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Scientists have shown that astrocytes — auxiliary cells of the nervous system — with various types of light stimulation either help to conduct nerve impulses, or prevent it. So, if proteins were artificially embedded in the astrocyte membrane — ion channels that pumped calcium into the cell when illuminated — the signal was inhibited. When astrocytes had proteins of a different nature — receptors — the speed and strength of the nerve impulse increased. The data obtained can be used in behavioral experiments to study the mechanisms of memory and learning. The results of the study, supported by a grant from the Russian Science Foundation (RNF), are published in the Hippocampus journal and in an earlier article.

The nervous system of animals includes several types of cells, the main of which are neurons involved in the transmission of a nerve impulse. They have a large number of processes, the contacts between which, called synapses, unite cells into a single network. Synapses consist of presynaptic and postsynaptic membranes — on the "transmitting" and "receiving" neurons, respectively — as well as the space between them. Special molecules are isolated on the presynaptic membrane, which, by binding to receptors on the postsynaptic membrane, trigger the formation and transmission of an electric pulse.

In addition to neurons, the nervous tissue consists of glial "helper cells". These include, for example, astrocytes, which regulate the composition of the intercellular fluid and the nutrition of neurons. In addition, astrocytes can affect the transmission of nerve impulses. They form processes in contact with synapses and secrete special substances into the near—synaptic space - gliotransmitters that determine the strength of a nerve impulse. At the same time, the number of gliotransmitters strongly depends on how many calcium ions are contained in astrocytes. Calcium in these cells can accumulate in two ways: either with the help of ion channels pumping it from the extracellular medium, or due to the release of calcium already stored in the so-called intracellular depots.

Scientists from the Institute of Higher Nervous Activity and Neurophysiology of the Russian Academy of Sciences (Moscow), Peter the Great St. Petersburg Polytechnic University (St. Petersburg) and the University of Texas (USA) investigated how the source of calcium during the excitation of astrocytes affects the transmission of nerve impulses, as well as the activity of genes in neurons. To do this, the authors used brain slices of mice and rats, whose astrocytes were genetically engineered with proteins that respond to light excitation of certain wavelengths. Due to this modification, the cells accumulated calcium ions under illumination, coming either from the extracellular space or from the intracellular depot. In the first case, photosensitive proteins acted as ion channels, and in the second case — receptors that trigger a chain of reactions for the release of calcium from the depot.

The researchers found that stimulation of photosensitive proteins operating on the principle of ion channels suppressed the transmission of nerve impulses by up to 54% in mice and up to 15% in rats. This effect is explained by the fact that in response to illumination and an increase in calcium levels, cells isolated two "inhibitory" gliotransmitters — adenosine triphosphate (ATP) and gamma-aminobutyric acid (GABA). The suppression was enhanced if the cells were additionally exposed to electric current, since it led to additional production of ATP and GABA.

Experiments with astrocytes containing photosensitive receptor proteins showed that lighting activated cells of this type and increased the strength of the nerve impulse between neurons by almost 62%, which was associated with the release of GABA exclusively. ATP was not released in this case. In addition, the activity of genes involved in the formation of long-term memory increased in the modified cells. Such a reaction may indicate that the enhanced transmission of impulses is able to persist for quite a long time.

"The use of different photosensitive proteins made it possible to regulate intracellular calcium-dependent processes in astrocytes with the help of light and to select parameters that improve or worsen the transmission of impulses between neurons. The data obtained will allow quite subtly controlling the activity of entire neural networks in the study of the brain in normal and pathological conditions. We will continue to investigate interactions between different cells of the nervous system in order to better understand the principles of memory and learning organization," says Anastasia Borodinova, PhD, researcher at the Institute of Higher Nervous Activity and Neurophysiology of the Russian Academy of Sciences.

PHOTO: Scheme of regulation of synaptic transmission in hippocampal neurons using different genetically encoded photosensitive proteins in astrocytes. Tetanus — high-frequency electrical stimulation; ChR2 — channel rhodopsin, working on the principle of an ion channel in response to a light stimulus; Opto-a1AR — synthetic protein, working on the principle of a receptor in response to a light stimulus. Source: Anastasia Borodinova

Information and photos provided by the press service of the Russian Science Foundation

The information is taken from the portal "Scientific Russia" (https://scientificrussia.ru/, Posted by Irina Usyk)