The sting of the Arizona bark scorpion is known to unleash a searing pain through its victim, but to grasshopper mice, which hunt the predatory arthropod, the venom feels like a soothing dose of morphine.
Researchers who study the unique pain-proofing tricks of the desert dwelling mice say the rodent's ability to turn the tables on the venom could inspire new pain-management therapies.
People who've been stung by scorpions have vivid memories of their experience. "They say it feels like being burned with cigarette, or like you've been branded, or like a nail being driven through your skin," Ashlee Rowe, a zoologist at Michigan State University, told NBC News.
But in grasshopper mice, the venom turns off pain receptors instead of activating them, Rowe and her colleagues explain in a new paper in the Thursday edition of Science.
The researchers lined up grasshopper mice and common house mice and injected them with a neutral salt solution, formalin — which the mice find slightly painful — and small doses of scorpion venom.
The grasshopper mice didn't notice a thing when they were dosed with bark scorpion venom. In fact, when that dose was followed by a shot of usually painful formalin, they shrugged that off as well.
But when Rowe injected house mice with the venom, she saw temporary paralysis, seizures, excessive swallowing and salivation as the toxins cranked up the electrical circuitry in the body. "It's like the circuits are going haywire," she said.
The bark scorpion venom is likely not just one compound, but a cocktail of up to 40 to 60 different toxins. The compounds home in on cellular on-off switches that are embedded throughout a mammalian system, that control the nervous signals and muscle movements.
Painful venoms target the switches in charge of pain receptors, and wreck havoc with the pain control in mammals (and humans). Like the bark scorpion venom, these toxins offer scientists a launching point to study how pain works, and perhaps create drugs that can better control it.
For example, in 2005, a synthetic cocktail of cone snail venom was approved by the FDA as a painkiller. Also on the list for study: tarantula venom and centipede venom, to inspire long-lasting, broad-spectrum treatments for chronic pain.
Grasshopper mice seem to have figured much of this out — in addition to hunting stinging scorpions, they also hunt and eat tarantulas, and are known to fight off predatory giant centipedes. For Rowe, the next steps are to investigate if the rodents are numb to the spider venom as well. "They actually are super mice," she said.
Ashlee Rowe, Yucheng Xiao, Matthew Rowe, Theodore Cummins, and Harold Zakon are authors of "Voltage-Gated Sodium Channel in Grasshopper Mice Defends Against Bark Scorpion Toxin."