The connections between "itch" and "ouch"

The biology of itching and the biology of pain are intertwined in interesting ways, writes graduate student and science blogger Aatish Bhatia. Understanding itching can help us better understand how to treat pain. I'd not seen Bhatia's blog before, but I'm really liking his style. He does a great job of breaking down the science in a clear way.

... In the last decade, researchers have learned about receptors in the nerves under our skin that react specifically to itchy substances. When these receptors fire, they send a signal racing up our spinal cord, headed to our brain where it creates an urge to scratch. Scientists now have a basic map of the roads that an itch takes on its way to our brain. And they have even been able to block some of these roads in mice, essentially preventing them from feeling an itch.
...The picture that is emerging is a complex one, where pain and itch signals are distinct yet subtly intertwined. Of the nerve cells under our skin, some are involved only in signalling pain, and they have pain receptors. Others are responsible for signalling different types of itches, and they have both itch and pain receptors. If the same cell has both receptors, how do we distinguish itch from ouch?
... As the biology of itching becomes better understood, the benefits are making their way from the lab to the clinic. The drug morphine is a powerful painkiller, but has a common side effect of itchiness. Women taking opiates to relieve their labor pain often experience a similar side effect. Zhou-Feng Chen and Yan-Gang Sun, authors of the GRPR receptor study, teamed up with colleagues at the newly founded Center for the Study of Itch and managed to tackle this problem. Their results, published in the current issue of the journal Cell, show that the benefits of morphine can be separated from the itch.