You Don't Know Sero

I’m going to preface this post by pointing out that while I have my mischievous side, I’m no super villainess, no Viper, no disillusioned jazz age heiress… but I do know an awful lot about poisons, venoms, and toxins.

Those molecular cocktails, which are admittedly not great to serve at happy hour, are worth knowing a lot about. Besides being downright fascinating, they hold the promise of new medicines, important physiological discoveries, and a deeper understanding of this crazy evolutionary ride we’re all on.

I’ve had the pleasure of working on two different poison and venom exhibits, most recently on The Power of Poison at the American Museum of Natural History. During that project, I kept coming across a word I’d seen many times before and assumed I understood: serotonin.

Doesn’t serotonin just hang out in your brain and make you happy? What the heck is it doing in venom? Why is it listed as a pain causing component?? I asked no one in particular. “Serotonin does so much more” came the reply…

Serotonin, or 5-HT (5-Hydroxytryptamine), is a crazy molecule. Its prevalence in our bodies and life processes is probably best illustrated by the fact that serotonin was discovered not once, not twice, but three times. First, it was found in the blood, where it was determined to help with clotting. Then it was identified as a neurotransmitter--a chemical substance that carries signals from one nerve to another. Finally, a whopping amount of it was found to be essentially running the show in your digestive tract, the alimentary canal to those of you partial to digestive slang.

It’s the serotonin in your brain that you’re likely most familiar with. But that accounts for less than 10% of all the serotonin you have in your body--a small but mighty percentage to be sure. Much of the brain is still a mystery, but at this point it seems clear that the serotonin there has a hand in determining everything from whether you’re a happy blob or a sad blob, to memory and learning, to the regulation of your sex drive.

 Apparently serotonin tattoos are all the rage.For those of you who want to test drive one before committing, there's an  Etsy shop  that sells temporary versions. (Image from  reddit )

Apparently serotonin tattoos are all the rage.For those of you who want to test drive one before committing, there's an Etsy shop that sells temporary versions. (Image from reddit)

A small percentage of serotonin hangs out in your blood doing it’s clotting thing, but the other 90% is mostly found in your gastrointestinal tract. This time instead of shuttling information between neurons in your brain, it’s keeping a network of over 100 million neurons focused on moving along the digestive process from your esophagus to your anus.

Known as the enteric nervous system, this “second brain” has more neurons than your spinal cord, but won’t help you contemplate a Monet, build a better mousetrap, or finish writing that awful love poem you’ve been meaning to send to your sweetie. (Seriously, it’s terrible.) But by running the show down below, serotonin keeps the brain from having to get its hands dirty. (Deduct five points for the awful mixed metaphor there). Without having to worry about digestion, your brain is free to engage in much loftier pursuits.

It’s important to remember that serotonin isn’t the only neurotransmitter at work in your gut, but it’s an obviously important one. It’s specialty, you see, is causing smooth muscles to contract. Smooth muscles are primarily found in your hollow organs--your stomach, your intestines, your bladder, your lungs… you know, the not very important parts of you. Smooth muscle contractions push food through your intestines; enable you to cough, throw up, and poo (hopefully not all at once); and are even responsible for the nervous feeling of butterflies in your stomach.
 

 His belly is smiling from all the serotonin! (Disclaimer: that's definitely not true. Also, don't let your asshat friends apply your sunscreen, folks.) (Image found  here )

His belly is smiling from all the serotonin! (Disclaimer: that's definitely not true. Also, don't let your asshat friends apply your sunscreen, folks.) (Image found here)

Ok, so what about venom?

Venoms are incredibly complex concoctions that contain a whole slew of chemicals, many of which are very precisely targeted to certain systems or organs. (By and large, they are much more precise than human-developed drugs.) Many venoms do their work by either disabling communication between nerves or speeding it up so quickly as to overwhelm the system. As a neurotransmitter, ie a substance that carries signals from one nerve to another, serotonin is a logical vehicle with which to accomplish that goal.

It appears as one component in many, but not all venoms. Bees have it. So do gila monsters and sting rays. Certain species of scorpions, vipers, centipedes, and bunches of spiders, including the Brazilian wandering spider, do too.

Serotonin in your brain probably helps keep you happy, hungry, and sexually active. Serotonin in your blood helps constrict blood vessels and stem bleeding. Serotonin in your gut pushes your last meal along and then helps expel it. But serotonin in venom is there to cause pain. It does this by co-opting serotonin’s normal functions and sending them into overdrive. Serotonin’s role in clotting is exploited to cut off blood flow. (In small prey, like mice, that can be lethal.) If you’ve ever inadvertently cut off blood flow to a finger, foot, or some other body part, you know a fraction of how painful that oxygen deprivation can be. Serotonin’s role in smooth muscle contractions is even more mightily abused as normal contractions go haywire. Lung contractions (breathing) become spasms (coughing and gasping). Normal gut contractions (you can’t even feel those) become nausea and cramping (you can definitely feel those). Ow ow and more ow.

 Subway Shark is just trying to get to work like the rest of us. (Photo Credit: Juan D. Cano via BBC)

Subway Shark is just trying to get to work like the rest of us. (Photo Credit: Juan D. Cano via BBC)

Even if most of these serotonin-laden venomous creatures don’t live where you do (though I don’t think anyone would be that surprised to hear about a scorpion on the subway), and even if you stubbornly refuse to be excited by a wasp sting, maybe, just maybe, you’ll feel a little pang of nerdy scientific knowledge excitement the next time you’re expertly removing a bee stinger from your arm. That’s serotonin, bro.