Psychophysiologic effects of early lead exposure

In several separate experiments neonatal rats were intubated daily with 9, 27 or 81 mg lead acetate/kg of body weight throughout their 3-week postnatal period of development. Based on average body weights, the total daily lead intake was 0.156, 0.454 or 1.384 mg lead per animal, respectively (in addition to normal lead intake from the environment). Subtle and specific behavioral changes, involving an inability to attenuate inappropriate behavior in a two-way shuttle or a habit-reversal operant task, occurred in offspring following exposure to a minimum of 0.454 mg lead per day. The specificity of this central dysfunction was such that motor activity was normal, stress responsiveness remained unaffected and simple learning ability was comparable to that of controls. The only indication of a central neurochemical modification accompanying this behavioral defect was a tendency for telencephalic acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) activities to be depressed, suggesting a possible involvement of the cholinergic system. Steady-state levels of brain monoamines were unaltered. The experimental weanlings displayed an inhibition of blood delta-amino levulinic acid dehydratase (ALAD) activity, a parallel reduction in regional brain ALAD activity, a moderate reduction in hematocrit and hemoglobin and an increase in kidney weight. This latter effect occurred even at the lowest level of lead intake, 0.156 mg lead per day.