Figure 4.

DNA methyltransferase activity in cortical neuronal cells of mice and in monkey brains. A, B, Control and Pb-exposed mouse cortical neuronal cells (A) and frontal association cortical tissue of 23-year-old control (Con) and Pb-exposed (Pb-E) monkeys (B) were used to estimate the DNA methyltransferase activity as described in Materials and Methods. Data shown represent the mean ± SEM for four independent determinations (4 animals in each group for monkey data). Values marked with an asterisk are significantly different from their corresponding controls (p < 0.05) as determined by Student's t test.