26 July 2017

Memory in an inaccessible archive

Laser brought back memories to mice with Alzheimer's disease

Natalia Pelezneva, Naked Science

Alzheimer's disease is one of the most common neurodegenerative diseases. According to 2015 data, it affects about 30 million people worldwide. Amyloid plaques and neurofibrillary tangles accumulate in the brain tissue of patients.

For a long time, it was believed that these changes completely erase memories of the past, affecting the neurons involved in preserving these memories.

A new experiment conducted by American scientists has shown that lost memories can be returned. The study was conducted using mice bred using genetic engineering. Some of the neurons in their brain were glowing: yellow – in the process of forming a new memory, red – in the moments of "calling" this memory. Two genetic lines of such mice were created: healthy animals and mice prone to the development of neurodegenerative diseases.

To find out how memories are reproduced in mice of different lines, scientists conducted a test. The mice received a stimulus (a sharp lemon smell), and then an electric shock. A week later, the mice were given the same lemon flavor to smell. The animals of the "healthy" line froze in anticipation of an electric shock. The mice of the "sick" line responded to the stimulus twice as often: some of them managed to forget about the connection between smell and current.

This result was confirmed by the activation of neurons. In healthy mice, the indicator cells, glowing red and yellow, were close to each other, sometimes "overlapping" each other. When recalling memories, the same cells were active as when remembering. In sick mice, the red and yellow cells could differ significantly, which means that in response to the stimulus, the animals received a false memory. The consequences of this phenomenon are described in people suffering from Alzheimer's disease. For example, patients incorrectly named the place where they were during the terrorist act of September 11, 2001.

It was possible to induce the correct reaction in mice with memory disorders using optogenetic methods. To do this, opsins, light–sensitive receptors, were introduced into the brain cells of rodents with the help of genetic engineering. The cells "storing" the necessary memories were stimulated with a laser. According to scientists, the return of memories shows that Alzheimer's disease does not permanently destroy memories. It is impossible to use such a technique in humans, but in the future, drugs that stimulate the necessary neurons may appear. In the next stages of the study, scientists plan to find out how similar the mechanisms of neurodegenerative diseases in humans and mice are. It has already been established that in rodents, Alzheimer's disease affects fewer brain cells.

The study was published in the journal Hippocampus (Perusini et al., Optogenetic stimulation of dentate gyrus engrams restores memory in Alzheimer's disease mice).

Portal "Eternal youth" http://vechnayamolodost.ru  26.07.2017

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