[Histonet] Frozen storage of tissue and sections, what is the correct temperature?

[Kelly D Mcqueeney]

I know that frozen tissue storage is a common topic, but I have a hard 
time finding the right answer throughout the histonet archives.

We are currently coating brain in embedding medium and snap freezing 
brains in isopentane followed by immediate storage at -80C. Then, we 
bring the brain up to -20C a few hours before sectioning. After 
sectioning, we dry the slides at RT for several hours and store at -80C 
until using the tissue for ligand binding,  IHC or insitu. This exact 
protocol has been moderately successful, so far so good. But, some of 
the staff store frozen brains at -20C. They feel that keeping the tissue 
at cryostat temperature reduces the amount of freeze artifact. I was 
always taught to freeze fresh frozen brain at a much lower temperature. 
None of this has been tested in our lab.  Any suggestions for long-term 
storage of whole brains after collection? Is -80C the correct 
temperature? Will ice crystals spread at -20C? Will the receptor 
affinity decrease or protein degrade more rapidly at -20C? Any feedback 
would be greatly appreciated.

Thanks again,
Kelly