Study of Pain in Mice Offers Hope for Improved Pain Management in Pets

I got excited when I found a link in my inbox yesterday. The subject line of the e-mail was "Research could help veterinarians decode animals'...

I got excited when I found a link in my inbox yesterday. The subject line of the e-mail was “Research could help veterinarians decode animals’ pain”.

I hate it when my patients feel pain. Although painful cats and dogs give many clues, they cannot communicate their level of pain simply and clearly to those of us who want to take steps to treat the pain. People who aren’t trained to recognize signs of pain in pets may not realize that their pets are suffering. I spend parts of nearly every day convincing pet owners that their pets need pain medicine.

An easy way to measure pain so that it could be treated appropriately would be a godsend for pets, their owners, and their veterinarians. I clicked on the link immediately. Here is an excerpt.

Humans are not the only ones to grimace when they are in pain, scientists have found. Mice show their discomfort in the same way.

Decoding animals’ facial expressions may allow researchers and veterinarians to monitor spontaneous pain over long timescales. This may also aid the discovery of painkillers, because this type of pain is similar to that experienced by humans.

So far, so good. The article continues:

To analyse facial expressions in mice, geneticist Jeffrey Mogil at McGill University in Montreal, Canada, and his colleagues have adapted a coding system used to measure pain in infants. The work is published today in Nature Methods.

Mogil teamed up with Kenneth Craig, a psychologist who studies human pain at the University of British Columbia in Vancouver. Expert expression-spotters from Craig’s lab compared video frames of mice filmed for up to 30 minutes before and after receiving a painful injection of acetic acid.

The researchers detected five signs indicative of pain in mice. Three are similar to human responses: the eyes close and the area around them tightens, and the nose and cheeks bulge. Mice also pull back their ears and move their whiskers.


I am not an opponent of animal research. Animal research has improved or even saved the lives of countless humans and animals. Animal research has contributed dramatically to the development of medicines that treat cancer, heart disease, and just about any other malady imaginable in dogs, cats, and people. Animal research helps physicians and veterinarians understand more about the hard science behind and pathology of disease. This helps us prevent and treat disease.

There is no doubt that animal research is a wonderful thing–unless you’re the one being experimented upon. Ethical standards have been developed to minimize the negative impact of experiments upon their involuntary animal participants. Researchers owe it to their subjects to maximize quality of life and minimize suffering.

In the experiment, the researchers intentionally inflicted pain upon their subjects by injecting them with vinegar. They were walking on some pretty thin ethical ice when they did that.

First, it is impossible to claim that one is being a careful steward of one’s research subjects’ well being when one is intentionally inflicting pain.

Second, the experiment did not yield a major scientific advance. Any veterinarian or person with significant animal experience can state that cats and dogs (and, it stands to reason, any mammals with highly developed nervous systems such as mice) have facial expressions that are similar to humans. Happy animals smile. Worried animals look worried. Mad animals look mad. Animals in extreme pain grimace. There are interspecies differences in body language, but the overall picture of something as dramatic as extreme pain is quite universal. Insights that would help me detect subtle pain in my patients would be very useful, but I already know what an animal in extreme pain looks like.

But wait! There’s more.

Grimaces were most pronounced for pain that lasted for a matter of minutes or hours, and for discomfort in joints and internal organs. Superficial harm such as immersing the tail in hot water evoked fewer grimaces. Mice and humans show similar variability in pain response, Mogil says.

Pained expressions differed from those associated with stress and illness, the team found. In addition, more harmful stimuli drew more pronounced grimaces, and pain relievers diminished them.

The article doesn’t go into the further methods used by the researchers. I’m glad I wasn’t involved in the experiment. In my line of work I see enough suffering animals each day with without anyone deliberately causing them pain.

Photo: No grimace seen. By the Wikimedia Commons user “Rama”.

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