Prolonged behavioral effects of early postnatal lead exposure in rhesus monkeys: fixed-interval responding and interactions with scopolamine and pentobarbital

Abstract

Three groups of rhesus monkeys (N = 4/group) were administered daily doses of lead acetate dissolved in milk throughout the first year of life. The doses of lead administered were 0.9 mg/kg/day (high lead group), 0.3 mg/kg/day (low lead group), and no added dietary lead (control group). These doses resulted in mean blood lead concentrations over the first year of 65, 32 and 4 micrograms/dl for the high lead, low lead and control groups, respectively. Lead administration was terminated at the end of the first year and blood lead concentrations fell steadily over the next 44 months. At no time were overt signs of toxicity apparent. The effects of prior lead exposure on a fixed-interval (FI) schedule of food presentation were examined beginning at 33 months of age, at which time blood lead concentrations of all animals were less than 12 micrograms/dl. Acquisition of the bar press response varied widely among individual monkeys and no group differences were observed. Throughout 20 sessions of responding under an FI 60 sec food schedule, the lead treated animals had a significantly lower index of curvature (IC) than controls indicating a less pronounced positively accelerated pattern of responding. The magnitude and consistency of this effect were directly related to the dose of lead administered. Overall FI response rate, running rate and postreinforcement pause duration were not altered by lead treatment. Pentobarbital (2.5-10 mg/kg) decreased IC and increased response rate; these effects were not altered by lead treatment.(ABSTRACT TRUNCATED AT 250 WORDS)