Unbearable itch may no longer be a pain in anaesthesia
THE intimate link between itch and pain has been teased apart for the first time – a development that could lead to powerful anaesthetics without any of that intolerable itching.
Itch is one of the most common side effects of the anaesthetics used in procedures such as epidurals. One explanation is that itch and pain receptors are intrinsically connected. "Itch and pain are two sensations that antagonise each other," says Zhou-Feng Chen from Washington University in St Louis, Missouri. "By scratching you create a kind of mechanical pain and suppress the itch. Conversely, if you suppress pain you see more itching."
To understand this mechanism better, Chen used mice to study the action of morphine, a painkiller that can cause itching. Morphine works through a receptor called MOR, and Chen suspected that different variants of the receptor might be responsible for the itch and pain responses. His team bred mice lacking one form of this receptor, called MOR1D. These mice did not scratch themselves when given morphine, though they still felt its painkilling effect (Cell, DOI: 10.1016/j.cell.2011.08.043).