Heavy metal staining in MND brain stem and cortical motor neurons. (A) Light AMG staining is present within the lipofuscin of three hypoglossal motor neurons. Bar = 15 μm. (B) These two nucleus ambiguus neurons contain light AMG staining. Bar = 20 μm. (C) Light AMG staining is seen within the lipofuscin of a trochlear nucleus neuron. Bar = 25 μm. (D) A shrunken cortical motor neuron (Betz cell, arrow) contains no AMG grains. Bar = 15 μm. AMG and hematoxylin.