Persistence of impaired reversal learning in young monkeys exposed to low levels of dietary lead

Abstract

Lead acetate in milk was fed daily to infant rhesus monkeys at doses averaging 0 (control), 0.287 (low‐Pb), or 0.880 (high‐Pb) mg/kg. for the first year of life. Pb concentrations in whole blood (PbB) averaged 4.15, 31.71, and 65.17 μg/dl for the control, low‐Pb, and high‐Pb groups, respectively, during the year of treatment and declined toward control levels when Pb dosing was stopped. Behavioral observations during the year of treatment had shown that both experimental groups were retarded in their acquisition of object‐cue discrimination reversal learning sets. At 4 yr of age, when PbB levels in all animals were normal, the ability of the same monkeys to acquire a series of 3 spatial‐cue reversal learning sets was examined; these data form the basis for this report. In the first problem, the high‐Pb group was significantly retarded in acquisition of the original discrimination and of most reversals, and the low‐Pb group was retarded on reversal 1 only. These deficits declined in severity across the three problems administered, in a manner similar to that seen in the tests given during the first year of life. These data demonstrate that reversal learning retardation, observed early in life, can recur in postadolescent primates with a history of chronic, low‐level Pb intoxication during infancy.