THE EFFECTS OF TRIETHYL LEAD ON THE DEVELOPMENT OF HIPPOCAMPAL-NEURONS IN CULTURE

Triethyl lead is:the major metabolite of tetraethyl lead, which is used in industrial processes and as an antiknock additive to gasoline. We tested the hypothesis that low levels of triethyl lead (0.1 nmol/L to 5 mu mol/L) interfere with the normal development of cultured E18 rat hippocampal neurons, possibly through increases in intracellular free calcium ion concentration, [Ca2+](in). The study assessed survival and differentiation using morphometric analysis of individual neurons. We also looked at short-term (up to 3.75-h) changes in intracellular calcium using the calcium-sensitive dye fura-2 Survival of neurons was significantly reduced at 5 mu mol/L, and overall production of neurites was reduced at greater than or equal to 2 mu mol/L. The length of axons and the number of axons and dendrites were reduced at greater than or equal to 1 mu mol/L. Neurite branching was inhibited at 10 nmol/L for dendrites and 100 nmol/L for axons. Increases in intracellular calcium were observed during a 3.75-h exposure of newly plated neurons to 5 mu mol/L triethyl lead. These increases were prevented by BAPTA-AM; which damps [Ca2+](in) at about 100 nmol/L. Culturing neurons with BAPTA-AM and 5 mu mol/L triethyl lead did not reverse the effects of triethyl lead, suggesting that elevation of [Ca2+](in) is not responsible for decreases in survival and neurite production. Triethyl lead has been shown to disrupt cytoskeletal elements, particularly neurofilaments; at very low levels, suggesting a possible mechanism for its inhibition of neurite branching at nanomolar concentrations.