Scientists based at Rutgers University in New Jersey, US have bred 'fearless' mice by deactivating a single gene. Studying the animals could help develop new treatments for anxiety and post-traumatic stress disorder in humans, say the researchers, who published their findings in the journal Cell. The mice are missing a gene called stathmin, which makes a key nerve cell connection protein.
The fear response in both mice and men is controlled by the amygdala - a small, almond-shaped area of the brain. Previous research has shown that mice with damage to this area are less fearful, but until now it has not been clear what controls the fear response. In the latest study, the scientists found that the mice bred to lack stathmin were braver than normal mice, and were also slower to learn fear responses associated with pain.
The altered mice wandered into the centre of an open box, rather than hiding along the edges to avoid predators. In another experiment, the researchers exposed altered and normal mice to a loud sound followed by a brief electric shock. A day later, the normal mice 'froze' when they heard the sound in anticipation of the shock, but the altered mice hardly reacted to the noise at all. The fearless animals were genuinely brave, and not just stupid, say the scientists - both types of mice performed equally well on a memory test.
The stathmin protein is found only in the amygdala and related areas of the brain, where it helps brain cells make new connections with each other - allowing animals to learn and process fear responses. Team leader Gleb Shumyatsky says that further research could lead to the development of new drugs for anxiety disorders that involve either innate or learned fear.
Earlier this year, another US group found that mice lacking one copy of the neuroD2 gene take more risks than normal mice, and are less able to form 'emotional' memories. The team, based at the Fred Hutchinson Cancer Research Center found that animals had fewer neurons in their amygdala than normal mice.