ARI SHAPIRO, HOST:
Time now for our science news roundup from our friends at NPR's Short Wave podcast. Aaron Scott and Regina Barber, welcome back.
REGINA BARBER, BYLINE: Hi, Ari.
AARON SCOTT, BYLINE: Thank you, Ari.
SHAPIRO: You have, as usual, brought us three science stories that grabbed your attention this week. What have you got for us?
BARBER: How about the weird anatomy of starfish?
SHAPIRO: Cool.
SCOTT: And staying up all night can ease depression - in mice.
SHAPIRO: Fun.
BARBER: And a record low for Antarctica's sea ice.
SHAPIRO: Bummer. Let's get the bad news out of the way first. You want to start with sea ice?
BARBER: Yeah.
SCOTT: Sure. So, Ari, this is, of course, not great news. Our NPR colleague Rebecca Hersher just reported on new science about melting ice across Antarctica. Today we're going to focus specifically on research about Antarctica's sea ice.
BARBER: And when we say sea ice, we mean the seawater around the continent that freezes and floats on the ocean's surface. And it happens there each winter.
SHAPIRO: Each Antarctic winter, which would be summer here in North America, where we are.
BARBER: Right. Deep winter in Antarctica is in July, August and September. And in September, the sea ice is at its most expansive for the year. And usually at that point, there's so much sea ice that it doubles the size of the continent.
SHAPIRO: Doubles. Wow.
SCOTT: Yeah. Sadly, the amount of sea ice has been shrinking, partly because of warmer ocean water from climate change. So this new analysis found that this year, there was substantially less ice than ever before, going back to when satellites started tracking this around 1980.
SHAPIRO: Less than ever before. What does that mean for Antarctica and the rest of the world?
BARBER: Well, one big thing is that it can contribute to global sea level rise, but not the way you might think. Like, disappearing sea ice doesn't actually add extra water to the ocean. It's kind of like an ice cube melting in your glass of water. The level of water in your glass is still about the same.
SCOTT: But Antarctica's sea ice does lead indirectly to sea level rise because it protects the continent's glaciers and the massive ice shelves from storms and ocean water that can eat away at their ice. So without that protective shield of sea ice, those glaciers and ice shelves on land can melt faster.
SHAPIRO: And that does lead to sea level rise.
BARBER: Exactly. And when we have a bad year like this one, it's difficult for sea ice to recover. The exposed ocean water that doesn't freeze absorbs more heat than ice does, and that makes it more difficult for ice to reform the next year.
SHAPIRO: All right. Let's stick with stories about the water. And, Regina, you have got something to cheer us up after that bad news about sea ice...
BARBER: I do.
SHAPIRO: ...A 200-year-old mystery about starfish anatomy.
BARBER: Yeah, Ari. So scientists have wondered, what's up with the body structure of starfish? As larvae, they start out with two distinct sides, like a lot of animals, actually. And then they transform into adults with five identical limbs. So there's no obvious head or tail.
SCOTT: And recently there have been these two leading hypotheses. They both involve the starfish losing their heads through evolution.
BARBER: Yeah. One idea was they became all tails.
SHAPIRO: Huh. What was the other?
BARBER: The other one argues that starfish were basically all limbs, with no real head or tail, just a mouth and an anus.
SHAPIRO: There's definitely a metaphor here, but I'm not going to guess what it is.
(LAUGHTER)
SCOTT: Right? So, yeah, this new paper out this week in the journal nature settles this debate once and for all. Ari, do you have a guess? Are starfish all tails or all limbs?
SHAPIRO: I have to confess, I saw a headline about this. So...
BARBER: Did you?
SHAPIRO: ...I have a clue that it's all limbs. Am I right?
BARBER: Funny enough, it's neither of those.
SHAPIRO: Oh.
BARBER: Yeah. So here's Christopher Lowe, an evolutionary biologist who was a co-author of the paper.
CHRISTOPHER LOWE: There are, in fact, a giant head, and they've lost their trunk rather than having lost their heads.
SHAPIRO: What does that even mean? What about the five starfish arms? What?
SCOTT: Yeah. Basically, all those arms are heads.
