Edgy Engineered Mice

Scientists have developed a new strain of genetically engineered mouse that's supersensitive to pain. The mice also tend to be more aggressive and anxious than normal mice, which may make them useful for studying the neurobiology of both pain and behavior, a team of neurobiologists reports in the 10 October issue of Nature.

"These mice overreact to different kinds of environmental stimuli," such as heat or unfamiliar odors, says Andreas Zimmer, whose group at the National Institute of Mental Health in Bethesda, Maryland, created this mouse strain. The "knockout" mice lack the gene for pre-proenkephalin, which the body converts to one of the three known natural peptides, enkephalin.

It appears that a shortage of enkephalin impairs pain perception in the brain but not in the spinal cord, where pain reflexes are initiated. For example, when placed on a warm surface, the engineered mice overreact, immediately lifting their paws rather than first exploring the surface. That result indicates that "enkephalin could be mediating the quality of the pain [perceived]," suggests Malcolm Low, a neurobiologist at Oregon Health Sciences University in Portland. Zimmer plans to look next for abnormalities in these opioid peptides in people with abnormal responses to pain.