STANFORD — Scientists have found unusual brain cells that may trigger epilepsy, a discovery they say could lead to improved drugs for the 2 million Americans who suffer from the disorder.
"The unique ability of these cells to readily discharge a volley of electrical impulses makes them likely instigators of epileptic seizures," said Dr. Barry Connors, assistant professor of neurology at Stanford University School of Medicine.
Seizures result when large numbers of nerve cells in the brain suddenly synchronize their electrical activity. The abnormal rhythm produces the convulsive movements, fainting or episodes of confusion characteristic of various forms of epilepsy.
Most victims live normal lives with the help of drugs that prevent seizures by stopping the spread of aberrant electrical activity, scientists said. But these medications can cause side effects and are ineffective in 10% to 20% of patients.
"If proved conclusively that the bursting cells indeed are the ones that start an attack, learning more about them could lead to the design of drugs to stifle epileptic discharges at their source," Connors said.
"We could target a drug towards them to shut them off specifically, rather than depress the whole central nervous system. This is the way anti-convulsants tend to work now."
Pyramid-Shaped Nerve Cells
In their research, funded by the National Institutes of Health, Connors and his colleagues found that bursting cells are a subset of pyramid-shaped nerve cells in the cortex, the outer shell of the brain especially prone to epilepsy.
These cells, which send out a network of spidery fibers that form an extensive web of connections with other nerve cells in the brain, normally fire one pulse at a time when activated. When bursting cells are stimulated they fire in rounds of three to five pulses.
Other scientists had previously found cells with this ability only in the hippocampus, a brain area also susceptible to seizures.
"In a normally functioning cortex, inhibitory neurons apparently hold the excitable bursting cells in check," Connors said. "In epilepsy, deficiencies in the chemistry of inhibitory cells may allow trigger-happy bursting neurons to overwhelm the brain's normal balance between excitation and inhibition."
Rat and Guinea Pig Brains
The research also may lead to an improved understanding of how the brain works, Connors said.
He located the bursting cells within the cortex of the rat and guinea pig brains. He pierced individual nerve cells within a thin slice of cortex, which he kept alive in a chamber that simulates the environment of a living animal's brain.
He used micro-electrodes, or needle-like glass tubes filled with a salt solution that conducts the electricity of nerve impulses.
After recording a neuron's electrical behavior, the scientists injected a fluorescent dye so the cell would show up under a microscope. Thus, they could correlate a cell's size and shape with its firing pattern.