When the brain memorizes something new, new interneuronal connections are formed between its neurons – synapses. Without new synapses, there will be no new neural circuits, and without new neural circuits, information in the brain will not be retained. Likewise, for memory to last long, these synapses must be strong enough.
Both in order for synapses to form and in order to make them stronger, neurons need to activate certain genes. Several years ago we wrote that these genes are activated by double breaks in DNA, when both strands of a molecule break at once. Generally speaking, there should be no breaks in DNA, and the cell has special molecular apparatus that monitor the integrity of the DNA. But in some cases, apparently, it is impossible to do without gaps.
Staff Massachusetts Institute of Technologywho discovered this, set up experiments on cell cultures, that is, on neurons that live in laboratory glassware in a nutrient medium. In a recent article in PLoS ONE they describe new experiments that have already been performed on mice. The animals were put into a cage, where they were slightly shocked on their paws – this is how the mice remembered that there were troubles with this cage. For comparison, other mice were placed in the same cage, which were not shocked, and therefore they did not have any special unpleasant memories.
Within half an hour after the mice were in the electrocell, double breaks appeared in the DNA of their neurons – there were twice as many of them as in those who were not electrocuted. Moreover, especially many breaks appeared in the neurons of the hippocampus and the prefrontal cortex – two areas of the brain that play a major role in remembering different life circumstances, including unpleasant ones. Breaks in DNA increased the activity of more than 100–150 genes, which, to one degree or another, regulate the strength of synapses.
DNA damage took place not only in neurons, but also in astrocytes – service cells, which, however, not only support and nourish neurons, but also directly affect neuronal impulses. It is known that astrocytes are also involved in remembering unpleasant events. It is also known that astrocytes are sensitive to glucocorticoids, hormones that increase with stress. The researchers showed that the breaks in astrocyte DNA depend on glucocorticoid signals: if hormone receptors were turned off, then DNA breaks appeared much less. It can be assumed that, upon feeling stress, astrocytes tear DNA and thereby activate their genes, which help neurons to form memory (which tear their DNA for the same).
However, despite the new findings, more evidence is needed to show that neurons and astrocytes rip DNA for memory. For example, it would be good to purposefully turn off the mechanism that makes breaks in neural DNA, and see if the brain’s memory after that deteriorates.
Source: Автономная некоммерческая организация "Редакция журнала «Наука и жизнь»" by www.nkj.ru.
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