Fact File: Astrocytes
by Maja Skrętowska
Many wondered what it was that made Einstein’s brain so special. Where is the genius located? Where does his ability to revolutionise physics come from? What made these neurons firing so special? The desire to uncover the mystery behind the famous physicist’s capability of turning the world upside down led Thomas Harvey, pathologist who performed autopsy after Einstein’s death, to remove the brain and keep it hidden in a jar for many decades. Although Harvey did not share his treasure with others eagerly, neurologists and neuroscientists managed to make an interesting observation. It is possible that what accounts for the unusual intellectual abilities is not the first violin of the brain – neurons, but astrocytes (they are like violas of the nervous system, if you like). The famous figure in science and pop-culture alike joked at people’s beliefs about the world once again.
Astrocytes are an easily overlooked type of cells as they are quite often labelled as ‘mere helpers’ of neurons. They are present only in the brain and spinal cord where they nourish and protect neurons from damage. Nevertheless, the duty of those star-shaped cells seems miniscule compared to neurons. While astrocytes sit in the brain performing the seemingly boring task of filtering the extracellular fluid, neuronal firing makes us capable of moving, understanding objects, having conscious thoughts. They make us who we are. We understand very little of how these strange networks of neural cells give rise to our consciousness, and as soon as we come to illusion that we do, a new discovery makes the issue even more puzzling.
Einstein’s astrocytes were observed to develop more and longer connections. Whether this was true or not is still debatable and so it will probably remain; however, it has been shown that mice with astrocytes transferred from humans (who have larger astroglia than rodents), were much smarter in finding their ways through mazes. Another study shows that astrocytes play a big role in creating new synapses and maintaining old ones – phenomenon known as long-term potentiation. Rats bred for this particular experiment lacked receptors to cannabinoids on their astrocytes. This family of chemical compounds contains molecules similar to THC, the substance in marijuana that is known to adversely influence mammals’ spatial working memory, which can again be observed as inability to get through a maze. Normally, a rodent after the injection of cannabinoids would be unable to reach the end of the maze quickly. Rodents lacking the receptor on astroglia could get through the maze as easily as those naturally occurring ones without the injection, what suggests that their synapses remained intact by cannabinoids because the substance could not bind to a receptor that would spur the change. Interestingly, rodents lacking the same receptors on neurons did not show resistance to detrimental effects of cannabinoids, which means that it is a certain activation of astrocytes, not neurons, by marijuana that makes synapses disappear.
What is actually the message to take home from the study? We are clearly unable to grow our astrocytes bigger than they already are. But you know what we can do in order to make our working memory function better? Avoid marijuana, and perhaps this is the most important aspect of that story.