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