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This episode was made in partnership with the Kavli Prize.
The Kavli Prize honors scientists for breakthroughs in astrophysics, nanoscience,
and neuroscience – transforming our understanding of the very big,
the very small, and the very complex.
And in 2020, the Kavli Prize in Neuroscience was awarded to two scientists,
David Julius of University of California, San Francisco and Ardem Patapoutian of
Scripps Research Institute, who studied how we feel pain, from heat to pressure.
We did not fully understand how that basic bodily function works until recently!
They cracked the code of these sensations with the help of lots of hot peppers
and skin pinches. Pain can come from quite a few different sources, but their
research suggests that pain from various sources can be
processed by our bodies in a surprisingly similar way.
Hot stoves and habañeros might seem like very different kinds of heat,
but they trigger the same internal response.
You see, some of your body’s pain sensors are sensitive to a
chemical found in hot peppers called capsaicin.
This chemical makes it easier for molecules with a positive charge,
or cations, to pass through the outer layer of a pain receptor cell.
When cations like sodium and calcium pass into a cell, its internal charge builds
up enough current to activate the cell to do its job. In this case, the cell’s job is to
alert the rest of the body to potentially dangerous stimuli like heat.
But until now, we didn’t know how capsaicin triggers this response in pain cells.
So David Julius’s team of scientists went on a search to find the gene that makes
capsaicin-responsive cells. Once they found that gene, they confirmed that it was
only found in sensory neurons that respond to heat.
So next, they tested how these cells respond to different kinds of heat.
In one experiment, they put some tissue into a petri dish and added a 65-degree
celsius solution for it to float around in. And in another experiment, they added
capsaicin to the solution that the tissue was floating in. Both kinds of heat
produced the same physiological response and activated cells in their dish.
And they found that the mechanism was calcium-dependent. Within seconds of
applying heat, they measured more calcium in the pain cells. So both kinds of
heat triggered similar increases in current flowing into the
pain cells, which were not observed in control cells.
From these experiments, they discovered that
capsaicin opens a channel that lets calcium flow in and activate pain cells.
And while several different kinds of heat can trigger this
mechanism in similar ways, heat is not the only thing that triggers it.
Ardem Patapoutian’s research team figured out that these
cation channels can also be activated by pressure.
Because pain doesn’t just come from touching a hot stove.
It can also come from like closing a drawer on your fingers.
In an experiment where the researchers applied pressure to individual cells,
they found that greater pressure leads to more current flowing into the cell.
So it works in a similar way to heat sensation.
And they named the gene that makes pressure-sensitive ion channels Piezo
after the Greek word “piesi,” which means “pressure.”
And then they found similar Piezo genes all over the plant and animal kingdoms.
Vertebrates, like us, have two piezo genes.
The channel that Piezo1 encodes for conducts cations with a preference for
calcium, similar to what was described by Julius’s group.
And it’s found around the membrane, where this kind of channel would be useful.
Piezo2 is similar to Piezo,1 but it works faster.
The Patapoutian lab concluded that without functioning Piezo2 channels, you
wouldn’t be able to differentiate between painful and harmless touch.
Everything would just feel like a nice touch.
They were able to do this in mice, with Piezo2 channels that they could basically
turn on and off, and when they turned the Piezo2 channels back on,
they would recover their ability to sense painful stimuli.
Now, you might be thinking you’d like to permanently close all your Piezo
channels because pain isn’t great. But individuals with CIPA, or congenital
insensitivity to pain and anhydrosis, don’t respond to noxious stimuli.
They often inadvertently harm themselves and many die before the age of 25.
So pain is protective and incredibly important to us. But we need a balance.
On the other end of the spectrum, there are people who are oversensitive to touch
and experience allodynia. If you have allodynia, you might feel chronic pain
triggered by a harmless touch, from like a paintbrush.
And Patapoutian’s team believes that Piezo2 is an
excellent candidate to treat allodynia.
These studies are piecing together the pain puzzle so more people can live in that
balanced sweet spot. And the more we understand the science behind the
everyday sensations of heat, and cold, and pressure, the better we can
understand how to treat conditions related to them.
Thanks for watching this episode of SciShow!
And thank you again to The Kavli Prize Foundation for
supporting this episode and for supporting science.
The Kavli Prize in Neuroscience is awarded for outstanding achievement in
advancing our knowledge and understanding of the brain and nervous system.
They also award a nanoscience and astrophysics prize, honoring researchers
for transforming our understanding of the science of the atomic, molecular, and
cellular structures, and advancing our knowledge of the
origin, evolution, and properties of the universe.
If you want to learn more about 2020’s Neuroscience laureates,
David Julius and Ardem Patapoutian, you can visit their page on the
Kavli Prize website by clicking on the link in the description.
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