I want to prove the existence of S100, S100A6, GFAP, MOG and MPZ in SG- and CN-sphere as well as in SG and CN tissue. What is more reliable; PCR or Western blot in this case?
If you want to prove the existence on the protein level, western blotting is of course your method of choice. You could also isolate RNA and do RT-PCR to check for mRNA, but with this you could only make indirect conclusions about protein abundance. With 'normal' PCR on genomic DNA you would only proof the existence of the gene in these tissues, which should be there anyways.
It actually depends on what you intend to show: WB is about protein and PCR is about nucleic acids (DNA, mRNA). Both may be used as quantitave techniques.
If you want to prove the existence on the protein level, western blotting is of course your method of choice. You could also isolate RNA and do RT-PCR to check for mRNA, but with this you could only make indirect conclusions about protein abundance. With 'normal' PCR on genomic DNA you would only proof the existence of the gene in these tissues, which should be there anyways.