If you are just interested in the GFP, it should be visible directly. We will routinely cut 10 um cross-sections of mouse muscles and allow them to dry on a charged slide. Then look at the sections under a microscope with GFP appropriate filters. No need to use use mounting media or a cover slip.

@ Jeffrey J Brault

thanks so much for this, is this using flash frozen tissue?

Dropping muscles directly into liquid nitrogen causes severe freezing artifacts -- ice crystals will form, which causes crushing/tearing of the muscle fibers. To avoid these artifacts, muscles can be frozen in isopentane cooled in liquid nitrogen: place a small container of isopentane in a larger container of liquid nitrogen; wait until the isopentane starts to freeze; you are ready to put in your muscle.

Good luck!