The protein in the peripheral nervous system that gives mice the ability to sense cold and menthol has been identified, according to three recent journal articles. Menthol receptor TRPM8, as this protein is known, is found in humans and researchers believe these findings extend to people.
“[The receptor] provides a target for studying acute and chronic pain, as can result from inflammatory or nerve injury, the researchers say, and a potential new target for treating pain.
“’By understanding how sensory receptors work, how thresholds for temperature are determined, we gain insight into how these thresholds change in the setting of injury, such as inflammatory and nerve injury, and how these changes may contribute to chronic pain,’ says senior author David Julius, PhD, chairman and professor of physiology at UCSF.” (from UCSF press release, Detecting Cold, Feeling Pain: Study Reveals Why Menthol Feels Fresh)
Although the article only addresses pain caused by physical injury, it seems that the findings can apply to headache too. Nerves outside the brain, which are called peripheral nerves, become sensitized in both migraine and tension-type headaches. This is the source of allodynia — being sensitive to touch or feeling like your hair hurts.
Central Sensitization Determines Ideal Time for Migraine Treatment is the most reader friendly article that describes the role of peripheral nerves in migraine. I can only find basic information on tension-type headache and peripheral nerves. Do you know of any good resources on the topic?
I know I’m skimming the surface here. Any comments on the study or the role of peripheral and central sensitization in headache and migraine will be greatly appreciated.
Yes–skimming the surface. There are both central and peripheral sensitization. There is also cutaneous allodynia in the trigeminal region (face & head), as well as peripheral allodynia, which is sometimes also called extracephalic allodynia–fancy words for allodynia outside from or away from the head.
There is still a lot of ongoing research on allodynia to understand its underlying pathophysiology better.
Most of the work with menthol has been on peripheral allodynia, and looks at allodynia induced by cold, although I did find one report of orofacial pain in rats.
The present target of most of this research is peripheral neuropathy. While I do not wish to dis anyone’s pain–or research–I will point out that the prevalence of peripheral neuropathy in the general population is 2.4%, and can rise to 8% with advancing age. The prevalence of migraine in the adult US population is 12%; the prevalence of chronic daily headache is 3%.
I would encourage anyone who is concerned about research priorities to discuss it with their legislators. We are making progress–finally–but need so much more. We need funding, but mostly, we–headache sufferers–need to not be invisible.
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Thanks for helping us understand it a little better. Interesting — and frustrating — stats on research priorities.
Kerrie
I’ve got a paper on migraines which includes a good deal of information that I think you’d find really helpful. It’s been posted to the migraines community on LiveJournal, but the formatting is crap. I can send you a copy in Word if you like (email me).
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Thanks!
Kerrie