Humans have a common facial expression that conveys pain - and now Canadian researchers have shown that mice make a similar "pain face."
A new "mouse grimace scale" will make it easier for researchers to assess the pain-control benefits of new drugs in lab animals, says Jeff Mogil, a pain researcher at McGill University in Montreal.
In the past, scientists have assessed pain in lab mice by how often an animal licked a sore paw, or by making other observations about the animal's behaviour. Dr. Mogil's research measured the experience of pain based on the rodent's facial expressions: They squeeze their eyes, scrunch up their noses and push out their cheeks, much like humans do.
They also push back their ears and move their whiskers, says Mogil, who collaborated with the University of British Columbia's Kenneth Craig on the project. When these features are combined in one expression, it means the mouse is hurting.
The new scale, published in the journal Nature Methods, could help scientists more accurately predict whether a pain-killing compound will work in humans. It will also help researchers who use laboratory mice in all kinds of experiments know if the creatures hurting.
Dr. Mogil and his colleagues are the first to formally study the facial expression of pain in animals. He says it is likely that horses, cats, dogs, rats and other species make a similar "pain face."
The mice in the study were given injections to cause inflammation and were in moderate pain, probably similar to what a human would experience from an infected finger, says Dr. Mogil.