Congo red staining can be performed on frozen sections, obtained from 
cryostat or microtome, without any troubles (see for instance 
http://www.ncbi.nlm.nih.gov/sites/entrez?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=16023262&query_hl=2&itool=pubmed_docsum).
You can use thioflavin-S as an alternative to Congo red. If results are 
still negative, it remains possible that amyloid-beta peptides are not 
aggregated (therefore not stained by the previous dyes) but only present 
in the tissue as diffuse deposits (you can do IHC with dedicated 
antibodies to check this possibility).

Benoît
> Message: 15
> Date: Thu, 26 Apr 2007 10:35:47 -0400
> From: "Monfils, Paul" 
> Subject: [Histonet] congo red on frozen sections?
> To: 
> Message-ID:
> 	<4EBFF65383B74D49995298C4976D1D5E273C72@LSRIEXCH1.lsmaster.lifespan.org>
> 	
> Content-Type: text/plain;	charset="iso-8859-1"
>
> I was asked to do a congo red for amyloid on a mouse brain that had been formalin fixed, sucrose infiltrated, and frozen.  The researcher was certain that this brain would have a high level of amyloid.  I used a positive control that was human  tissue, formalin fixed, paraffin embedded.  The control slide stained perfectly.  The mouse brain shows absolutely nothing. Has anyone successfully done congo red staining on frozen sections?  Do you see any other possible problems in what I described?
>   

-- 
Laboratoire de Neurobiologie de l'Apprentissage,
de la Mémoire & de la Communication,
NAMC, CNRS UMR 8620, Bât 446
Université Paris-Sud
91405 Orsay Cedex, FRANCE
Email  benoit.delatour@u-psud.fr
Web    http://www.namc.u-psud.fr


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