Low lead exposure from birth produces behavioral toxicity (DRL) in monkeys

Cynomolgus monkeys (Macaca fascicularis) were dosed from birth with 100, 50, or 0 micrograms/kg/day of lead. This treatment resulted in blood lead concentrations of 25, 15, or 3 micrograms/dl, respectively, before withdrawal of infant formula at 200 days of age, and steady-state concentrations of 13, 11, or 3 micrograms/dl. At approximately 3 years of age, monkeys were tested on an intermittent schedule, differential reinforcement of low rate (DRL). This schedule required the monkey to withhold responding for a specific time in order to be reinforced. The performance of treated monkeys did not improve as rapidly as controls as measured by increase in reinforced responses and decrease in nonreinforced responses during initial sessions. In addition, treated monkeys exhibited greater between session variability during terminal sessions. These effects were dose related. The results of the present experiment in conjunction with those of previous experiments with this same group of monkeys suggest that blood lead concentrations presently found routinely in the human population may produce neurotoxicity.