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Mouse pain study stirs debate

Canadian scientists vindicated after being accused of mistreating laboratory animals.

A study monitoring facial expressions of mice in pain drew fire but was ruled as complying with Canadian regulations.

A Canadian research team that induced pain in mice to help develop a 'grimace scale' recently came under fire from a researcher-support organization, which posted an online commentary suggesting that the scientists may not have complied with Canada's animal welfare regulations. But Canadian officials have since determined that the study did follow national rules for the care of laboratory animals.

The research team, led by pain geneticist Jeffrey Mogil of McGill University in Montreal, Quebec, videotaped the facial expressions of mice during 14 pain-inducing procedures, such as immersing the tail in hot water, putting a binder clip on tails, cutting the paw, injecting chemicals into the paw or stomach and constricting or damaging nerves during surgery. The researchers coded the intensity of facial expressions and reported their technique this May in the journal Nature Methods1.

Two weeks ago, the Principal Investigators Association, a non-profit organization in Naples, Florida, that "communicates and promotes best practices and continuing professional education", posted a discussion-board topic about the study on Lab Animal eAlert, its online subscription newsletter for researchers. The commentary accused the McGill team of causing severe pain to mice that were not anaesthetized, and questioned whether Mogil and his collaborators followed regulations set by the Canadian Council on Animal Care, the national organization that oversees the use of animals in research.

Canadian animal-research guidelines preclude or strongly discourage procedures that elicit severe pain "at or above the pain tolerance threshold".

More than 100 people have responded on the discussion board. "One thing is clear," says Leslie Norins, the publisher and chief executive of the Principal Investigators Association, who approved the items posted on the online forum. "The cliquish fraternity of mouse pain experimenters will be much more careful in the future about explaining in great detail just what they are doing."

Standard techniques

The McGill researchers used standard experiments that are permitted in many countries. "There are papers published every week that use those techniques," says pain researcher Paul Flecknell, who develops ways to assess and alleviate pain in animals at Newcastle University, UK.

"As far as I can tell, the scientists followed ethical guidelines," says Allan Basbaum, a pain researcher at the University of California, San Francisco, who contributed to the 2009 US National Research Council report Recognition and Alleviation of Pain in Laboratory Animals.

This report states that the presence of ongoing discomfort or pain may be acceptable if it is warranted by the experimental objectives. "I doubt very much that I would have done anything differently," Basbaum adds.

In light of the controversy, the Canadian Council on Animal Care re-evaluated the McGill study and announced last week that it did comply with national rules for the care of laboratory animals. The council promotes the adoption of a set of research principles known as the 'three Rs' — replacement, reduction and refinement of animal use to minimize pain and distress.

At the local level, McGill University's animal care committee and a separate ethics subcommittee approved the study before its implementation and at one-year intervals over its three-year duration. Although replacing mice with tissue cultures or less-sentient species was not possible in this case, the committee provided guidance on the minimum number of animals needed to attain significant results, says Jim Gourdon, director of the Comparative Medicine and Animal Resources Centre at McGill.

The university's ethics committee, composed of veterinarians, scientists, community representatives and ethicists, also weighed the potential benefits of the study against its risks and looked for appropriate 'endpoints' — the earliest possible point at which the animal could be euthanized, determined by the study's objective and appropriate criteria — says Lorraine Chalifour, chairwoman of McGill's animal care committee. A lab-animal veterinarian also supervised some of the experiments, she adds.

To reduce pain in the mice, the research team anaesthetized them when they underwent nerve surgery and stopped some experiments as soon as the animals showed signs of discomfort, such as reflexively withdrawing the tail from a heat source or attempting to remove a clip from the tail. The team also used the same mice for other experiments and humanely killed them as soon as the behavioural tests ended, Mogil says. "What we did was 100% by the book, and it was no different from pain research going on everywhere in the world right now every day."

Tentative trade-offs

The controversy seems to have arisen, in part, because of a misunderstanding over ambiguous wording in the paper1. Mogil and his team used the word "severe", but to describe facial expressions, not the intensity of pain. "There's no way of knowing for sure how much pain an animal is ever feeling," Mogil explains.

Still, the mice used in his experiments did not show obvious signs of extreme pain, such as immobility, vocalizations or lack of grooming or eating, he says.

Perhaps the biggest cause for concern is the nerve-injury models the team used, Flecknell says. Mice were kept alive without pain relief for up to two weeks after surgery. "If it's severe neuropathic pain, we know that people find that very distressing and debilitating."

However, he adds, it is important to test procedures for assessing pain in rodent models of neuropathic pain — caused by nerve damage or dysfunction rather than stimulation of pain receptors. Traditional painkillers do not always successfully alleviate neuropathic pain, so such models are important in the development of new pain-killing drugs, he says. But in Mogil's experiment, the animals with neuropathic pain showed no detectable change in facial expression, so "it's too early to determine how useful the whole approach is going to be", Flecknell notes.


  1. Langford, D. J. et al. Nature Methods 7, 447-449 (2010).

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Jeffrey Mogil’s website

Paul Flecknell’s website

Allan Basbaum’s website

Principal Investigators Association

Canadian Council on Animal Care

McGill University: Comparative Medicine and Animal Resources Centre

Lab Animal eAlert discussion board

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Weaver, J. Mouse pain study stirs debate. Nature (2010).

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