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What can drunk crayfish tell us about how being social can affect our physiology?
*Our apologies to Dr. Jens Herberholz, who spells Herberholz the best and only way to spell Herberholz! (Special thanks to Steven!)

Hosted by: Hank Green
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Sources:
https://www.eurekalert.org/emb_releases/2017-04/tcob-scg041317.php
http://jeb.biologists.org/content/220/8/1516.abstract

https://www.eurekalert.org/emb_releases/2017-04/mdcf-mcf041117.php
http://dx.doi.org/10.1172/JCI88530
https://doi.org/10.1172/JCI88532

Image/Video Sources:
https://commons.wikimedia.org/wiki/File:Urea_3D_ball.png
Crayfish Video Published with permission of The Company of Biologists and Jens Herberholtz
Hank: A trio of scientists at the University of Maryland have spent a lot of time spiking the water in tanks of crayfish with booze... for science! The experiment sounds kind of ridiculous, but drunk crayfish actually act a lot like inebriated humans – and could help us figure out the mystery of how alcohol affects the nervous system.

In this particular study, researchers were looking at how being social seems to affect drunkenness. And this week, they reported in the Journal of Experimental Biology that it’s harder to get a crayfish drunk if it’s kept in a tank alone. If you add some ethanol to their tanks, crayfish start acting noticeably drunk.

What does that look like? Well, if they’re a little bit intoxicated, they stand up in an aggressive-looking pose. A bit more, and they’ll start flipping their tails. And eventually, they lose motor control, and fall onto their backs, and get stuck there.

Now these last two stages of crayfish tomfoolery are easy to spot, so the neuroscientists decided to set up video cameras to film the drunk crustaceans one at a time – kind of like crayfish ‘Animal House.’ The researchers experimented with crayfish that had been housed in a large tank with 50 to 100 of their buddies, and crayfish that had lived in an isolated tank for one week.

After swimming around in the highest tested concentration of alcohol, the social crayfish took around 20 minutes to start flipping their tails, while the loner crayfish needed about 28 minutes in their boozy bath. The loners also took longer to end up helpless on their backs than the social ones. So, something about being isolated made them less sensitive to alcohol!

Now because we know which neural circuits are involved in tail-flipping, the scientists stuck silver wires in crayfish abdomens and gave them electric shocks to test how excitable the neurons were. Which doesn’t sound nice, but at least the mice are catching a break on this one.

Alcohol seems to make those behavior-related neurons more sensitive, so that a weaker shock will stimulate the circuit more easily and cause some tail-flipping. But if a crayfish was by itself before soaking in the alcohol, it needs a bigger jolt of electricity to activate that tail-flipping circuit than one of its social peers. The researchers think that ethanol is interacting with some neurotransmitter systems to cause these signs of drunkenness, and that being social might change how certain neurotransmitter receptors are distributed on cells.

This, in turn, could change how ethanol molecules interact with neurons, which could affect how easily different circuits are stimulated, and make the weird behaviors more intense. Now, even if their drunkenness seems like Saturday night shenanigans on a college campus, crayfish are obviously really different from humans. So, it’s hard to draw direct comparisons to people.

But, eventually, this area of research could help explain why drunkenness might be different in people who drink with others and those who drink alone.

Now, maybe you’re feeling a little parched from all that talk about drinking. So if you were to go get a snack, you would want to stay away from salty foods so you don’t get even thirstier... right?

Well, a pair of studies out this week in the Journal of Clinical Investigation challenges that conventional wisdom. This research was based on a simulated mission to Mars conducted in Russia, and a team of mostly-German scientists found that participants actually seemed to drink less water if they ate saltier food.

In space, it really matters how much you eat, drink, and pee, since it’s expensive to send food and water up on rockets.. So researchers have extra reason to test things out like how salty foods affect your thirst! In this mock mission, two groups of 10 guys were sealed inside a fake spaceship in Moscow and ate either low-, medium-, or high-sodium diets during their stay. And for 105 days or more, the researchers tracked how much the pseudo-cosmonauts drank and urinated.

For a long time, it was assumed that lots of sodium would cause a person to drink more. The extra fluid would increase the amount of urine and allow the body to get rid of the excess salt. But here, the men on the highest sodium diet consistently drank the least.

To figure out why this happened, the researchers turned to mice, and found that the key was a molecule called urea. Urea is normally thought of as a waste product. It’s made in your liver and muscles when proteins get broken down, and is how your body gets rid of excess nitrogen when you pee.

But urea also acts as an osmolyte in your kidneys, helping your body reabsorb some water and concentrate your urine. So, if you’re eating a high-salt diet, your body responds by making more urea. That way, you can pee out the extra salt through urine, but you conserve more water by reabsorbing it to avoid getting dehydrated.

In fact, because making extra urea takes a lot of energy, and you get energy from food, it seems like you’re actually more likely to get hungry and eat more if your diet is super salty. So it still might be worth watching your salt, whether you’re staying here on Earth or going up into space.

Thanks for watching this episode of SciShow News! If you like this kind of weekly science update – and especially studies about simulated missions to Mars – check out SciShow Space, where we also post weekly News episodes every Friday! And don’t forget, if you just want more of this kind of stuff, to go to youtube.com/scishow and subscribe.