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Patrick Guilfoile: How to eat a scorpion

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A word to the wise — don’t eat a live scorpion unless you happen to be a grasshopper mouse.

Scorpions live in deserts around the world.  

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The bark scorpion, the nastiest of the bunch in North America, is found in Arizona and surrounding areas.  

Each year, these scorpions sting thousands of people.  Although occasionally deadly, the typical result of a sting is temporary loss of function in the affected appendage and extreme pain.  

Victims describe the sensation as repeatedly experiencing a severe electric shock or an intense throbbing pain that lasts for hours. There is an antivenom available, which shortens the duration of the painful symptoms if administered quickly enough.

The pain from a scorpion’s sting can be a strong deterrent to predators. But predator-prey relationships often have an element of an arms race — an innovation by prey often leads to a counter-response by a predator.  

In a recent report, researchers from several U.S. universities revealed how grasshopper mice manage to get stung repeatedly while feeding on scorpions, without any lingering ill effects.

Generally, you sense pain when an unpleasant stimulus activates your nerve cells, and transmits that stimulus to your spinal cord and then your brain.  

Scorpion venom binds to nerve cells, and essentially turns the nerve “on,” sending a constant pain signal to the spinal cord and brain.  

To understand how grasshopper mice avoided the effects of scorpion venom, researchers first tested the hunch that these mice didn’t feel pain when injected with scorpion venom.  

They injected small doses of scorpion venom into the hind paws of grasshopper mice and house mice, and observed how long the mice licked their paws (a measure of pain).  

House mice licked their paws much longer than the grasshopper mice; in fact the grasshopper mice experienced more pain from injections of saline compared to the scorpion venom.  

The scientists next studied the effect of the venom on isolated nerves.  

In nerves from grasshopper mice, they found that the toxin shut down one type of pain-transmitting nerve, whereas in house mice, the toxin had no effect on that nerve.

The researchers then probed the molecular details of how scorpion venom turned off the pain signals in grasshopper mice.  

They studied the structure of a protein on the surface of nerves that likely bound the scorpion toxin.  

Ultimately, they found a couple of small differences in the structure of that protein that explained why house mice were affected by the venom, but grasshopper mice were not.

These experiments showed that, in grasshopper mice, the nerve cells closest to the skin react to scorpion venom as if they are experiencing pain.  

However, the next type of nerve cell in the pathway to the spinal cord reacts in just the opposite way.  

The scorpion venom binds to the second type of nerve cell and shuts the nerve down.  

Consequently, the grasshopper mice feel no pain, since the pain signal never reaches the spinal cord.  Something to chew on the next time you’re eating fried scorpion on a stick.

More information is available in an article by Ashlee Rowe and others “Voltage-gated sodium channel in grasshopper mice defends against bark scorpion toxin.” Science 342: 441-446, October 25, 2013.  A film showing grasshopper mice eating scorpions can be viewed at:  http://www.sciencemag.org/content/suppl/2013/10/23/342.6157.441.DC1/1236...

PATRICK GUILFOILE has a Ph.D. in bacteriology and is the associate vice president at Bemidji State University.

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