NEW YORK (Reuters) -- Harvard researchers say a study on the nerves responsible for sensation in the head and face may yield clues to the origin of migraines.
"No one had been directly studying these nerve fibers -- the trigeminal ganglia -- before," said Dr. Andrew Strassman, assistant professor at Harvard Medical School's Department of Anesthesia.
Strassman says the origins of headache pain remain obscure. "It's just about the most common type of pain," he admits. "But paradoxically, it's been just about the hardest to understand because there's nothing there in the vast majority of headaches to physically point to the source."
For decades, severe headaches were blamed on swollen blood vessels, according to Strassman. But recent technology has proven that's usually not the case.
So, he and his Harvard colleagues turned to the trigeminal ganglion, a branch of the nervous system supplying facial and head sensation, whose home lies under the skull and just below the brain. Strassman says theories linking the highly sensitized endings of this nerve pathway to headache pain have been floated for years.
In their study, anesthetized rats were used to examine the reaction of certain chemicals on these nerve endings. The chemicals have the potential to be produced in meningeal tissues under conditions of inflammation or irritation, Strassman says.
He said the effect on the nerve endings was dramatic. "Some of the neurons were activated and fired impulses at high frequency." And if they weren't activated, there was a second effect. Even after washing the chemical off the nerves, Strassman says, "they became more sensitive to mechanical stimulation -- just poking the meninges with controlled force."
Researchers say this increased sensitivity to touch and movement may be linked to the unexplained increase in pain migraine sufferers feel when coughing, shaking their heads, or holding their breath. "Migraine headache is characterized by features that suggest an exaggerated intracranial mechanosensitivity," researchers explained. "Normally innocuous activities that produce an increase in intracranial pressure or altered intracranial haemodynamics (blood flow)... evoke dramatically increased head pain during such headaches."
The job now, says Strassman, is to pinpoint exactly which chemicals might switch on this heightened neural sensitivity. "We do know that potassium, for example, is released by neurons and neural tissue in the brain during excitation," he says. Potassium has been linked to a neurological condition called 'spreading depression', which study authors say "is accompanied by chemical disturbances."
Strassman says if the connection between increased chemical production, increased neural sensitivity, and heightened pain is confirmed, it could lead to effective migraine treatments. He says further studies are needed, "both to ask what's behind the pain, and to test and investigate the action of drugs that block headache."
SOURCE: Nature (1996;384:560-564)
