Dear Andrea,

	I worked in a research lab a couple of years ago where tissue would be
first frozen then stored  before cutting, & occassionaly stored again for
later use.  I did all my storage for such samples in the freezer section of
the lab refrigerator.  By doing this I recognised that I would get ice
crystal formation, but I considered that as long as the samples were
carefully wrapped in parafilm during storage, once frozen the micro
morphology would not change too much.  

	By moving between -80 & -22 in LN (-180?) your allowing the ice in the
tissue to transform from amorphous ice to ice crystals & back again.  This
must turn the cells in the sample to mush after a number of repeats.

	I must admit I am considering the ice damage to the tissue in terms of EM
study, but just the same there must be visible effects under LM.

	Regards

	Rob W.

At 12:06 AM 7/7/99 PDT, you wrote:
>Hi Gayle
>I work with PFA fixed frozen mouse and rat tissue. What I usually do is 
>embedding the (wiped off) fixated tissue in OTC, put it in marked plastic 
>containers and simply put in in the -80 freezer. The tissue can withstand 
>several freeze-'thaw' cycles, by thawing I mean bringing the tissue to the 
>cryostat (-22) and back to the freezer (tranported in liquid nitrogen).
>Kind regards Andrea
>
>
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R. Wadley, B.App.Sc, M.L.S
Laboratory Manager
Cellular Analysis Facility
School of Microbiology & Immunology
UNSW, New South Wales, Australia, 2052
Ph (BH) 	+61 (2) 9385 3517
Ph (AH)	+61 (2) 9555 1239
Fax 	+61 (2) 9385 1591
E-mail	r.wadley@unsw.edu.au
www	http://www.micro.unsw.edu.au/caf.html