A lot of us grew up hearing that you can't regrow brain cells -- usually after we bumped
our head on something.
Scientists still debate whether that's actually true, but one thing's for sure: brains aren't
nearly as good at replacing cells as other parts of the body.
And when the brain gets damaged by something like a stroke, that damage stays instead of
getting fixed.
But a new study in the journal Nature Materials suggests a way of reversing that destruction.
For the first time, by injecting a specially made gel into mice, scientists were able to
successfully coax the mice's brains into growing back cells and structures that were
destroyed by a stroke.
And with millions of people suffering from the long-term consequences of strokes, this
could be a first step toward repairing their brains, too.
Strokes happen when blood is blocked from certain parts of the brain, cutting off oxygen
and nutrients and eventually killing the starved cells.
And if those cells do something important, like control your hands or safeguard your
memories, that job stops being done — which is why people who have had strokes can have
long-term memory issues or muscle control problems.
While interventions like physical therapy can sometimes significantly improve people's
symptoms by teaching the brain to find ways around the stroke's scar, there's always
a scar.
And for a little while, before that scar forms, there's basically a hole where the cells
once were.
That's because brains aren't as good at replacing dead cells as other organs — many
scientists say they can't naturally do it at all — so new neurons don't grow in
to fill the gap.
Adult human brains basically wall off the wounded area after cells die, keeping new
blood vessels from bringing in nutrients and oxygen and preventing the hole from filling
with the body's structural goo that supports cell growth.
Scientists with UCLA and Duke University wondered if they could design a material that would
essentially take that goo's place and—with any luck—help the brain heal.
What they came up with was a special kind of water-based gel which provides structure
to the empty space left by the cells.
They tried a few formulations, pitting the plain gel against ones with added goodies.
Those goodies included molecules that stimulate blood vessel growth and reduce inflammation,
which helps bring down barriers between the gel and the rest of the brain and allow nutrients
in to feed any new cells.
They gave mice strokes, then injected a tiny amount of gel into the holes left behind five
days later, with several mice receiving each formulation or nothing, as a control.
Afterwards, they checked in on the mice for weeks, both by looking at their actual brains
and by having them do certain kinds of physical tasks.
And over time, one thing became clear: one of their formulations was very effective.
Whole new structures including neural networks formed in the place of the stroke-killed cells,
and the mice mastered tasks their untreated counterparts couldn't.
But, there were some limitations to the study.
A big one is that the mice they used were young.
They were given strokes when they were more like teens than adults, so the experiments
happened as they grew into young adults — which is a stage in life when both mouse and human
brains are thought to be better at regrowing brain tissue, and not the age when strokes
usually occur.
So more research will need to be conducted on adult mice to see if their brains are also
able to benefit from the gel.
There's also the always important caveat that mice aren't people.
Even adult rodent brains seem to be better at growing neurons than adult human brains,
so what works for them might not work for us.
And the scientists still aren't sure exactly how the gel works, so they want to study it
further to figure more of that out.
So there's a lot to do before anything even approaching a human trial.
But, the fact that any gel formulation worked at all, let alone so well, makes the study
an exciting proof-of-concept.
And it's certainly a step in the right direction for millions of people who become disabled
by strokes every year.
Unfortunately, it's not all good news this week.
Because a paper in last week's issue of the journal Nature reports that someone, somewhere
in the world, apparently decided that the ozone layer is overrated, and has been releasing
alarming amounts of ozone-damaging CFCs into the atmosphere for the last few years.
"CFC" is short for "chlorofluorocarbon" -- a huge class of molecules that, as the
name implies, contain chlorine, fluorine, and carbon.
They were invented in the 1920s.
And at first, they seemed perfectly inert, which made them ideal for applications where
you don't want chemical reactions: Firefighting, pressurizing hairspray, cooling refrigerators
— you name it.
But when CFCs reach the upper atmosphere, they're broken down by ultraviolet light,
creating super-reactive pieces.
And those pieces eat away at our ozone layer, which is bad because that layer blocks a lot
of harmful radiation before it reaches the ground and does terrible stuff like cause
cancer in people or harm crops.
CFCs are also powerful greenhouse gases that trap thousands of times more heat than carbon
dioxide.
So they're not something you want in your atmosphere.
Which is why, in 1987, countries worldwide signed the Montreal Protocol, promising to
phase out CFCs over time and switch to less-destructive molecules.
Since then, atmospheric CFC concentrations have gradually dropped while the ozone layer
has gradually recovered.
But a new paper published last week reports that since about 2012, scientists have detected
far more CFCs in the atmosphere than there should be—about 13 million kilograms more.
Concentrations are still dropping worldwide, but not as much as they should be, which is
significantly slowing the progress of the last few decades.
And, maybe unsurprisingly, no one is taking credit.
The paper's authors have been monitoring the amount of CFCs in the atmosphere for a
long time, mostly by catching a bunch of air every once in a while and seeing what kinds
of molecules react with what's in the air.
And they noticed that around 2012, the rate of decline of CFCs slowed, suggesting a 25%
increase in emissions.
They didn't just automatically accuse people of violating the Montreal Protocol, though.
They considered other potential CFC sources before concluding that someone is making them.
They wondered if, maybe, buildings with a lot of CFCs in them were being demolished,
or if the way CFCs leave the atmosphere had changed, or if CFCs were trapped in ice that's
melting because of climate change.
But there's so muchunexpected CFCs that demolished buildings can't explain things.
And also, none of the other possibilities they considered fit the observations, because
it isn't just that CFC emissions in general have increased.
All of the new emissions are a specific kind of CFC called CFC-11 or trichlorofluoromethane.
And we don't know anything other than human production that would single out a single
CFC like that.
So the scientists had to conclude that humans are making and releasing new CFCs again, in
defiance of the Montreal Protocol.
But air in the atmosphere is so thoroughly mixed that, right now, no one can say where
the CFC-11 is coming from.
There are strong hints that it might be from eastern Asia, based on when winds brought
the new CFCs toward an observatory in Hawaii.
But that's about all they can say.
Getting a better idea of the source might require something like measurements from planes,
or closer analysis of any other chemicals that have also been increasing in the same
way, which might provide clues as to who's to blame.
For now, all we can say confidently is that someone is making new CFCs again, despite
how harmful we know they are.
If you're watching...stop!
And if you're not releasing new CFCs into the atmosphere, thank you for that, and for
watching SciShow!
If you want to keep up to date on all the latest news in science, make sure to click
on that subscribe button and check out all of our news episodes that we post every single Friday.
Also, if you're curious about the full history of CFCs, you might want to watch the episode
we did last year over on SciShow Space that's all about that.
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