Stimulating Environment Protects Brain Against Damage From Lead Exposure

Jay Schneider, Ph.D., professor of pathology, anatomy and cell biology and neurology at Jefferson Medical College of Thomas Jefferson University in Philadelphia, and his colleagues compared groups of rats given lead-laced water for several weeks in two different environments. They found both a better ability to learn and higher levels of various brain chemicals important to brain cell health in the brains of rats in the enriched, stimulating environment than in the animals that were isolated and exposed to lead. In many cases, the lead-exposed animals in the stimulating environment did just as well as those animals that weren't exposed to lead.

"Behaviorally, being in an enriched environment seemed to help protect their brains," says Dr. Schneider.

Dr. Schneider and colleagues at the Institute for Basic Research in Developmental Disabilities in Staten Island report their results March 30 in the journal Brain Research.

In the study, the researchers compared rats that were housed alone and others that were housed eight at a time in a more stimulating, enriched environment, where they could interact and play.

One-half of the animals in the enriched environment received lead in the drinking water, and half did not. Similarly, half of the animals in the isolated environment received lead in their drinking water and half did not. After a period of time, the scientists tested the animals' ability to learn and remember with a standard test that is used for rats. "We wanted to know if being raised in this environment would lessen the effects of lead on the brain," he explains. "Animals that are exposed to lead early in life usually perform poorly."

The scientists also examined the animals' hippocampus, an area of the brain responsible for learning and memory. They measured the ability to produce neurotrophic factors, chemicals that play an important role in the growth and maturation of brain cells. They did this by measuring levels of the genes that encode for these factors.

They found that isolated animals that were exposed to lead in their drinking water had low levels of gene expression for neurotrophic factors - much lower than the animals in the isolated environment not exposed to lead. Animals in the enriched environment and not exposed to lead had the highest levels of neurotrophic factor gene expression. Enriched animals that were exposed to lead had higher neurotrophic factor gene levels than isolated animals exposed to lead or not.

"Just by being in the enriched environment causes a significant increase in neurotrophic factors in the brain," Dr. Schneider says. "Just being in the impoverished environment causes lower levels. The double hit of impoverished environment and exposure to lead is the worst situation.

"When we measured the lead in the blood and brain, there were no differences - they all had the same exposure, the only thing that was different was the environment in which they were raised.

"The magnitude of the protective effect surprised me," he says. "It raises some interesting questions about how we might handle lead exposure in the environment. This raises the possibility of mitigating the effects of lead by manipulating the socio-behavioral environment. If it's true, this might be a weapon to attenuate the damage done to kids. This might lead to an early educational intervention for at-risk populations."

"At present, the way we deal with the dangers of lead poisoning is to try to limit the possibility of exposure," says Theodore Lidsky, Ph.D., a co-author of the paper and a neuroscientist at the Institute for Basic Research in Developmental Disabilities. "Despite enormous progress in eliminating sources of lead poisoning, unacceptably high numbers of children are poisoned by lead each year. Unfortunately, once a child is found to have elevated lead levels, there is little to be done to treat the brain injury that has already been inflicted. However, our research suggests the possibility that environmental enrichment may make the brain more resistant to lead's toxic effects, lessening the effects on a child's development."

The researchers would like to continue the animal studies to test if there is a critical duration of exposure to an enriched environment that may protect against lead, both in terms of behavior and brain chemistry. Also, the researchers would like to find out if there is a critical age after which environmental enrichment is no longer neuroprotective.