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		Step Two: Explant Culture The neural tubes were placed, one to a well, in a 24 well culture plate with each well containing 2 mL of medium. The dish was then placed in a 37oC and 5% CO2incubator where the tubes were left to grow for four days. During this time, cells migrated out of the neural tube and differentiated into neurons. Step Three: Pb-Acetate On the fourth day of culturing, the plates were removed from the incubator. A solution of lead-acetate was then added to four of the wells. The solution was 4 mg of lead-acetate mixed with 10 mL of Dulbecco's Modified Eagle's medium with 10% fetal calf serum supplemented with penicillin and streptomycin. Following serial dilution of the medium, we added 0.2 mL of 1 mM lead-acetate to two of the wells and 0.2 mL of 0.1 mM to two other wells. The last two were left as controls. All wells also contained 2 mL of medium. The cultures were then replaced into the incubator and allowed to sit for another 24 hours.