Task dependent neurobehavioral effects of lead in rats

In order to test neurobehavioral effects of low-level lead exposure during early development, Wistar-rats were given pre- and postnatal dietary lead as lead acetate in four concentrations: 0, 80, 250, and 750 ppm. These diets, known to give rise to blood lead-levels (PbB) of less than 5, 11, 18, and 31 micrograms/dl, resulted in erythrocyte ALAD-inhibition of 40, 73, and 83%, respectively. The animals were tested first at 70 to 100 days postnatal (PN 70-100) in a 2-way active avoidance-task, and then at PN 190-250 in a visual discrimination-task. Lead-exposure was associated with performance-disruption in the discrimination-task, significant (p less than 0.001) already for the 250 ppm-exposure, but with significant (p less than 0.05) performance-facilitation in the avoidance-task. If learning and retention in animals is taken as a measure of cognitive performance neurobehavioral lead-toxicity cannot easily be explained in terms of cognitive deficit. An interpretation in terms of emotional reactivity or behavioral disinhibition would seem more convincing, which covers the results from activity-studies as well. 70% ALAD-inhibition corresponds to PbBs of about 20 micrograms/dl in rats, and to about 40 micrograms/dl in children. Some implications of animal studies for neuropsychological results from Pb-exposed children are discussed.