Glial Cells Regulation of Neurons
Answer by Jens Mowatt:
The term “glia” comes from the Greek word literally meaning “glue”. Scientists who first discovered them thought they were merely placeholders for neurons, cells to fill in the gaps. We now know this isn’t the case. Glial cells have a wide range of functions in the brain. They both directly and indirectly regulate neurons, allowing them to function properly.
To function properly, neurons need a constant flow of blood carrying vital nutrients. Astrocytes, a type of glial cell, have little “feet” that contact capillaries in the brain. They can constrict or dilate blood vessels.
(image taken from)
Astrocytes are able to do this because there are receptors on their membranes. When there is activity at a glutamatergic synapse, glutamate receptors are activated on the astrocyte. This results in the release of prostanoid on nearby capillaries, causing vasodialtion . The blood vessel widens, allowing more blood flow and nutrients to reach the neurons at the synapse as needed.
In addition, astrocytes help recycle the neurotransmitters GABA and glutamate:
(image taken from Clinical Neuroanatomy and Neuroscience, Sixth edition).
After these neurotransmitters have been used at a synapse, nearby astrocytes take them up via transporters, breaking them down into metabolites, and then feeding these materials back to the neurons for further neurotransmitter synthesis. As you can see, astrocytes are far more than just brain glue.
To take things a bit further, astrocytes directly participate in transmission at synapses. They release their own transmitters in a process known as “gliotransmission”. In fact, they have vesicles with transmitters just like neurons .
There is some evidence that astrocytes release their gliotransmitters into the synapse in response to an increase in their intracellular calcium levels. Both glutamate and ATP can be released by astrocytes . Depending on the transmitter being used, this either inhibits or excites the synapse in question.
So yes, glial cells (especially astrocytes) can regulate neurons in many ways. They do this by regulating blood flow, recycling neurotransmitters, and releasing their own gliotransmitters. There are probably many other functions yet to be identified. We have barely scratched the surface of glial cells because the majority of researchers have been focusing on neurons.