I am currently sectioning paraffin embedded mouse brains (for IHC) but as the sections dry I am suspicious that the tissue may not have been properly fixed. I received these brains from a collaborator who perfused the animals with ice cold PBS followed with 4% PFA. As the sections are drying, the edges are turning white (as I would expect) but the center remains more translucent (something I have not observed before). Can anyone explain to me what this observation might mean? Also, does anyone know if I can re-fix this tissue (if neccessary) by either removing the tissue from the paraffin block and "hard-fixing" or by running the slides through a fixation series (as with in situ's)?
