Neuron Path Discovery May Change Our Conception of Itching

Hugh Pickens writes "Historically, many scientists have regarded itching as just a less intense version of pain, though decades spent searching for itch-specific nerve cells have been unfruitful. Now, Nature reports that neuroscientist Zhou-Feng Chen and his colleagues at Washington University in St. Louis, Missouri have found the first behavioral evidence that there are separate circuits of nerve cells to convey itchiness and pain, and their studies suggest that itch and pain signals are transmitted along different pathways in the spinal cord. 'Most people accept that there are specific, highly specialized neurons for sensations like taste,' says Chen. 'But for pain and itch this is much more controversial.'" (Continues below.)

"Two years ago, Chen's group discovered that a cell-surface protein called the gastrin-releasing peptide receptor (GRPR) is important for sensing itchiness but not pain in mice. When Chen and his colleagues destroyed GRPR-bearing neurons by means of a cell toxin, the mice reacted to painful stimuli just like normal mice, licking themselves and flinching or jumping in response to heat, highly irritant chemicals and mechanical pressure. But when the researchers injected the animals with chemicals that normally cause scratching, such as histamine, they barely responded, and the greater the number of GRPR-expressing neurons destroyed, the more subdued was the scratching response."

Ouch. Torturous.

[BobSixtyFour]

"Mice that had lost the GRPR-producing neurons reacted to painful stimuli just like normal mice, licking themselves and flinching or jumping in response to heat, highly irritant chemicals and mechanical pressure."

Poor mice :(

Itch

[Tofof]

Great. After reading that, now I'm keenly aware of itching sensations all over my body - not unlike watching someone yawn.

Re:Interesting from an evolution POV

[ZackSchil]

Removal of parasites, probably.

Re:Ouch. Torturous.

[DNS-and-BIND]

If hooking a car battery up to a monkey's brain will help find the cure for AIDS and save somebody's life, I have two things to say... the red is positive and the black is negative.
--Nick Dipaolo

Re:Ouch. Torturous.

[Rakshasa Taisab]

Hey, I'd be all ok even if it was your brain being wired up for some car battery shocks.

Re:Itch

[6Yankee]

I was already itching - stupid eczema.

Now hopefully these people will hurry up and find a way to turn this off. I can't wait.

Re:Pondering the luck of others

[DMUTPeregrine]

Some do, actually. Phantom Limb syndrome does weird things. The worst bit is it's totally impossible to scratch it.

Re:Interesting from an evolution POV

[Renraku]

The reason for pain is to make you escape something.

Such as burning yourself on a stove, getting stabbed, bitten, stung, etc. You don't want these things to happen. Pain is strongly connected with negative in most minds. At least, most pain..

The reason for itching is to call your attention to something.

It's kind of the difference between a critical error and an error. One's a dire warning, and the other one is just an exclamation. It would be very fucking useful to distinguish between the two. One, so that you don't freak out every time you walk through some grasses that tickle your legs. Two, so you don't beat your bed-mate to death when they rub up against you. Three, so you don't let bugs chew on you or flip out every time one does.

I'll bet the 'itching' pathways have other uses as well. Perhaps the tickling response is there?

Important and relevant research

[rrohbeck]

Remember, every successful FOSS project started with a developer who had an itch to scratch. Clearly we need more itching.

Re:Ouch. Torturous.

[dcollins]

"If hooking a car battery up to a monkey's brain will help find the cure for AIDS and save somebody's life, I have two things to say... the red is positive and the black is negative.
--Nick Dipaolo"

What if it's a hundred monkeys? A million monkeys? A billion? What if there's a 5% chance it might help? What if it's a researcher who thinks it might help, but hasn't been right to date?

Re:Interesting from an evolution POV

[reverseengineer]

Actually, this is possibly an excellent example of evolution minimizing complexity through the tactic of re-purposing the same system to be used in different ways in different parts of an organism. As the article notes, the neurons that may be specific to itchiness have a cell surface protein called gastrin-releasing peptide receptor. Gastrin, as the name might suggest, also plays a role in the gastrointestinal system, where it is involved in signaling the release of hydrochloric acid. What do your digestive juices have to do with itchy skin? Notably, gastrin does not work directly to release stomach acid, but rather it binds to what are called ECL cells, which secrete histamine, which then stimulate the parietal cells of the stomach to release acid. Histamine is a versatile molecule that is particularly useful for organizing inflammatory responses, though these responses aren't always welcome. That's why you might take diphenhydramine for allergies and ranitidine for heartburn- both are antihistamines, though for different histamine receptors.

Thus, strangely enough, skin itches share many of the same signaling pathways as digestion. The cell types involved (epithelial tissue) are similar though, so during the evolutionary development of skin, cells would already have inherited a sensitive network of cell surface receptors and signal transduction pathways. Why not find a way to put them to good use?