pH-dependent (pH 4 to pH 7) β-gal activity in frozen sections of mouse choroid plexus. 9 months old C57/Bl6J. Nuclear Fast Red was used for counterstaining. At pH 6, specific for SA-β-gal, bluish color from β-gal activity is evident specifically in ependymal cells in the choroid plexus. Representative images from 3 different mice are shown.