It’s no news that medical scientists use animals such as mice to test drugs, including pain-relief drugs. It also should be no surprise that, in order to assess the effectiveness of pain relief drugs, scientists first inflict pain on the animals.

What’s in the news at the moment is that some scientists are currently performing tests to improve the accuracy of their assessment of how much pain the lab animals are in, based on the animals’ facial expressions when hurt.

The final line of the article mentions that the scientists are going to continue these experiments on other animals, but it doesn’t specify what animals. (To give you a general idea, an example is that animals used in excruciatingly painful experiments on spinal cord injuries include cats, dogs and monkeys.)

The original AFP article can be found here, at news.com.au.

Mice injected with acid, mustard oil in study to measure facial grimace

SCIENTISTS have injected mice with acetic acid and mustard oil in order to record their facial expressions.

The research has for the first time created a sliding scale of pain for mice based on facial expressions named a “mouse grimace scale” or “MGS”.

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.

To find out whether rodents grimace when it hurts, McGill University professor Jeffrey Mogil and colleagues monitored and recorded facial movements before and during the injection of substances known to cause painful inflammation.

The substances included acetic acid, mustard oil, and capsaicin – the “hot” ingredient in chillies – and was delivered to the stomachs and paws of the mice.

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.

The MGS 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.

Doctors and nurses routinely use such scales to assess pain in individuals unable to communicate verbally, such as infants and the cognitively impaired.

Using an intensity scale based on changes in five facial features, persons trained to “read” pain in expressions correctly assessed discomfort levels in the mice, based on photographs, with 80 per cent accuracy.

Looking at high-resolution video images, accuracy rates went up to 97 per cent.

The study, published in the journal Nature Methods, also bolstered 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 supported 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.

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