abnormally active but only in a localized area of the brain. Instead, glial cells showed large burst of synchronous activity that are widely dispersed across the brain. During the actual seizure, the neuronal activity increased abruptly. The functional connections between the nerve cells and glial cells became vigorous. When this happened, generalized seizure spread like a storm of electrical activity across the entire brain due to a strong increase in the level of glutamate, a chemical compound that transmits signals between neuronal cells. Glutamate was secreted by glial cells, which convert themselves from a friend to a foe.
The findings indicate that epilepsy may occur not only due to anomalies in neurons, but also in glial cells. "Our results provide a direct evidence that the interactions between glial cells and neurons change during the transition from a pre-seizure state to a generalized seizure. It will be interesting to see if this phenomenon is generalizable across different types of epilepsies," says Prof. Emre Yaksi. Normally, the glial cells absorb the excess glutamate that is excreted during the increased activity of the nerve cells. This study assumes that the secretion process of the glial cells that we observed in combination with their hyperactivity just before a seizure is a defence mechanism of the brain.
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