A study of young adult rats by researchers from the Johns Hopkins Bloomberg School of Public Health provides evidence that explains exactly how exposure to lead during brain development produces learning deficits.

The study shows that exposure to levels of lead that are similar to those measured in lead-intoxicated children reduces the birth and survival of new neurons (neurogenesis) in the brain. Lead also alters the normal development of newly born neurons in a part of the brain (hippocampus) known to be important for learning and memory. The study is published in the March 30, 2007, issue of Neuroscience.

"There was a dogma in neuroscience that you were born with all the neurons you would ever have, but that thinking has changed dramatically in the last 20 years," said Tomás R. Guilarte, PhD, senior author of the study and professor of environmental health sciences at the Johns Hopkins Bloomberg School of Public Health. "The exciting idea is that scientists have discovered ways to increase the number of new neurons, and this may facilitate learning in the hippocampus portion of the brain."

The researchers studied young adult rats, using a group of lead-treated and non-treated (control) rats. When they examined the brains of lead-exposed rats, they found that fewer neurons were born and those neurons that were born survived for a shorter amount of time and had abnormal development.

Guilarte has studied lead's effects at the molecular level on rat brain development for more than a decade. In November 2002, Guilarte and colleagues reported that environmental enrichment that stimulates brain activity can reverse the long-term learning deficits caused by lead poisoning.

"Environmental Lead Exposure During Early Life Alters Granule Cell Neurogenesis and Morphology in the Hippocampus of Young Adult Rats" was supported by a grant from the National Institute of Environmental Health Sciences.

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