Processing rodent tissues

From:Gayle Callis <>

You can purchase larger cassettes, called megacassettes, from various
vendors.  These hold large or whole tissues from rodents.  A whole mouse
head or rat head will fit in them (example of size) but extended processing
will be needed even with some whole large tissues  A whole mouse head was
done at 2 hours per station, 70, 80, 95% x 2, 100% x 2, xylene X 2,
Clearite 3 x 1, paraffin X 4. Total times in all four paraffins can be
reduced to 4 hours to prevent overexposure to heat. vacuum/pressure, RT in
solvents on a VIP automatic processor.  We use graded ethanols and overall
try to avoid overprocessing animal tissues due to their leaner, lack of fat
nature.  They can be very dry and hard to cut.  

In general, murine tissue samples or rat are processed in this lab at 30 -
40 minutes per station, if the sample size is really tiny, time is reduced
again.  A lot depends on fixative, how they are stored after fixation, size
of sample, etc.  We tend to customize processing schedules according to
study, tissues involved (tiny lymph nodes, etc) so hard and fast rules for
processing often don't apply. We find that processing tissues together
which have similar sectioning properties helps.  Spleen goes with liver,
brain with spinal cord, that sort of thing.  

Embryos are another story.  Check the Histonet Archives, there have been
some nice schedules put out on Histonet in the last couple of years.

The Veterinary, Industry and Research Committee of National Society for
Histotechnolgy has an animal processing manual coming out very soon.  It is
in final preparation stages, will be printed after that.  When this
happens, I will be glad to forward information on accessing this manual.
This will be for all species, special tissues, etc.  Exciting eh!! 

Gayle Callis
Histopathology Supervisor
Veterinary Molecular Biology
Montana State University - Bozeman

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