Dear Irene,
the OCT compound and others like it is merely a support medium for the
tissue on the cryostat block, and when you have very small samples which you
do not wish to loose any edge of section due to "roll-over" then the OCT can
be poured around the sample and all frozen solid. The compound even though
described as "embedding compound" is not usually used as an embedding
compound.
Some of our older microtomists still use just water to fasten the tissue to
the chuck- I prefer the OCT.
As a rough rule of thumb, get your cabinet down as low as you can get it; if
the tissue is too cold then the tissue will shatter on the knife edge as it
is cut, gently rub the surface of the block with your thumb and quickly try
to get a few sections (This will raise the surface of the block a few
degrees only), if they still shatter, repeat with your thumb a bit longer
and try again. If the material appears compressed or squashed on the knife
it is too warm. Trial and error till you get it.
You might in fact find that your concentration of sucrose is sufficiently
high to act as an "Anti-freeze" and lower conc. of sucrose infusion may be
required.
Regards Mike (Downunder)
-----Original Message-----
From: I.H.Straatsburg DIVG <I.H.Straatsburg@AMC.UVA.NL>
To: histonet@pathology.swmed.edu <histonet@pathology.swmed.edu>
Date: Thursday, 14 January 1999 6:36
Subject: cutting fixed "sucrose" livers


To start with: thank you for the suggestion to infuse fixed tissue
with a sucrose gradient before cutting cryostat sections. Without
sucrose, the morphology of the sections was awful. Unfortunately, the
procedure I am using at the moment requires fixation of the liver
tissue prior to freezing. I would rather do without.

Here comes the problem: the liver and kidney tissue infused with 50%
sucrose in 0.1 M Phosphate buffer (until it sank) is very difficult
to cut in a cryostat (-20 degrees Celsius; 8-10 micrometers
thickness).
Note: The tissue samples were not impregnated in OCT compound (I take
that is 'Tissue Tec' or something similar) before freezing, but
directly frozen either in liquid N2 or on a cryo-boost-plate in the
cryostat cabinet.

Should I cut a lower temperatures? I have got the impression, the
tissue is too soft, too sticky.
Is the impregnation with OCT compund essential?

I am very curious and thankful for any help!
Irene
===========================================================
Dr. I.H. Straatsburg
IWO1-155, Dept. Exp. Surg., Surgical Lab.,
AMC, Amsterdam, NL 1105 AZ
tel. +31.20.5666653