A new autometallographic (AMG) technique
for staining myelin in formaldehyde- or
paraformaldehyde- (PFA) fixed tissue is presented. The
tissue sections were exposed to AMG development
without prior treatment with silver salts. The method
was examined on PFA-fixed tissue from mouse, rat, pig,
and formaldehyde-fixed human autopsy material.
Samples from brain, spinal cord, cranial, and spinal
nerves were either cut on a vibratome, frozen and
cryostat sectioned, or embedded and microtome
sectioned, before AMG development and
counterstaining.
The AMG-myelin technique results in a specific
black/dark-brown staining of myelin in all parts of the
CNS and PNS. It works on all species examined,
independent of the histological preparation techniques
applied. The AMG staining is stable, stays unchanged
through decades, allows counterstaining, and has
previously been used with immunohistochemical
techniques. On perfusion-fixed tissue the technique
works without further fixation, but the intensity of the
AMG-myelin staining is increased by increased
postfixation time. Additionally, immersion fixation has
to last for days depending on the size of the tissue block
in order to obtain proper myelin staining.
The most feasible explanation of the chemical events
underlying the AMG-myelin technique is that nano-sized
clusters of metallic silver are formed in the myelin as a
result of chemical bounds with reducing capacity,
exposed or created by the formaldehyde molecule.
The AMG method is simple to perform and as
specific as the conventional osmium and luxol fast blue
stainings. The present technique is thus an effective,
simple, inexpensive, and quick myelin staining method
of formaldehyde- or PFA-fixed tissue