Science magazine reports: To most people, the phrase “I feel your pain” is just an expression of sympathy. But it’s also a real biological phenomenon, a new study in rodents suggests. Healthy mice living in the same room with mice experiencing pain are up to 68% more sensitive to pain themselves, regardless of their stress levels, according to the new study, which found that mice could scent when their fellows were suffering. The discovery suggests that current methods for studying rodent pain may need to be overhauled, and it may even point to a novel mechanism for pain transmission between humans, the authors say.

Andrey Ryabinin, a behavioral neuroscientist at Oregon Health & Science University in Portland, and colleagues stumbled on the phenomenon largely by accident. They were studying the effects of alcohol withdrawal in mice, looking for new ways to help people overcome addiction. One of the most common, but challenging, symptoms of alcohol withdrawal is an intense, generalized pain throughout the body—a difficult-to-define condition that often leads people back to drinking, he says. Recreating those painful withdrawal symptoms in mice is difficult, leading some researchers to question whether the rodents are a good model for alcohol addiction.

Ryabinin and his team were using a standard setup: The mice are allowed to lap freely at an ethanol and water solution, but then go into withdrawal after the bottle is removed. A control group, housed in the same room, drinks only water. Using multiple measures of pain sensitivity—including brushing their forepaws with a thin hair and dipping their tails into hot water, the researchers attempted to gauge how withdrawal might be affecting the addicted rodents.

The initial results were disappointing, showing no significant difference between the two groups. Before giving up, however, the scientists decided to cage the control mice in a different room. This time, the sober controls showed far less pain sensitivity than the controls in the previous experiment, suggesting that the latter group had somehow acquired a heightened pain sensitivity from their roommates, Ryabinin says. [Continue reading…]