Immunohistochemical staining for (a-c) cyclinD1, (d-f) p16INK4a
(g-I) bromodeoxyuridine.Positive staining cells appear brown, counter-stained negative cells appearpurple. (a), (d), and (g) are serial sections of an intraductal proliferation(IDP) from a Copenhagen rat; (b), (e), and (h) are serial sections of a largeIDP from a Wistar-Furth rat; and (c), (f), and (I) are serial sections of atumor from a Wistar-Furth rat. Note the overexpression of cyclin D1in Wistar-Furth lesions (b and c) but not in the Copenhagen IDP (a). Alllesions are from mammary glands of rats 37 days after MNU treatment. (a-f)1000× magnification and (g-I) 400× magnification.