Enduring effects of early lead exposure: evidence for a specific deficit in associative ability

Long-Evans dams were exposed to Pb acetate in the drinking water during bot h gestation and lactation, or lactation only. This report presents the resu lts of an automated, olfactory, serial reversal task administered to the ad ult offspring. Although overall learning rate was not significantly affecte d by Pb exposure, analyses of specific phases of the learning process revea led that all three exposed groups required significantly more trials than c ontrols to reach criterion from the point at which perseverative responding to the previously correct cue ended. These in-depth analyses revealed that the reversal learning impairment of the Pb-exposed animals was not due to a deficit in inhibiting responses to the previously correct cue, the mechan ism commonly assumed to underlie impaired reversal learning. Instead, the a nalyses revealed that two other independent Pb effects were responsible for the prolonged postperseverative learning period: a response bias and an im paired ability to associate cues and/or actions with affective consequences . The contribution of these two factors varied as a function of the timing and intensity of the Pb exposure. It is hypothesized that the Pb-induced as sociative deficit may reflect lasting damage to the amygdala and/or nucleus accumbens, which comprise a system thought to modulate the process by whic h environmental cues acquire affective significance. (C) 2000 Elsevier Scie nce Inc. All rights reserved.