Well, I've cut lots of cortex tissue on the sliding microtome @
thickness ranging from 30-50 microns and when I've done IHC I
always free-float them through the immunostaining method I'm using.
The immunostaining protocols I do are the standard immuno detection
methods. I don't know anything about PGP 9.5. When you cut the
sections store them in tissue wells w/0.1M PB (use tissue well size
equal to the size of the tissue) and place in the refrig @ 4C. I
always store tissue, if need to store for long term, in the 
following solution:
30gm sucrose
1gm PVP-40 (1% polyvinylpyrolidone, Sigma cat# PVP-40
30ml ethylene glycol
Make up the volume to 100ml w/0.1M PB @ pH 7.4

Hope this bit helps.
regards
Maria Mejia
Smith-Kettlewell Eye Res. Inst.
S.F.CA