To the victims of Pfiesteria, a toxic marine microorganism that has killed scads of fish and sickened some people from Delaware to the Gulf of Mexico, add laboratory rats. In the December issue of Environmental Health Perspectives, researchers report that rats exposed to Pfiesteria have learning difficulties. The work provides an animal model for identifying and studying the Pfiesteria toxins that threaten human health.
Pfiesteria piscicida and related microscopic algae ordinarily hide out in sediments at the bottom of bays and estuaries, but they can rise into the water and release fish-killing poisons. People exposed to the unidentified toxins also seem to suffer a number of symptoms, such as skin sores, difficulty breathing, and problems with short-term memory. Now Edward Levin, director of the Integrated Toxicology Program at Duke University, and collaborators have documented Pfiesteria-induced learning difficulties in lab rats.
Levin and collaborators used a maze to compare the short-term memory of two groups of rats: those that had been injected with Pfiesteria-tainted aquarium water, and uninjected animals. The maze consisted of a central platform and eight planks, like the spokes of a wagon wheel, leading to food rewards. Pfiesteria-injected rats took longer to learn that it was not worth going up the same plank again after they had eaten the food. Once the uninjected rats learned the rules of the game, however, a shot of Pfiesteria had no effect, implying that the toxin interferes with learning but not with existing memories. The Pfiesteria-injected rats had no apparent brain abnormalities or other health problems. "There may be more subtle effects," says Levin, such as interfering with the activity of neurotransmitters such as acetylcholine or glutamate.
"The next step is to try to isolate the toxic component and to see how that works," says Hugh Tilson, a neurotoxicologist at the Environmental Protection Agency in Research Triangle Park, North Carolina. And that may mean more addled rats.