BARBER: Yeah. So Christopher and his team used new biomedical technology to look at genes that turn on and off from the starfish larval stage through the metamorphosis to an adult starfish.
SCOTT: And what they found was that the genes that are commonly associated with the head area in other creatures - you know, humans, flies - those are the genes that are being expressed in the arms of the starfish. So the arms, genetically speaking, are heads.
SHAPIRO: The term head has just become completely meaningless to me in this context.
BARBER: I know, right?
SCOTT: Heads are arms.
BARBER: Yeah. But I also talked to Mansi Srivastava, an evolutionary developmental biologist that didn't work on the study, but she was delighted by the research because she said, quote, "it teaches us to be humble as scientists and should get everyone excited about what other novel things we might learn about the natural world."
SHAPIRO: Who knows? Maybe my arms are actually heads, too.
BARBER: They might be.
SHAPIRO: OK. Our last topic - how one sleepless night can ease depression for several days, at least in mice. And I'm curious about this 'cause I always heard that people who suffer from clinical depression, it can worsen if you don't get enough sleep. Aaron, what's going on in this study?
SCOTT: Yes. So - and that is chronic sleep loss. But this is just looking at, like, a single all-nighter, which I'm going to guess you've probably pulled.
SHAPIRO: Once or twice.
SCOTT: Once or twice. Do you - what did you feel like the next day? What was your mood?
SHAPIRO: Delirious, dizzy, chaotic.
LOWE: So it's, like, that kind of, like, slap-happy - scientists refer to it as, like, a tired and wired state.
SHAPIRO: Yeah.
SCOTT: And they found that it occurs in both mice and humans after staying up all night for a single night, this jittery, hyperactive, more aggressive, more sexual kind of behavior that is like a brief manic state.
BARBER: And scientists found that it can also have a strong antidepressive effect in people that lasts for several days, like, long after the other changes wear off. It can be as drastic as some of the fast-acting drugs scientists are testing for depression, like ketamine or psilocybin.
SCOTT: But what researchers haven't figured out is the why. Like, what's happening in the brain of someone who stays up all night that causes these mood changes, especially this antidepressant effect?
SHAPIRO: So did scientists test this at, like, a mouse rave discotheque or what? Like...
BARBER: Kind of.
SCOTT: All the Day-Glo and black lights that mice could handle. Yes. So in the study that came out this week in the journal Neuron, researchers kept mice up all night. I don't think there is any pumping music, but they found that, sure enough, the mice were more excitable, more aggressive, more sexual and less depressed.
SHAPIRO: How did they know the mice were less depressed?
SCOTT: Of course, we can't check in with mice about the feelings. They don't go to therapists. So what scientists do is they kind of create what they see as a depression-like state in the mice by repeatedly giving them small pinches or shocks to their arm...
BARBER: Aw.
SCOTT: ...Until certain mice stop trying to escape and basically give up hope that the world's going to get better.
BARBER: Yeah. And in this case, staying up all night made the mice rebound and once again try to avoid these unpleasant sensations.
SHAPIRO: Do scientists know what it is about sleeplessness that seems to trigger this change in outlook, at least in mice?
BARBER: Yeah. So researchers found that several places in the mice's brain released a lot more dopamine.
SCOTT: And that dopamine literally rewired neurons in the brain to maintain that upbeat mood for several days. It's called neuroplasticity, and it's one of the promising things researchers look for when they're treating depression.
SHAPIRO: So what are the conclusions here for people with depression?
SCOTT: Yeah. I mean, the authors do not recommend that people change their sleeping habits and start pulling all-nighters because this is a short-term effect in mice. Whereas we do know that chronic sleep loss has all sorts of long-lasting negative effects in humans.
BARBER: But they see this as helping scientists understand how our moods transition both naturally and from drugs like ketamine.
SCOTT: And it could give researchers a target in the brain to look at for creating new types of antidepressants.
SHAPIRO: All right. That's a hopeful note to end on. Regina Barber and Aaron Scott from NPR's science podcast Short Wave, where you can learn about new discoveries, everyday mysteries and the science behind the headlines. Always good having you both here. Thanks.
BARBER: Thank you, Ari.
SCOTT: Thanks, Ari.
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