A ‘face-book’ to measure pain in mice
Scientists have for the first time created a sliding scale of pain
for mice based on facial expressions, according to study published
recently.
The so-called “mouse grimace scale” will speed up the development of
new analgesics for humans, and could help reduce unnecessary suffering
of mice and other animals in biomedical research, the researchers said.
“There are also serious implications for the improvement of
veterinary care,” said Jeffrey Mogil, a professor at McGill University
in Montreal and the main architect of the study.
Research on pain and how to relieve it depends heavily on the use of
rodents as stand-ins for humans, so accurate measurement of pain
intensity in lab mice is crucial.
Up to now, however, it was not known whether degrees of discomfort
and suffering in mice correspond to spontaneous facial responses, as is
the case for people.
Doctors and nurses routinely use such scales to assess pain in
individuals unable to communicate verbally, such as infants and the
cognitively impaired.
Line drawings of faces showing different levels of discomfort are
also used to help manage chronic pain in children asked to match what
they feel with the appropriate images.
To find out whether rodents grimace when it hurts, Mogil and
colleagues monitored and recorded facial movements before and during the
injection of a substance known to cause painful inflammation.
The mice showed discomfort through facial expressions in a way
similar to humans.
When pain was more intense, for example, the eyes narrowed, the
bridge of the nose and cheeks bulged, the ears moved down and back, and
the whiskers either bunched up or flattened out against the face.
Using an intensity scale based on changes in these five facial
features, persons trained to “read” pain in expressions correctly
assessed discomfort levels in the mice, based on photographs, with 80
percent accuracy.
Looking at high-resolution video images, accuracy rates went up to 97
percent.
In another set of experiments, the researchers created a so-called
“knock-in” mouse with a genetic mutation known to cause migraine
headaches in humans.
As expected, the mice displayed the same telltale grimaces as seen in
the animals who had been injected with an inflammatory substance.
When pain-relieving drugs were administered, facial expression
returned to normal.
The study, published in the journal Nature Methods, also bolsters
Charles Darwin’s belief that non-human animals express emotion including
pain through facial expression, and that such displays emerged from the
process of natural selection.
In evolutionary terms, the ability to communicate pain experience to
others may benefit both the sender and receiver, such that help might be
offered or a warning signal heeded.
The fact that three of the facial pain cues in mice are found in
humans narrowing eyes, along with bulging nose and cheeks also support
Darwin’s century-old prediction that facial expressions have deep
evolutionary roots.
Following up on these findings, the researchers are currently
investigating whether the scale works equally well in other species, and
if mice can respond to facial pain cues in each other.
PARIS, AFP |