Experiments in mice, conducted by Stanford University researchers led by Tony Wyss-Corey, have shown that chemical compounds in the blood of aging animals inhibit the formation of new neurons in the young brain. At the same time, young blood can give an aging brain new life
Scientists came to such conclusions as a result of studying the functioning of the brain of two mice (young and old), the circulatory systems of which were surgically connected in the thighs. This system of existence of two organisms with a common circulatory system is called parabiosis and is found naturally in Siamese twins.
Figure: Usually, fewer new neurons (dark brown) appear in the brain of an old animal (left) than at an earlier age. However, young blood entering the old body noticeably stimulates neurogenesis (right)
Parabiosis had a beneficial effect on the brain of the old mouse, this was manifested by the appearance of new neurons (neurogenesis), suppression of the inflammatory status and higher synaptic activity. In the brain of a young animal, things were exactly the opposite.
To study the possible behavioral manifestations of the patterns observed in parabiosis, the researchers introduced the plasma of old animals to young mice, and the plasma of young mice to old animals. At the same time, as expected, the "old" plasma impaired the ability of young animals to learn and perform memorization tasks, while the "young" plasma improved the corresponding abilities of old animals.
Blood cells cannot move in the brain tissue, as they are delayed by the so-called blood-brain barrier, so the researchers concluded that the revealed effect is due to chemical compounds dissolved in blood plasma. Analysis of 60 chemokines - chemical signals secreted by cells into the bloodstream - revealed several compounds associated with the harmful effects of the blood of old animals. Administration of one of them, CCL11, to young mice suppressed neurogenesis and impaired cognitive ability. This compound was previously studied as a possible component of the mechanisms underlying the development of allergic diseases, including asthma, but its effect on neurons remains a mystery today.
The researchers plan to continue to study the specific factors they have identified and the functions they perform. They also emphasize that blood is a much more readily available material for analysis than brain tissue, so these factors can be used as biomarkers of neurogenesis and other parameters of the state of the central nervous system.
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