Originally published December 3 2005
New study isolates gene associated with inhibition
by Mike Adams, the Health Ranger, NaturalNews Editor
Cell magazine has published a study that demonstrated the absence of a certain gene known as stathmin promotes fearless behavior.
The researchers found that the gene stathmin--normally present in high levels in a part of the brain called the amygdala--controls both innate and learned fear.
Mice without the gene show abnormally low levels of anxiety in situations that should instinctively inspire fear.
Stathmin-deficient animals also show less reaction to conditions that have previously proven unpleasant, an indication that the mice lack a normal memory for fear.
"While one of the best understood memory-related neural circuitries within the mammalian brain is that which controls fear conditioning, little is known about the molecular mechanisms underlying fear reactions," said lead author of the study by Gleb Shumyatsky of Rutgers University.
Knockout mice, which lack the gene, show a decreased memory for fear and fail to recognize danger in innately aversive environments."
By contrast, he added, the mice depleted of stathmin perform normally in a test of spatial learning.
In the laboratory, fear can be conditioned by linking a neutral stimulus, such as a light or sound, to something unpleasant or painful, such as an electric shock, he explained.
As a first step to unravel the molecular events underlying fear learning, Shumyatsky's group recently identified several genes present at particularly high levels in the lateral nucleus and in the structures that relay information about learned and instinctive fear to the amygdala.
In the current study, the researchers found that the brains of mice lacking stathmin showed an unusual number of microtubules, which are structural components of the cytoskeleton.
"For memory, the brain needs to quickly disassemble and rebuild microtubules to form connections where they are needed," Shumyatsky said.
While both groups displayed some fear response by freezing immediately after a shock and later after hearing the tone, knockout mice reacted less strongly, they found, suggesting that they had an impaired ability to learn fear.
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