Dangerous Delight of the Tropics
Parkinson's and Alzheimer's disease are common on the island of Guam, as are sandy beaches, emerald seas… and palm-like trees called cycads. Only recently have scientists discovered that the seeds of cycads, a favorite food of local people, contain an amino acid that causes neurological damage in mammals. dr Dennis Wm. Stevenson, director of the Harding and Lieberman Laboratories at the New York Botanical Garden and leading expert on cycads, studied mechanisms in the brain by which that amino acid causes Parkinson's and Alzheimer's disease. The study -- a joint project by New York University and the University of Cape Town -- provides new insights into these neurological disorders in humans, which remain largely a mystery.
The cycads, which are currently threatened, can boast the title "living fossil of the plant world". Their family tree goes back 290 million years, meaning they were contemporaries of the dinosaurs. However, unlike the dinosaurs, the cycads knew how to get by in the survival game. To ward off various predators, the cycads produced various carcinogens and the amino acid BMAA (beta-methylamino-alanine or 2-amino-3-(methylamino)-propanoic acid), which blocks glutamate receptors. These are responsible for neuronal activity in the mammalian brain. A blockage of this type prevents the transmission of information to the brain and leads to neurological disorders in mammals and Parkinson's-like diseases or premature Alzheimer's in humans. The incubation period in humans can span decades.
In a similar study with weevils, none of the insects were harmed by BMAA, although each cycad species has its own species of beetle by which it is fertilized. Stevenson's team discovered that BMAA is produced and stored in specialized cells. They are called "gold cells" because of their color. While the weevils fertilize the cycads, they eat the cycads' tissues, but their digestive system does not break down the gold cells. Instead, the gold cells are excreted intact as part of the beetle's cocoon. Together with the integrated gold cells, these have a toxic effect on insect predators.
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