Astrocytes, guardian cells of brain plasticity

In our skull, a mighty shadow army is at work. Stealthy but hyperactive, it has long been scorned for the benefit of the brain’s elite troops, neural networks. It must be said that it mobilizes discrete cells, which do not emit an electrical signal. The noisier neurons communicate by producing an easily detectable electrical message, the nerve impulse.

This army of shadow is the glial cells. For a long time, this “glie” was reduced to a passive role of “glue” of the brain. Rude mistake! For thirty years the imbroglio around the glie has been partly unraveled: its missions have not ceased to be enriched. This is evidenced by the French study published on July 2 in the journal Science.

The researchers were interested in one of the three battalions of glial cells, the astrocytes. Until now, these star-shaped cells have been known to act as nurses and scavengers for neurons. They provide them with essential nutrients, such as lactate. And they eliminate the toxic waste they produce. They also modulate the strength of the connections between neurons at synapses.

Reshape the wiring

This new job reveals another of their facets. “Astrocytes also control a crucial period of brain development after birth: the ‘critical period’, marked by high but transient plasticity of neural networks”, summarizes Nathalie Rouach, who coordinated this study with Glenn Dallérac, at the Collège de France (CNRS, Inserm) in Paris. Cerebral plasticity is the brain’s ability to reshape the wiring of neurons according to the external stimuli received (sensory, cognitive, etc.). For each of our mental capacities (vision, hearing, language, etc.), there is a “critical period”, during young age, which is characterized by maximum plasticity of the neural networks concerned. These can then be reorganized by refining themselves. “We are born with many more neural connections than we need, explains Stéphane Oliet, director of the Neurocentre Magendie (Inserm, University of Bordeaux), who did not participate in this study. During critical periods, unnecessary wiring is eliminated, while relevant wiring is maintained or even strengthened. » Once this period has passed, the brain loses its plasticity, even if it has a little left over.

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