specimens.
15,16
Proper fixation may be critical for the preservation of proteins,
particularly cytosolic proteins.
17
In general, quick and even fixation must be
assured through perfusion fixation via the vasculature with an appropriate
fixative for that tissue. The only other alternatives for
in vivo
studies are drip
fixation
in situ
or careful removal of fresh tissue and immersion fixation of small
2- to 3-mm tissue blocks dissected with the utmost of care. In addition, the
fragility of nervous tissue is such that during the slow chemical process of
aldehyde fixation, there must be no trauma to the tissue from rough handling
or dissection. Dark neurons can be produced by postmortem changes through
improper fixation or handling of brain.
18,19
Liver is also a difficult tissue for
immersion fixation. For certain other tissues, fixation can be reliably performed
by immersion fixation with relatively acceptable results for ultrastructure.
20
These tissues include spleen, kidney, pancreas, heart, and muscle.