Duke Researcher Finds That Toxic Marine Organism Causes Learning Impairment In Rats

March 11, 1997

DURHAM, N.C. -- Researchers at Duke University Medical Center have shown that a toxic one-celled organism found in North Carolina coastal waters causes a serious learning impairment in rats.

The team's earlier animal studies demonstrated that the toxin caused cognitive deficits, but could not distinguish between learning and memory disorders. The most recent studies have shown that the learning of new tasks is severely affected.

"When we used pretrained rats, we did not see the dramatic effect on memory that we saw on spatial learning," said Dr. Edward Levin, lead investigator of the study, associate professor of psychiatry and director of the Integrated Toxicology Program at Duke. "We confirmed that the toxin affected the learning aspect of their behavior."

Levin prepared his findings for presentation at a poster session Monday at the annual Society of Toxicology Meeting in Cincinnati. His collaborators on the study include assistant botany professor JoAnn Burkholder and botany research associate Howard Glasgow of North Carolina State University, and Duke associate professor of neurobiology Donald Schmechel. Funding for the research was provided by the National Oceanic and Atmospheric Administrations' Sea Grant College Program, and in part by the National Science Foundation.

Levin began conducting experiments on the effects of the toxic organism Pfiesteria piscicida because people who had been exposed to it exhibited dramatic mental impairment, serious disorientation, emotionality, immune problems and dermatological problems. Since Burkholder identified Pfiesteria in 1988, it has also been implicated in about 30 percent of all fish kills in North Carolina. The organism virtually melts the fishes' flesh away, killing them within minutes.

The Duke experiments involved injecting rats with the Pfiesteria. The researchers then conducted classic animal experiments in two stages, measuring the effects of the toxin on the rats' ability to learn and remember a task.

For the first stage of the experiment, scientists trained a non-injected group of rats over 18 sessions on a radial arm maze -- a platform with planks radiating from it. At the end of each plank was half a Fruit Loop. Once eaten, the food was not replaced, and the rats learned quickly that it was not worth their effort to go down the same plank twice. When the researchers tried to train rats to perform the task after injection with the toxin, they learned at a significantly slower rate than rats that had not been injected. In contrast, when the rats first were trained on the maze and then injected, they performed the tasks just as well.

Then, in the second stage of the experiment, the researchers had the rats learn a different task. They baited only three of the planks, each day changing which three were baited. The rats were allowed to find the food, and the researchers counted how many errors they made and how long they took. They repeated this exercise five times a session, baiting the same three planks. The injected rats, though they remembered their pre-injection training, showed very poor ability to learn the new task.

"The high dose group was retarded in their learning," said Levin. "And the effect was very persistent, even 10 weeks after the injection."

Future research, said Levin, will involve trying to determine what kind of learning is affected, whether it is only spatial learning or also involves other types of tasks. He also plans to work with chemists to isolate the toxic chemical in the algae.

Pfiesteria is a bizarre creature, possessing at least 20 different forms. It photosynthesizes like a plant. When threatened it can turn from a tiny dinoflagellate -- a cell with a tail -- into a large amoeba and engulf its predator. While lying dormant in cyst form in sediment, it senses the presence of fish and emerges into the water to poison them.
-end-


Duke University

Related Learning Articles from Brightsurf:

Learning the language of sugars
We're told not to eat too much sugar, but in reality, all of our cells are covered in sugar molecules called glycans.

When learning on your own is not enough
We make decisions based on not only our own learning experience, but also learning from others.

Learning more about particle collisions with machine learning
A team of Argonne scientists has devised a machine learning algorithm that calculates, with low computational time, how the ATLAS detector in the Large Hadron Collider would respond to the ten times more data expected with a planned upgrade in 2027.

Getting kids moving, and learning
Children are set to move more, improve their skills, and come up with their own creative tennis games with the launch of HomeCourtTennis, a new initiative to assist teachers and coaches with keeping kids active while at home.

How expectations influence learning
During learning, the brain is a prediction engine that continually makes theories about our environment and accurately registers whether an assumption is true or not.

Technology in higher education: learning with it instead of from it
Technology has shifted the way that professors teach students in higher education.

Learning is optimized when we fail 15% of the time
If you're always scoring 100%, you're probably not learning anything new.

School spending cuts triggered by great recession linked to sizable learning losses for learning losses for students in hardest hit areas
Substantial school spending cuts triggered by the Great Recession were associated with sizable losses in academic achievement for students living in counties most affected by the economic downturn, according to a new study published today in AERA Open, a peer-reviewed journal of the American Educational Research Association.

Lessons in learning
A new Harvard study shows that, though students felt like they learned more from traditional lectures, they actually learned more when taking part in active learning classrooms.

Learning to look
A team led by JGI scientists has overhauled the perception of inovirus diversity.

Read More: Learning News and Learning Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.