Without Gene, Timid Mice Turn Into Daredevils

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"Therefore, our earlier and current work provide a first glimpse at how genes may regulate instinctive and learned fear based on their anatomic locations in the neural circuits of fear."

Danger Signal

To test their theory, Shumyatsky and his colleagues bred genetically modified mice stripped of the stathmin gene. The mice were then tested to assess their inborn and learned fears.

One experiment tested an instinctive mouse fear—that of open spaces. Researchers placed the rodents on a maze-like platform that had walls on one end and an open area at the other. The mice lacking the stathmin gene were very comfortable in the open area. But the unaltered mice remained in the closed area of the maze or close to the walls.

Another experiment tested a learned fear. Scientists paired a soft sound with a mild electrical shock. Normal mice quickly learned that the sound was a danger signal, and responded by freezing. The mutant mice, on the other hand, had diminished responses.

The researchers found that the stathmin gene encodes a protein that inhibits the formation of microtubules, building blocks that help connect neurons. Without the gene, mice could not rebuild the microtubules to update their ability to recognize fear.

Anxiety Disorders

The study could help scientists understand how the inborn response to fear develops and how the brain takes fearful experiences and logs them into its memory.

The brain system that regulates fear is similar in all mammals. As a result, the new findings may have important implications for the study of anxiety disorders in humans.

The discovery may help in the development of potential drugs to treat phobias, post-traumatic stress syndrome, fear-related behaviors, and social abnormalities in autism and anxiety-related illnesses.

The research suggests that the amygdalae of people with anxiety disorders may have high levels of stathmin protein. If scientists can manipulate the production of stathmin, they could possibly change the level of anxiety.

"Our findings pave the way for future fundamental and clinical studies, which will eventually optimize the treatments for anxiety disorders," said Bolshakov, who directs the cellular neurobiology laboratory at McLean Hospital in Belmont, Massachusetts.

However, scientists are only beginning to discover all the genes that control the brain. It is likely that stathmin is just one of several genes that regulates fear.

"The gene identified in our study is likely to act together with other genes to provide an adequate fear response," Bolshakov said.

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