So far on Neuro Transmissions, we’ve given
a lot of attention to the brain’s superstars...neurons.
Neurons get a lot of attention from researchers and the public.
Rightfully so, because these are the cells that do all of the
communicating to keep us walking and talking.
But as I mentioned in our first video, neurons aren’t the only brain cells.
About half of the cells in your brain are called glia.
Literally, brain glue.
For a long time, scientists thought these cells were unimportant.
Only there to support neurons.
But we’ve been learning that that’s definitely not true.
Hey there!
I’m Alie Astrocyte.
And on the next few episodes of Neuro Transmissions, we’re going to be talking about
the underappreciated brain cells.
And this week, I get to talk about my favorite cells.
Astrocytes!
Astrocytes are awesome!
But you probably already knew that I like them.
Did you know that when researchers looked at Einstein’s brain under a microscope,
the only difference they could find was that Einstein had
a lot more astrocytes than the average person?
So there must be something pretty special about them.
Astrocytes are named because of how they looked when
scientists first saw them through a microscope.
The name comes from the Greek astron, meaning star, and kyttaron, meaning cell.
These starry cells make up a pretty big chunk of the brain.
Many scientists estimate that almost half of all glia are astrocytes.
They’re big and bushy, with lots of teeny, tiny, super-fine branches
called processes that touch a lot of neurons.
Seriously, one astrocyte can be in contact with thousands of neurons!
Scientists have known for a long time that astrocytes are really important for providing
nutrients to neurons
by shuttling them from the blood vessels to the neurons themselves.
They also help buffer, or balance, the ion concentrations in the brain.
And they’re a part of the repair and scarring that happens after brain injury.
All of that’s pretty important, but not necessarily super interesting.
So it’s understandable why scientists ignored them in favor of their
electrically excitable cousins for so long.
But around 20 years ago, researchers began to learn more about these unassuming cells
and found out they were a lot cooler than anyone had previously guessed.
So what makes them so cool?
Astrocytes can communicate with neurons
and play really important roles in the development and stability of synapses.
Most synapses actually have three parts,
even though we usually only talk about two.
A presynaptic terminal, a postsynaptic terminal, and
an astrocytic process wrapped around the outside.
This lets the astrocyte monitor the neuron’s signaling and help keep things functioning
by releasing different proteins can influence receptors at the synapse.
Astrocytes are also really important for helping neurons recycle their neurotransmitters.
At excitatory synapses where glutamate is released,
astrocytes can suck up the extra glutamate from the synapse after a signal has been sent
and recycle that glutamate back to neurons in the form of glutamine, where it can be
reused.
Like neurons, astrocytes can respond to neurotransmitters, too.
Only instead of using electrical signals, they use calcium.
Calcium waves allow astrocytes to communicate with each other too.
So those waves can travel long distances in the brain.
Interestingly, calcium can signal to the astrocytes to release other substances
that signal back to neurons, creating a sort of repetitive loop.
Astrocytes are also really important during development.
Dr. Ben Barres’ early, groundbreaking work in this field helped demonstrate
how critical astrocytes are to helping neurons grow properly and form
efficient connections with one another.
In 1997, along with his colleague Dr. Pfrieger, Ben showed that retinal ganglion cells,
RGCs for short, grown in a dish by themselves didn’t do so well.
Even though they could survive okay, only about half of the cells became active.
And their signals were pretty weak.
But when RGCs were grown with astrocytes, around 90% of the cells became active.
And their signals were much stronger.
This was the foundation of a lot of research that’s still ongoing.
Including my own thesis project!
Researchers are trying to understand how, exactly,
astrocytes are encouraging these neurons
to form synapses and become active.
Some scientists have identified specific astrocyte proteins like
thrombospondins 1 and 2 and hevin as part of this process.
My own advisor, Dr. Nicola Allen, who trained as a postdoc with Ben Barres,
identified two key proteins.
Glypicans 4 and 6 are proteins released by astrocytes that help recruit
AMPA receptors containing the GluA1 subunit to the postsynaptic membrane,
leading to more active excitatory synapses.
But because astrocytes haven’t been studied in a lot of depth,
there’s a lot about them that’s still unknown!
Our lab, and others like it, are working hard to understand what exactly
these proteins are doing to help neurons create better synapses.
And to identify new proteins released by astrocytes that might also be
playing a role in synapse formation.
So in the next 20 years, we’ll learn a lot more about these beautiful, starry cells.
And their important roles in the brain.
Thanks for watching this episode of Neuro Transmissions!
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We really love making these videos, and we’re grateful for your support.
Until next time, I’m Alie Astrocyte.
Over and out!