Figure 4: A photomicrograph of buccal mucosa of rat treated by 80 mg/kg methotrexate showing a decrease in the thickness of the epithelium and keratin layer, flattening of rete ridges (Al, H&E x100), extensive cytoplasmic vacuolation of epithelial cells with hyperchromatic nuclei (A2, H&E,x400), cytoplasmic vaculation most commonly seen at the tip of rete ridges (A3, PAS x100), with vascular hyperemia in the connective tissue (A4, Trichrome,x100). Immunohistochemical expression of ki-67 in the buccal mucosa of rat showing mild positive immunoreaction in some nuclei of basal epithelial cells (A5,immunohistochemistry x400). Negative immunohistochemical expression of Bc1-2 in the epithelial cells cytoplasm of the buccal mucosa of rats (A6, immunohistochemistry x100).