Healing the Brain with Snail Venom

Image: COURTESY OF STEW ELLINGTON

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Conotoxins?the chains of amino acids found in the venom of a cone snail?are medical marvels. In 2003 psychiatrist and environmentalist Eric Chivian of Harvard University described these sea creatures as having ?the largest and most clinically important pharmacopoeia of any genus in nature.? Scientists believe conotoxins could help treat epilepsy, depression and other disorders by interacting with the nervous system.

Why do neuroscientists care about cone snails?

Cone snail venom contains neurotoxins that can target specific locations in the brain and spinal cord. For example, some species of cone snail possess a compound that can act on the same receptors as nicotine. These receptors, located on the surface of neurons, help to govern signaling in the brain.

Neuroscientist J. Michael McIntosh of the University of Utah has found that selectively blocking some of these receptors with a cone snail compound can decrease the use of addictive drugs (so far, just in laboratory animals). Blocking a different subset of those receptors can trigger more consumption of a drug instead. Other compounds have been found to interact with receptors that influence feelings of pain or the growth of tumors.

How dangerous is a cone snail's venom?

The cone snail uses a toxin-filled tooth to harpoon its prey, injecting chemicals that can paralyze, stun or kill an unfortunate fish. Attracted by their colorful shells, divers occasionally collect the snails and make the mistake of stowing them in their swim trunks. The results range from a nasty sting to painful lesions and, in a few cases, death.

Tales of the calamitous cone snail have crept into fiction: the toxin was featured as a murder weapon in the 1970s television show Hawaii 5-O, and in the more recent film Jurassic Park 2 only cone snail venom was powerful enough to fell a Tyrannosaurus rex. Most of the more than 700 species of cone snail, however, are not toxic to humans.

How do people collect these poisonous sea creatures?

The mollusks are typically found in warm and tropical waters, such as in the Caribbean and near the Philippines. ?We can collect snails using a deepwater submersible, scuba diving, deepwater dredging, or simply bending over in the water and picking them up,? says Frank Mari, a biochemist at Florida Atlantic University, one researcher who collects and studies the venom of cone snails.

But the loss of coral reefs and overzealousness of shell collectors have made finding certain species increasingly difficult, which could curtail our access to and understanding of this natural pharmacy. Once researchers have a cone snail, however, they can keep milking it for years in a lab.

How do you milk a cone snail?

Neuroscientist Baldomero Olivera of the University of Utah was faced with this puzzle in the 1980s. One enterprising undergraduate tried inflating a condom and rubbing it against a goldfish. He then set the fish-scented latex into the cone snail's tank. Almost immediately the snail struck, lodging its tooth into the faux fish.

?The sight of an inflated condom floating at the [water's] surface, with a tethered snail swinging like a pendulum below it, was one of those moments that should have been recorded with a camera,? Olivera wrote in the journal Toxicon in 2000.

Today researchers use real fish bait with a latex-topped tube to collect venom. Some scientists now clone genetic material to produce a specific toxin.

What do you do with the venom?

Every cone snail species has easily 1,000 peptides of medical interest, which means cone snails offer millions of research possibilities. Some cone snail toxins show promise as muscle relaxants during surgery and as fast-acting interventions after a stroke or heart attack.

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