Subacute Pb exposure during development and unbaited tunnel maze performance in mice

Although research has linked chronic, low-level Pb exposure to behavioral and cognitive changes in humans and animals, far less is known about the effects of transient, subchronic Pb exposure during early postnatal development. The need to understand such effects is underscored by the possibility that subchronic Pb exposure may not produce chronically elevated blood-Pb levels, but may produce long-term behavioral changes. To test this hypothesis, we investigated the effect of low-level Pb exposure on unbaited tunnel maze performance in Binghamton Heterogeneous Stock mice. Mice were either nontreated or given subchronic sodium acetate, 5, 10, or 25 mg/kg Pb acetate intragastrically on postnatal (PN) days 6, 9, 12, 15, and 18. No further Pb exposures were given after postnatal day 18. Blood-Pb measurements were taken from selected mice on PN 18, 19, 23, 28, and 38. On PN 38-42, all mice were individually tested in an unbaited tunnel maze under nondeprived conditions. Locomotor activity, exploration, and experience-dependent changes in cul-de-sac entries were recorded. Although Pb did not affect bodyweight and blood-Pb levels were below 10 microg/dl at the time of behavioral testing, a history of low-level preweaning Pb exposure caused a dose-dependent increase in cul-de-sac entries. This behavioral change was dissociable from changes in bodyweight, degree of exploration or an a priori bias to enter cul-de-sacs. The current results support the hypothesis that brief, subchronic Pb exposure during development produces behavioral changes that last well beyond the exposure period, even when blood Pb declines to within "acceptable" levels (l0 microg/dl).