Changes in operant behavior of rats exposed to lead at the accepted no-effect level

After weaning, male and female Wistar rats were fed a daily diet containing 1 g lead acetate/kg food until a level of about 20 micrograms/100 mL blood was obtained. The male rats were subjected to the different behavioral tests, whereas the females were mated to untreated males and further exposed until weaning of the offspring. Behavioral testing of the male offspring was performed between 3 and 4 months of age. General behavior of both groups was tested in the open-field task including locomotion, local movements, and emotionality. The conditioned instrumental behavior was tested in the Skinner box from simple to more complex programs. The blood-lead level was measured by flameless atomic absorption spectrometry. No behavioral changes became apparent in the open-field task and in the preliminary operant training. In the more complex programs (DRH = Differential Reinforcement of High Rates), the rats exposed to lead after weaning showed slight changes of DRH performance. By contrast, in pre- and neonatally exposed animals, DRH performance was significantly increased, although blood-lead levels had returned to normal at the time of testing. A comparison of lead effects in animals to possible effects in man is discussed in this paper, and it is concluded that lead exposure to man at doses which presently are suggested to be innocuous may result in subclinical functional changes of the central nervous system.