The mice were photographed while they were in pain to help the researchers understand how the animals express it. (CBC)

A Montreal study that observed the expressions of mice in pain has been found to comply with Canadian ethical guidelines for animal research.

The Canadian Council on Animal Care, which regulates the use of laboratory animals, made the ruling Thursday after investigating the study led by Jeffrey Mogil at McGill University.

The council reviewed documentation about the study and interviewed an animal compliance representative at the university after criticism of the study was published in a U.S. subscription newsletter called the Laboratory Animal Welfare Compliance.

The research in question took place over many years and involved inducing various degrees of pain in mice using methods such as dipping their tails in hot water or injecting them with mustard oil or vinegar. The faces of the mice were then photographed to understand how they express pain.

"No one likes putting animals in pain," said Mogil, who holds a Canada research chair in the genetics of pain. But he said in the case, the pain was necessary and scientifically justified.

"To study pain, we need to produce pain — there's simply no way around it."

He believes the research could lead to better ways of treating post-operative pain in humans.

'To study pain, we need to produce pain — there's simply no way around it,' says researcher Jeffrey Mogil.

Mogil said the researchers try to use the smallest number of mice and the mildest amount of pain possible for the purposes of the experiments, which were approved by McGill University.

However, Leslie Norins, the publisher of the newsletter that led to the council's investigation, questioned Mogil's research methods.

"Mice were purposefully subjected to intense pain without anesthesia," said Norins. "In our reading of the national guidelines, this came very close to a violation."

Publisher says study 'seemed frivolous'

Norins is president and CEO of the Principal Investigators Association, the non-profit organization that publishes Laboratory Animal Welfare Compliance.

He said he thinks the study deals with subject matter that is already well-understood.

"And the study seemed frivolous to us," he added.

However, the Canadian Council on Animal Care said Thursday that it thought the results of Mogil's study might be useful as a tool to assess mouse welfare. It suggested that would make it easier to intervene early in cases where mice are put in situations where they could experience pain.

Dr. Mary Lynch, president of the Canadian Pain Society, said scientists might be quick to judge research where pain plays a role.

However, she said animal studies in Canada and around the world are strictly regulated "and addressed in a way that minimizes the amount of discomfort."