On a hot summer day, I like to watch a rat or two foraging on the tracks of the New York City subway system. No-one is entirely sure how many of the whiskered beasties live in the city, although, thanks to New York’s electronic rat map, a catalog of rat hot spots such as lived-in burrows and telltale gnaw marks on plastic garbage bags, the population is apparently on the decline.
In short, I am quite fascinated by these rodents, who have so much in common with humans: they share our homes, form social communities, engage in playful behavior (young Norway rats, which originated in Asia, spend a lot of time chasing, fleeing, rolling over, and jumping on each other) and of course they are exceedingly fond of our leftover lollipops and hot dogs. Naturally, if I saw a rat in my own apartment, I would probably leap on a chair, shrieking and clutching my petticoats. It seems that mice have a very similar response – unless they are mutants with an inactive vomeronasal organ.
Neurons in the vomeronasal organ (VNO) detect specific chemicals, including pheromones that act as communication signals from other individuals of the same species. Neurobiologist Lisa Stowers of The Scripps Research Institute in La Jolla, California, suspected that mice may use the same organ to sniff out predators such as rats, snakes and cats. So she dropped cotton balls saturated with cat saliva, rat urine or snake skin essence into the cages of both normal mice and mutant mice with inactive VNOs. The normal mice were terrified, but the mutants were blasé: so relaxed, Stowers told Science Now, “that they actually curled up and went to sleep,” next to an anaesthetized rat plopped into their cage.
Humans, it seems, share similar forms of fear behavior with mice, and it now appears that we also express our pain in similar ways. In other major mouse news, psychologist Jeffrey Mogil and his colleagues at McGill University’s Pain Genetics Lab have developed a “Mouse Grimace Scale,” a coding system that assesses pain in mice through their facial expressions.
Nonhuman animals, as Charles Darwin noted in his marvelously-illustrated book “The Expression of the Emotions in Man and Animals,” are capable of expressing emotion, including pain, through facial expression; and he detailed some familiar signs, including elevation of the eyebrows, opening the mouth, protrusion of the lips and erection of the hair. Until now, however, there has been no study of facial expressions of pain in any nonhuman species.
Mogil has now filled that lacuna with his Mouse Grimace Scale, which is described in the May 9 issue of Nature Methods. He injected an inflammatory substance into the mice, inducing a level of pain comparable to “an inflamed and swollen finger,” and analyzed, with digital video cameras, images of the mice before and during the painful stimuli. A team of human “facial pain expression experts,” detailed five facial features indicative of pain: tightly closed eyelids; nose bulges; cheek bulges; ears pulled apart and back; and whiskers moved either backward or forward, as if standing on end.
An accurate measurement of pain in mice is important, Mogil says, because pain research in humans relies so heavily on rodent models. “The Mouse Grimace Scale provides a measurement system that will both accelerate the development of new analgesics for humans, but also eliminate unnecessary suffering of laboratory mice in biomedical research.” For a soft-hearted lass like me, that’s a relief.
Image courtesy of Aaron Logan
