Mechanisms of neurotoxicity and their relationship to behavioral changes.

In this review some of the evidence relating behavioral alterations induced by 2 neurotoxic chemicals, lead acetate and methyl mercury is presented with an attempt to relate these changes to the underlying neurobiological mechanisms. In the case of neonatal lead poisoning, the results of the early behavioral studies were confounded by excessive lead concentrations resulting in undernutrition of the pups. Subsequent studies in both rodents and monkeys have shown that blood-lead concentrations comparable to those seen in children can induce behavioral alterations that may be related to hippocampal damage. In the case of methyl mercury which is a potent cytotoxic agent, prenatal exposure results in widespread cortical, and cerebellar alterations characterized by reduced myelination, delayed migration and loss of neurons. These morphological alterations are accompanied by permanent alterations in learning and memory as well as altered pharmacological sensitivity in catecholaminergic systems. Recommendations are made for better formulated behavioral and neurobiological assays in neurotoxicology in order to lead to a better understanding of the toxicity of chemicals.