The overlap of green (glial cells) and purple (water channels embedded in the walls of those cells) show the tubes.
Your blood vessels aren’t the only network of tubes winding through your body. The lymph vessels, or lymphatics, shadow blood vessels wherever they go and collect waste from around the body, as well as shuttling around immune cells and performing other functions. But the lymphatics never make it to the brain, scientists were surprised to find some years ago. Some other, mysterious method for removing waste from the brain must exist.
In a new paper in Science Translational Medicine, a team of neuroscientists reports that they’ve discovered a system of tubes that encircle the blood vessels that feed the brain. The walls of these tubes are made up of spindly projections from brain cells called glia, that, in the same way that trees’ arching limbs form a tunnel over a road, arch around the blood vessels to form the tubes. And these tubes seem to drain the way lymphatics do, suggesting that they might be long-sought gutter of the brain.
Human astrocyte. The vivid color is from GFP, not drugs.
The real news is the importance of a type of brain cells called astroglia, which have long been ignored while researchers focus on neurons. THC, the psychoactive chemical in marijuana, impairs working memory by connecting to astroglia, according to a new paper published in Cell. So the star-shaped astroglia turn out to be the real star of this study.
Astrocytes, it was long believed, were little more than the scaffolding of the brain—they provided a support structure for the stars of the show, the neurons. But a study out in this week’s Science is the latest to suggest that this is far from the whole story. The study says that astrocytes (whose “astro” name come from their star-shape) may in fact play a critical role in the process of breathing.
Astrocytes are a type of glial cell — the most common type of brain cell, and far more abundant than neurons. “Historically, glial cells were only thought to ‘glue’ the brain together, providing neuronal structure and nutritional support but not more,” explains physiologist Alexander Gourine of University College London, one of the authors of the study. “This old dogma is now changing dramatically; a few recent studies have shown that astrocytes can actually help neurons to process information” [Nature].
Gourine’s team peeked into the brains of rats to figure out the connection between astrocytes and breathing. In humans and in rodents, the level of carbon dioxide in the blood rises after physical activity. The brain has to adjust to this, setting the lungs breathing harder to expel that CO2.