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Without Gene, Mice Don't Know Meaning of Fear

November 19, 2005|Alex Raksin | Times Staff Writer

Scientists have identified a "fear" gene in mice that when removed turns them into daredevils, seemingly heedless to both inborn fears and risky situations that normal mice have learned to avoid through experience.

The gene, known as stathmin, controls the production of a protein linked to the creation of long-term fear patterns, said Rutgers University geneticist Gleb Shumyatsky, who led the study, published Friday in the journal Cell.

Because the brain system that regulates fear is similar in all mammals, the research could help develop drugs that reduce anxiety by inhibiting the gene's expression.

"This has become a huge area of academic interest because around 20% of the American public suffers from anxiety disorders, and an estimated 15% of our troops in Iraq are expected to come back with post-traumatic stress disorder," said Dr. Mark Baradan, a professor of brain research at UCLA.

The gene functions primarily in the amygdala, a part of the lower brain long recognized as a nimble "first responder" to danger in all mammals.

In one test, to assess inborn fear, mice were placed on a platform that had low maze-like walls on one end and an open area on the other end. The mice lacking the stathmin gene explored the open area, while the others remained in the maze or close to the walls for security.

In a second test, for learned fear, the mice were exposed to a loud sound followed by an electric shock from the floor. When the sound was repeated a day later, the normal mice seemed to freeze in fear, while the mutant mice barely reacted.

Analyzing brain tissue, Shumyatsky found that stathmin worked primarily by encoding a protein that makes microtubules, building blocks that help connect neurons.

Mice lacking the gene were unable to disassemble and rebuild microtubules to update their "fear maps."

In essence, "the mice lose their flexibility to react to fear," Shumyatsky said.

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