Ouahiba: 
If your specimen contains the EGFP variant and you are going to freeze the tissue samples in OCT, you can cut the sections, collect them onto superfrost plus or similar slides then fix in acetone, methanol or formalin as you choose. The EGFP variant is stable in any of these fluids. Then simly apply a fluorescence mounting media, like Prolong AntiFade (Molecular probes) and a No 1 thickness cover glass.  Now, if the tissue is especially bloody (e.g. spleen, liver or bone marrow) autofluorescence may be a problem. There have been several good discussions on the histonet and the Confocal listserve regarding quenching of autofluorescence. See the archives. Hope this helps, Donna Montague

University of Arkansas for Medical Sciences
Department of Physiology & Biophysics and
Center for Orthopaedic Research
4301 W. Markham St. # 505
Little Rock, AR 72205