Fear changes DNA in the brains of mice

Australian researchers have observed that when a frightening memory enters the memory of mice, the double helix structure of DNA changes. Fortunately, an enzyme allows DNA to return to its normal state.

Fear is probably one of the oldest emotions in animals. It is an essential survival mechanism. But once the fear event has passed, the brain must return to normal and free themselves from this emotion.

Australian researchers from the University of Queensland studied changes in theDNA in the brains of mice when they build memories of fear. In their works published in Nature Neuroscience, the Australian team has shown that the DNA of the prefrontal cortex then takes on an unusual structure.

The Z structure of DNA

DNA, molecule who door the Genoa, consists of two strands which wrap around each other to form a double helix about two nanometers of diameter. It exists in three different structural forms: DNA-A, DNA-B and DNA-Z. B-DNA is the most common form: the double helix rotates clockwise.

However, in the fear experiment carried out in mice, Australian scientists observed a less common form of DNA in the prefrontal cortex of rodents : DNA-Z. This is kind of the mirror distorted B-DNA. The double helix of DNA-Z turns counterclockwise, but it is also more elongated, since there are 12 base pairs per turn of helix on DNA Z against 10.5 for DNA-B . So when the mouse accumulates memories of fear, the amount of Z-DNA increases. What happens when scientists "extinguish" these memories?

A return to normal

They studied the role of a enzyme, Adar1, known for editing theARN. The latter will bind to DNA-Z and make it repend its normal structure, DNA-B.

As in many experiments, the researchers inhibited the action (we speak of knockout) of Adar1 to better understand its role. When Adar1 stops working, mice are still able to build memories of fear but they are unable to get rid of it.

The creation of memories of fear and their disappearance would be all the more quickly as the brain is plastic and flexible, since the transition from form Z to form B would be facilitated. Fear is an essential emotion but when it is too present, it can also become debilitating, especially in the case of syndromes of post-traumatic stress or some phobias.

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