Got an itch to scratch? Scientists have pinpointed a key group
of cells that sends itch-alerts to the brain.
When researchers at Washington University in St Louis knocked
out those cells in mice, it alleviated their itchiness without
affecting their ability to sense pain - work that opens a possible
new target for creating better itch relievers.
Don't underestimate that need. The kind of itch caused by bug
bites or allergies typically goes away with a little scratching or
But some people can scratch themselves raw
without relieving serious, daily itching triggered by a variety of
conditions, such as certain cancers, chronic kidney failure, and
even use of certain narcotic pain relievers.
Indeed, pain and itch have been difficult to separate. Previous
research has found various nerve pathways that seem involved in
What the researchers found
But the report in the journal Science is the first to
identify itch-specific cells in the spinal cord, that highway that
delivers sensation to the brain.
"It's exciting," said well-known itch specialist Dr Gil
Yosipovitch of North Carolina's Wake Forest University Baptist
Medical Centre, who wasn't involved in the new research. "This
comprehensive study opens the field."
Lead researcher Zhou-Feng Chen, a Washington University
associate professor of anaesthesiology, in 2007 discovered the first
gene related to itchiness, named GRPR. They found that mice with an
inactive version of the gene scratched less when exposed to itchy
things than mice with an active gene.
But that didn't prove that the spinal cord neurons, or nerve
cells, that harboured this gene were itch-specific. They could also
be important to genes related to pain sensation.
So this time, Chen's team injected the spinal cords of mice with
a neurotoxin that seeks out the GRPR receptor, sort of a docking
site. Over about two weeks, the toxin killed about 80% of
the cells that harboured that gene.
Hope to block the urge to scratch
Before those injections, the mice scratched vigorously. But
after the itch cells were killed off, their scratching plummeted -
in some cases stopped completely - when Chen introduced one after
another itchy substance.
They weren't simply numbed: Their motor function remained
normal, and so did their response to pain from heat and pressure in
a series of common experiments that show animals flick their tails
or pull away their paws during various stresses.
This isn't the only itch pathway to the brain, stressed Wake
Forest's Yosipovitch. Nor does anyone know if this gene would
behave similarly in people.
But researchers have been hunting
itch-specific receptors in hopes of eventually learning how to
block their "scratch-me" signals to the brain and help relieve at
least some types of itch. – (Sapa, August 2009)