AW: [Histonet] Proof that fixation in formaldehyde solution can bereversible?

[Geoff McAuliffe]

Gudrun is correct, formaldehyde penetrates quickly but fixes slowly.

Geoff
Gudrun Lang wrote:

> Sorry Rene,
>but isn't it the other way round? That penetration is rather fast and
>fixation in the sense of making methylenbridges is rather slowly? So tissue
>of 5 mm is penetrated within a few hours, but fixation takes much longer?
>
>I also learned that fixation with formaldehyd can be reversed by washing in
>tapwater for several weeks. In some old books they recommend washing the
>tissue the same duration as fixation was done.
>
>Gudrun
>
>-----Ursprüngliche Nachricht-----
>Von: histonet-bounces <@t> lists.utsouthwestern.edu
>[mailto:histonet-bounces <@t> lists.utsouthwestern.edu] Im Auftrag von Rene J
>Buesa
>Gesendet: Dienstag, 03. Oktober 2006 19:05
>An: GT Hebert; histonet <@t> lists.utsouthwestern.edu
>Betreff: Re: [Histonet] Proof that fixation in formaldehyde solution can
>bereversible?
>
>GTH:
>  A piece of tissue sitting in PBS for 1 month after being fixed for 24-48
>hours only is likely to have suffered tissue decomposition at the center of
>it, specially if it was a thick piece. Formalin is an extremely fast
>fixative but with a very slow rate of penetration, this would have
>determined external fixation but not complete fixation.
>  Fixation is not really reversible in a strict way and that is why you need
>a strong Heat Inducet Epitope Retrieval (HIER) before IHC to "undo" or
>"unfix" the crosslinkage produced by formalin.
>  The damage to the tissue could have been caused by improper storage = PBS
>at room temperature during 1 month. If processed that tissue is very likely
>to present altered microscopic appearance.
>  Just my opinion!
>  René J. 
>
>GT Hebert <emerald_lake77 <@t> yahoo.com> wrote:
>  Hello,
>
>I am in a heated debate with an investigator regarding his samples. They
>were shipped to me after (24-48hrs fixation - 10% NBF or 4% PF unsure
>exactly which one) and then switch to PBS for shipment. They sat at room
>temperature for over 1 month before being processed routinely and embedded
>in paraffin wax. 
>
>Can someone tell me if indeed the fixation is reversible, or once they have
>been fixed for over 24hrs they remain fixed?? Can anyone refer me to books
>or papers that talk about this?? 
>
>Also, what affect on antigenicity will such storage in PBS have on these
>samples?
>
>Thank you all so much for your help.
>
>G. H.
>Cambridge, MA
>
>
>
>Key words:
>NBF, Alcohol, 10%, paraformaldehyde, 4%, fixation, fix, ethanol, 70%,
>reverse, reversible.
>
>
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Geoff McAuliffe, Ph.D.
Neuroscience and Cell Biology
Robert Wood Johnson Medical School
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