FROGS could help resolve one of the toughest dilemmas in animal
experimentation. Because they lack the brain structures which allow mammals to
feel pain, they might be used as a less contentious way of testing new
painkilling drugs.
The crux of the problem is that you can鈥檛 find out how well an analgesic
works without first inflicting pain. In a typical experiment you would compare
how long it takes for a rat on a hotplate to raise one of its hind legs before
and after it receives a new drug.
Now Craig Stevens of Oklahoma State University in Tulsa has developed the
first amphibian model for testing painkillers. He drips acetic acid on the hind
legs of the leopard-spotted frog, Rana pipiens, and times how long it
takes the frog to wipe the acid away. His studies show that well-known
painkillers such as the opiates morphine and codeine have similar effects on
this response as they do in the rat hotplate test.
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鈥淚t does have an ethical advantage,鈥� says Stevens. 鈥淔rogs don鈥檛 have any of
the structures that in humans and other mammals are used for pain perception.鈥�
They have no limbic cortex, which is responsible for emotional responses like
dread and fear, and also can鈥檛 be conditioned to learn to expect the acid
application. 鈥淭hey don鈥檛 jump away. They don鈥檛 show any of the fear responses,鈥�
he says.
鈥淚f it proved to answer the same questions, pharmaceuticals companies will be
embracing that,鈥� predicts Kerry Taylor of the Southern Research Institute in
Frederick, Maryland. Stevens also says he can buy and keep six frogs for the
price of one rat, so his model is cheap as well.