paraformaldehyde and colloidal iron staining of mouse tissue
I work in a University research setting. I have been helping someone
who knows absolutely nothing about histotechnique with Colloidal iron
staining of various mouse tissues (including liver, spleen and kidney).
The mice were perfused with 4% formaldehyde (made from paraformaldehyde)
and the tissues were then stored in 10% neutral buffered formalin (made
in the lab). He is using Van Gieson solution as a counterstain. He tried
the stain several times and each time his sections turned green. So, we
each ran the stain side by side and threw in human appendix that had
been fixed in commercially made 10% neutral buffered formalin.
Everything turned green except the appendix!!
I have read many of the past postings about paraformaldehyde vs.
formaldehyde, especially Dr. Kiernan's postings. Many, many people here
at the university make their own 4% formaldehyde (from paraformaldehyde)
and that is all they will use. Dr. Kiernan said in his posting that the
reason this is done is "tradition, dating from about 1960." Some
professors claim morphology is better. I also think it is used because
some of the tissues used to be set aside for EM and 4% formaldehyde
(from para) worked for both EM and light microscopy. I have 10% formalin
on my tissue processor only for running cell blocks, but some people get
very upset when they see it there. They don't want 10% formalin touching
In the colloidal iron staining situation above, I suggested perfusing
the animals with 10% NBF instead. I got the same reaction as always,
WHY?--they are both formaldehyde and what if the methanol in the
commercial preps does something awful to my tissue??
This email is getting awfully long, so I guess what I want to know
is...Can perfusion fixation in 4% formaldehyde (made from
paraformaldehyde) interfere with colloidal iron staining? Secondly, how
can I convince people that there is no reason to fear commercial
preparations of formaldehyde (especially since no one in my department
does EM anymore)?
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