Mike,
          I use a counter stain called Vectasheild (cat # : H-1200, vector labs , 10 ml vial) with DAPI to counter stain (flourescent blue) nuclei. DAPI is 4',6'diamindino-2-phenylindole, it also comes with PI. 
It is a mounting media (with DAPI in it) that I use after sectioning and deparaffinzing /hydrating my sections for GFP analysis. It works well the only drawback is it doesn't harden like glycerin based mounting media so the coverslip is very moveable. I have a poster at NSH on GFP that has more info if you need it. Hope it helps.

Jamie Erickson

>>> Mike Bromley <MBromley@PICR.man.ac.uk> 10/05 9:00 AM >>>
Hi All,
A researcher  has asked me if there was a suitable counterstain for 
GFP. She has formalin fixed bone marrow cytospins labelled with GFP 
now in buffer and wants to identify cells containing the GFP.


Mike Bromley PhD
Histology Department
Paterson Institute
Wilmslow Road
Manchester
M20 9BX
UK