PFA increase autofluorescence in tissues.  You could use a different color 
fluorophore if you are doing immunofluorescent staining.  I am attaching a 
review of autofluorescence to you privately, although it is related to GFP 
it is still a very fine review of what you are experiencing.

You may not be able to reduce autofluorescence, although some have used 
borohydride treatments with some success, and various other means, but it 
is a problem.

At 05:08 PM 3/31/2005, you wrote:

>I have a different but similar problem with Immunofluorescence and
>background. I'm cutting rat spinal cord sections that have been perfused and
>post fixed in 4% paraformaldehyde, cryoprotected and cut as frozen sections.
>
>
>The autofluorescence in the tissue is so high I am unable to clearly see
>fluorescent labelled cells.
>
>
>Is this a problem of the fixation in 4% paraformaldehyde? or a property of
>spinal cord? or is there something obvious I should or shouldn't be doing?
>
>
>Regards, cath
>
>----------------------------------------------------------------------------
>
>Catherine Gorrie
>School of Medical Sciences
>University of New South Wales
>Sydney, NSW
>
>ph: 02 9385 2462
>fax: 02 9385 8016
>e-mail: c.gorrie@unsw.edu.au
>----------------------------------------------------------------------------
>
>
>
>
>
>
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Gayle Callis
MT,HT,HTL(ASCP)
Research Histopathology Supervisor
Veterinary Molecular Biology
Montana State University - Bozeman
PO Box 173610
Bozeman MT 59717-3610
406 994-6367 (lab with voice mail)
406 994-4303 (FAX)



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