if it is florescence staining you can rinse them three times in Xylene and then 2 times wash and do some H&E staining, even though it will reduce the image quality but still it is applicable.
can not use sample of immunohistochemical analysis for histological analysis, because the stain of immunohistochemical use for demonstrate of specific cells or structure, whereas the histological analysis need special stain such as H&E to demonstrate all structure of brain tissue.
There is an option of staining slide for H&E and after it's analysis (including photography or ideally scanning) destain and then stain for IHC. However it demands a very skilled lab.work; also, some markers may not potentially work.