[Histonet] optic chiasmata

[John Kiernan]

Slow freezing results in formation of ice crystals. In brain tissue (fresh or formaldehyde-fixed) these destroy the architecture, which is replaced by a sponge-like texture of approximately cell-sized holes. Cryoprotection of fixed tissue with 30% sucrose ameliorates this, but freezing at -4C or -20C is asking too much of the cryoprotective action. You need a surface at or below -80C. A cryostat chuck standing in a slush of solid CO2 and acetone is OK. Isopentane in a small metal can standing in liquid nitrogen is better. Test your technique first on an unimportant piece of white matter about the same thickness as the optic chiasma, and cut test sections through different levels in the specimen, because some parts will freeze more slowly than others.

John A. Kiernan 
Anatomy & Cell Biology
University of Western Ontario
London, Canada 
= = =
On 10/05/15, Salomao Segal  <ssegal2 at slu.edu> wrote:
> I intend to use a cryostat to cut 70 - 100 micron thick sections of human
> optic chiasmata.
> 
> Tissue is cryoprotected with 30% sucrose solution.
> 
> My question relates to the freezing process per se.
> 
> Would it be enough to place the tissue in a -4 freezer to harden and then
> transfer to the cryostat chamber at say -20 wait a while and cut? Or is it
> necessary to introduce an intermediary step for freezing?
> 
> Thanks
> 
> SS
> 
> 
> *Solomon Segal, M.D.*
> 
> 
> 
> 
> *Associate Professor of Anatomy in SurgeryCenter for Anatomical Science and
> Education (CASE)Department of SurgerySchool of MedicineSaint Louis
> University*
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