I freeze unfixed embyos in a cryo mold surrounded by OCT with
isopentane-liquid nitrogen. I do have the cracking problem occur
sometimes. It seems more of a problem for larger specimens. For
fixed specimens, I make certain they are thoroughly fixed in
either 10% formalin or 4% paraformaldehyde (usually overnight
fix); then, I protect in 25% sucrose until the embryo
sinks-overnight is usual. Sometimes, researchers here want to do
a light fix in 2% paraformaldehyde. This light fix  dosen't give
successful results in my opinion. I generally section unfixed
embryos at -10 to -12C. The sucrose-protected specimens can be
cut much colder.

Good luck!

Lorraine

On Thu, 27 Apr 2000, Garry Ashton wrote:

> 
> Histology Department
> Paterson Institute
> Wilmslow Road
> Manchester
> M20 9BX
> UK
> 
> -----Original Message-----
> From:	Garry Ashton
> Sent:	27 April 2000 13:46
> To:	'histonet@pathology.swmed.ed'
> Subject:	frozen embryos
> 
> Dear all,
> I am having a couple of problems with the freezing down of some mouse 
> embryos.
> Firstly can anybody suggest the best way to freeze down unfixed (about 
> day 14) embryos without them cracking.
> Secondly what's the best way to freeze down fixed embryos. The problem 
> with these is that if I cryoprotect them with 30% sucrose, this 
> concentrates in the body cavities and then prevents me from sectioning 
> them.
> Thanks for any help in advance
> Garry
> 
> Histology Department
> Paterson Institute for Cancer Research
> Wilmslow Road
> Manchester
> M20 9BX
> UK
> 
> 
>