Search to find frog poison ends in Papua New Guinea

By Thomas H. Maugh II
Los Angeles Times

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After more than a decade of work, a California researcher thinks he has solved the 40-year-old mystery of where poisonous South American frogs get their deadly neurotoxin — and surprisingly, the lead came from birds in Papua New Guinea.

The poison has been used for centuries by indigenous Colombians to coat the points of their tiny blow darts, allowing them to bring down large prey — as well as humans — with relative ease.

Called batrachotoxin, the lethal agent is more powerful than curare and 10 times as deadly as the tetrodotoxin from the puffer fish.

Simply handling the frogs that secrete it from their skin can be fatal.

Ornithologist John Dumbacher of the California Academy of Sciences in San Francisco and his colleagues reported last week in the Proceedings of the National Academy of Sciences that the ultimate source of the poison most likely is a little-studied family of "Choresine" beetles.

The discovery is of more-than-academic interest because batrachotoxin — from the Greek "batrachos," or frog — is used widely in studying the function of sodium channels, gates in the cellular membrane that are implicated in a variety of diseases, such as multiple sclerosis.

Currently, everyone who works with the toxin must obtain it from the National Institutes of Health, which collected a small supply 25 years ago. That supply is running out rapidly, and researchers cannot return to Colombia to collect more because of the political situation there. The discovery could lead to new ways to collect the useful poison.

Dumbacher got a lead in 1992 when he heard from local people in Papua New Guinea about a bird called a Pitohui that, when eaten, caused numbing or burning sensations. He ultimately found batrachotoxin in five species of Pitohui.

Elders in the tiny village of Herowana told team members about a beetle called nanisani, which produced numbing or tingling sensations when touched.
 
Samples of the beetles were collected for the scientists, who analyzed them and found the toxin. They also found the remains of the beetles in the birds' stomachs. Significantly, the nanisani beetles belong to the Melyridae family, also found in Colombia.

Dumbacher cautioned that they are still not sure that the beetles are producing the toxin. They might be collecting it from some plant instead, he said. That might be better in the long run, he added, because a plant would be easier to grow in the laboratory.