Effect of low-dose lead acetate exposure on the metabolism of nucleic acids and lipids in cerebellum and hippocampus of rat during postnatal development

Glucocorticoid potentiation of lead neurotoxicity in the mouse HN9 hippocampal cell line

The biochemical events underlying neurobehavioural deficits following persistent low-level lead exposure during embryonic and early postnatal development remain unclear. Because glucocorticoids have previously been demonstrated to potentiate the action of certain neurotoxins, their role in low-level lead-mediated neurotoxicity was examined using a glucocorticoid-responsive immortalized hippocampal neural cell line (HN9). Low-level lead (10(-10)m) reduced the cell number by approximately 30% over a 5-day treatment period. This effect was potentiated by treatment with the synthetic glucocorticoid dexamethasone, with a 52% decrease in cell number. Lead toxicity in actively differentiating cells was also potentiated by dexamethasone. However, while neither lead nor dexamethasone alone was toxic for cells that had previously been induced to differentiate, a combination of both drugs significantly reduced cell number. These results suggest that lead is preferentially toxic in actively dividing cells and that glucocorticoids may play a role in the potentiation of the lead-induced neurotoxicity.

Developmental profiles of ornithine decarboxylase activity in the hippocampus, neocortex and cerebellum: modulation following lead exposure

Ornithine decarboxylase (ODC) is a growth-associated enzyme which is critical for cell growth and transformation. ODC activity follows a specific ontogenetic pattern of activity in distinct brain regions according to their developmental stage. Perturbations in the pattern of ODC activity have been associated with brain damage including arrested cerebral growth. Modulations in the pattern of ODC activity were examined in the hippocampus, neocortex and cerebellum of neonatal rats (PND 3, 6, 9, 15) exposed via the dam to 0.2% lead-acetate (Pb2+ prenatally (gestational day 13 to birth), postnatally (PND 1-15) or perinatally (gestational day 13 to PND 15). Prenatal exposure to Pb2+ perturbed the profile of ODC activity in all three brain regions examined, while postnatal exposure to Pb2+ resulted in prolonged stimulations of ODC activity in the cerebellum. Following prenatal exposure, these effects were manifested as a stimulation of ODC activity in the hippocampus, a repression of activity in the neocortex and a combination of these effects in the cerebellum. Perinatal exposure to Pb2+ transiently modulated the pattern of ODC activity similarly in all three brain regions, in a characteristic manner irrespective of their developmental stage. These Pb(2+)-induced modulations of ODC activity suggest that polyamine-dependent processes may play a significant role in the manifestation of Pb(2+)-induced neurotoxicity dependent upon developmental factors at specific exposure periods.