Neurotoxicity of Zn2+ and the induction of ZnT-1 mRNA expression by exposure to Zn2+. A, Control hippocampal neurons cultured in growth medium. B, Hippocampal neurons cultured in growth medium containing 150 μmZn2+ for 12 hr. C, Hippocampal neurons cultured in 200 μm Zn2+ for 12 hr. Scale bar, 60 μm. D, Pattern of ratZnT-1 mRNA expression in primary cultures after exposure to 150 μm Zn2+. Rat glyceraldehyde 3-phosphate dehydrogenase (GAPDH) mRNA was used as a control.