Duke Studies Show Toxic Organism Impairs Learning And Memory In Animals
DURHAM, N.C. -- Researchers at Duke University Medical Center have found that a toxic one-celled organism common to North Carolina's estuaries causes serious learning and memory impairment in rats. They say this is the first step toward determining if there is a similar effect in humans.
Anecdotal evidence of its risk to mammals has existed for several years, but the Duke research is the first to scientifically confirm that Pfiesteria piscicida, often referred to as algae, impairs learning and memory in animals, said Edward Levin of Duke, lead investigator of the study.
The researchers' next step is to determine which region of the brain and what specific neurotransmitters are affected, so they can assess the potential risk and develop therapies for the cognitive disorder, said Levin, associate professor of psychiatry and director of the Integrated Toxicology Program at Duke.
Levin prepared his findings for presentation Saturday (Nov. 9) at the fall meeting of the Southeastern Estuarine Research Society in Atlantic Beach. The research was sponsored by the National Oceanic and Atmospheric Administration's Sea Grant College Program and in part by the government's National Science Foundation.
Since its identification in 1988 by North Carolina State University researcher JoAnne Burkholder, Pfiesteria piscicida has been implicated in about 30 percent of all fish kills in North Carolina, home to the nation's second-largest estuary. Some experts say the appearance of toxic algal blooms, also known as red tides, is increasing along the East Coast and possibly worldwide, perhaps due to greater pollution from river runoff, killing millions of fish every year.
The Pfiesteria kills fish within minutes, virtually melting their flesh. It also has inadvertently poisoned researchers, causing temporary but severe disorientation, memory loss, fatigue, nausea and skin lesions.
In a series of three studies on the organism, Duke researchers confirmed that it causes an unequivocal memory and learning deficit in animals. But, Levin cautioned, "The relationship of our findings to potential human effects is still to be determined."
"This is the first experimental step to understanding the effects of Pfiesteria on small mammals, which is a more analogous case to humans than fish are," said Burkholder, who collaborated with Levin and others on the study.
The Duke researchers conducted classic animal experiments to judge learning and memory retention. The rats were placed on a platform with planks radiating out from it in a star pattern. At the end of each plank, the rats found half a Fruit Loop. Once eaten, the food was not replaced, so it wasn't worth the rats' time to go down an already-traveled plank.
Within 18 sessions, normal rats learned the task entirely, using the minimum amount of energy to retrieve the Fruit Loops. Rats that had been injected with cells of the Pfiesteria didn't learn the routine at all during the normal training period. With a few additional sessions, they started to learn a little, Levin says. For two months after the injection, the rats had a learning deficit, but other behaviors did not appear to be affected.
Pfiesteria is single-celled dinoflagellate, meaning it uses a tail for mobility. Dinoflagellates are one of the oldest forms of life, and this is one of the strangest, researchers say. It has many guises; about 20 are known. It photosynthesizes like a plant. When threatened, it can turn within seconds from a tiny dinoflagellate into a large amoeba and engulf its predator. While lying dormant in a cyst on the sea floor, it senses the presence of fish and then comes out of its repose to fill the water with poison and kill the fish. It then devours the fish flesh, often leaving deep wounds the size of quarters.