Gayle wrote:
>Have been a private discussion with someone, who brought up the point that
>fixation can reverse itself, and in the context of formalin?  but that the
>fixation process is eventually irreversible.
>
>Any comments on this, I found it interesting, and know the other party is
>looking in.
>
>I have never experienced this, or even heard of it happening, but am always
>ready for enlightenment, could be something I have missed in reading,
>listening or discussion.
-----------------
Dear Gayle,

When I am correct initial stablization of tissue with aldehydes is by
formation of a Schiff's base. A Schiff's base is only stable in a
non-watery environment. This explains the defixation effect when using
short fixation times of 30 minutes to ? (depends a.o. on specimen
thickness). Prolonged fixation (e.g. overnight or longer)  will give the
formation of methylols than will react with mainly arginine to form
intra-molecular methylene bridges. These are are chemically stable and not
reversible.

 More on fixation properties of formaldehyde can be found e.g. in:
Hopwood (1985) Histochemistry 17, 389
Puchtler and Meloan (1985) Histochemistry 20, 201
Tokuyasu and Singer (1976) Cell Biology 71, 894
Fox et al. (1985) Histochem. Cytochem. 33, 845

Hope this is of help, Peter


========================================
Peter van de Plas
AURION
Costerweg 5
6702 AA Wageningen
The Netherlands
phone: (31)-317-497676
fax: (31)-317-415955
http://www.aurion.nl