Re: Gluteraldehyde

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From:"Barry Rittman" <> (by way of histonet)
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		one thing that is constantly disregarded in the discussion
on fixation is
that fixation procedes in stages.
The initial stage is a prefixation if you will in which the fixative
reaches the cells and essentially stops their metabolic processes.
The second is a stage in which tenuous bonds are formed. This stage is
often reversible by processes such as washing in water.
The final stage is one in which stable bonds are formed.
This final process may continue for several years and as it progresses
there are fewer reactive groups available for reactions.
Success of antigen retrieval will vary with the degree of fixation and if
tissues are fixed beyond a certain point will not work without extensive
damge to tissue.
Most fixatives are used for such a time period that the tissue is
"partially fixed" and the third stage of fixation is not complete. The
subsequent processing is in fact a secondary fixation. It has been
determined that in order for a tissue to be completely fixed in formalin
that it needs to be exposed to the fixative foe several days at room
tmeperature. This is obviously not an option for most individuals and would
result in a tissue whcich has relatively few reactive groups. An overcooked
turkey may be fully fixed but.....

Glutaraldehyde is much more rapid than formaldehyde at reaching tissues and
stopping metabolic processes.
Glutaraldehyde is a dialdehyde and has a greater number of reactive groups
available to bond with tissue groups and form stable cross links, these
bonds are also more difficult to break. In general, glutaraldehyde is
therefore much less useful in preservation of tissue which is to be
subjected to immunohistochemistry than that fixed in formalin.
It is critical therefore that when discussing fixation and processing that
the discussion includes some details of concentraton of fixative , time and
conditions of application and times for subsequent processing.

I wish y'all a very merry and a peaceful holiday,and a suitable cooked
turkey with all the "fixins"

 At 05:46 PM 12/10/1999 -0600, you wrote:
>Hi histonetters,
>Again I have a fixative question. What is the difference between
>paraformeldehyde and gluteraldehyde, chemically speaking. I recently
>used a fixative that was part of each for an EM project and noticed
>quite a difference in how they worked on the tissue.
>I am sure that Jon Kiernan among others will be able to help me out.
>Thanks to all,
>Colleen Forster
>U of MN, Dept. of Neurology

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