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<DIV><FONT face=Arial size=2>A discovery among blind people has helped
scientists resolve a mystery why light can make a migraine go from headache to
head-splitter, according to a study<BR>published. </FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>The problem appears to lie with a newly-discovered
bunch of cells in the retina, its authors say.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>Researchers from Beth Israel Deaconess Centre, an
affiliate of the Harvard Medical School, made the find after pondering why some
blind people who suffer<BR>from migraines also experience photophobia – an
extreme sensitivity to light that horribly worsens these headaches.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>In a paper published online in the journal Nature
Neuroscience, the team reported how they probed two groups of migraine-suffering
blind individuals.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>One group, of six people, was totally blind and
immune to the normal sleep-wakefulness cycle caused by daylight and
night.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>The other, numbering 14, was "legally blind"
because of degenerative diseases of the eyes. They could detect the presence of
light and followed the sleep-wakefulness<BR>cycle although they could not
perceive images.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>"While the patients in the first group did not
experience any worsening of their headaches from light exposure, the patients in
the second group clearly<BR>described intensified pain when they were exposed to
light, in particular blue or grey," said senior author Rami
Burstein.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>"This suggested to us that the mechanism of
photophobia must involve the optic nerve, because in totally blind individuals,
the optic nerve does not carry<BR>light signals to the brain."</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>The team theorised that the culprit had to be
recently-discovered retinal cells which have melanopsin photoreceptors –
light-sensitive biological triggers<BR>for sleep and wakefulness. </FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>"These are the only functioning light receptors
left among patients who are legally blind," Burstein explained.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>The next step was to test the ideas on lab rats.
Using dyes injected into the rodents’ eyes, the scientists were able to trace
the pathway from the melanopsin<BR>retinal cells through the optic nerve and to
the brain, where they found a group of neurons which became activated during
migraines.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>Tiny electrodes inserted into the rats’ brains
determined that, within seconds, light unleashed a surge of electrical activity
in these cells – and the<BR>cells remained switched on even after the light was
removed.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>"This helps explain why patients say that their
headache intensifies within seconds after exposure to light and improves 20 to
30 minutes after being in<BR>the dark," Burstein added.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>The work could be a boon for migraine sufferers. It
opens up exploratory options for drugs that block the pathway, enabling a
migraine patient to endure<BR>light without added pain.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Migraines are believed to develop when protective
membranes surrounding the brain become irritated. This stimulates pain receptors
and, in turn, causes<BR>sensory neurons to become activated for long
periods. </FONT></DIV>
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