X-Message-Number: 12442
References: <>
Date: Mon, 20 Sep 1999 09:03:13 -0700
From: "Joseph J. Strout" <>
Subject: Re: freezing and fixation of rat cerebral cortex

>From: Doug Skrecky <>
>Subject: freezing and fixation of rat cerebral cortex

>Title
>  A comparative fine
>  structure study of rat cerebral cortex following ultra-rapid
>  freezing and conventional chemical fixation procedures.

>  ... Although these
>  morphological differences are minimal, there can be no question of the fact
>  that ultra-rapid-freeze followed by freeze-substitution is morphologically
>  superior to chemical fixation alone. Ultra-rapid-freeze, 
>eventually utilizing
>  other substitution agents than osmium tetroxide, will offer several
>  advantages and should be particularly useful for investigators involved in
>  cytochemical and immunochemical methods.

Just so everybody's clear: the "slam-freezing" technique they're 
talking about here involves cooling a copper block to liquid helium 
temperature, then taking a small amount of tissue, and literally 
slamming it against the block.  It freezes almost instantly.  But it 
only works for small bits of tissue.

This is an encouraging bit, though:

>  Cellular and organelle morphological differences
>  were minor beyond the general 'smoothness' of membranes and a more intense
>  background, electron density found in tissue prepared by rapid-freeze. Of
>  particular interest was the practically identical images found in the four,
>  chemical techniques not preceded by ultra-rapid freezing.

So it seems they're looking at this tissue under EM, and finding that 
the four slower, gentler techniques all produced good ultrastructure, 
apart from some wrinkling of the membranes.  That's good news for 
us... but again, they were probably working on small bits of tissue, 
for which fixative and cryoprotectant penetration is easy.  Still, 
it's encouraging to see this sort of research (I just hope 
slam-freezing doesn't become too popular!).

Cheers,
-- Joe

,------------------------------------------------------------------.
|    Joseph J. Strout           Biocomputing -- The Salk Institute |
|                 http://www.strout.net              |
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