Elevated Pb body burden is a particular problem for low
socioeconomic status children in the US, populations also considered to sustain
the highest levels of environmental stress. Since both Pb and stress target the
same brain sites and behavioral functions, their potential interactions were
examined here. Dams exposed to 150 ppm Pb in drinking water during gestation
and lactation were subjected to restraint stress 3 times per day on gestational
days 16-17 yielding 4 groups: control no-stress (C-NS), control stress (C-S),
Pb no-stress (Pb-NS) and Pb stress (Pb-S). In assessments of fixed-interval
(FI) schedule controlled behavior of adult female offspring, stress alone (C-S)
increased overall response rates and decreased pause time, while Pb exposure alone
(Pb-NS) had no effect. In contrast, Pb-S significantly decreased response
rates. To assess impacts on the HPA axis, blood basal and stress-induced
corticosterone (CORT) levels were measured. Prenatal Pb exposure alone
permanently increased CORT levels (Pb-NS and Pb-S groups). Restraint stress
resulted in maximal CORT levels in all groups and no differences in subsequent
FI performance. However, a brief
exposure to a cold environment increased CORT levels above baseline in all
groups except the Pb-S group. Finally, monoamines and metabolites were
determined to evaluate long-lasting effects of the combined Pb/stress exposure
in mesolimbic and nigrostriatal terminals. In nucleus accumbens, Pb-induced
changes in levels of dopamine (DA) and 5-HT and metabolites were not altered by
stress. However, in striatum, multiple interactions between Pb and stress were
found in which generally Pb increased but Pb-S decreased neurotransmitter
levels. A significant elevation in frontal cortex DA levels was observed only in
the Pb-S group. Since Pb and stress can modulate each other?s effects, the
study of Pb as a risk factor in isolation may be unrepresentative of its actual
adverse effects. ES05017 and
ES01247.
