Toxic Influence

Rats exposed to toxic chemicals lose ability to focus

Tuesday, December 21st, 2010 

URBANA-CHAMPAIGN, ILL. — They won’t sit on a couch and confide their escapades to a therapist, but researchers have devised other means to detect when rats are behaving badly. A battery of laboratory tests can measure rats’ hyperactivity, poor impulse control, cognitive difficulties and other impaired aspects of what researchers call executive function.

At the College of Veterinary Medicine here at the University of Illinois, scientists study the effects of chemical pollutants on Long Evans rats, a furry, black-and-white breed. They then correlate their findings with parallel studies done on humans exposed to the same pollutants through the environment.

In an interview at her laboratory, bioscience professor Susan Schantz explained her motivation to study contaminants like PCBs, mercury and lead, plus newer chemicals of concern, such as bisphenol A and phthalates. “Every one every day is exposed, and there’s no way to avoid it,” she said.

In one room of the Schantz lab, researchers are placing the rats into large, rectangular test chambers. The three-month-old rats were exposed to PCBs in utero and while nursing. They have spent part of their early days learning how to press a lever that dispenses a food treat.

Now researchers will test the rats’ ability to control their impulses. They’ve changed the timing of the dispenser, so the rats will only earn their reward if they can wait 30 seconds or so in the chamber before pulling the lever with their paw.

“If the rat presses the lever before the time is up, then the clock resets, and it has to wait again,” Paul Eubig, a research assistant professor, said. “Animals or people who have problems with impulsivity want to press that lever. They just can’t wait. They keep resetting the clock.”

The researchers found that the rats with the highest exposure to PCBs performed worse on the tests than rats who were less contaminated. A review of the results of their studies, along with an analysis of related work by other scientists, appears in the December issue of Environmental Health Perspectives, which is published by the National Institute of Environmental Health Sciences.

In the article, Eubig, colleague Andréa Aguiar and Schantz survey the results from studies of exposed human populations and laboratory animals. They conclude that deficits in attention and executive function associated with exposure to lead or polychlorinated biphenyls (PCBs) are similar to those reported in children diagnosed with Attention Deficit Hyperactivity Disorder.

The researchers said that “exposures to environmental contaminants, including lead and PCBs, may increase the prevalence of ADHD.” Their article suggests that the findings from animal studies can be used to guide the questions that need to be asked about human health problems resulting from environmental exposure to the same chemical pollutants.

 

 

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Sheila Kaplan