Mercury staining in human brain after exposure to metallic mercury. (A) Mercury in locus ceruleus neurons is seen as small black HgAMG grains, which can readily be distinguished from the pale yellow-brown neuromelanin granules in the cytoplasm. An occasional glial cell (arrow) contains a few HgAMG grains. (B) The cytoplasm of this corticomotor neuron (thick arrow) in the frontal motor cortex contains numerous HgAMG grains. Two nearby small neurons (thin arrows) contain no mercury. The cytoplasm of some glia (asterisks) contains mercury. (C) Mercury staining is seen in the region of this capillary wall (arrow) in the frontal motor cortex. No adjacent small neurons or glia contain mercury. LFB-HgAMG, bar = 50 μm.