Like humans, mice express pain through expressions

TORONTO - Like humans, mice also show pain through facial expressions, says a new study.

Jeffrey Mogil and Kenneth Craig, psychology professors at McGill University and British Columbia University, respectively, and their teams discovered that mice showed discomfort through facial expressions just as humans did, when subjected to moderate pain.

Their study also details the development of a Mouse Grimace Scale that could inform better treatments for humans and improve conditions for lab animals.

Because pain research relies heavily on rodent models, an accurate measurement of pain is paramount in understanding the most pervasive and important symptom of chronic pain, namely spontaneous pain, says Mogil.

“The Mouse Grimace Scale provides a measurement system that will both accelerate the development of new analgesics (pain killers) for humans, but also eliminate unnecessary suffering of laboratory mice in biomedical research,” says Mogil.

This is the first time researchers have successfully developed a scale to measure spontaneous responses in animals that resemble human responses to those same painful states.

Mogil, graduate student Dale Langford and colleagues in the Pain Genetics Lab at McGill analysed images of mice before and during moderate pain stimuli - for example, the injection of dilute inflammatory substances, as are commonly used around the world for testing pain sensitivity in rodents.

The level of pain studied could be comparable, researchers said, to a headache or the pain associated with an inflamed and swollen finger easily treated by common analgesics like Aspirin or Tylenol.

Mogil then sent the images to Craig’s lab at British Columbia University where facial pain coding experts used them to develop the scale, says a McGill release.

Craig’s team proposed that five facial features be scored: orbital tightening (eye closing), nose and cheek bulges and ear and whisker positions according to the severity of the stimulus.

Craig’s lab had previously established studying facial expression as the standard for assessing pain in human infants and others with verbal communication limitations.

These findings were published online Sunday in Nature Methods.