Vol. 7, No. 1, 2001 Page 3&6

Lead's damaging effects on brain cells identified

Lead toxicity is strongly linked to learning deficits, delinquency, antisocial behavior, and aggression (see related article, Crime Times, 1996, Vol. 2, No. 2, Page 1). Studying the deleterious effects of lead on learning and behavior, researchers at Johns Hopkins say they have identified one mechanism by which lead impairs the function of brain cells.

Michelle Nihei and colleagues tested rats with blood lead levels comparable to those of children suffering from lead toxicity. As expected, the lead-exposed rats performed more poorly than non-exposed rats in a test of learning, involving finding a hidden platform in a pool of opaque water. Testing another group of rats, the researchers found that the neurons of lead-exposed rats were unable to establish strong connections in response to conditioning.

Molecular studies of a third group of lead-exposed rats revealed that the effects of lead were due to the inhibition of the NMDA receptor, which plays a key role in learning. Normally, the NMDA receptor is triggered when it receives two incoming signals—for instance, messages resulting from the sight of snow and the sensation of coldness—and initiates chemical changes that lead to memory formation.

"We believe that lead, by decreasing these NMDA receptors, is interfering with calcium's entry into the neuron," says Nihei. "This is noteworthy since calcium is responsible for a huge cascade of cellular signals that ultimately propagate information and continue the nerve impulse on to the next synapse and neuron."

"N-methyl-D-aspartate receptor subunit changes are associated with lead-induced deficits of long-term potentiation and spatial learning," M. K. Nihei, N. L. Desmond, J. L. McGlothan, A. C. Kuhlmann, and T. R. Guilarte, Neuroscience, Vol. 99, No. 2, 2000, pp. 233- 242. Address: Michelle K. Nihei, Department of Environmental Health Sciences, Johns Hopkins School of Public Health, 615 N. Wolfe Street, Baltimore, MD 21205.

"Scientists discover how lead changes brain to impair learning, memory," U.S. Newswire, August 3, 2000.

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