STAY ON STROKES

Scientists may have discovered a way 
to prevent stroke after cerebral trauma, reports Biplab Das 

Strokes claim numerous lives every year. Those who survive the ordeal remain physically or mentally handicapped for the rest of their lives. The toll would be a lot less if medical assistance could be provided within an hour. For this, a tailor-made therapy is needed. 

When a stroke occurs, large amounts of the neurotransmitter glutamate are released, which over-excite the N-methyl D-aspartate (NMDA) receptors, resulting in nerve cell death. According to a report published in Science, a research team led by Matthew During of the University of Auckland, New Zealand, and Thomas Jefferson University, Philadelphia, has developed a treatment which has prevented brain cell death in stroke-affected rats. They selected a virus to carry a gene that codes for a portion of the NMDA receptors. This genetically engineered virus generates antibodies which reach the stroke-damaged site and halt the NMDA receptors' excitement, thereby checking nerve cell death. 

Normally, a structure called the blood-brain-barrier prevents large protein molecules from entering the brain. But in the case of strokes or other trauma, the barrier is broken down, so the NMDA antibodies are able to enter the brain. 

In tests, researchers injected a single dose of the modified virus to laboratory rats. Two months later, sufficient amounts of NMDA antibodies accumulated in the blood. Now, to mimic a stroke, an artery supplying the brain was injected with a compound that disrupts the flow of blood. Deprived of blood, large portions of the brains were damaged. But the vaccinated rats suffered less damage. 

To garner further information, During's team induced prolonged seizures known as status epilepticus in the rats, by injecting them with kainaiste, a compound which triggers excessive release of glutamates. In humans, these seizures kill cells in the hippocampus. Rats without the virus developed severe status epilepticus and displayed scars clearly in the hippocampus. But the vaccinated rats showed no discernible signs of hippocampal damage. 

"Immunising people with neural antigens might have unwanted effects, including encephalitis or learning disruptions," cautions James McNamara, a neuroscientist in the University of Duke in Durham, North Carolina. His apprehension is not baseless. NMDAs currently in use in humans have been reported to cause hallucinations and other symptoms of psychosis. 

Until now, that had been an acceptable price in the quest to save brain cells. But During's initial results show that his treatment does not cause such disruptions. 

However, it would be impractical to use it as a vaccine. After profuse bleeding on the brain surface, the chances of developing a stroke within a week are 50 per cent. Since the treatment prepares the brain for impending danger, During foresees that directly injecting NMDA antibodies into the bloodstream would protect such highrisk people from going on to suffer a stroke.