Revisiting the grimacing mouse

Earlier this month, I wrote about a recent paper which looked at creating a “pain scale” based on the facial expressions of mice. I finally got around to reading the actual published paper.

Here’s the reference: Langford, DJ et al. Nature (2010). Some interesting things I noted:

“Causing headaches in mice”
This one made me blink when I read it in a news release. How can you claim to cause headaches in mice when your study is looking at how to classify pain in mice? Well, apparently, some of the mice used were transgenics which carried a gene linked to familial hemiplegic migraine in humans. These mice seemed to exhibit a baseline level of pain, presumably due to the transgenic gene they carry. I wouldn’t say that’s equivalent to “causing mice headaches” but hey, I don’t write for newspapers.

They measured what?!
When I read the news releases, I was under the impression that lots of fancy imaging software was being used, that microscopic twitches and fine-detail facial expressions were being mapped, and in general, crazy stuff was going on. How wrong I was! The original article included representative images used to rate different levels of mouse pain. For each trait, there were three images. Images set to a scale of 1 to 3 – 1 being “normal” and 3 being “severe pain”. After looking at the pictures, I had a “And this needed to be a scientific study… why?” moment. For example, under “orbital tightening”, there was a normal mouse, a slightly squinty mouse, and a mouse whose eyes were dry and narrowed to slits. Any animal technician would (or at least, should) be able to tell you that the mice in the #3 category were in pain and that the animals in the #2 category were not doing well.

But, to be fair, it is true that recognizing and using something daily is not the same as having a defined, well-studied scale to refer to. If making an official scale helps animal care, I’m all for it. To be honest, I’m a little surprised that a scale as not been officially developed (studied and peer reviewed) before, considering that the majority of animal facilities use some sort of point-scale for rating animal health.

Looking forward to hearing more from this group. Hopefully they’ll go into some more applications next time.