Scientists have learned how marijuana affects the brain

Research into the effects of marijuana on the brain has led to an unexpected discovery: it turns out that the brain's service cells, whose function was previously considered to be only to support and nourish neurons, can actively control the state of interneuronal contacts and influence the functioning of neural circuits.

Marijuana has helped scientists reconsider the principles of the brain's cellular architecture. It turns out that the auxiliary cells of the nervous tissue, which are necessary for the nutrition and support of neurons, can actively interfere with the work of interneuronal connections. These auxiliary cells are called astrocytes; no one had previously suspected them of controlling neural circuits.

Researchers from research centers in Canada, China, France, the United States, and Spain studied the effects of tetrahydrocannabinol, the active ingredient in marijuana, on short-term memory. It is known that smoking marijuana has a negative effect on this type of memory, but how does the drug do this? Using electrodes implanted in the brain of a rat, scientists found that tetrahydrocannabinol weakens synapses in the hippocampus, the part of the brain responsible for memory. This was an expected result: it is known that learning and memorization processes are accompanied by the formation of new interneuronal connections in the brain.

Then the researchers decided to look at the effect of marijuana at the molecular level - at the level of cellular receptors. On the surface of neurons there are special receptors for tetrahydronabinol, called CB1. The scientists obtained GM mice in which the hippocampal neurons stopped synthesizing this receptor. In some animals, CB1 synthesis was switched off in neurons that use dopamine as a neurotransmitter, in others - in neurons that use gamma-aminobutyric acid. The authors of the work believed that without the appropriate receptors, marijuana would stop influencing synapses, and the molecular mechanism of its effect on memory could be considered revealed. Mice with a mutant receptor gene had to remember the route in the maze before and after taking tetrahydronabinol. But even with the receptors switched off, the mice still forgot the route they had just learned.

This led scientists to the idea that the whole thing could be in the same CB1 receptors, only located on the membranes of astrocytes. When these receptors were also turned off, marijuana stopped weakening synapses in the hippocampus and the animals stopped rushing around the maze, as if they were there for the first time in their lives. As the researchers write in an article published in the journal Cell, activation of marijuana receptors in astrocytes led to the fact that interneuronal connections lost receptors for glutamic acid, another neurotransmitter. And this, in turn, led to a weakening of the synaptic connection.

Tetrahydrocannabinol has a similar effect on the memory of rats and humans, so despite all the differences in the structure of the nervous system, in this case we are talking, most likely, about the same processes. But the main result here is not even the clarification of the mechanisms of marijuana's effect on memory, but the discovery of new functions in astrocytes. Apparently, neuroglia cells can be more than just a support service: they are able to take an active part in the management of neural circuits, although they themselves do not conduct nerve impulses. However, the authors also talk about the possible practical application of the results obtained. It is known that marijuana is often used for medical purposes to relieve pain and stress, so knowing exactly how it works, it is possible to create no less effective, but less ambiguous analogues.

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