Mice make dramatic faces when they're in pain, and now their expressions have been cataloged scientifically on a "mouse grimace scale" (pictured below). A paper published in Nature Methods yesterday explains the ways researchers hurt mice, and why.
Just to be clear, the reason why this group of researchers studied mouse pain is not to get their jollies. Mice are often used in studies of pain management and pain relief, which means researchers need to be able to recognize what mice look like when they hurt - and when they don't. Unfortunately, that means hurting mice to create this unsettling "mouse grimace scale."
How did the researchers make the mice ache? Sometimes, they engaged in "precise aiming of a noxious stimulus using a restraining apparatus." That means, I'm guessing, they restrained the mice while poking them in what the researchers call "joints and viscera." They also used various chemicals to induce extreme arthritis pain in mouse joints, as well as bladder infections. Also used were: an "abdominal constriction test," or really tight stomach squeezing; and in one memorable part of the paper, the researchers talk about "application of a binder clip to the ipsilateral hindpaw of nerve-damaged mice."
They learned that mice make their most intense pain faces when receiving "noxious stimuli" of "moderate duration (10 min-4 h)." Long-term pain yielded almost no pain faces at all. Possibly, the researchers speculate, they can't recognize long-term pain expression. Or maybe pain faces are associated with short-term pain, before facial expression control kicks in.
After putting the mice through all this abuse, the researchers gave some of the creatures pain killers and reported that the pain faces went away.
This research is important because we need to learn more about how to stop pain. But at the same time, I couldn't help but feel horrified at the thought of all these animals being tormented with disease and "noxious stimuli." This is the necessary darkness at the heart of science, I suppose.
via Nature Methods