[Histonet] Frozen tissue to be embedded in OCT later

[Gayle Callis]

Tissues frozen in Liquid nitrogen but NOT embedded in OCT can be embedded
in OCT.  Do NOT thaw the tissue, that is not necessary.  Just embed your
frozen tissue in cold (refrigerated OCT).  Surround tissue as usual, and
then freeze this whole thing.  You can actually do this in the cryotat on a
Peltier platform, OR you can sit this embedded tissue block on dry ice.
Immersion in Liquid nitrogen sometimes cracks OCT in our lab, but you may
get away with doing that to have block form rapidly.  

You can also immerse block in dry ice/isopentane or hexane slurry - the
same as snap freezing an OCT embedded tissue.  The cold OCT does not
appreciably thaw the frozen tissue, and OCT will interface with the frozen
tissue surfaces nicely.  Make sure you don't get bubbles. 
 
Juan's suggestion of mounting frozen tissue from -80C freezer directly on a
cryostat block holder with OCT is excellent, you can add more OCT around
tissue if needed for additional support, it works well and does not
appreciably thaw the tissue. 

I would avoid thawing tissue if it is destined for cryomicrotomy and keep
it frozen while making a block.
Gayle Callis
MT,HT,HTL(ASCP)
Research Histopathology Supervisor
Veterinary Molecular Biology 
Montana State University - Bozeman
PO Box 173610
Bozeman MT 59717-3610
406 994-6367 (lab with voice mail)
406 994-4303 (FAX)